Review Metal

8/10/2019 Review Metal

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Short

review

on

metal


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ev ew

To have better properties, materials can be fabricated and be

composed of different compounds / atoms alloys material. Example : to imoprove mechanical properties and corrosion resistance such asvarious steels

characteristic of microstructure of the alloys.

e c arac er s c on e a oys can e escr e us ng ase

Diagram of the alloys. The characteristic is determined by elements

present, composition, heat treatment.

Valuable informations of alloys are often explainable from their

Phase Dia ram


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Material erformance de end on

micro structure

Material processing

Material properties

Material performance


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Phase

Diagrams

for

meta csystem

hasedia ram

The

iron

carbon

system


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ome e n onsomponent : pure sta e compoun s meta s or ox es o w c an a oy

is composed

System : material under consideration or possible alloys consisting of the

same components.

Solid solution : a solution that consists of at least two differentcomponents.

homogeneous throughout.

solid solution : impurity atoms are randomly and uniformly distributed within the solid

Solubility limit : maximum concentration of solute can be dissolved in the

solvent in a solid solution.

Phase : homogeneous portion of a system that has uniform physical andchemical charateristics


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ome e n ons

Equilibrium : a state or condition where free energy of the system is

minimum (time independent property)

a function of temperature,

Phase equillibrium: equillibrium state when it applies to a system

.

Metastable state: a non equilibrium condition of a system since the

equ r um s a e s very s ow y o reac .


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-

If more than one phase exist in a given system, each will have its

own distinct properties A boundary separating the phases will exist across which there will be

discontinuous and abrupt change in physical and/or chemical properties

Water and ice, as well as, a substance with two or more polymorphic forms

,

differ.


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Nickel - Copper Meltingpoint of Ni

Three different phase regions or

fields appear on the diagram :

phase, liquid L and two phase

Below 1080 C, copper and

each other in the solid state forall composition

Melting

The copper-nickel system are

termed isomorphous due to this

Cu

complete liquid and solid

solubility of the two component.

Why???


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e p ase compos on

rature, L (liquid)

ATA

Tempe

L +

TB

Tie line / Isotherm

CTC

Composition, wt%CoCL C


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Development of

microstructure

With continued cooling, both compositions and relative amount each of the phases willchan e The composition of the liquid and the phase will follow the liquidus and solidus lines, respectively

The fraction of phase increases with continued cooling.

Over all alloy composition remains unchanged during the cooling -


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Develo ment of

microstructure

nonequilibrium

Condition of equilibrium solidification is realized only for extremely slow cooling rates

In practical situations, cooling rates is too rapid to allow compositional readjustments (by diffusionalprocesses .

Diffusion rates are slow for solid phase and decrease with the decrease in temperature.

The degree of displacement of non-equilibrium solidus curve from the equilibrium onedepends on the cooling rate, the slower cooling rate, the smaller the displacement

Important consequences for alloys that have solidified under non-equilibrium condition

Segregation : concentration gradients are established across the grains (not in liquid phase) This can be eliminated by a homogenization heat treatment carried out below the solidus curve.


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ron- ron ar e e- e3 ase agram

BCC

FCC

BCC

Iron carbide


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- -

u ec c reac on a :

cooling

3. . .heating

Eutectoid reaction at 727C:

3(0.76 % ) (0.022 % ) (6.7 % )

cooling

heatingwt C wt C Fe C wt C


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Development of microsructure in iron-carbon alloys

The most commond Fe-C alloys:

Pure iron (< 0.008 wt%C) Steel (0.008 wt%C 2.14 wt%C)

Cast iron (2.14 wt%C 6.70 wt%C)

The microstructure of the alloys is strongly dependent onboth the C content and tem erature treatment durin

fabrication.


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Development of microsructurein iron-carbon alloys

Heating or cooling through eutectoid


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in iron-carbon alloys

for an iron carbon alloy of hypo-eutectoid composition as it is cooled from withinteh austenite phase region to below the eutectoid temperature


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Photograph of a 0.38 wt % C steel having a microstructure consisting of pearlite

and proeutectoid ferrite


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for an iron carbon alloy of hyper-eutectoid composition as it is cooled from withinthe austenite phase region to below the eutectoid temperature


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rans ormas us en e

Slow RapidModerate

+ +

oo ng uenc ngCooling

a proeutectoid phase

( + cm phase) (BCT phase)

Reheating Most of hase transformation do not occur instantaneousl

Tempered Martensite

consideration is given to the dependence of transformation

progress on time (the transformation rate).

cm ase Phase transformation is divided into 3 classification

simple diffusion-dependent transformation, ex. Pure

metal

diffusion-dependent transformation, pearlite, spheroidite

diffusion-less transformation, ex. Martensitic


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transformationdiagram

austenite to pearlite

trans ormat on


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Isothermal transformation diagram for a eutectoid iron-carbon alloys withsuperimposed isothermal heat treatment curve (ABCD)


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Isothermal transformation diagram for a eutectoid iron-carbon alloys that has beenextended to lower temperatures


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Photomicrograph of steel having a spheroidite microstructure and the

martensite microstructure


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e comp e e so erma rans orma on agram or an ron car on a oy o

eutectoid composition (left) and that for an alloy steel (type 4340)


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-

determination for

three isothermal

eat treatments


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-

alloys


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-

alloys


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of iron-carbon alloys


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-

alloys

Electron micrograph of tempered martensite


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Mechanical behaviour of iron-carbon alloys

Hardness versus tempering time for a water quenched eutectoid plain carbon (1080) steel


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Review of phase transformations and

mec an ca proper es or ron-car onalloys


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Review of phase transformations and

mec an ca proper es or ron-car onalloys

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Review Metal