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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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