Course Objectives. MSE 260 Phase Transformations. Prerequisites. Course Outcomes 1/16/2017. Forms of Assessment. Course Outline. Dr.

Transcription

1 ME 26 Phse Trnsformtions Kwme Nkrumh University of cience & Technology, Kumsi, Ghn Dr. Anthony Andrews Deprtment of Mterils Engineering Fculty of Mechnicl nd Chemicl Engineering College of Engineering Course Ojectives Develop n understnding of why mterils nd microstructures undergo chnges Provide n understnding of how diffusion enles chnges in the chemicl distriution nd microstructure of mterils Formulte nd discuss vriety of phse trnsformtions Discuss effects of temperture nd driving force on the nture of the trnsformtion nd its impct on the resulting microstructure 2 Course Outcomes Understnd thermodynmics of single nd multiple component systems nd their reltionship to the equilirium phse digrm Understnd fundmentl mechnisms of diffusion nd the importnce of processing conditions Prerequisites Principles of Mterils cience I & II (ME 154, ME 255) Knowledge of how driving forces of vrying types nd rriers due to surfce energy effects interct to dictte the rte of phse trnsformtion nd microstructurl chnge Understnd how through mnipultion of temperture, driving force, nd initil microstructure, wide rnge of finl microstructures cn e produced 3 4 Forms of Assessment Quizzes 1 Mid-em Exm 2 Finl Exm 7 Totl 1 Course Outline Microstructure nd Phse Trnsformtions in Multicomponent ystems Definition nd sic concepts Phse nd microstructure Binry isomorphous systems Binry eutectic systems Binry systems with intermedite phses/compounds Gis phse rule The iron-cron system 5 6 1

2 Temperture (ºC) Wter ugr 1/16/217 Course Outline Phse trnsformtion in metls nd lloys Kinetics of phse trnsformtions Multiphse trnsformtions Phse trnsformtions in Fe-C lloy Isotherml trnsformtion digrms Mechnicl ehviour Tempered mrtensite Continuous cooling trnsformtion digrms Recommended Books Phse trnsformtions in metl nd lloys, 3 rd edition, D. A. Porter nd K. E. Esterling Fundmentls of mterils science nd engineering, 7 th edition, W.D. Cllister 7 8 Components & Phses Component chemiclly recognizle species. A inry lloy contins two components, ternry lloy three Components & Phses (lighter phse) Phse portion of system tht hs uniform physicl nd chemicl chrcteristics. Two distinct phses in system re seprted from ech other y definite phse oundries. Homogeneous system Aluminum- Copper Alloy (drker phse) Mixtures or hetrogeneous systems 1 olvent, olute, olution, Mixture olvent host or mjor component in solution; solute minor component olution solid, liquid, or gs solutions, single phse Mixture more thn one phse oluility imit oluility limit: the mximum mount of the component tht cn e dissolved in phse ugr/wter Phse Digrm oluility imit (liquid solution i.e., syrup) C = Composition (wt% sugr) (liquid) + (solid sugr) 2

3 Temperture (ºC) Free Energy 1/16/217 Effect of Temperture & Composition 1 B (1ºC,C = 7) 1 phse D (1ºC,C = 9) 2 phses Criteri for olid oluility imple system (e.g., Ni-Cu solution) wtersugr system Adpted from Fig. 9.1, Cllister & Rethwisch 8e (liquid solution i.e., syrup) C = Composition (wt% sugr) (liquid) + (solid sugr) A (2ºC,C = 7) 2 phses 13 Both hve the sme crystl structure (FCC) nd hve similr electronegtivities, vlence electron nd tomic rdii W. Hume Rothery rules - suggesting high mutul soluility. 14 Equilirium nd Metstle ttes Equilirium: t constnt temperture, pressure nd composition system is stle (not chnging with time) Equilirium is chieved given sufficient time, ut tht my e very long. Metstle: ystem ppers to e stle. Equilirium nd Metstle ttes Under conditions of constnt temperture, pressure nd composition, chnge is towrd lower free energy. tle equilirium is stte with minimum free energy. Metstle stte is locl minimum of free energy. equilirium metstle Phse Digrm for Cu-Ni system Phse Digrms (liquid) (FCC solid solution) wt% Ni 2 phses: (liquid) (FCC solid solution) + 3 different phse fields: Isomorphous Binry ystem Isomorphous system complete soluility of one component in nother (liquid) (FCC solid solution) wt% Ni 17 3

4 Phse Digrms: Determintion of phse(s) present Rule 1: If we know T nd C o, then we know which phse(s) is (re) present. Exmples: (liquid) 15 A (11 o C, 6 wt% Ni) Cu-Ni 1 phse: α phse digrm B (125 o C, 35 wt% Ni) 2 phses: + α (FCC solid solution) wt% Ni 22 Phse Digrms: Determintion of phse compositions Rule 2: If we know T nd C, then we cn determine the composition of ech phse. Cu-Ni Exmples: system Consider C = 35 wt% Ni T A At T A tie line A = 132ºC: 13 (liquid) Only iquid () present C = C ( = 35 wt% Ni) B T B At T D = 119ºC: Only olid () present D (solid) C = C ( = 35 wt% Ni) T D At T B = 125ºC: Both nd present C = Cliquidus ( = 32 wt% Ni) = Csolidus ( = 43 wt% Ni) C C C C wt% Ni 23 Phse Digrms: Determintion of phse weight frctions Rule 3: If we know T nd C, then we cn determine the weight frction of ech phse. Exmples: Cu-Ni system Consider C = 35 wt% Ni At T A : Only iquid () present T A A tie line W = 1., W = 13 (liquid) At T D : Only olid ( ) present B T W =, W = 1. B R At T B : Both nd present D (solid) T D W R CC C wt% Ni W R R + = Mss frctions: The ever Rule W /( R ) ( C o C ) /( C W R /( R ) ( C C ) /( C o C ) C ) Phse Digrms: Determintion of phse volume frctions Conversion of mss frction to volume frction For n lloy consisting of α nd β phses, the volume frction of the α phse, V α, is defined s V α = υ α υ α + υ β υ α + υ β = 1 where v α nd v β denote the volumes of the respective phses in the lloy V α = V β = W α ρ α W α ρ α + W β ρ β W β ρ β W α ρ α + W β ρ β ρ α nd ρ β re the densities of the respective phses 4

5 Conversion of mss frction to volume frction V α ρ α W α = V α ρ α + V β ρ β V β ρ β W β = V α ρ α + V β ρ β ρ α nd ρ β re the densities of the respective phses Development of Microstructure in Isomorphous Alloys: Equilirium (very slow) Cooling Phse digrm: Cu-Ni system. Consider microstructurl chnges tht ccompny the cooling of C = 35 wt% Ni lloy (liquid) 13 : 35 wt% Ni : 46 wt% Ni (solid) A 35 B 32 C 24 D 36 E : 35wt%Ni Cu-Ni system : 32 wt% Ni : 43 wt% Ni : 24 wt% Ni : 36 wt% Ni Adpted 9.4, C wt% Ni from Fig. Cllister & Rethwisch 8e. 29 Cored vs Equilirium tructures C chnges s we solidify. Cu-Ni cse: First to solidify hs C = 46 wt% Ni. st to solidify hs C = 35 wt% Ni. low rte of cooling: Equilirium structure Uniform C: 35 wt% Ni Fst rte of cooling: Cored structure First to solidify: 46 wt% Ni st to solidify: < 35 wt% Ni Development of Microstructure in Isomorphous Alloys: Non-equilirium Cooling Consequences: Nonuniform distriution of two elements within grins. Upon heting, grin oundries will melt first. This cn led to premture mechnicl filure 3 Mechnicl Properties of Isomorphous Alloys Binry Eutectic ystems Effect of solid solution strengthening 5

6 Binry Eutectic ystems Binry Eutectic ystems Compositions nd reltive mounts of phses re determined from the sme tie lines nd lever rule, s for isomorphous systems A B Eutectic isotherm Invrint or eutectic point C Development of Microstructure in Eutectic Alloys: Cse I Development of Microstructure in Eutectic Alloys: Cse II In this cse of P-rich lloy (-2 wt% of n) solidifiction proceeds in the sme mnner s for isomorphous lloys (e.g. Cu-Ni) α + α α + α α+β Development of Microstructure in Eutectic Alloys: Cse III - olidifiction t the Eutectic Composition Development of Microstructure in Eutectic Alloys: olidifiction t the Eutectic Composition This simultneous formtion of α nd β phses results in lyered (lmellr) microstructure tht is clled eutectic structure. α + β In the microgrph the drk lyers re P-rich α phse, the light lyers re the nrich β phse 6

7 Development of microstructure in eutectic lloys: Cse IV - Composition other thn eutectic α + α+β Development of Microstructure in Eutectic Alloys eutectic structure primry α phse Microstructurl Developments in Eutectic For lloys for which 18.3 wt% n < C < 61.9 wt% n Result: α phse prticles nd eutectic microconstituent 1 3 P-n system 2 T E + R R + : C wt% n C, wt% n + primry eutectic eutectic Just ove T E : C = 18.3 wt% n C = 61.9 wt% n W = =.5 R + W = (1- W) =.5 Just elow T E : C = 18.3 wt% n C = 97.8 wt% n W= =.73 R + W = Hypoeutectic & Hypereutectic 3 2 T E (P-n ystem) C, wt% n eutectic hypoeutectic: C = 5 wt% n hypereutectic: (illustrtion only) mm eutectic: C = 61.9wt% n 16 mm eutectic micro-constituent 45 Phse Digrm with Intermetllic Compounds Eutectic, Eutectoid, & Peritectic Eutectic - liquid trnsforms to two solid phses cool + (For P-n, 183ºC, 61.9 wt% n) het This digrm cn e thought of s two joined eutectic digrms, for Mg- Mg 2 P nd Mg 2 P-P. In this cse compound Mg 2 P cn e considered s component. Intermetllic compound Eutectoid one solid phse trnsforms to two other solid phses intermetllic compound - cementite cool + Fe 3 C (For Fe-C, 727ºC,.76 wt% C) het Peritectic - liquid nd one solid phse trnsform to second solid phse cool het (For Fe-C, 1493ºC,.16 wt% C) 47 7

8 Cu-Zn Phse digrm Eutectoid & Peritectic Peritectic trnsformtion + Congruent Phse Trnsformtions A congruent phse trnsformtion involves no chnge in composition (e.g. llotropic trnsformtion such s α-fe to γ-fe or melting trnsitions in pure solids). Congruent melting of γ Ni-Ti Eutectoid trnsformtion + 48 The Gis Phse Rule The phse rule llows one to determine the numer of degrees of freedom (F) or vrince of chemicl system. This is useful for interpreting phse digrms. P + F = C + N where P is the numer of phses present F is the numer of degrees of freedom or the numer of externlly controlled vriles (e.g., temperture, pressure, composition). C is the numer of components in the system. N is the numer of noncompositionl vriles (e.g., temperture nd pressure). Binry T-C Phse Digrm nd Phse Rule Pressure constnt (1tm); N=1 C = 2 P + F = F = 3 P For single phse filed, P = 1 F = 2 The Iron-Iron cride (Fe-Fe 3 C) Phse Digrm Comments on Fe-Fe 3 C ystem 1. Mechnicl properties: Cementite is very hrd nd rittle cn strengthen steels. Mechnicl properties lso depend on the microstructure 2. Mgnetic properties: α-ferrite is mgnetic elow 768 o C, ustenite is non-mgnetic 3. Clssifiction: Three types of ferrous lloys: Iron: less thn.8 wt% C in α-ferrite t room temperture teels: wt% C (usully < 1 wt%) α-ferrite + Fe 3 C t RT Cst iron: wt% C (usully < 4.5 wt%) 8

9 Fe 3 C (cementite) Fe 3 C (cementite) Fe 3 C (cementite) Fe 3 C (cementite) Fe 3 C (cementite) 1/16/217 Eutectic nd Eutectoid Rections in Fe-Fe 3 C Eutectic: 4.3 wt%c, 1147o C γ + Fe 3 C Iron-Cron (Fe-C) Phse Digrm 2 importnt points - Eutectic (A): + Fe 3 C - Eutectoid (B): +Fe 3 C ºC (ustenite) 8 B A +Fe 3 C 727ºC = Teutectoid +Fe 3 C 6 +Fe 3 C Eutectoid:.76 wt%c, 727 o C γ (.76 wt%c) α (.22 wt%c) + Fe 3 C 12 mm Result: Perlite = lternting lyers of nd Fe 3 C phses (Fe) C, wt% C Fe 3 C (cementite-hrd) (ferrite-soft) 55 Hypoeutectoid teel Microstructure ºC +Fe (ustenite) 3 C + Fe 3 C ºC + Fe 3 C (Fe) C C, wt% C perlite perlite (Fe-C ystem) 1 mm Hypoeutectoid steel How mny microconstituents present? proeutectoid ferrite Hypoeutectoid teel Composition (Fe-C ºC +Fe (ustenite) 3 C ystem) W = s/(r + s) + Fe 3 C 8 W r s 727ºC =(1 - W ) R 6 + Fe 3 C perlite W perlite = W (Fe) C C, wt% C W = /(R + ) W Fe 3C =(1 W ) perlite 1 mm Hypoeutectoid steel proeutectoid ferrite Hypereutectoid teel Microstructure Fe 3C ºC (ustenite) 8 6 +Fe 3 C +Fe 3 C +Fe 3 C 4 1 C (Fe) C, wt%c perlite perlite (Fe-C ystem) 6 mm Hypereutectoid steel proeutectoid Fe 3 C 58 Fe 3C Hypereutectoid teel Composition ºC (ustenite) +Fe 3 C +Fe 3 C 8 v x W =x/(v + x) W V X Fe 3C =(1-W ) 6 +Fe 3 C perlite 4 1 C (Fe) C, wt%c W perlite = W W = X/(V + X) W =(1 - W ) Fe 3C perlite (Fe-C ystem) 6 mm Hypereutectoid steel proeutectoid Fe 3 C 59 9

10 Exmple Prolem For 99.6 wt% Fe-.4 wt% C steel t temperture just elow the eutectoid, determine the following: ) The compositions of Fe 3 C nd ferrite (). ) The mount of cementite (in grms) tht forms in 1 g of steel. c) The mounts of perlite nd proeutectoid ferrite () in the 1 g. 62 1