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4.Kristal
Farid Wa di2013
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andmechanical
properties
isrelatedtothecharacteristicsofits
phase
.
Phasediagramsprovidevaluableinformation
a outme t ng,cast ng,crysta zat on,an otherphenomena.
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Componentsarepuremetalsand/orcompoundsofwhichanalloyiscomposed.E.g.:acopperzincbrass,thecomponentsareCuandZn.
Asystemmayrefertoaspecificbodyofmaterialunderconsideration(e.g.,aladleofmoltensteel).
Oritmayrelatetotheseriesofpossiblealloysconsistingofthesamecomponents,butwithoutregardtoalloycomposition(e.g.,theironcarbonsystem).
Asolidsolutionconsistsofatomsofatleasttwodifferenttypes;
Thesoluteatomsoccupyeithersubstitutional orinterstitialpositionsinthesolventlattice,andthecrystalstructureofthesolventismaintained.
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temperature,thereisamaximumconcentrationofsoluteatomsthatmaydissolveinthesolventtoformasolidsolution
(solubility
limit). Theadditionofsoluteinexcessofthis
solubilitylimitresultsintheformationof
anot erso so ut onorcompoun t at asadistinctlydifferentcomposition
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Thesugarwater(C12H22O11H2O)system.Initially,assugarisaddedtowater,asugarwatersolutionorsyrupforms.
moreconcentrated,untilthesolubilitylimitisreached
orbecomessaturatedwithsugar.Atthistimethe ,andfurtheradditionssimplysettletothebottomofthecontainer.
,substances:a
sugarwater
syrup
liquid
solution
andsolidcrystalsofundissolved sugar.
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Thissolubilitylimitofsugarinwaterdependsonthetemperatureofthewa eran composition(in
weightpercent
Increasingsugarconcentrationis
,andpercentageofwaterisreadfrom
.
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A hasema bedefinedasahomo eneous
portionofasystemthathasuniformphysicalandchemicalcharacteristics.
;soalsoiseverysolid,liquid,andgaseoussolution.
system,eachwillhaveitsowndistinctproperties,andaboundaryseparatingthephaseswillexist
abruptchangeinphysicaland/orchemicalcharacteristics.
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Whentwophasesarepresentinasystem,itisnotnecessarythatere ea erence n o p ys ca an c em ca proper es;a
disparityinoneortheothersetofpropertiesissufficient. Whenwaterandicearepresentinacontainer,twoseparatephases
,liquid)butidenticalinchemicalmakeup.Also,whenasubstancecanexistintwoormorepolymorphicforms(e.g.,havingbothFCC
andBCCstructures),eachofthesestructuresisaseparatephaseecause e rrespec vep ys ca c arac er s cs er.
Asinglephasesystemistermedhomogeneous.Systemscomposedoftwoormorephasesaretermedmixtures
or
heterogeneous
.
Ordinarily,thephasesinteractinsuchawaythatthepropertycombinationofthemultiphasesystemisdifferentfrom,andmoreattractivethan,eitheroftheindividualphases.
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Equilibriumisanotheressentialconceptthatisbestdescribedintermsofathermodynamicquantitycalledthefreeenergy.
system,andalsotherandomnessordisorderofthe
atomsormolecules(orentropy).Asystemisatsomespecifiedcombinationoftemperature,pressure,andcomposition.
,characteristicsofthesystemdonotchangewithtimebutpersistindefinitely;thatis,thesystemisstable.
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Phaseequilibrium,referstoequilibriumasitappliestosystemsinwhichmorethanonephasemayexist,reflectedbyaconstancywithtimeinthephasecharacteristicsofasystem.
E.g.sugarwatersyrupiscontainedinaclosedvesselandthesolutionisincontactwithsolidsugarat20C.Ifthe
systemisatequilibrium,thecompositionofthesyrupis65w w ,an eamoun san compositionsofthesyrupandsolidsugarwillremainconstantwithtime.Ifthetemperatureofthesystemis
, istemporarilyupsetinthatthesolubilitylimithasbeenincreasedto80wt%C12H22O11
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,
isheldconstant(i.e.,thephasediagramisforauresubstance thismeansthat ressureand
temperaturearethevariables.
This onecom onent hase dia ram unar hase
diagram)alsocalledapressuretemperature(or
PT)
diagram]
is
represented
as
a
two
dimensional
plotofpressureversustemperature
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temperatureandcompositionarevariableparameters,andpressureisheldconstantnormally1atm.
Anexplanationoftheprinciplesgoverningandtheinterpretationofphasediagramscanbedemonstratedusingbinaryalloyseventhough
mosta oysconta nmoret antwocomponents.
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Thecoppernickelsystem
isomorphouskarena keduanya
terlarut sempurna
struktur FCC,radiusatom,
elektronegativitas,kovalensi
: qu
:solid
Tmelt Cu10850C,Ni14530C
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Paduan kristal logam A
tercampur sempurna,pada bentuk solid
terpisah
ogam murn mem
titik leleh dan titik beku.
Diantaranya terdapat
titik dimana beberapa
saat berubah fasa
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Paduan logam
sempurna pada
kondisi solid.
Paduan tembaga
ni e ,emaspera
Paduan logam
tercampur terpisah
pada kondisi solid.
Pada komposisi
tertentu terdapat
titik Eutectium E
tidak mengalami
trayek.
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Besi murni memiliki struktur BCC(ferrite)
Pa a temp.768 C e i angan si at magnetisnya
Pada temp.9060Cstruktur FCC(austenite)
Pada temp.14010Cstruktur BCC()
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00,43%C,austenitecristals FCC
Cementite +L
Maximal2,14%C
= qu us
Perlite =ferrite+cementite
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Bentuk kristal ter antun dari
kadar Cdan perlakuan panas
Klasifikasi Ferrousalloys:
Irons(0.008wt%C)
ee s . w o . w
Castirons(2.14wt%C)
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thanferrite.Thus,increasingthefractionof
microstructural elementsconstantwillresult
.
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