Lecture 1 Biomaterial

8/12/2019 Lecture 1 Biomaterial

1/55

BE906

Biomaterials and Biocompatibility

Lecture 1

Biomaterial. Introduction

Dr Alexander GallowayDr Patricia Muoz-Escalona


2/55

Growth of Engineering Materials


3/55

Materials

Alumina

Silicon carbideCement and concrete

Ceramics and

glassesBoro-silicate glass

Soda glass

PE, PP, PS

PVC, PMMA, PCEpoxy, polyester

Polymers and

elastomersButyl rubber

Isoprene

Steels

Cast irons

Al-alloys

Metals and alloys

Polymer,

Metal matrix,

Ceramic composites

Hybrid materialsFoams, sandwiches

Wood, bone

Cu-alloys

Ni-alloys

Ti-alloys


4/55

The

database

Links

Links

The structure of the CES Edu database

Materials

data-tableProcesses

data-table

Suppliers

data-table

References

data-table


5/55

Organising information: the MATERIALS TREE

Family

Metals

& alloys

Polymers

& elastomers

Hybrids

Structured

information

Unstructured

information

Class

Glass

Technical

ceramic

Non-technical

ceramic

Ceramics& glasses

Member

Alumina

Aluminanitride

Boroncarbide

Silicon

Tungstencarbide

Material records

Attributes

Boron carbide

Density

Mechanical props.

Thermal props.

Electrical props.

Optical props.

Corrosion props.

Documentation

-- specific

-- general

Kingdom

Materialsdata-table

Silicon

Density

Mechanical props.

Thermal props.

Electrical props.

Optical props.

Corrosion props.

Documentation

-- specific

-- general

Alumina

Density

Mechanical props.

Thermal props.

Electrical props.

Optical props.

Corrosion props.Documentation

-- specific

-- general


6/55

Structured information for Alumina


7/55


8/55

Unstructured information for Alumina


9/55

The world of manufacturing processes

Joining

Welding

Primary

shapingHeater Screw

Granular PolymerMould

Nozzle

Cylinder

No.8-CMYK-5/01

Injection moulding

Secondary

shaping

Machining

Surface

treating

Casting Rolling

Rapid

prototyping

Adhesives

Fasteners

Heat treating

Polishing Surface coatings

Drilling Turning

Milling


10/55

Organising information: the PROCESS TREE

Kingdom

Processesdata-table

Family

Joining

Shaping

Surfacing

Class

Casting

Deformation

Moulding

Composite

Powder

Rapid prototyping

Member

Molding

Injection

Tape casting

Pressing

Attributes

Process records

Pressing

Material

Shape

Size Range

Min. section

Tolerance

Roughness

Economic batch

Documentation

-- specific

-- general

Structured

information

Unstructured

information


11/55

Structured information for pressing


12/55

Unstructured information pressing


13/55

The 3 levels of the CES EduPack Software

Level 1

1st yearstudents:

Engineering, Materials

Science, Design

64materials, 75processes

The CES EduPack

Level 2

2nd - 4th year

students of Engineering

and Materials Science

and Design.

94materials, 107processes

Level 3

4th year, masters

and researchstudents

of Engineering

Materials and Design.

2916materials, 233 processes

Materials

science

Polymer

engineering

Mechanical

engineering

Architecture

& civil eng

Aeronautical

engineering


14/55

Age hardening ALUMINUM ALLOYS

The material

The high-strength aluminum alloys relyon age-hardening: a sequence of heatreatment steps that causes the precipitation

of a nano-scale dispersion of intermetallicshat impede dislocation motion and impart strength.

General propertiesDensity 2500 - 2900 kg/m^3Price 1.423 - 2.305 USD/kg

Mechanical propertiesYoung's modulus 68 - 80 GPaElastic limit 95 - 610 MPaTensile strength 180 - 620 MPaElongation 1 - 20 %Hardness - Vickers 60 - 160 HVFatigue strength at 10

7cycles 57 - 210 MPa

Fracture toughness 21 - 35 MPa.m^1/2

Thermal propertiesThermal conductor or insulator? Good conductor

Thermal conductivity 118 - 174 W/m.KThermal expansion 22 - 24 strain/CSpecific heat 890 - 1020 J/kg.KMelting point 495 - 640 CMaximum service temperature 120 - 170 C

Electrical propertiesElectrical conductor or insulator? Good conductor

Adding the science

Youngs modulus

Definition.

.

.

Measurement

.

.

Origins

.

.

Definition,

Measurement,

Science

Thermal expansion

Definition.

.

.

Measurement

.

.

Origins

.

.


15/55

Mechanical attributes Minimum Maximum

Density Mg/m3

Youngs modulus GPa

Elastic limit MPa

Thermal a ttributes

Max. service temp. C

T-expansion 10 -6/K

T-conductivity W/m.K

Electrical attributes

Good insulator

Poor insulator

Poor conductor

Good conductor

A limit stage Graph stage

Limit stage

Tree stage

Screening

Browse Select Search Print Search webToolbar

0.1

Metals

Polymers &

elastomersComposites

Foams

10301 1010 1020

Electrical resistivity (mW.cm)

Thermalconductivity

(W/m.s

)

Ceramics

10

1

100

0.01

Proces

s

Join

Shape

Surface

Cast

Deform

Mold

Composite

Powder

Prototype

A tree stage


16/55

Introduction

Metallic Elements:

Mg - magnesium

Al - aluminium

Ti - titanium Fe - iron

Na - sodium

Zr - zirconium

Non-Metallic Elements:

C - carbon

Si - silicon

S - sulphur N - nitrogen

B - boron

O - oxygen

What is a ceramic?

Ceramics can be a combination of:

Non-metallic and non-metallic elements

Metallic and non-metallic elements

Keramikos -- Burnt stuff


17/55

Traditional Ceramics

Clay based products

e.g. pottery, porcelain, bricks and tiles

Applications of Ceramics


18/55

Ceramics are refractory polycrystalline compounds:

Usually inorganic

Highly inert Hard and brittle

High compressive strength

Generally good electric and thermal insulators

Good aesthetic appearance


19/55

Advanced Ceramics

Developed to fulfil a particular need

Improved temperature resistance

Improved mechanical properties

Special electrical properties

Improved chemical resistance

Applications of Ceramics


20/55

Properties of Ceramics

Intrinsic Properties: Melting point

Youngs modulus

Coefficient of thermal expansion

Extrinsic Properties: Mechanical strength

Dielectric constant

Electrical conductivity


21/55

Intrinsic Properties

Determined by: Chemical composition

Atomic structure

E i i P i


22/55

Extrinsic Properties

Determined by:

Microstructure Grain size

Shape of grain

Volume fraction of phases

Porosity

Dense Microstructure Porous Microstructure


23/55

Microstructure

Property Desired Microstructure

High Strength Small grain size

Uniform microstructure

Flaw free

High Toughness Duplex microstructure with high

aspect ratios

High creep resistance Large grains

Absence of amorphous grainboundary phases


24/55

Production Process

DensePolycrystallineCeramic

Firing

Shaped Powder Form (Green Body)

Forming

Mixing

Powder


25/55

Forming Methods

Plastic Forming Extrusion

Injection moulding

Pressing Die pressing

Isostatic pressing

Casting Slip casting

Tape casting

P i


26/55

Pressing

Die Filling

Requires good flow characteristics

Powder Compaction

Initial structure contains large and small voids

Ejecting the Powder Compact

Elastic compression during pressing is released

resulting in strain recovery (springback)


27/55

Additives

Plasticisers

Softens the binder in the dry state and increases the

flexibility of the green body

Plasticiser molecules get between the polymer chains of

the binder

Softening the binder also decreases the green strength

Binders Provide bridges between particles

Aid granulation

Provide strength in the green body


28/55

Additives

Lubricants

Reduce friction between particles

Reduce friction between particles and die wall

Leads to high and more uniform packing density

Dispersants

Stabilise the slurry

Prevents particles sticking together- Absorbed onto particles which increases the repulsive forces by electrical

charging

Additives must be removed prior to sintering


29/55

Pressing

Die Pressing (uniaxial pressing) Simultaneous uniaxial compaction and shaping ofpowder in a rigid die

Advantages:

Good dimensional control due to

rigid die

Disadvantages:

Agglomeration of dry powder

Non-uniform transmission of

applied pressure


30/55

Pressing

Isostatic Pressing The application of a uniform pressure to the powder

contained in a flexible rubber container

Advantages: Less powder movement

No die walls

Ability to press relatively complex

shapes to a uniform density

Disadvantages: Inferior dimensional control

2 classes of isostatic pressing Wet bag pressing

Dry bag pressing


31/55

Pressing

Wet bag Pressing

a. The powder is placed in a watertight die with flexible walls

b. The die is immersed in a liquid in the high-pressure chamber

c. The pressure of the liquid increases deforming the die wall (pressure is transmit uniformly to the powder)

d. Green body is removed after compaction


32/55

Pressing

Dry bag Pressing


33/55

Casting

Involve the consolidation of powders from aconcentrated slurry (or slip)

Requires slip with:

Highest concentration of solidsto minimise shrinkage

Low enough viscosity to pour

Microstructural uniformity of the green body can be

controlled by the dispersants

C ti


34/55

Casting

Advantages: Uniform packing density

Can form large components and

complex shapes

Disadvantages: Narrow range of wall

thicknesses

Variable wall thickness is difficult

to cast Shrinkage control is complex

C


35/55

Casting

Tape casting

Slurry is spread over a surface covered with a removable

sheet of plastic using a carefully controlled blade

The resulting tape is then dried

The thickness of the tape is controlled by the height ofthe blade and the speed of travel


36/55

Plastic Forming Methods

Involves the plastic deformation of a mouldable powderadditive mixture

In the form of a paste

2 plastic forming methods Extrusion

Injection moulding



37/55


Important Considerations

Paste should exhibit plastic behaviour

At stresses below yield the paste should behave like a rigid solid

At stresses above yield the paste should deform

Extrusion

- The extruded body must be strong enough to be transported to a

drying rack without significant distortion

Achieved using a high viscosity binder


38/55


Injection Moulding

Important Considerations

Mixture must have low enough viscosity for mould filling

Controlled by binder

Advantages:

Good die filling for complex

shapes

Homogeneous green body due

to fluidity of mixture

Disadvantages:

Long processing cycle

Complicated to optimise

Time required to remove binder

from thick bodies can be long Moulds are expensive

hardened tool steel for abrasion

resistance

P d ti P


39/55

Production Process

DensePolycrystallineCeramic

Firing

Shaped Powder Form (Green Body)

Forming

Mixing

Powder

Fi i ( i t i )


40/55

Firing (sintering)

Firing of ceramic body at high temperature (below the meltingpoint) to obtain a dense component

Desired characteristics of final microstructureDense materials

Uniform grain size

Narrow grain size distribution

In order for sintering to occur we need the presence of:

A mechanism for material transport 1. Diffusion2. Viscous flaw

A source of energy to activate and

sustain the material transport

1. Heat

2. Energy gradients

Sintering Stages


41/55

Sintering Stages

Initial stage

Particles maintain their identity

Neck growth occurs

Little shrinkage occurs

Bonding occurs at the point of contact where

materials transport can occur and where the

surface energy is the highest

Si t i St


42/55

Sintering Stages

Intermediate stage Particle contacts have grown

Porosity forms interconnected network of channels

Majority of densification occurs

Shrinkage equivalent to the amount of reduction in porosity

Sintering Stages


43/55

Sintering Stages

Final stage

Isolated pores

Grain growth occurs

Mi t t


44/55

Microstructure

Important microstructural features Grain size

Shape of grain

Volume fraction of phases

Porosity

Densification


45/55

Densification

Driving force

Elimination of pore space

Reduces surface area of solid phase

Thereby reducing the surface energy

Densification lowers the free energy

M h i f M T t


46/55

Mechanisms of Mass Transport

Solid-state Sintering

Volume Diffusion

Occurs by the movement of point defects

Grain boundary diffusion

Grain boundaries are highly defective

Surface diffusion

Free surface of solid is not perfectly flat

Evaporation/Condensation

Volume Diffusion


47/55

Volume Diffusion

Vacancy mechanism Interstitial mechanism

Interstitialcy mechanism

Grain Boundary Diffusion


48/55

Grain Boundary Diffusion

Surface Diffusion


49/55

Surface Diffusion

Surface diffusion rates and mechanisms are affected by a variety of factors:

- Strength bond

- Orientation of the surface lattice

Liquid-Phase Sintering


50/55

Liquid-Phase Sintering

Composition of starting powder is tailored to form a small

amount of liquid

Small amount of liquid phase formed to enhance the sinteringprocess

Major commercial importance

Faster than solid state sintering

Results in uniform densification

Liquid Phase Sintering Stages


51/55

Liquid-Phase Sintering Stages

Particle rearrangement

Particle rearrangement due to capillary forces

Filling of pores by the liquid phase

Solution precipitation Small amounts of the solid particles are able to dissolve in the

liquid

The material can be reprecipitated into pore regions

Solid-state sintering

Once a rigid skeleton is formed, liquid phase sintering ends and

solid state sintering takes over

Li id Ph Si t i St


52/55

Liquid-Phase Sintering Stages

Summary 1


53/55

Summary 1

Forming

Ceramics can not be cast like metals due to their high

melting pointstypically formed from powders

3 main green forming techniques

Pressing

Casting

Plastic forming

Summary 2


54/55

Summary 2

Sintering

Firing of ceramic body at high temperature (below

melting point) to obtain a dense component

2 Sintering techniques

Solid State

Liquid phase

Small amount of liquid phase formed to enhance sintering

process

Much faster than solid state sintering


55/55

Documents

Lecture 1 Biomaterial