PY2N20 Material Properties and Phase Diagrams

Transcription

1 PY2N20 Mteril Properties nd Phse Digrms ecture 5 P. tmenov, PhD chool of Physics, TCD PY2N20-5

2 Phse Digrms - Introduction How much cn be done with pure elementl compounds? How mny combintions of elements could be imgined? 2 100??? How mny of these combintions will hve the structure (crystllogrphic, nnoscle, microscle, etc. ) of the end members? How is mixing them going to ffect the resulting mechnicl, electronic nd other physicl nd chemicl properties? Cn the properties of the end members be improved on?

3 Phse Digrms Why? When we combine two or more constituents (elements)... wht equilibrium stte do we get? In prticulr, if we specify... c, p, T, but lso H, E (ll re intensive thermodynmic prmeters) - composition (e.g., wt% Cu - wt% Ni), nd - temperture (T ) then... How mny phses do we get? Wht is the composition of ech phse? How much of ech phse do we get? Phse A Phse B Nickel tom Copper tom Does this phse segregtion relly occur for Cu 1-x Ni x?

4 Pure Wter Pure ugr Temperture ( C) Phse Equilibri: olubility imit Introduction olutions solid solutions, single phse Mixtures more thn one phse olubility imit: Mx concentrtion for which only single phse solution occurs. Question: Wht is the solubility limit t 20 C? Answer: 65 wt% sugr. If Co < 65 wt% sugr: syrup If Co > 65 wt% sugr: syrup + sugr ucrose/wter Phse Digrm olubility imit (liquid solution i.e., syrup) (liquid) + (solid sugr) Co =Composition (wt% sugr)

5 Components nd Phses Components: The elements or compounds which re present in the mixture (e.g., Al nd Cu) Phses: The physiclly nd chemiclly distinct mteril regions tht result (e.g., nd b). Aluminum- Copper Alloy b (lighter phse) (drker phse)

6 Temperture ( C) Effect of T & Composition (C o ) Chnging T cn chnge # of phses: pth A to B. Chnging C o cn chnge # of phses: pth B to D. wtersugr system ( liquid solution i.e., syrup) B (100 C,70) 1 phse (liquid) + (solid sugr) A (20 C,70) 2 phses D (100 C,90) 2 phses C o =Composition (wt% sugr)

7 Phse Equilibri imple solution system (e.g., Ni-Cu solution) Crystl tructure Electroneg. r (nm) Ni FCC Cu FCC Both hve the sme crystl structure (FCC) nd hve similr electronegtivities nd tomic rdii (W. Hume Rothery rules) suggesting high mutul solubility. Ni nd Cu re totlly miscible in ll proportions. Hence, the nswer to the erlier question is No

8 Phse Digrms Indicte phses s function of T, C o, nd P. For this course: -binry systems: just 2 components. -independent vribles: T nd C o (P = 1 tm is lmost lwys used). T( C) Phse Digrm for Cu-Ni system (liquid) (FCC solid solution) phses: (liquid) (FCC solid solution) 3 phse fields: + wt% Ni

9 Phse Digrms: Number nd types of phses Rule 1: If we know T nd C o, then we know: - the number nd types of phses present. Exmples: A(1100 C, 60): 1 phse: B (1250 C, 35): 2 phses: + T( C) (liquid) B (1250 C,35) (FCC solid solution) Cu-Ni phse digrm 1100 A(1100 C,60) wt% Ni

10 Composition of phses Rule 2: If we know T nd C o, then we know: - the composition of ech phse. Exmples: C o = 35 wt% Ni At T A = 1320 C: Only iquid () C = C o ( = 35 wt% Ni) At T D = 1190 C: Only olid ( ) C = C o ( = 35 wt% Ni ) At T B = 1250 C: T( C) T A 1300 T B 1200 T D 20 Both nd C = C liquidus ( = 32 wt% Ni here) C = C solidus ( = 43 wt% Ni here) (liquid) Cu-Ni system A B D C o C tie line (solid) C wt% Ni

11 Weight frctions of phses Rule 3: If we know T nd C o, then we know: - the mount of ech phse (given in wt%), vi the so-clled: centre of grvity principle or the lever rule Exmples: C o = 35 wt% Ni At T A : Only iquid () W = 100 wt%, W = 0 At T D : Only olid ( ) At T B : W W W = 0, W = 100 wt% Both nd R + R R = 27 wt% 73wt % T( C) T A 1300 T B 1200 T D 20 (liquid) Cu-Ni system A B R D C o C tie line (solid) C wt% Ni

12 The ever Rule Tie line connects the phses in equilibrium with ech other - essentilly n isotherm T( C) 1300 T B (liquid) R B wt% Ni tie line (solid) 30 C C o C How much of ech phse? Think of it s lever M M R M M R W M M M R C C C C 0 W R R C C 0 C C

13 Cooling in the Cu-Ni Binry ystem Phse digrm: Cu-Ni system. ystem is: - binry i.e., 2 components: Cu nd Ni. - isomorphous i.e., complete solubility of one component in nother; phse field extends from 0 to 100 wt% Ni. Consider C o = 35 wt%ni. T( C) 1300 : 35 wt% Ni : 46 wt% Ni (liquid) (solid) A B C D E 35 C o : 35wt%Ni wt% Ni Cu-Ni system : 32 wt% Ni : 43 wt% Ni : 24 wt% Ni : 36 wt% Ni

14 Cored vs Equilibrium Phses C chnges s we solidify. Cu-Ni cse: Fst rte of cooling: Cored structure First to solidify hs C = 46 wt% Ni. st to solidify hs C = 35 wt% Ni. low rte of cooling: Equilibrium structure First to solidify: 46 wt% Ni st to solidify: < 35 wt% Ni Uniform C : 35 wt% Ni

15 Tensile trength (MP) Elongtion (%E) Mechnicl Properties: Cu-Ni ystem Effect of solid solution strengthening on: - Tensile strength (T) - Ductility (%E,%AR) T for pure Cu Cu Ni T for pure Ni Composition, wt% Ni %E for pure Cu Cu Ni %E for pure Ni Composition, wt% Ni - Mximum s function of Co - Minimum s function of Co

16 Binry Eutectic ystems ευτηκτικός - from Greek esiest to melt

17 Binry-Eutectic ystems Cu-Ag system 3 single phse regions (,, b ) imited solubility: ) : mostly Cu b : mostly Ag T E : No liquid below T E C E : Composition with min. melting T E Eutectic trnsition T( C) TE (C E ) (C E ) + b(c be ) + (liquid) b Cu-Ag system + b b 779 C C E C o, wt% Ag

18 Pb-n Eutectic ystem (1) For 40 wt% n-60 wt% Pb lloy t 150 C, find... - the phses present: - compositions of phses: T( C) W = C O = 40 wt% n C = 11 wt% n C b = 99 wt% n - the reltive mount of ech phse: = W b = = R R R+ = = C b - C O C b - C = C O - C C b - C = = 67 wt% = 33 wt% (liquid) 183 C + b R + b Pb-n system C C o C b Adpted from Fig. 9.8, Cllister 7e. C, wt% n b

19 Pb-n Eutectic ystem (2) For 40 wt% n-60 wt% Pb lloy t 220 C, find... - the phses present: + Pb-n - compositions of phses: T( C) C O = 40 wt% n C = 17 wt% n C = 46 wt% n - the reltive mount of ech phse: W = C - C O C - C = = 6 29 = 21 wt% W = C O - C = 23 C - C = 79 wt% R (liquid) 183 C + b system + b C C o C C, wt% n b

20 Microstructures in Eutectic ystems: I C o < 2 wt% n Result: - t extreme ends - polycrystl of grins i.e., only one solid phse. T( C) T E : C o wt% n : C o wt% n + (Pb-n ystem) b 0 C o (room T solubility limit) 30 C o, wt% n

21 Microstructures in Eutectic ystems: II 2 wt% n < C o < 18.3 wt% n Result: Initilly liquid + then lone finlly two phses polycrystl fine b-phse inclusions T( C) T E + + b : C o wt% n : C o wt% n b Pb-n system C o (sol. limit t T room ) 18.3 (sol. limit t T E ) 30 C o, wt% n

22 Microstructures in Eutectic ystems: III C o = C E Result: Eutectic microstructure (lmellr structure) - lternting lyers (lmelle) of nd b crystls. 300 Pb-n system 200 T E T( C) C : C o wt% n b b Microgrph of Pb-n eutectic microstructure 100 b b: 97.8 wt% n : 18.3 wt%n 160 m Adpted from Fig. 9.14, Cllister 7e C E C, wt% n

23 mellr Eutectic tructure Other possible eutectic structures re: rod-like, globulr nd ciculr.

24 Microstructures in Eutectic ystems: IV 18.3 wt% n < C o < 61.9 wt% n Result: crystls nd n eutectic microstructure Just bove T E : T( C) 300 Pb-n system 200 T E R R + b : C o wt% n b C o, wt% n b primry eutectic eutectic b C = 18.3 wt% n C = 61.9 wt% n W = = 50 wt% R + W = (1- W ) = 50 wt% Just below T E : C = 18.3 wt% n C b = 97.8 wt% n W = = 73 wt% R + W b = 27 wt%