2. 2
Introduction
• Metallurgy is adomain of material science and engineering that studies the physical and chemical
behaviour of metallic elements, their intermetallic compounds and their mixtures, which are called
alloys.
• Metallurgy is also the technology of metals, the way in which science is applied to production of
metals and the engineering of metal components for usage in products for consumers and
manufactures.
• Theproduction of metals involves the processingof ores to extractthe metalthey contain andthe
mixtureofmetals,sometimeswithotherelements,toproduce alloys.
• In nature all metals will not be available in pure metallic forms rather they are present in the
combinedformminerals.Theycanbesulphidesoroxides,etc.
• Inminerals,it isnotthattheyhaveonlymetalbutwithmetaltherearesome unwantedelements.
• Metallurgy is distinguished from the craft of metalworking, although metalworking relies on
metallurgy.
3. MethodsofMetal Extraction
• The process of taking out pure metal from its ore is called as
Metal Extractionorit is alsocalledasExtractiveMetallurgy.
3
8. 8
Pyrometallurgy
Advantages:
• Asit is ahightemperatureprocess,theprocessofreactionisfast. Therefore
moremetalisproduced.
• Thecostofreducingagentandrawmaterialsisless.
• Liquidmetalandslagseparatesoutandhelpsinmetalextraction process.
• ThismethodcanbeusedforextractionofreactivemetalslikeZr.
Application:
MetalslikeFe,Zn,Pb,Cu,Al,Mg,As,etc.areextractedfromthis method.
9. 9
Hydrometallurgy
• Hydrometallurgy is concerned with processes involving aqueous
solutionstoextractmetalsfrom ores.
• Inearlierdays,hydrometallurgywasusedforlowgradeore.
• Removal of impurities by different physical methods, grinding are the basic
processesinpreparationoforeinhydrometallurgy.
• The first step in the hydro metallurgical process is leaching, which involves
dissolution of the valuable metals into the aqueous solution or a suitable
solvent.
11. 11
Hydrometallurgy
Afterthesolution is separatedfromtheoresolids, theextractis oftensubjected
to various processes of purification and concentration before
the valuable metal is recoveredeither in its metallic state or as
achemical compound.
Therateofprocesswill varywithtemperatureandpressureof liquor.
This may include precipitation, distillation, adsorption and
solvent extraction.
Example:AmajortargetofhydrometallurgyisCopper.
14. 14
Electrometallurgy
• It is a branch of metallurgy that deals with the application of electric
current either for electrolytic deposition or as a source of
heat. In other words it is a processes that take place in some form of
electrolyticcell.
• Electrometallurgy is the field concerned with the processes of
metal electrodeposition.
• Therearefollowingfourcategoriesoftheseprocesses
17. 17
CastIronVsWrought Iron
Cast Iron
• Castironsarebasicallythealloysofironandcarboninwhichthecarbon varies
between2.0to6.67 %.
• Commercial cast irons are complex in composition and contain carbon in the
rangeof 2.3 to 3.75 % with otherelementssuchassilicon, phosphorus,sulphurand
manganeseinsubstantialamount.
• Because of their poor ductility and malleability, they cannot be forged, rolled,
drawnor pressedinto the desired shape;but areformed by melting andcastingwith or
without machining to the required final shape and size, and hence the same “Cast
Irons”.
18. 18
CastIronVsWrought Iron
ApplicationsofCast Iron:
• Automobile engine blocks & heads, manifolds for internal
combustion engines, gasburners, machine tool bases, cylinder liners, intake
manifolds,soil pipes,counterweights,enclosures andhousings.
• Steering knuckles, gears, automotive and truck suspension components,
brake components, valves, pumps, linkages, hydraulic components, wind
turbinehousing.
• Parts for chemical processing plants, petroleum refining, food handling,
marineservice,controlofcorrosivefluids,pressure valves.
19. 19
CastIronVsWrought Iron
WroughtIron:
• Wroughtironis amechanicalmixtureofaverypureironandasilicate slag.
• Generally,wroughtironconsists0.02% carbon,0.05% Phosphorus, 0.02
% Silicon,0.008% Sulphur,0.05to1.50% slagandremainingamountof iron.
• Wrought iron is never cast, because it’s shaping is accomplished by
hammering,pressing,forging,etc.
• Wroughtironis popularforits highductility andfortheeasewithwhich it canbe
forgedandwelded.
• Theultimatestrengthofwroughtironcanbe increased considerablyby cold
working.
• Ithashighresistance towardsshock,fatigueandcorrosion.
21. CastIronVsWrought Iron
ApplicationsofWrought Iron:
Wroughtironis availableinvariousformssuchasplates,sheets, bars,structures,
rivets, chains, welding fittings, nipples and a wide range of tubular products
(pipes, tubes, and castings), etc. Hence, it is widely used in the following
applications:
Buildingconstruction:Undergroundservicelinesandelectrical conduit.
Rail road and marine: Diesel exhaust and air brake piping, tanker heating
coils,etc.
Industrial: Condensertubes,unfiredheatexchangers,acidand alkaliprocess
lines,etc.
Public works:Bridgerailings,drainagelines,slugetanksandli2n1 es.
22. CastandWrought Products
22
• When we say wrought material it basically means work which is
havingmanyconstituentslikeslagin it andcanbefurther processedforother
manufacturingprocesses.
• When we say cast structure or casting, it is one of the
manufacturingprocessinwhichrequiredworkpiece/materialis converted
intousefulform,shapeandsize.
• Castingis alwaysasolid formof materialconvertedinto the useful formfrom
liquid material. Casting has dendritic structure as cast conditioned products
which has specific mechanical properties that can be changed by giving
properheattreatment.
• Wroughtproductscanbefurtherprocessedforall manufacturing
processeslikerollingextrusion,etc.
23. 23
Comparisonbetween CastProductsandWroughtProducts
Sr.No. CastProducts WroughtProducts
1
Castproductsareobtainedfromliquid metal
byconversioninsolid.
Wrought products are obtained
whenexternalloadis subjectedon metal.
2 Castingisfinalmanufacturingprocess.
Further manufacturing
processes areapplied.
3
Castinggivessamepropertiesin all
directions.
Itshowsdirectionalproperties.
4 Itmayleadtoporosityproblem.
Porosity is almost zero as it
gets eliminatedin
mechanicalworking.
5
Canbemanufacturedinanyshapeand size. Largeandcomplexshapesarenot easyto
manufacture.
6 Brittlemetalscanalsobecasted.
Brittle material will break in
processeslikerolling.
24. 24
EquilibriumDiagram
• One of the important objectives of engineering metallurgy is to determine the
propertiesof material.
• The properties of material is a function of the microstructure which is further
dependent on the overall composition and variables such as temperature, pressure and
composition.
• Hence, to determine the phases present in the material system, an equilibrium or phase
diagramisplotted.
• Equilibrium diagram or phase diagram is a graphical representation of
various phases present in the material system at various temperature
andcomposition points.
• All phasediagramshavetemperatureastheordinate (Y-axis) andpercentage composition
byweightastheabscissa(X-axis).
26. 26
EquilibriumDiagram
Usesofequilibriumorphase diagram
It shows the various phases present at different composition and
temperature.
Itindicatesthesolidsolubilityofoneelementintheother.
Itshowsthetemperaturerangeoverwhichsolidificationorliquificationof materialsystem
occurs.
Inindicatesthetemperatureatwhichdifferentphasesstarttomelt.
27. 27
RelatedTermsandTheir Definitions
• System
• The substances that are isolated and unaffected by their surrounding are known as
system.
• The term system has a wider application, in that it refers to any portion of
objective space within specified boundaries subject to specified
variables.
• It may be composed of solids, liquids, gases or their combinations and may
havemetalsandnon-metalsseparatelyorinany combination.
• A system is capable of changing its composition, temperature, pressure,
density etc.if sucharequirementarises.
• Systems are classified according to the number of components that constitute
thesystem.Acomponentisaunitofthecompositionvariableof thesystem.
28. 28
RelatedTermsandTheir Definitions
• Phase
• Aphaseis definedashomogeneous,physicallydistinct portionsofthe system.
• Eachportion is homogeneous throughout, and regardless of where asample is taken in
that portion, the composition will be the same. These homogeneous, physically distinct
portionsofthesystemarecalledphase. Or
• It is a physically and chemically homogeneous composition of a
substance (system), separated from other portions by a surface and an
interface. But, each portion have different compositionand properties.
• In an equilibrium diagram, liquid is one phase and solid solution is another
phase.
29. 29
RelatedTermsandTheir Definitions
• Variable
• Avariableis definedasrelatedtomaterialsaretemperature,pressureand composition.Or
a particular phase exists under various conditions of temperature, pressure and
concentration.Theseparametersareknownas thevariablesofthephase.
• Theimportantstatevariableoverwhichthematerialsengineerhascontrol in establishing
microstructurearetemperature,pressureandcomposition.
• Withinthesystem,therearevariablethatspecifythecompositionsofthe phasespresent.
30. 30
RelatedTermsandTheir Definitions
• Component
• Thecomponentofthesystemmaybeelements,ionsorcompounds.They referto
the independent chemical species that comprise the system is called as
component.
• These are the substances, either chemical elements or chemical compounds whose
presenceis necessaryandsufficienttomakeasystem.
• A pure metal is a one-component system whereas an alloy of two metals is a two
component(binary) systemetc.
• In the ice water-steam system, the component is H2O.In the Cu-Nisystem, the elements
CuandNiarethecomponents,whereasin theAl2O3-Cr2O3 system,thetwo oxidescanbe
takentobecompounds.
31. 31
RelatedTermsandTheir Definitions
• Alloy
• Alloyis definedascombinationoftwoormoremetaltoform alloy.
• It is amixture of two or more elements having metallic properties. In the mixture, metal is
inthelargeproportionandtheotherscanbemetalsor non-metals.
• The element in the largest amount is called as base metal (parent
metal) or solvent and the other elements are called as alloying
elementsor solute.
32. 32
RelatedTermsandTheir Definitions
• SolidSolution
• The atoms of one element become a part of the space lattice of the other element, thus
formingasolidsolution.
• The element present in the alloy in the largest proportion is referred as base metal or
parentmetalorsolventandtheotherelementsarereferredas alloyingelementsorsolute.
• Solid solution is a type of alloy in which the atoms of alloying elements
are distributed in the base metal and both have similar crystal
structure.
• The composition of alloying elements may vary but the structure
shouldbe similar tothebase metal.
39. 39
RelatedTermsandTheir Definitions
• Hume–Rothery’sRulesforSolidSolubility
• Solidsolutionisanalloyoftwoormoreelementswhereintheatomic crystalstructure
ofthealloyingelement(solute) issameasthatofthe basemetalmatrix(solvent).
• The solubility limit of the solute in the solvent (of the alloying
element inthebasemetalmatrix)is governedby certainfactors.
• These governing factors are known as Hume – Rothery’s rules for solid
solubility.
40. 40
RelatedTermsandTheir Definitions
• Hume–Rothery’sRulesforSolidSolubility
1. AtomicSize
• Alloying elements having similar atomic size as that of the
base metalmatrixhavebetter solid solubility.
• Thegreaterthedifferenceinsizebetweentheatomsofthetwometals involved,the
smaller will be therangeoverwhichthey are soluble.
• If atomdiameterdiffer by more than 15% of that of the solventmetal thensolid
solubility is generally extremely small. But if diameter differ by less than
7% then, other things being equal, they will be likely to form solid
solutioninall proportions.
• Anydifferenceinatomicsizewill ofcourseproducesomestrainin the
resultant crystal structure.
41. RelatedTermsandTheir Definitions
• Hume–Rothery’sRulesforSolidSolubility
1. AtomicSize
Atomicradiusofaluminium(rAl) =0.142nm
Atomicradiusofsilicon(rSi) =0.112nm
% 𝐴𝑡𝑜 𝑚𝑖𝑐𝑠𝑖𝑧𝑒𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒=
0.142− 0.112
0.142
× 100
=
0.03
0.142
× 100
N1.1
The atomic radii of aluminium and silicon are 0.142 nmand 0.112 nm
respectively. Is they satisfy Hume Rothery Rule for complete solid
solubility?
= 21.12
Theatomicsizedifferenceexceeds15%,soHumeRotheryRulecannotsatisfy for
completesolidsolubility. 41
42. RelatedTermsandTheir Definitions
• Hume–Rothery’sRulesforSolidSolubility
1. AtomicSize
Atomicradiusofiron(rFe) =0.162nm Atomic
radiusofcarbon(rC) =0.120nm
% 𝐴𝑡𝑜 𝑚𝑖𝑐𝑠𝑖𝑧𝑒𝑑𝑖𝑓𝑓𝑒𝑟𝑒𝑛𝑐𝑒=
0.162− 0.120
0.162
× 100
=
0.042
0.162
× 100
N1.2
The atomic radii of Iron and carbon are 0.162 nm and 0.120 nm
respectively. Is they satisfy Hume Rothery Rule for complete solid
solubility?
= 25.92
Theatomicsizedifferenceexceeds15%,soHumeRotheryRulecannotsatisfy for
completesolidsolubility. 42
43. 43
RelatedTermsandTheir Definitions
• Hume–Rothery’sRulesforSolidSolubility
2. ElectrochemicalProperties/ Chemical Affinity
• The ions of all metals are electropositive but some are more
electropositivethan others.
• Generally,the greater difference in electropositivity, the greater will be the
chemical affinity of one ion for another so that they will tend to
formacompoundratherthanasolid solution.
• Ifontheotherhandtheirelectropositivearesimilar,thenotherthings beingequal,they
will veryprobablyfromasolidsolution.
45. 45
RelatedTermsandTheir Definitions
• Hume–Rothery’sRulesforSolidSolubility
3. Crystal Structure
• Crystal structure will have greater solubility. Since atoms tend to assume
relativelyfixedpositions.
• This givesrise to theformation of crystals in thesolid state.The atoms oscillate
about fixed locations and are in dynamic equilibrium rather than
statically fixed.
• From the above, it can be concluded that two metals are most likely to form
substitutional solid solutions over a wide range of compositions. If their atomic
sizes are about equal and if their electrochemical properties are
similar.
46. 46
RelatedTermsandTheir Definitions
• Hume–Rothery’sRulesforSolidSolubility
3. Crystal Structure
• These conditions are fulfilled when two metals are very close together in
the periodic classification of the elements. Usually side by side in the
same period (nickel and copper) or one above the other in the same group (silver
andgold).
• Alsoif singlytheycrystallizein thesamepatternthiswill assistsimple disordered
substitution.
• Pairsofmetalswhichfulfil theseconditionsanddissolvein eachother inall
proportionsin thesolidstate.
48. 48
RelatedTermsandTheir Definitions
• Allotropy:
• Itis definedastheability ofasinglesubstancetoexist inmorethan one
physical form. These allotropes are generally stable over different
temperature ranges.
• Thusiron (α – iron) is bodycenteredcubicatambienttemperaturesbut onheatingit
loses its ferromagnetism at 780°C (Curie temperature) though retaining its BCC
structure.
• This phase is judged to be a different allotrope, β – iron. Further heating to 910°C
leads to recrystallization to afacecenteredcubicstructure (ɣ - iron) which at 1400°C
reverts to a body-centered cubic form (δ – iron to distinguish it from the BCCform
existingbelow910°C).
50. RelatedTermsandTheir Definitions
• Allotropy:
• In this diagram, the gamma solid- solution
field is ‘looped’. The pure metal A and
alloys rich in A undergo two
transformations.
• Many of the equilibrium diagrams involving
iron suchasFe–Si,Fe–Mo and Fe–Cr
showthisloopedsolid solutionfield.
• Since the type of iron that exists in this
temperature range is gamma iron, the field is
usuallycalledthegammaloop.
50
51. RelatedTermsandTheir Definitions
51
• Polymorphism:
• Manysubstancesexist inmorethanonestable crystallineform. The
various forms have the same composition but different crystal
structures. Change in crystal structure is observed due to either
change in pressure or temperature or both. Such a change of
structureis called polymorphism.
• Polymorphismis observedin pureelementsaswellasinchemical compounds,both
inorganicandorganic.
• The polymorphism of metals is frequently called as allotropy and the transformation
isreversiblewithchangein temperatureatagiven pressure.
• The materials of same composition and of different crystal structures are called
polymorphs, analogus toisomers whicharemoleculesof
identicalcompositionwithdifferentstructures.
52. 52
RelatedTermsandTheir Definitions
• Polymorphism:
• These polymorphs have different densities and mechanical properties. A substance
which exhibits polymorphism is described as di – or trimorphic depending on the
numberofpolymorphicformsinwhichit exists.
• Polymorphictransformationareclassifiedintotwotypesonthebasisof reversibility
oftransformationasbelow:
a) Enantiotropy
b) Monotropy
53. 53
RelatedTermsandTheir Definitions
• Enantiotropy
• Enantiotropy forms are mutually transformable reversibly at some
temperature.
• This temperature is called transition temperature or transformation
temperatureorinversionpoint.
• At this temperature, the two crystalline forms co-exist under
equilibrium condition at a given pressure. Any deviation from this
temperatureresultsinthetransformationofoneformintotheother.
• Examples:Fe,Zr,Ti, etc.
54. 54
RelatedTermsandTheir Definitions
• Monotropy
• Monotropic forms are irreversible in the solid state and cannot be transformed one
intotheother.Monotropictransitionoccursata temperatureabovethemeltingpointof
thematerial.
• These forms are obtained either from the liquid state or the vapour state of the
materialbyrapidstatebychangeoftemperatureandhenceare irreversible.
• Examples:Phosphorus,Aluminaetc.
55. 55
Gibb’sPhase Rule
TheGibb’sphaserulestatesthatunderequilibriumconditions,the followingrelationmust
besatisfied.
𝑃 + 𝐹= 𝐶 + 2
Where,
P=Numberofphasesexistinginasystemunderconsideration.
F =Degree of freedom i.e. the number of variables such as temperature, pressure or
concentration (i.e. composition) that can be changed independently without changing
thenumberofphasesexistinginthe system.
C=Number of components (i.e. elements) in the system, and 2 represents any two
variablesoutoftheabovethreei.e.temperature,pressureand concentration.
56. 56
Gibb’sPhase Rule
Most of the studies are done at constant pressure i.e. one atmospheric pressure and
hencepressureisnomoreavariable.Forsuchcases,Gibb’s phaserulebecomes:
𝑃 + 𝐹= 𝐶 + 1
Intheaboverule,1representsanyonevariableoutofthe remainingtwo
i.e.temperatureandconcentration.
57. ConceptofSolidificationofPureMetalsand Alloys
SolidificationofPure Metal
• Solidification involves two steps. In the first step, nuclei of a solid phase
(crystallite) form from the liquid. In the second step these solid
crystallites begins to grow as an atoms until complete liquid
solidifies.
57
58. ConceptofSolidificationofPureMetalsand Alloys
58
SolidificationofPure Metal
• Hencesolidificationis theprocessofforminggrains(nucleation)andits growthin the
melt.Themetalexistsinliquidformabovethemelting point.
• Whenthemetalis cooledbelowitsmeltingpoint,nucleibegintoformin differentparts
ofthemeltatthesametime.
• The rate of formation of nuclei depends upon the degree of undercooling or
supercoolingandonthepresenceofimpuritieswhich mainlyfacilitatenucleation.
• Atanytemperaturebelowthemeltingpoint,anucleushastobeofa certainminimum
sizesothatit will grow.Thissizeiscalledascritical sizeofnucleus.
• The critical size is maximum near the melting point, but there are less
chancesofformingsuchalargenucleus.
60. 60
ConceptofSolidificationofPureMetalsand Alloys
Solidificationof Metals
• Moltenmetalpossesseshighenergyandit will lostwhenmetalcoolsto formcrystals.
• Astheheatlossis morerapidnearmouldwallsthanits centre,the formationofnuclei
(crystallites)startshere.
• The molten metal finds difficulty in starting nucleation process if there is no nuclei in
theformofimpuritiesarepresenttostart the crystallisation.
• In such cases, undercooling is done to accelerate nucleation and thus nuclei or
crystalsareformed.
62. 62
ConceptofSolidificationofPureMetalsand Alloys
Solidificationof Metals
a) Shapeof Crystals:
• Thegrowthofthecrystalvariesin differentcrystallographicdirections.
• Slow cooling rate gives growth of crystals uniformly in all the directions of growth.
Also, it gives equiaxed crystals (the crystals with equal dimensions in all the
directions).
• Similarly, rapid cooling rate gives crystals like tree which are called as
dendrites.
• Theexactshapeofthecrystalsdependontheconditionsthatexist during
solidification.
63. 63
ConceptofSolidificationofPureMetalsand Alloys
Solidificationof Metals
b) Dendritic Growth:
• Adendrite is a crystal with a tree-like branching structure. In the current context, we
are interested in metallic dendrites formed when a metal or an alloy of multiple
metals,inliquidformfreezesiscalled dendriticgrowth.
• Alargeamountoflatentheatis generatedinthedirectionofcrystal growththat
increasesthetemperatureoftheadjacentliquid.
• Thistemperatureexceedsthefreezingtemperatureofametalhence furthergrowthof
thecrystalinthisdirectionwillbestopped.
• Theliquidregionwill havealowertemperatureinaperpendicular direction,because
thereis nocrystallisationandnoheatgeneration.
73. 73
Nucleation
• Nucleation is defined as to bethe process that determine how long an observer has
towaitbeforethenewphase.
• Nucleationisthebeginningofaphasetransformation.Itismarkedby theappearance
in themoltenmetaloftiny regionscallednucleiof the newphasewhichgrowto solid
crystalsuntilthetransformationis complete.
• Thesolidificationofmetalsoccursbynucleationandgrowth.
• Thus, it is possible to achieve significant supercoiling of pure metal liquids.
Undercooling or supercooling is achieved by suppressing heterogeneous
nucleation.
75. Nucleation
HomogeneousorSelf Nucleation:
• Homogeneous nucleation is a type of the nucleation process where formation of
nucleistartsintheinteriorofauniformsubstancesuchas pureliquidmetals.
• Homogeneous nucleation occurs when where there areno special objects inside a
phasewhichcancausenucleation.
75
76. Nucleation
HomogeneousorSelf Nucleation:
• The free energy available from solidification process depends on the
volume of particle formed. Due to change in phase (molten to solid) a free
energy decreasesand it makesthe new phase morestable.
4 3(− 𝜋𝑟 × ∆𝑓𝑣)
3
• Another factor is the energy required to formasolid-liquid interface. Solid-
liquid phasespossessasurface in between them.
3
76
𝑣
4
∆𝑓 = − 𝜋𝑟3 × ∆𝑓 + 4𝜋𝑟2× 𝛾
77. Nucleation
HomogeneousorSelf Nucleation:
• Critical radius
𝑐𝑟=
2𝛾
𝑓𝑣
• Total Freeenergy
∆𝑓 =
16 𝜋𝛾3
77
3(∆𝑓 )2
𝑣
Thereafter increase in the radius will tend to decrease the free energy till it
becomes negative.
78. 78
Nucleation
Heterogeneous Nucleation:
• Heterogeneous nucleation consisting of dissimilar elements or ingredients;
not having uniform quality.
• Heterogeneous nucleation is a type of nucleation which starts at the
surfaces, imperfections and severely damagedregions.
• As the presence of impurities in molten metal lowers the liquid-solid
interface energy, the amount of supercooling (undercooling) required to
start nucleation will beless.
• Hence, nucleation process takes place easily.
79. Nucleation
Heterogeneous Nucleation:
• The foreign particle hence act as a
nucleus forming a low contact angle
and must possess some structural
affinity with the solidmetal.
• The foreign matter or impurity is
wetted by both solid and liquid.
Hence the force of equilibrium where
three surfaces meet together is given
by,
𝛾. 𝑓 𝑚. 𝑠= 𝛾𝑓 𝑚. 𝐿− 𝛾𝑠. 𝐿.𝑐𝑜𝑠𝜃
79
80. 80
Supercooling
• Supercooling also known as undercooling is the process of lowering the
temperature of a liquid or a gas below its freezing point without it
becoming asolid is called assupercooling.
• A liquid below its standard freezing point will crystalline in the presence
of a seed crystal or nucleus around which a crystal structure can form
creating asolid.
• However, lacking any such nuclei, the liquid phase can be maintained all
the way down to the temperature at which crystal homogeneous
nucleation occurs.
81. 81
Supercooling
• As the liquid is cooled, more molecules can form into nuclei. When the
nucleus is big enough (because of undercooling) the supercooled liquid
suddenly changesto asolid.
• Metals often experience undercooling of 50°C to 500°C. Homogeneous
nucleation usually only occurs in thelaboratory.
82. 82
Supercooling
Application ofSupercooling:
• Onecommercial application of supercooling is inrefrigeration.
• For example; there are freezers that cool drinks to a supercooled level so
that when they are opened, they formaslush.
• Another example is a product that can super cool the beverage in a
conventional freezer.
• The Coca-Cola Company also briefly marketed special vending machines
containing sprite in the UK, and coke in Singapore, which stored the
bottles in a supercooled state so that their content would turn to slush
upon opening.
83. Grain&GrainBoundary Effect
83
• In this figure, one of the axes of each grain is
parallel to the other while one of the other axes is
rotated.
• At the interface between these two crystals, the
atomic distances are not correct, so that atoms are
therefore not in stablepositions.
• These atoms are in a higher energy state. They will
tend to adjust their positions to a condition of
minimum energy.
• The lower density of atoms at the boundary
provides a place for impurity atoms to reside, it is
common to observe impurity atoms at the grain
boundaries.
84. 84
CoolingCurves
• Cooling curve is the graphical plot of phasesof element on temperature
v/s time.
• The resulting phases during solidification is different for various alloy
composition.
• Themost common curves are:
1. Pure metals
2. Binary solid solution alloys
3. Binary eutectic alloys
4. Off-eutectic binary alloys
93. Numerical
Acooling curve is shown in fig.
Determine the following
1. Thepouring temperature
2. Thesolidification temperature
3. The superheat
4. The cooling rate, just before
solidification beings
5. Thetotal solidificationtime
6. Thelocal solidification time
93
97. LeverRule
It is the method used to find out the exact amount of a particular phase
existing in a binary system for a given alloy at any temperature under
consideration.
97
99. Coring
• At room temperature variation in composition is observed from point to
point or centre to surface of agrain or dendrite in asolidified alloy.
• Thismicrosegregation is known ascoring.
99
100. 100
Eutectic System
• Eutectic system represents all alloys wherein the two metals have
complete solubility in liquid state and complete insolubility in solid state.
• Thesesystemsform aV-shaped equilibrium diagram.
• Examples: Pb-As,Bi-Cd,Au-Si etc.
• Eutectic reaction is also called asinvariant reaction.
• Invariant reactions are those reactions which occur under equilibrium
conditions at a specific temperature and alloy composition that cannot be
varied.
103. 103
Isomorphous System
• Isomorphous system represents all alloys wherein the two metals have
complete solubility in solid and liquidstates.
• Thesesystemsform aloop type equilibrium diagram.
• Examples:Cu-Ni,Au-Ag,Au-Cu,Au-Ni, Bi-Sb etc.
105. 105
Partial Eutectic System
• Partial eutectic system represents all alloys wherein the two metals have
complete solubility in liquid state and partial solubility in the solid state.
• These systems also form a V-shaped diagram with adjoining solid
solutions on the left and rightside.
• Examples:Ag-Cu,Pb-Sn,Sn-Bi,Pb-Sb,Cd-Zn,Al-Si etc.
