HIGH SPEED ELECTROPLATING OF NICKEL OVER STAINLESS STEEL

AHMAD ABDOLAHI

UNIVERSITI TEKNOLOGI MALAYSIA

HIGH SPEED ELECTROPLATING OF NICKEL OVER STAINLES STEEL

AHMAD ABDOLAHI

A dissertation submitted in partial fulfillment of the

requirements for the award of the degree of

Master of Engineering (Materials)

Faculty of Mechanical Engineering

Universiti Technologi Malaysia

DECEMBER, 2010

To my beloved parents and wife thanks for all your affectionate caring and

supporting, and above all your sacrifices and prayers accorded to me until the successful

completion of this project.

“ My Success Is Yours Too”

ACKNOWLEDGEMENT

In the Name of God Most Gracious, Most Merciful

First of all I would like give thanks to Almighty God that has protected and guided me

throughout my academic pursuit, then my sincere gratitude to my supervisor Assoc,

Prof. Dr. M. S. Hussain, Faculty of Mechanical Engineering, (Material Department),

University Technology Malaysia. His knowledge and logical way of thinking have been

of great value to me. His guidance has provided a good basis for this thesis.

ABSTRACT

Electrodeposition of nickel has been investigated intensely during the past

decades in relation to its particular mechanical properties and numerous applications in

industry. Electroplating of nickel coatings is frequently used for corrosion protection of

stainless steel, also nickel electroplating plate is one of the protective-decorative

electrodeposited metallic coating for stainless steel. Usually the electroplating process of

nickel over stainless steel is done by common methods needed to some pretreatments

such as preparation of surface, activating of the surface, striking a thin layer of nickel on

the surface. In these methods there are some problems including: Poor level of

Adhesion. Peeling off, Sometimes even after following all the proper pre-plating

treatment the adhesion is also poor. Another problem is that a strike deposits usually

very thin and examination of the strike layer may not show any signs of pitting and

roughness. Because of these problems the nickel layer can not stick to stainless steel

properly and it can peel off from the surface. In this study high speed electroplating will

be applied to solve the problems and without any preparation the nickel will deposited

on stainless steel

ABSTRAK

Penyelidikan mengenai pemendapan nikel telah lama di lakukan dan ia

berhubung kait dengan sifat-sifat mekanikal dan banyak kegunaannya di dalam industri.

Penyaduran nikel sering digunakan untuk melindungi keluli tahan karat dan melindungi

bahan hiasan yang diperbuat daripada keluli tahan karat dari berkarat. Lazimnya, proses

penyaduran nikel pada keluli tahan karat di lakukan dengan kaedah biasa dimana

beberapa pra-rawatan perlu dilakukan seperti penyediaan awal permukaan keluli tahan

karat, pengaktifan permukaan keluli tahan karat dan penghasilan lapisan nikel di

permukaan keluli tahan karat. Bagaimanapun, melalui kaedah ini terdapat beberapa

masalah yang di hadapi seperti tahap perlekatan yang rendah, mudah tertanggal dan

walaupun selepas melakukan semua rawatan pra-saduran, lekatan yang dihasilkan juga

tidak memuaskan. Selain daripada itu, saduran yang dihasilkan juga sangat nipis dan

ujian yang dilakukan tidak dapat menunjukkan sebarang tanda bopeng dan kesat.

Disebabkan oleh masalah ini, lapisan nikel tidak dapat melekat di permukaan keluli

tahan karat dengan baik dan mudah tertanggal. Dalam kajian ini, high speed

electroplating akan digunakan untuk menyelesaikan masalah yang dihadapi tanpa

melakukan sebarang penyediaan untuk menyadur nikel pada keluli tahan karat.

TABLE OF CONTENTS

CHAPTER TITLE PAGE

1 INTRODUCTION 1

1.1 Background of the Project 1

1.2 Problem statements 2

1.3 Objectives 2

1.4 Scope of project 2

1.5 Thesis outline 3

2 LITERATURE REVIEW 4

2.1 Overview 4

2.2 Properties of Nickel Electroplating 5

2.3 Solution are used for nickel electroplating 7

2.4 Watts bath operation 9

2.4.1 pH 9 2.4.2 Agitation and Temperature 10

2.4.3 Filtration 11

2.4.4 Additives 11

2.5 Problems with Watts bathe 12

2.5.1 Roughness 12

2.5.2 Adhesion 13

2.5.3 Ductility and stress 14

2.5.4 Dull deposits 15

2.5.5 Purification of Nickel Solution 15

2.6 Problems with Ni striking 17

2.7 Process of nickel electroplating over stainless steel 17

2.7.1 Background of process 18

2.7.2 Summery of process 19

2.8 Factors for good electroplating 21

2.8.1 Surface preparation 21

2.8.2 Anode 21

2.8.3 Current efficiency 21

2.8.4 Anti-pitting additive 22

2.8.5 Filtration 22

2.8.6 Air agitation 22

2.8.7 Temperature 23

2.9 Problems and corrective action 23

2.9.1 Roughness 23

2.9.2 Pitting 24

2.9.3 Poor adhesion 24

2.9.4 High stress and low ductile 24

2.9.5 Brighteners 25

2.9.6 Current density 25

2.9.7 Nickel striking 26

2.9.8 Pre-treatment process 26

2.10 High speed electroplating 27

3 METHODOLOGY 30

3.1 Introduction 30

3.2 Experimental Setup 30

3.3 Stainless steel sample preparation 32

3.4 Solutions preparation 32

3.5 Experimental Setup 33

3.6. Sample preparation 35 3.7. Preparation of samples (for SEM) 36

3.8. Sample preparation for TEM 37

3.9. Adhesion testing 38 3.9.1 Scratch test 39

3.9.2. Nano scratch test 40

3.9.3 Tape test 40

3.10 Expected findings

4 RESULTS AND DISSCUSION 42

4.1 Introduction 42

4.2 Effect of temperature on rate of deposition 42

4.3 Effect of solution on rate of deposition 44

4.4 Effect of current density on rate of deposition 45

4.5 Nano scratch test Analysis 48

4.6 Tape test analysis 50

4.7 Type of failure 51

4.8 Ni Electro crystallization 55

5 CONCLUSION 59

5.1 Conclusion 59

REFERENCES 60

LIST OF TABLES

TABLE NO TITLE PAGE

2.1 Typical ranges for the components in Watts bath 8

2.2 Typical Operating Parameters for Watts Nickel 9

3.1 shows various current densities applied at three different pre-set

temperatures 36

3.2 Rate of deposition is increased by increasing temperaturer and

current density 41

LIST OF FIGURES

FIGURE NO TITLE PAGE

2.1 Schematic diagram of nickel electroplating set up 5

3.1 Flowchart to conduct the electroplating process 31

3.2 Project specimen dimensions of the stainless steel rod 32

3.3 Schematic diagram showing the setup of high speed

Electroplating of nickel on stainless steel. 34

3.4 High speed electroplating equipment invented by Dr. Sakhawat

Hussain A)Surface of cathode B)anode and cathode positioned

close togetherC)Water pomp to supply the speed of solution 35

3.5 a) Cross section of sample b) Mounted sample

c ) polished sample 37

3.6 a)make a layer as thin as possible b) punching c)very small

sample for ion polishing 37

3.7 Schematic image of scratch test 39

3.8 scratch test on samples 39

3.9 Tape test 41

4.1 SEM image shows the thickness of nickel layer at T=60°C,

C.D=1.3A/cm2 42

4.2 SEM image shows the thickness of nickel layer

at T=55°C,C.D=1.3A/cm2 43

4.3 SEM image shows the thickness of nickel layer at T=60°C,

C.D=0.13 A/cm2 Watts solution 44

4.4 SEM image shows the thickness of nickel layer

at T=60°C, C.D=0.13 A/cm2 Sulphate based solution 44

4.5 SEM image shows the thickness of nickel layer

at T=55°C,C.D=0.25A/cm2 45

4.6 SEM image shows the thickness of nickel layer

at T=55° C, C.D=1.14 A/cm2 46

4.7 Optical micrograph showing dendritic growth of the nickel

deposits at higher current density 47

4.8 SEM image showing the dendritic growth 47

4.9 Nano scratch tests across interface 48

4.10 Friction against distance 49

4.11 Oblique scratch across interface 50

4.12 nickel layer is peeled off (T=60°C, C.D=2.6A/cm2) 51

4.13 SEM image of exterior layer of stainless steel

at C.D <1.3 A/cm2 by peel test 51

4.14 SEM image of interior layer of nickel

at C.D <1.3 A/cm2 by peel test 52

4.15 EDAX of exterior layer of stainless steel

at C.D <1.3 A/Cm2 52

4.16 EDAX of interior layer of nickel at C.D <1.3 A/Cm2 53

4.17 SEM image of exterior layer of stainless steel

at C.D>1.3 A/cm2 53

4.18 SEM image of interior layer of nickel

at C.D>1.3 A/cm2 54

4.19 EDAX of exterior layer of stainless steel

at C.D> 1.3A/cm2 54

4.20 EDAX of interior layer of nickel

at C.D> 1.3A/cm2 55

4.21 Schematic diagram of electrochemical growth 56

4.22 SEM image of nickel layer was peeled off

At C.D=2.6A/cm2,T=60°C 57

4.23 Optical micrograph showing dendritic growth of

the nickel deposits at higher current density 57

4.24 a)TEM image of nano-crystalline nickel over stainless steel

b) particle size of nickel deposites 58

1

CHAPTER 1

INTRODUCTION

1.1. Background of the Project

It is common practice to nickel plate many different types of industrial parts

which are made of stainless steel in order to give the parts a bright, shiny surface. By

way of example, automotive vehicle body moldings, door handles, and other functional

or decorative parts are nickel-plated for appearance purposes. In commercial practice,

nickel plating stainless steel parts typically is accomplished by initially buffing the

stainless steel to achieve a high luster and then electroplating with chromium to retain

the high luster and to make the finished surface more durable[1].

In the past, stainless steel parts have been electroplated with nickel before the

chromium electrolytic plating step. But, the adhesion between the nickel plating and the

stainless steel part has been erratic. It has been understood that proper adhesion and

good red rust resistance could not be consistently achieved when electroplating nickel

over stainless steel. Particularly, conventional pre-plating surface treatment followed by

conventional plating has not been effective in producing sufficient chemical bond

between the stainless steel surface and the nickel coating [1]. This has been especially

true in the case of bright annealed stainless steel.Thus, there has been a need for a

process to strongly adhere nickel plating to a stainless steel parts. This study relates to

an improvement in the nickel-plating process by using high speed electroplating method

2

which causes the plating to better adhere to the stainless steel while, simultaneously, not

destroying the red rust resistance of the stainless steel surface[1,3].

1.2. Problem Statement

Common electroplating methods of nickel over stainless steel have some

problems. The adhesion between the nickel plating and stainless steel part has been

erratic. Also the preparation of the surface for electroplating is difficult, for example

wood’s nickel strikes are very sensitive to metallic impurities or the strike deposit is

usually very thin and examination of strike layer may not show any signs of pitting and

roughness. Sometimes even after following all the proper pre-plating treatment the

adhesion is also poor .Further, the red rust resistance of the nickel plated part has been

erratic because this oxide layer is not electrical conductive and so it should be removed

from the surface and it’s removing is a hard work. These problems lead to use better

methods for nickel electroplating over stainless steel such as high speed electroplating.

1.3. Objectives Study on:

� Common methods for nickel electroplating over stainless steel.

� Problems with common methods.

� High speed electroplating of nickel over stainless steel.

� Characteristics of nickel deposited on stainless steel.

1.4. Scope of Project

The scope of this research is:

• Using equipments for high speed electroplating of nickel over

stainless steel.

3

• Using SEM / EDX to study the microstructure of plating interface.

• Using nano hardness equipments to study the nature of adhesion

between nickel and stainless steel.

1.5. Thesis Outline

This thesis consists of six main chapters that are covering introduction,

literature review, research methodology, experimental working, results and

discussion and conclusion. First three chapters are covering proposal for the research

and next chapters are focusing on proposed method and validating it.

4

CHAPTER2

LITERATURE REVIEW 2.1. Overview

Electroplating is the electrodeposition of a layer of metal on a substrate. The aim of the

former is to manufacture metallic articles and the latter is to produce surface coatings [1]. To a

large extent, articles and coatings with different properties can be obtained by properly selecting

and control the conditions of electrodeposition.

Electroplating is the application of a metal coating to a metallic or other conducting

surface by an electrochemical process. The article to be plated (the work) is made the cathode

(negative electrode) of an electrolysis cell through which a direct electric current is passed. The

article is immersed in an aqueous solution (the bath) containing the required metal in an

oxidised form, either as an equated cation or as a complex ion. The anode is usually a bar of the

metal being plated. During electrolysis metal is deposited on to the work and metal from the bar

dissolves:

At cathode: Mz+(aq) + ze- → M(s)

At anode: M(s) → Mz+(aq) + ze-

Articles are electroplated to (i) alter their appearance, (ii) to provide a protective

coating,(iii) to give the article special surface properties,(iv) to give the article engineering or

mechanical properties.[2]

5

Figure 2.1: simple schematic of nickel electroplating

In figure 2.1 first the cell is filled with a nickel chloride which is dissolved in

water and a little acid. The NiCl2 salt ionizes in water into Ni++ ions and two parts of Cl-

ions. A wire is attached to the object, and the other end of the wire is attached to the

negative pole of a battery (with the blue wire in this picture) and the object is immersed

in the cell. A rod made of nickel is connected to the positive pole of the battery with the

red wire and immersed in the cell. Because the object to be plated is negatively charged

(by being connected to the negative pole of the battery), it attracts the positively charged

Ni++ ions. These Ni++ ions reach the object, and electrons flow from the object to the

Ni++ ions. For each ion of Ni++, 2 electrons are required to neutralize its positive charge

and reduce it to a metallic atom of Ni0. Thus the amount of metal that electroplates is

directly proportional to the number of electrons that the battery provides [2,3].

Meanwhile back at the anode, electrons are being removed from the nickel metal,

oxidizing it to the Ni++ state. Thus the nickel anode metal dissolves as Ni++ into the

solution, supplying replacement nickel for that which has been plated out. As long as the

battery doesn’t go dead, nickel continues to dissolve from the anode and plate out onto

the cathode. [2]

2.2. Properties of Nickel Electroplating

Electroplated nickel is used extensively in many engineering applications,

ranging from simple thin film for decorative purposes to corrosion and wear-resistant

6

coating [2,3].Nickel is plated for many reasons. First and foremost, nickel provides a

decorative appearance because of its ability to cover imperfections in the basis metal

(leveling). This deposit can be made brilliant and, when covered by a thin layer of

decorative chrome, will maintain its brilliance even under severe conditions [3]. When

nickel is applied in “duplex” form, excellent corrosion protection can also be achieved.

This requires plating two different kinds of nickel (semi-bright and bright nickel).

Nickel deposits also offer more wear ability than softer metals such as copper or zinc

and thus can be used when wear resistance is needed [3]. Because nickel is magnetic, it

can sometimes be plated where the ability to be magnetized is needed. Finally, nickel

can be made to plate with little or no stress and is therefore used for electroforming or

aerospace applications where stress needs to be held to a minimum [5]. In many

applications, many of these requirements are specified simultaneously, so that nickel is

often plated for more than just one reason [4].

There are some properties we can get from nickel plating:

• Decorative appearance. Lustrous bright, satin semi-bright or black nickel

coatings may be obtained by different plating methods.

• Corrosion protection.

• Wear resistance. Nickel deposited on a part made of a softer metal protects the

part from wear. Hardness of nickel plating may be controlled by the plating

process parameters.

• Low coefficient of friction.

• Ferromagnetism. Ferromagnetic parts (steel) may be plated by nickel without

changing their magnetic properties.

• Controllable internal mechanical stresses. Low stress coatings are important in

electroforming and applications, in which Fatigue strength is critical.[3,4]

Bright nickel plating is used extensively in automotive applications such as on

plated wheels, bright trim, truck exhausts, bumpers and restorations. In other

transportation areas, nickel is used for the bright work on motorcycles and bicycles.

Nickel is used to achieve brightness on hardware, such as hand tools [6]. In the home,

7

bright nickel is used on plumbing fixtures, light fixtures, appliances and wire goods

(racks). Bright nickel is also used for tubing applications such as on furniture and wheel

chairs. Most of these applications for bright nickel rely on the nickel for a decorative

appearance with corrosion protection and wear ability [3,5].

Bright nickel coating has been widely used in the area of decoration because of

its sound appearance and protective performance. Also, bright deposit is useful for the

electroforming of articles because it is always attended by the improvement of other

properties, such as leveling, grain refined [5]. Nickel is also used for engineering

purposes where brightness is not required. Thus, nickel is used on molds to provide wear

ability. As a barrier layer, nickel is plated on coins, jewelry and circuit boards. On strip

steel and in aerospace applications, it is used for low stress or for resizing. And nickel is

used in composites where a dispersed inorganic is codeposited (such as silicon carbide).

Most engineering applications use sulphate nickel, although nickel-plated strip steel uses

a nickel chloride/nickel sulfate bath. [3,28].

2.3. Solution are used for nickel electroplating

Different electrolyte solutions can be used for nickel electroplating

• Watts nickel plating solutions

• Nickel sulphate solutions

• All-Chloride solutions

• Sulfate-Chloride solutions

• All-Sulfate solutions

• Hard nickel solutions [3]

The most commonly used nickel baths are Watts baths, which use a combination

of nickel sulphate and nickel chloride. This combination of nickel salts allows for a

variety of characteristics. [4]

8

Table 2.1: Typical ranges for the components in watts bath

A typical Watts bath contains nickel sulphate, nickel chloride and boric acid.

Table 1 presents typical ranges for the components. Each component of the Watts

formulation performs a very important and necessary role in the production of

satisfactory deposits. [4].The mechanism of nickel electrodeposition from Watts

electrolytes was extensively studied. It was suggested that there are two successive

faradic reactions, the first involving the formation of nickel ads, followed by subsequent

reduction of nickel. However, in acidic electrolytes in the presence of freshly deposited

nickel, H+ is reduced to H ads, which strongly adheres to the electrode surface and

inhibits further reduction. The Watts electrolyte that contains nickel sulphate, nickel

chloride, and boric acid is widely applied for nickel electrodeposition, and its impact on

the development of modern nickel electroplating technology cannot be overestimated.

The dominant position of Watts solutions in industrial processes has been challenged

from time to time, but the only alternative adopted on a substantial scale are nickel

sulphamate solutions.[13]

9

2.4. Watts operation

The operating conditions for almost all Watts-type nickel baths are similar.

These typical parameters are given in Table 2.

Table 2.2: Typical Operating Parameters for Watts Nickel

2.4.1. pH

Bright or semi-bright baths are generally operated between pH 3.5–4.2.

Most organic addition agents give optimum brightness and leveling in this range. Higher

pH values always present the danger of adverse effects from the precipitation of metallic

contaminants and increased consumption of brightener components [4].

The pH should rise slowly during operation, since cathode efficiency is

slightly lower than anode efficiency. Sulfuric acid should be used for pH adjustment,

although hydrochloric acid may also be used with the added advantage of maintaining

the chloride ion concentration. However, the disadvantages of using hydrochloric acid

include not only the higher amounts required but the escaping hydrogen chloride gas,

10

especially from a hot, air-agitated solution. Nickel carbonate is preferred for increasing

the pH. It dissolves quite readily below a pH of 4.0. Very small adjustments to air

agitated solutions can be made below this value by adding water-carbonate slurry while

the tank is not in operation. Larger adjustments are best made in a treatment tank,

followed by filtration [4].

If the pH requires no adjustment or if it decreases, look for anode problems.

Insufficient anode areas, the overuse of inert auxiliary anodes, plugged anode bags or

poor anode contact might be the cause. If not eliminated, these problems can quickly

lead to salt depletion, poor plate distribution and off-color deposits from brightener

decomposition. If the pH rises abnormally, it is rarely a cathode efficiency problem,

provided the solution is in chemical balance. It is more likely that the acid is reacting

with dropped parts, a portion of the tank wall or alkaline cleaner solution carried in on

poorly maintained racks.[4]

2.4.2.Agitation and Temperature.

Agitation and temperature increase the diffusion rate of ions into the

cathode film. This is required in order to prevent burning and also to allow the

brightener additives to reach the cathode film. Air agitation from a low-pressure blower

has been universally accepted and is a contributing factor in many improvements in

nickel plating, especially in the decorative area. Air agitation has broadened operating

ranges of bath ingredients, reduced the required concentrations of addition agents and

minimized the use of wetting agents and hydrogen pitting problems. Note that the use of

air agitation will cause particulate matter to become suspended in the solution, resulting

in rough deposits unless good filtration practices are used.[4]

The temperature range is important in terms of physical properties and, along

with agitation, aids in keeping the bath components mixed and solubilized.

The temperature range is also an important factor in addition to agent response. If the

temperature is too high, the addition agent consumption is increased, adding to the

11

expense of operation and possible plating problems. If the temperature is too low, the

boric acid will begin to precipitate and the brighteners will not respond efficiently. [4]

2.4.3.Filtration.

The value of adequate continuous filtration for prevention of roughness and

pitting cannot be over-emphasized. Most bright nickel addition agents are not removed

to any great degree by activated carbon. Therefore, good filtration over an activated

carbon pack tends to keep concentrations of foreign organics, brightener decomposition

products and particulate matter at a minimum. A well-maintained, carbon-packed filter

of adequate capacity tends to keep the physical properties of the deposit near optimum

and minimizes the need for frequent batch treatments. It is better to apply smaller

amounts of carbon at regular intervals over the normal repacking cycle than to add the

total amount in one charge. This maintains the efficiency of the carbon pack by keeping

fresh carbon on the surface and minimizing the tendencies of channeling of the solution

through less restricted areas. A suggested rate of use for carbon packing filters is 1–2 lb

of carbon per 1,000 gal of nickel solution per 40–80 hr of operation. The rule of thumb

is that the minimum hourly discharge rate of the filter should equal the volume of the

solution. To achieve this with a carbon pack and as insoluble are collected, the filter

should have two to three times the capacity in order to avoid frequent repacking. [4]

2.4.4. Additives

It is known that organic additives are introduced in trace amounts to the plating

solutions to modify the structure, morphology and properties of the deposits. Thus

12

search and studies of the news additives are of large interest. For nickel plating from the

Watts bath, two types of additives, such as aromatic sulphones or suphonates and

compounds containing unsaturated groups such as >CfO, >CfS, −CfN, etc., are

recognized as brighteners. The influence of the additives on mechanism of

electrodeposition is not yet clearly understood. However, it is known that the additives

can act as wetting, leveling, brightening or buffering agents. [14]

2.5. Problems with Watts bathes

2.5.1. Roughness.

Roughness is generally the result of particulate matter suspended in the solution

and adhering to the work, especially on shelf areas. Gross roughness may be traced to

improper cleaning, torn anode bags, airborne dirt, dropped parts, precipitated calcium

sulfate, inadequate filtration or carbon and filter aid from an improperly packed filter. A

very fine type of roughness may be caused by precipitation of metallic contaminants in

the cathode film where the roughness may be confined to a particular current density

region. Chromium, iron and aluminum can precipitate as hydrates in the higher-current-

density areas, where the film pH is normally higher than that of the body of the solution.

A lower operating pH may be helpful in such cases. On occasion, high-current-density

roughness has also been traced to a magnetic condition of the work. Another source of

roughness can be the air blower used for air agitation. Inspection of the filter on the air

blower may reveal that it could be defective or missing.

If an external cause of roughness is not apparent, the quickest remedy is to

pump the solution to a spare tank and inspect the plating tank. The cause may be

apparent; dropped parts and torn anode bags are the most common sources. [4]

13

2.5.2. Adhesion.

Poor adhesion appears in many forms: nickel from basis metal; nickel from

nickel; bright nickel from semi-bright nickel; or subsequent chrome plate from nickel

plate. Separation from the basis metal generally indicates that undesirable surface films

are present and thus surface preparation has been inadequate. Poor cleaning may be

caused by improper chemical maintenance and control of cleaners and acid dips;

contamination and deterioration from prolonged use; poor rinsing; acid dips

contaminated with copper, chromium or oil; or an inadequate process cycle for a

particular soil or basis metal. Surface contamination will often be clearly visible or may

be indicated by water breaks after rinsing. Cleaning problems generally involve much

trial and error to identify their source. Try hand scrubbing between and skipping certain

operations, hand precleaning or hand dipping parts in buckets of fresh acid solutions.

If poor adhesion to the basis metal is traced to the nickel solution, severe contamination

is indicated. Chances are that other problems such as poor ductility and stress will have

given prior warnings. Of course, this does not rule out accidental spills and additions of

wrong chemicals.

Nickel peeling from nickel is generally caused by complete or partial loss of

contact during nickel plating. Total loss may result in an overall peeling condition.

Momentary or partial loss creates a bipolar condition in which current flow is from the

lesser negative (poor or no contact) rack to the more negative (good contact) rack

adjacent to it, resulting in an anodic oxide film. This will normally be confined to one

area, such as the trailing edges of parts plated in an automatic machine. Bipolarity

toward the end of the nickel cycle may appear as though the chromium is coming off as

a powder. A thickness check of the peeled versus the adherent portion will help locate

the general area of the problem. If there is no clear pattern and the condition is

intermittent, a faulty rack is indicated. Knowledge of bipolarity and other electrically

related problems is essential in nickel and chromium plating.

Poor adhesion of bright nickel from semi-bright nickel or chrome plate from

bright nickel, if not the result of electrical problems, can be caused by the nickel

14

passivating during transfer. Long transfer times or warm rinses will increase the chances

for nickel passivation. In these situations, the most common remedy is to activate the

nickel prior to plating using an acid or acid salt [4].

2.5.3. Ductility and stress.

Poor ductility and high stress are primarily an indication of a poor condition of

the plating solution. These properties are influenced by metallic and organic

contaminants, improper chemical or brightener balance and, in some cases, brightener

decomposition products. In all bright nickel processes, a balance of primary and

secondary addition agents is required, as they function synergistically to maintain

minimum stress and maximum ductility at the optimum degree of leveling and

brightness. Many ductility, stress and chromium plating problems have been traced to

out of balance secondary brightener levels.

Abnormally high voltages resulting from a lack of anode area may result in

oxidation or chlorination of some organic additives, which may not be removed by

carbon. Check all materials that are to come in contact with the solution, such as filter

aids and anode bags, for soluble organics that may be harmful. Good housekeeping,

solution control, continuous carbon filtration and periodic batch carbon treatments are

essential to control ductility problems [4].

15

2.5.4. Dull Deposits.

Lack of brightness can be the result of poor cleaning, solution contamination,

non-uniform agitation, improper chemical or brightener balance or failure to exercise

proper control of operating conditions. A low pH or low temperature may cause an

overall loss of brightness and poor leveling. Loss of brightness in a particular current

density may be the first clue to organic or metallic contamination. Dullness from poor

cleaning or organic contamination may appear in any current density area. Metallic’s

generally exhibit their effects by either co-deposition in the low-current-density area or

as hydrates in the high-current-density areas. Chemical analyses and plating tests will, in

most cases, reveal the course of corrective action that should be taken if the problem is

in the plating solution [4].

2.5.5. Purification of Nickel Solution.

There has been so much progress in nickel plating, and especially bright nickel,

that prolonged and frequent purification treatments are rare. A simple carbon treatment,

which may include peroxide, is generally sufficient and can be performed at some

convenient production interval. When the need for purification is indicated and the

cause of the problem is not readily apparent, chemical analyses and plating tests should

always be performed to determine the best course of action. If the tests duplicate the

plating results, the task is somewhat easier, but, if they do not, further investigation in

other areas would be in order. [4,11]

Too often, oxidation with peroxide or permanganate is tried without sufficient

investigation. Commonly, one hears that these oxidizers “burn out” organics and oxidize

16

them to carbon dioxide and water. In fact, sometimes the organic material is altered

structurally, making carbon adsorption more efficient, or it may be oxidized to a more

soluble form that has less deleterious effects on the deposit. But the oxidation could also

result in a more soluble product that has a greater detrimental effect. Carbon treatment is

usually better as the first step. First carbon treat, then filter, then determine if an

oxidization treatment is required.

Permanganate is a more powerful oxidizer than peroxide, but its use as a

treatment must include increasing the solution pH to precipitate and remove the

manganese dioxide. This, coupled with unreacted carbonate and carbon, may result in

filtration difficulties and abnormal solution losses. To avoid using excess permanganate,

which can result in serious loss of ductility and other deposit properties, dilute a 25–50

ml bath sample to 100–150 ml, adjust to a pH of 3.0–3.5, heat to 150°F and titrate with a

standard permanganate solution to a pink endpoint. Calculate the amount of

permanganate reacted; then try about one-half of this amounts in the plating bath in the

lab. This technique is also useful in checking the effectiveness of other organic removal

treatments.

.

Several suppliers offer equipment that purifies nickel and dye-free acid copper

plating solutions that operate like an ion-exchange unit. Like ion-exchange, this

purification system can be regenerated giving the purifying material many years of

useful life. These units can replace batch carbon treatments by keeping the plating

solutions at the purity level of almost new solutions for optimum plating performance.

Some of these purification units remove more organic contaminates than carbon (even

with peroxide/permanganate) and some have additional columns to remove metallic

impurities. Copper, lead, zinc, cadmium and some organics can be removed by low-

current-density electrolysis.[6,28] The most efficient current density may vary to some

degree for each metal, but 2–5 asf of cathode surface will be effective. Corrugated iron

is ideal for cathodes since it will provide a favorable distribution of current density. The

17

pieces of corrugated iron should be as long as the plating rack and should be cleaned,

pickled and nickel plated first at normal current density in order to avoid additional

contamination of the solution being dummied. The cathode area should be as large as

possible and good circulation or agitation of the solution should be employed. Inspect

the cathodes for flaky or powdery deposits and occasionally raise the current density a

few minutes as a seal. When finished, be sure to raise the current density again to seal in

the contaminants. [4,16]

2.6. Problems with woods nickel striking

1. Wood’s nickel strikes are very sensitive to metallic impurities. When the strike bath

is contaminated with heavy metals, the usual results are brittleness and a darking of the

deposit.

2. A strike deposit is usually very thin and examination of the strike layer may not show

any signs of pitting and roughness. [5]

2.7. Process of nickel electroplating over stainless steel

The stainless steel is very difficult to be coated with nickel because the oxide

layer which form on it’s surface is non conductive and it’s insulator so it can not transfer

electrons. It requires a different preplate sequence including a nickel strike. . A nickel

strike is a very thin coat of a nickel that will stick to stainless that has been properly

cleaned and activated. If a plating process is done wrong, there is no upper limit on the

percentage of rejects. Wood's nickel is the most popular. Typically a Woods Strike is

used. It is a very high chloride bath at a very low pH that plates very slowly and is

extremely highly compressive stressed. [6].

18

In a process for plating nickel upon a surface of a workpiece made of stainless

steel, the workpiece is immersed in an electrolytic sulfuric acid bath, with the workpiece

anodically connected. Thus, DC current flows from the workpiece, through the bath, to a

separate cathode in the bath. Thereafter, the sulfuric acid is rinsed from the workpiece

and the workpiece surface is electroplated with nickel which will strongly adhere to the

surface. Finally, the nickel-plated part may be conventionally electroplated with chrome

.A process for electroplating a stainless steel part comprising essentially the steps of:

(a) Cleaning the surface of the part;

(b) Treating the surface of the part by immersing it in an electrolytic bath, sid

electrolytic bath consisting of sulfuric acid, the concentration of said sulfuric acid being

about 10% by volume, with the part connected to be anodic, such that DC current flows

from the part through the bath to a separate cathode in the electrolytic bath;

(c) Rinsing the sulfuric acid off the part;

(d) Electroplating nickel upon the surface of the part by immersing it in an electrolytic,

nickel solution; whereby the nickel plating will strongly adhere to the surface of the

part without destroying the red rust resistance of the stainless steel part.[7]

2.7.1. Background of Process

It is common practice to nickel plate many different types of industrial parts

which are made of stainless steel in order to give the parts a bright, shiny surface. By

way of example, automotive vehicle body moldings, door handles, and other functional

or decorative parts are chrome-plated for appearance purposes. Frequently, such parts

are made of stainless steel to prevent rusting [4].

19

In commercial practice, nickel plating stainless steel parts typically is

accomplished by initially buffing the stainless steel to achieve a high luster and then

electroplating with chromium to retain the high luster and to make the finished surface

more durable. In the past, stainless steel parts have been electroplated with nickel before

the chromium electrolytic plating step. But, the adhesion between the nickel plating and

the steel part has been erratic. Further, the red rust resistance of the nickel plated part

has been erratic [14].

It has been understood by those skilled in the art that proper adhesion and good

red rust resistance could not be consistently achieved when electroplating nickel over

stainless steel. Particularly, conventional pre-plating surface treatment followed by

conventional plating has not been effective in producing sufficient chemical bond

between the stainless steel surface and the nickel coating. This has been especially true

in the case of bright annealed stainless steel. Thus, there has been a need for a process to

strongly adhere nickel plating to an annealed stainless steel workpiece and to maintain

red rust resistance of the plated part [15,20, 23].

This study relates to an improvement in the nickel-plating process by high speed

electroplating of nickel over stainless steel which causes the plating to better adhere to

the stainless steel while, simultaneously, not destroying the red rust resistance of the

stainless steel surface. [19,22]

2.7.2. Summary of Process

The study herein contemplates an improvement in the conventional, nickel

plating process for plating stainless steel workpieces wherein the pre-plating,

electrolytic sulfuric acid surface treatment step is performed with the workpiece

20

connected as an anode in the electrolytic bath circuit. That is, current flows from the

work pieces, through the bath to a separate cathode, during the time that the surfaces are

subjected to the electrolytic acid bath. Thereafter, the sulfuric acid is rinsed away, and

the nickel plating and chrome plating are applied in the conventional manner.[7]

By connecting the workpieces anodically in the electrolytic acid bath, there is a

marked improvement in the adherence between the nickel plating to the surface of a

workpiece or part made of bright, stainless steel. This adherence is unexpected and

contrary to the normal understanding of the art that the part, under electrolytic acidic

exposure, should be cathodic or neutral in the electrical system. That is, by reversing the

flow of electrons, namely by flowing them away from the part rather than to the part, the

surface is remarkably activated to strongly adhere to the subsequently applied nickel

plating.[7,21]

An object of this study is to produce good, commercial nickel plating of

stainless steel, and especially bright, annealed stainless steel, which previously could not

be satisfactorily plated because the nickel did not consistently adhere to the surface of

such metal. A further object of this study is to enable the application of a conventional

nickel electroplating procedure to be used for nickel plating bright, annealed stainless

steel without materially changing the conventional procedure or increasing the expense

of operating it. That is, by reversing the flow of current in the electrolytic circuit so that

the current flows to the anodically-connected workpieces, without otherwise changing

the procedural steps or the equipment, it becomes commercially feasible to produce

strongly adhering nickel plating upon stainless steel parts. A further object of this study

is to improve the process for electroplating nickel upon the surface of a part made of

stainless steel while not adversely affecting or destroying the red rust resistance of the

stainless steel. By this process, the part retains, and may even have improved, resistance

to red rust, i.e., iron oxide formation.

21

2.8. Factors for good electroplating

2.8.1. Surface Preparation

Prior to plating operation the cathode (work piece) surface should be cleaned

from mineral oils, Rust protection oils, Cutting fluids (coolants), greases, paints, animal

lubricants and vegetable lubricants, fingerprints, miscellaneous solid particles, oxides,

scale, smut, rust [7].

2.8.2. Anodes

Small parts of high purity primary nickel (nickel rounds or nickel squares)

loaded into titanium baskets are used as anodes for nickel electroplating. Dimensions of

nickel rounds: 1” (25 mm) diameter and up to 0.5” (12 mm) thick. Dimensions of nickel

squares: 1”x1” (25×25 mm) and up to 0.5” (12 mm) thick. Sometimes nickel bars and

rods are used as anodes [7,24].

2.8.3. Current Efficiency

Current efficiency is a ratio of the current producing nickel deposit to the

total passing current.Anode current efficiency in nickel electroplating is about 100%. It

may decrease at high PH when nickel dissolution is accompanied by discharging

hydroxyl ions (OH-).

22

Cathode efficiency of nickel electroplating is 90-97%. 3-10% of the electric

current is consumed by discharging hydrogen ions (H+), which form bubbles of gaseous

Hydrogen (H2) on the cathode surface[7].

2.8.4. Anti-pitting additives

Hydrogen bubbles formed on the cathode surface and adhered to it may cause

pitting of the deposit. In order to enhance removal of the bubbles wetting agents are

added to the electrolyte. Wetting (anti-pitting) agents (e.g. sodium lauryl sulphate)

decrease the surface tension of the cathode and force the hydrogen bubbles out of the

surface [7].

2.8.5. Filtration

Continuous filtration of nickel plating baths with active carbon filters permits

to control both presence of foreign particles and organic contaminations (products of

brightener decomposition etc). The filtration pumps should turn over the solution a

minimum 1-2 times tank volume per hour [7].

2.8.6. Air agitation

Air agitation by low pressure blowers is used in nickel electroplating to

enhance removal of the hydrogen bubbles discharged at the cathode[7].

23

2.8.7. Temperature

Nickel electroplating processes are conducted at increased temperature, which

results in lower electrolyte resistance and therefore permits to decrease the voltage.

Additionally higher temperatures aid dissolution and prevent precipitation of boric acid

and other components[7].

2.9. Problems and Corrective Actions

2.9.1. Hydrogen evaluation

While the electrodeposition of these materials has been widely attempted in

aqueous solutions, hydrogen evolution reaction often occurs in the course of

electrodeposition resulting in profound effect on current efficiency and quality of the

nickel deposits, so that different additives may be needed to suppress such difficulties

[17].

2.9.1. Roughness

Roughness of nickel coating is generally caused by foreign particles suspended

in the electrolyte solution: air dust, torn anode bags, dropped parts, precipitates of boric

acid, metallic impurities or drag-in of incompatible solutions, particles of filter carbon

powder, parts of filter paper. Roughness may be also a result of deposition in low

brightener solutions at high current density.

Corrective actions: proper filtering, preventing drug-in, temperature control[8].

24

2.9.2. Pitting

Pitting is a result of hydrogen bubbles adhered to the cathode surface. It

usually occurs at low concentrations of wetting agent, low air agitation, high current

densities, and low boric acid concentrations.

Corrective actions: check the concentrations of ant-pitting (wetting) agent and

boric acid, increase air agitation, decrease the current density[8].

2.9.3. Poor Adhesion

Poor adhesion (peeling, blisters, low adhesion strength) of nickel coatings

may be generally caused either by poor pretreatment cleaning or poor acid activation of

the part surface. Activation acid contaminated with copper or chromium or improper

activation acid cause adhesion problems. For example: lead containing alloys are

activated by methane sulphonic acid or fluorides.

Corrective actions: check cleaning operations, check the activation acid[8,10].

2.9.4. High stress and low ductility

Different nickel electroplating solutions produce coatings with different levels

of internal mechanical stress and ductility. The lowest stress and maximum ductility are

provided by nickel sulphamate solutions. Brittle coatings are caused by excessive

25

concentrations of organic agents (levelers, brighteners), decomposition products of

brighteners, nickel chloride and metallic contaminants.

Corrective actions: active carbon treatment, control of nickel chloride[8].

2.9.5. Brighteners

In order to achieve bright and lustrous appearance of nickel plating organic and

inorganic agents (brighteners) are added to the electrolyte. It is known that organic

additives are introduced in trace amounts to the plating solutions to modify the structure,

morphology and properties of the deposits. Thus search and studies of the news

additives are of large interest. For nickel plating from the Watts bath, two types of

additives, such as aromatic sulphones or suphonates and compounds containing

unsaturated groups such as >CfO, >CfS, −CfN, etc., are recognized as brighteners.

The influence of the additives on mechanism of electrodeposition is not yet

clearly understood. However, it is known that the additives can act as wetting, leveling,

brightening or buffering agents.[14]

2.9.6. Current Density

Nickel electroplating involves a wide range of current density levels. Current

density directly determines the deposition rate of nickel to the base material—

specifically, the higher the current density, the quicker the deposition rate. Current

density, however, also affects plating adherence and plating quality, with higher current

density levels delivering poorer results. Therefore, the optimal level of current density

depends on the type of base material and specific type of results the final product

requires[8,25].

26

One way to avoid working at lower current densities is by employing a

discontinuous direct current to the electroplating solution. By allowing between one and

three seconds of break time between every eight to fifteen seconds of electrical current,

high current densities can produce a higher level of quality. A discontinuous current is

also beneficial for avoiding over-plating of specific sections on the base material [8,12].

2.9.7. Nickel Striking

Another solution to the current density issue involves incorporating a strike

layer to the initial electro nickel plating process. A strike layer, also known as a flash

layer, adheres a thin layer of high-quality nickel plating to the base material. Once up to

0.1 micrometers of nickel coats the product, a lower quality current density is used to

improve the speed of product completion. When different metals require plating to the

product’s base material, striking can be used. In cases where nickel serves as a poor

adherent to the base material, for example, copper can be a buffer prior to the electro

nickel-plating process [8].

2.9.8. Pre-treatment Process

Proper pre- and post-treatment of the base product has a direct correlation to

the quality and deposition rate of electro nickel plating. To help ensure uniform and

quality adhesion, chemical or manual preparation includes the following three steps:

• Pre-treatment surface cleaning: Surface cleaning entails eliminating

contaminants through the use of solvents, abrasive materials, alkaline cleaners,

acid etch, water, or a combination thereof.

• Surface modification: Modifying the exterior of the base product improves

adhesion through processes such as striking or metal hardening.

27

• Post-treatment surface cleaning: Performing finishing operations, such as

rinsing, end the electroplating process.

Once pre-treatment cleaning is complete, testing the level of cleanliness in the

base material prior to beginning the electro nickel plating process is a good idea. To do

this, the waterbreak test is recommended. In this test, the treated substrate is rinsed and

held vertical. If contaminants such as oils are absent, then a thin sheet of water remains

unbroken across the entire surface of the base material. [8]

2.10. High Speed Electroplating

The rate of electrodeposition , being governed as it is by Faraday’s law,

depends directly upon the current density applied on the cathode, but this current density

has a limiting value above which acceptable plate is not obtained. The anion present in

the nickel plating bath can affect this limiting current density, chloride and chloride

solutions has been investigated by Wesley et al amongst others, claims being made that

with a solution velocity of 23m/min, sound deposits could be obtained at

450A/dm2.Sulphate baths have been described in detail in many papers which

Hammond has recently reviewed [9].

The rate at which the electrolyte solution passes over the surface of cathode

has a considerable effect on the maximum current density at which satisfactory

electrodeposits are obtained. This has been recognized for many years and was the

reason for the introduction first of cathode movement, usually at the rate of about 0.1

m/s, and then air agitation , as means of providing solution movement over the cathode

and thus reducing the thickness of the diffusion layer. The most recent paper on this

28

effect is that by Gabe. The application of ultrasonic energy as a means of agitating

electroplating baths has been tried in the laboratory and its effect described, but this

technique does not seem to have been adopted for commercial nickel plating, possibly

because it appears that its benefits are little different from those obtained when using

violent air agitation [9,10,26].

Other means of speeding up electrolyte solution movement have been tried,

such as pumping, paddle rotation and impingement of jets, and some have been used on

a production scale. In particular, claims have been made that current densities up to

10A/dm2 can be achieved by the use of paddles or impellers which are said to give

solution speeds of about 0.5m/s, even in platting baths of large volume. However, as yet

no methods has been so revolutionary as to make electroplating fit readily into the

modern concept of high speed, continuous and automated production, as carried out in

many et al forming shops. However, General Motors did apply the principle of rapid

transfer between consecutive operations in what they termed their contour High Speed

Plating Machine. In this machine, the total time required for depositing 30 µm of multi-

layer nickel onto car bumper was less than 2min. The bumpers were mounted on

fixtures and passed one at a time through an automatic plant containing 25 successive

closed cells, one for each different cleaning, plating and rinsing treatment. In each

electrolytic cell, the bumper was placed only 10mm away from a conforming electrode.

Through this gap the electrolyte solution was pumped very rapidly to give solution

movement which was said to be 8m/s when the equipment was first installed, although

later it was lowered to5m/s. Nickel deposition was at first conducted at about

150A/dm2, but at the slower rate of solution movement this was reduced to about

100A/dm2.Not only did this technique result in a very high deposition rate but the use of

a conforming, insoluble anode meant that the metal distribution was much better than

when plating the same bumpers in the conventional manner. A ratio of 2:1 between

maximum and minimum thicknesses of nickel plate was achieved, compared with the

normal 8:1, thus saving 250 g nickel on each bumper. The nickel plating solutions were

conventional Watts’s type, but since lead anodes were used the bath did not contain

chlorides; even he proprietary brighteners were standard ones. The pH of the nickel

29

solutions fell as their nickel ion concentrations were depleted and so this was restored

by additions of nickel carbonate, which dissolved readily in the acidic solution (pH 3 or

less).Although the chemical a electrochemical operation f the plant was not without

difficulties, it was mainly he inability to solve the man engineering problems associate

with this machine and its ancillary equipment that led to this laudable pioneer effort

being brought to an end after two year. However, this topic is still interesting

electrochemists, as indicated by recent conference in Moscow [9,23].

30

CHAPTER 3

RESEARCH METHODOLOGY

3.1. Introduction

The main purpose of this study is learning high speed electroplating of

nickel over stainless steel, investigating of the level of adhesion between nickel layer

and stainless steel and deposition rate of nickel layer on stainless steel. To asses and

study on these purposes the need to apply SEM/TEM for microstructure of interface is

necessary. For studying the nature of adhesion nano hardness tools are needed to know

ductile or brittle nature of adhesion. To study the level of adhesion the need to some

scratch and adhesion tests including tape test are necessary.

3.2 Experimental Design

The methodology of this research is to directly electroplating of nickel over

stainless steel by using high speed electroplating technique. High speed electroplating is

a technique where the high speed movement of the plating solutions is 2.7 m/s and the

high rate of plating is more than 600 µm/h (Hussain, 2009)(20). In this research, three

parameters are involved during the electroplating processes which are different values of

current density, different values of temperature and different type of solutions used. The

type of nickel plating solution which will be used to plate nickel on the aluminium is

Watt’s bath solution and sulphate based nickel solution. Finally the nickel deposits will

31

be analyzed by using Scanning Electron Microscope (SEM) and adhesion testing. Figure

3.1 shows the flowchart used to conduct the electroplating process in order to achieve

the study

Figure 3.1: Flowchart to conduct the electroplating process

32

3.3. Stainless steel sample preparation

Specimen coupon size for the project study will be prepared where, stainless steelrod will be of diameter 10 mm and length 50 mm. Figure 3.2 illustrates the dimension of the specimen coupon.

Figure 3.2: Project specimen dimensions of the stainless steel rod

3.4. Solutions Preparation In this experiment, two different solutions were prepared for plating nickel on aluminium which are Watt’s solution and sulphate based nickel solution. Table 3.1 shows the summary of solution preparation according to their composition.

33

Solution I ( Watts) Solution II

q 300g ⁄ l Nickel Sulphate 300g ⁄ l Nickel Sulphate

100 g ⁄ l Boric Acid (H3BO3)

q 100 g ⁄ l Boric Acid (H3BO3 )

q 40 g/l Nickel chloride (NiCl2.6H2O)

3.5. Experimental Setup

Stainless steel samples were electroplated as follows:

• 10 mm rod with a diameter of 1 cm was used.

• Prepare watts solution or Sulphate based solution as an electrolyte

• Making anode and cathode close together and pass a high current density

through an electrolyte.

• The solution flows through anode and cathode at a rate of 2.7m/s.

• The experimental work will be done at different temperatures and current

densities but constant time.

• Nickel layer (10-80µm) will deposit on stainless steel without peeling of later.

• Using SEM /EDX to study the microstructure of interface and study the rate of

deposition versus changing the current density and changing the time.

• Using nano hardness tools to know the nature of adhesion.

Figure 3.3 shows the schematic diagram of the high speed plating equipment while

Figure 3.4 show the high speed plating equipment developed by M S Hussain (Patent

pending).

34

Figure 3.3: Schematic diagram showing the setup of high speed electroplating of nickel

on stainless steel. (Patent pending)[18]

35

Figure 3.4: High speed electroplating equipment invented by Dr. Sakhawat Hussain

A)Surface of cathode B)anode and cathode positioned close together C)Water pomp to

supply the speed of solution (Patent pending)

3.6. Sample preparation

To explore the level of adhesion between nickel layer and stainless steel part

and to investigate the rate of deposition of nickel on stainless steel, experimental tests

has been done at different temperatures (55 ° C, 60 ° C, 70 ° C), different Current

densities (0.13- 1.3 A/cm2) and different electrolyte solutions (Watts ,Sulphate based

solution).Experimental working has done at these temperatures and current densities in

nickel Watts solution.

36

Table 3.1: shows various current densities applied at three different pre-set temperatures

T=55 °C T=60 °C T=70 °C

C.D=0.13 A/cm2 C.D=0.13 A/cm2 C.D=0.13 A/cm2

C.D=0.26 A/cm2 C.D=0.26 A/cm2 C.D=0.26 A/cm2

C.D=0.39 A/cm2 C.D=0.39 A/cm2 C.D=0.39 A/cm2

C.D=0.52 A/cm2 C.D=0.52 A/cm2 C.D=0.52 A/cm2

C.D=0.65 A/cm2 C.D=0.65 A/cm2 C.D=0.65 A/cm2

C.D=0.78 A/cm2 C.D=0.78 A/cm2 C.D=0.78 A/cm2

C.D=0.91 A/cm2 C.D=0.91 A/cm2 C.D=0.91 A/cm2

C.D=1.17 A/cm2 C.D=1.17 A/cm2 C.D=1.17 A/cm2

C.D=1.3 A/cm2 C.D=1.3 A/cm2 C.D=1.3 A/cm2

3.7. Preparation of samples (for SEM)

A selected numbers of nickel plated stainless steel samples were prepared for

SEM as follows:

I. Wire cutting the cross section of sample

II. Cold or hot mounting

37

III. Grinding and polishing the surface

IV. Gold sputtering

V. Using SEM for characterization

Figure 3.5 a) Cross section of sample b) Mounted sample c) polished sample

3.8. Sample preparation for TEM

TEM requires a very lengthy and sensitive sample preparation. A selected numbers of

plated samples were given the following treatment:

I. Using a wire cutting machine samples were cut to a thickness of 0.5 mm

II. These samples were ground to a thickness of 0.5 µm

III. Punching

Figure 3.6:a)make a layer as thin as possible b) punching c)very small sample for

ion polishing

38

IV. Ion milling

Ion milling is the last but the most important step of the preparation process.

The sample is mounted on a specimen holder and ion beam-polished to generate an

electron transparent area. This is accomplished by turning the ion guns on and off during

the sample rotation. The left and right ion guns are tilted at 10° from the top and the

bottom, respectively. As soon as the perforation is detected, the voltage of the ion beams

is reduced to a lower level and the incident angle is changed to 4° to enlarge the

transparent area for TEM investigation. In preparing TEM, it is sometimes observed that

the films might be completely removed by ion bombardment before there was a thin

area on the metallic substrates. Because of this situation, it is not feasible to specify the

ion milling time required for the creation of a thin area in metallic substrates. For each

combination of substrate and film, the conditions and time required for the milling must

be confirmed by a specific analysis or an elaborate experiment to make sure there is a

thin area in the films suitable for TEM observation.

3.9. Adhesion testing

After the electroplating process, adhesion testing was required to quantify the

strength of the bond between the nickel layer and the stainless steel substrate. Adhesion

testing in the paint and coating industries is necessary to ensure the paint or coating will

adhere properly to the substrates to which they are applied. The adhesion between a

coating and its substrate has been measured in various ways. For example, coatings are

often evaluated by a scratch test. A calibrated scratching tool is applied to a test sample.

A high quality adhesion between the coating and the substrate prevents the penetration

of the scratching tool and the workpiece passes. If the adhesion is low, however, the tool

can penetrate and scratch the coating, in which case the sample fails.

39

3.9.1. Scratch test

Scratch Test is a method used for determining the adhesion strength of a

nickel layer on Stainless steel. Figure 3.7 shows a schematic diagram of a scratch test

equipment.During the scratch test, the stage moves in the x direction and a probe

remains stationary while applying a controlled load on the specimen and the load is

applied by a pin.

Figure 3.7: Schematic image of scratch test

Figure 3.8: scratch test on samples

40

3.9.2. Nano scratch test

Nano scratch test has been done across the interface. (Load=50.05 mn)

These experiments were carried out three times:

Trial1 = Long scratch across interface (normal to scratch)

Trial2 = 40 mm scratch across interface (normal to scratch)

Trial3 = 60 mm scratch across interface (oblique angle to scratch)

A 4.4 mm spheronical indenter used as scratch probe

3.9.3. Tape test

Another test to investigate the level adhesion is tape test. In this test, a knife

was used as a cutting device. Two cuts were made into the coating with a 30 – 45 degree

angle between legs and down to the substrate which intersects to form an “X”. Tape was

placed on the centre of the intersection of the cuts and then removed rapidly. The X-cut

area is then inspected for removal of coating from the substrate or previous coating and

rated. A standard method for the application and performance of these tests is available

in ASTM D3359.

41

Figure 3.9 shows the tape test on the sample.

Figure 3.9: Tape test

3.10. Expected findings

It is expected by increasing the temperature of the electrolyte solution the rate of

deposition will be increased and also by increasing the current density the rate of

deposition will be increase however the level of adhesion will being decrease by

increasing these two factors.

Table 3.2. shows the expected results after experiment

Parameters be change purpose Expection

Temperature To look at changing of

thickness

By increasing temperature

→Thickness will be increase

Solutions To see different rates of

electroplating

Watt’s solution→ slow rate

Sulphate solution→ high rate

Current density To look at changing of

thickness

By increasing current density

→ Thickness will be increase

42

CHAPTER 4

RESULTS AND DISCUSSION

4.1 Introduction

This chapter will discuss the results of plating nickel on stainless steel samples

that are produced via high speed electroplating method. This result is divided into two

different analyses: which are adhesion analysis, and morphology analysis for adhesion

analysis, the samples were analyzed using the knife and tape test. For morphology

analysis, the samples were characterized using a Scanning Electron Microscope (SEM)

to measure the thickness of the layer and Transmission Electron Microscopy to

investigate the particle size of nickel over stainless steel. In this chapter, the effect of

current density, temperature and type of solution on thickness of nickel plated, are

discussed.

4.2. Effect of temperature on rate of deposition

By increasing the temperature deposition rate will be increased.Relatively

high temperatures from55 c° to 70c° are helpful for supporting high current densities.

Figure 4.1: SEM image shows the thickness of nickel layer at T=60°C, C.D=1.3A/cm2

43

Figure 4.2: SEM image shows the thickness of nickel layer at T=55°C,C.D=1.3A/cm2

As shown the thickness of nickel layer is increased by increasing the temperature.

Table4.1: Rate of deposition is increased by increasing temperature and current density

44

4.3. Effect of solution on rate of deposition

Watts solution showed higher rate of plating compared to the sulphate based

nickel solution.

Figure 4.3: SEM image shows the thickness of nickel layer at T=60°C, C.D=0.13

A/cm2 Watts solution

Figure 4.4: SEM image shows the thickness of nickel layer at T=60°C, C.D=0.13

A/cm2 Sulphate based solution

45

4.4. Effect of current density on rate of deposition

Nickel electroplating involves a wide range of current density levels. Current

density determines the deposition rate of nickel to the base material .The higher the

current density, the faster the deposition rate. Current density, however, also affects

plating adherence and plating quality, with higher current density levels produces poorer

results. Therefore, the optimal level of current density depends on the type of base

material and specific type of results the final product requires.

One way to avoid working at lower current densities is by employing a discontinuous

direct current to the electroplating solution. By allowing between one and three seconds

of break time between every eight to fifteen seconds of electrical current, high current

densities can produce a higher level of quality. A discontinuous current is also beneficial

for avoiding over-plating of specific sections on the base material.

By increasing the current densities from 0.13 A/cm2 to 1.3 A/cm2 the rate of deposition

was increased however the level of adhesion was lowering due to high current density.

By current densities above 1.3 A/cm2 nickel layer could not be electroplated on

stainless steel. On the edges of Ni layer there were dendrites growth.

Figure 4.5: SEM image shows the thickness of nickel layer at T=55°C,C.D=0.25A/cm2

46

Figure 4.6: SEM image shows the thickness of nickel layer at T=55° C, C.D=1.14

A/cm2

As shown in figure 4.5 and figure 4.6 the rate of deposition was increased by

increasing the current density because the rate of transferring of nickel atoms was

increased and more nickel atoms were deposited on nickel layer. Current density

directly determines the deposition rate of nickel to the stainless steel specifically, the

higher the current density, the faster the deposition rate. Current density, however, also

affects plating adherence and plating quality, with higher current density levels

delivering poorer results and the quality of nickel layer lowered. At currents higher than

1.3 A/cm2 the nickel layer could not deposit on the stainless steel surface and dendrite

growth on the edges of nickel could be shown. Figure 4.7 shows the dendrite growth of

nickel and it could not deposit on the stainless steel surface. So the optimum current

density for high speed electroplating is below 1.3 A/cm2, and at higher than 1.3 A/cm2

the quality of nickel layer is lowered and also the adhesion is very low.

47

Figure 4.7 and figure 4.8 show the dentritic growth of nickel at current higher than

1.3 A/cm2.

Figure 4.7: Optical micrograph showing dendritic growth of the nickel deposits at

higher current density

Figure 4.8: SEM image showing the dendritic growth

48

4.5. Nano scratch test Analysis

Figure 4.9 shows the results after first and second trials.

Scratch test was done on the samples. The results show the electroplated samples with

current density less than 1.3 A/cm2 have good adhesion and the samples with current

densities higher than 1.3 A/ cm2 did not show good adhesion.

Figure 4.9: Nano scratch tests across interface

As shown in figure 4.9 there is no debonding between nickel layer and stainless steel

part so the adhesion level is good.

49

Figure 4.10 shows the hardness of nickel layer and Stainless steel part.

Figure 4.10: Friction against distance

As shown in figure 4.10 the stainless steel part is harder than nickel layer.

50

Figure 4.11 shows the oblique scratch test across the interface of sample. This

test is useful for assessing coating adhesion.

Figure 4.11: oblique scratch across interface

As shown in figure 4.11 there is no deboning between nickel layer and stainless

steel part and this shows a good adhesion.

4.6. Tape test analysis

The results show that the adhesion of samples which electroplated in current

densities below 1.3A/cm2 have good adhesion but the samples which electroplated in

current densities greater than 1.3 A/ cm2 don’t have good adhesion and the nickel layer

peels off easily.

51

Figure 4.12: nickel layer is peeled off (T=60°C, C.D=2.6A/cm2)

4.7. Type of failure

If current densities less than 1.3 A/cm2 a ductile type of failure was observed,

because some nickel amounts are in the stainless steel and some amounts of stainless

steel elements are in nickel layer.

Figure 4.13: SEM image of exterior layer of stainless steel at C.D <1.3 A/cm2 by peel

test

52

Figure 4.14: SEM image of interior layer of nickel at C.D <1.3 A/cm2 by peel test

Figure 4.15 and figure 4.16 show the EDAX of exterior layer of stainless steel and

interior layer of nickel after peel test.

Figure 4.15: EDAX of exterior layer of stainless steel at C.D <1.3 A/Cm2

53

Figure 4.16: EDAX of interior layer of nickel at C.D <1.3 A/Cm2

As seen in figure 4.15 small amounts of nickel are present in stainless steel and

some elements from stainless steel are seen on the peeled nickel layer.

When the current density is greater than 1A/cm2 the type of failure observed after peel

test is brittle type of failure. EDAX- elemental analysis does not show any elemental

transfer from the stainless steel to the peeled nickel layer and vice versa.

Figure 4.17: SEM image of exterior layer of stainless steel at C.D>1.3 A/cm2

54

Figure 4.18: SEM image of interior layer of nickel at C.D>1.3 A/cm2

Figures 4.19 and 4.20 show the EDAX of interior layer of nickel and exterior layer of

stainless steel.

Figure 4.19: EDAX of exterior layer of stainless steel at C.D> 1.3A/cm2

55

Figure 4.20: EDAX of interior layer of nickel at C.D> 1.3A/cm2

As shown in figure and 4.20 EDAX of interior layer of nickel there is no net

elemental transfer of stainless steel to the nickel layer and vice versa.

.

4.8. Nickel Electro crystallization

Electrocrystallization is the process of absorption, nucleation and growth of

particles (12).Nickel electrodeposition takes place at electrode: electrolyte interfaces

under the influence of an electric field and include a number of phase formation

phenomena.Fundamental aspects of electrocrystallization of metals are directly related

to nucleation and crystal growth processes. There are some growing centres in the

processes of multiple nucleation and growth.

56

Figure 4.21 : Schematic diagram of electrochemical growth of a stepped crystal surface

(1) ion in the electrolyte (2) adatom on the flat terrace (3) atoms in kink site (4) vacancy

(5) atoms in two atomic cluster(1 2 3) surface diffusion mechanism (1 3) direct

attachment mechanism (a,b,c) distribution of adatoms concentration

The basic thermodynamic concepts of nucleation and crystal growth electro

crystallization includes nucleation ad growth processes.Nucleation and growth processes

in electrochemical metal deposition determine the physical, chemical, electric properties

of Ni on stainless steel.

In conventional methods such as electroplated nickel the nucleation and

growth stages take place slowly. In high speed electroplating the nucleation and growth

stages take place very rapidly. At current densities greater than 1.3 A/cm2 dendritic

growth took place very rapidly.

57

Figure 4.22: SEM image of nickel layer was peeled off at C.D=2.6A/cm2,T=60°C

Figure 4.23: Optical micrograph showing dendritic growth of the nickel deposits at

higher current density

Figure 4.24 a) shows a TEM images(top view) of nickel deposited on stainless steel by

high speed electrodeposition .

Figure 4.24(b) shows the particle size of the nickel deposits. The particle size

measurements shows that the electroplated nickel particles are very fine and are

nanocrystalline.As these are presence of particles as small as 4nm in diameters

58

Figure 4.24: a)TEM image of nano-crystalline nickel over stainless steel b) particle size

of nickel deposites

59

CHAPTER 5

5.1. Conclusion

I. Stainless steel was electroplated directly with nickel without the need for any

pre-treatment.

II. The rate of electrodeposition by high speed electroplating method has been

found to be 30 times faster than conventional electroplating using Watts type of

electrolyte

III. The rate of electrodeposition by this process increased by increasing temperature

and current density

IV. Watt’s nickel electrolyte gave faster rate of plating than sulphate based nickel

solution.

V. The level of adhesion was much higher at lower current densities.At current

densities higher than 1.3 A/cm2 the level of adhesion becomes

unacceptable/peels of easily.

VI. The electrodeposited nickel has been found to be nano-crystalline_TEM images

show presence of particles as small as 4 nm in diameter

60

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