Chapter 9: Phase Diagrams

Transcription

1 Chapter 9: Phase Diagrams IUE TO ADDE... Common types of phase diagrams Isomorphous Eutectic Others Phase diagram and microstructure evolution Chapter 9-1

2 What is a phase? What is a component? Class Exercise (1) For the following system, how many phases and how many components are present? What are they Pure water with ice cubes in it? Uniform hydrochloric acid solution in water? ugary water with pure ice cube in it? A uniform solid solution of Cu and Ni Cooking oil dropped into a cup of water and shaken up For binary phase diagram, what do the typical x-axis and y axis represent for? ight or Wrong: A phase diagram describes the states for any condition for that given system Chapter 9-2

3 elative Amount of Each Phase in Two Phase egion - The Lever ule Tie line connects the phases in equilibrium with each other under isothermal (same temperature) condition 13 T B 12 W 2 L ML M M L B wt% Ni tie line (solid) 3 C C 4 5 L o C C C In two phase region, what is the relative weight fraction (W, in unit of wt%) of each phase? Lever rule Adapted from Fig. 9.3(b), Callister 7e. Weight fraction (in unit of wt%) of liquid L phase C C L Weight of L phase W M L M M L C C M Weight of α phase Weight fraction (in unit of wt%) of α solid solution phase C C L L Chapter 9-3

4 What type of phase diagram is it? Binary (isomorphous) phase diagram How many components? What are they? Two: Cu and Ni What are the phases that can be present in the phase diagram? L and α What are the single phase regions and two-phase region? ingle phase region: L, α; Two phase region: L+α What are the phases, their composition, & relative amount (weight fraction) for A system with C=2 wt% at ~14C? 1 wt% L, C L = 2 wt% Ni; wt% α C=6 wt% at ~11C? 1 wt% α, C α = 6 wt% Ni, wt% L C=25wt% at ~12C? C α 3 wt% Ni; C L 2 wt% Ni W α =(25-2)/(3-2)=5wt%, W L =1-W α =5wt% Class Exercise Cu Phase Diagram for Cu-Ni system (FCC solid solution wt% Ni Adapted from Fig. 9.3(a), Callister 7e. (Fig. 9.3(a) is adapted from Phase Diagrams of Binary Nickel Alloys, P. Nash (Ed.), AM International, Materials Park, OH (1991). Chapter 9-4 Ni

5 Application of Phase Diagram Microstructure Evolution Phase diagram: Cu-Ni system. ystem is: --binary i.e., 2 components: Cu and Ni. --isomorphous i.e., complete solubility of one component in another; phase field extends from to 1 wt% Ni. Consider C o = 35 wt%ni. 13 L: 35 wt% Ni : 46 wt% Ni (solid) Adapted from Fig. 9.4, Callister 7e A B C D E 35 C o L: 35wt%Ni wt% Ni Chapter 9-5 Cu-Ni system L: 32 wt% Ni : 43 wt% Ni L: 24 wt% Ni : 36 wt% Ni

6 Microstructures in Isomorphous Alloys Microstructures will vary on the cooling rate (i.e. processing conditions) 1. Equilibrium Cooling: Very slow cooling to allow phase equilibrium to be maintained during the cooling process. a (T>126 o C): start as homogeneous liquid solution. b (T ~ 126 o C): liquidus line reached. phase begins to nucleate. C = 46 wt% Ni; C L = 35 wt% Ni c (T= 125 o C): the composition of each phase: C = 43 wt% Ni; C L = 32 wt% Ni d (T~ 122 o C): solidus line reached. Nearly complete solidification. C = 35 wt% Ni; C L = 24 wt% Ni e (T<122 o C): homogeneous solid solution with 35 wt% Ni. Chapter 9-6

7 2 components Binary Eutectic Phase Diagram Ex.: Cu-Ag system ingle phase regions: 3 of them L,, b Two-phase regions: 3 of them +b, +L and b+l Limited solubility: : mostly Cu w/ a little Ag dissolved in it b : mostly Ag w/ a little Cu dissolved in it Eutectic temperature T E No liquid below T E C E : Composition for eutectic point or min. melting T E has a special composition with a min. melting T L + Cu-Ag system b Adapted from Fig. 9.7, Callister 7e. Chapter 9-7 L + b b T C E C E C (wt% Ag) Eutectic transition/reaction cool L(C E= 71.9wt% Ag) (C E =8wt%Ag) + b(c be =91.2%Ag) heat C E C be

8 EX: Pb-n Eutectic ystem (1) For a 4 wt% n-6 wt% Pb alloy at 15 C, find... --the phases present: and b (i.e., two phases) --composition of each Pb-n system phase (in wt% n): C = 11 wt% n C b = 99 wt% n --the relative amount of each phase: W = = W b = = = = C b - C O C b - C = C O - C C b - C = = 67 wt% = 33 wt% L C b L + b C Adapted from Fig. 9.8, Callister 7e. C o C, wt% n Chapter 9-8 C b b

9 EX: Pb-n Eutectic ystem (2) For a 4 wt% n-6 wt% Pb alloy at 22 C, find... --the phases present: + L (i.e., two phases) --compositions of each Pb-n system phase (in wt% n): C = 17 wt% n C L = 46 wt% n --the relative amount of each phase: W = C L - C O C L - C = = 6 29 = 21 wt% W L = C O - C = 23 C L - C = 79 wt% L C + b L + b C o C Adapted from Fig. 9.8, Callister 7e. C L C, wt% n Chapter 9-9 b

10 Application of Phase Diagram (1) tability/eactivity/olubility of Engineering Materials Based on the Cu-Ag phase diagram, will a very thin Ag coating over Cu be stable at elevated temperatures? NO because the system is very rich in Cu and low in Ag (near pure Cu in the phase diagram). At high T (e.g., 6C), Ag will form solid solution with Cu and mix uniformly instead of only staying over Cu surface Chapter 9-1

11 ummary Binary eutectic phase diagram is another type of binary phase diagram with lowest melting point at intermediate composition. Phase change at eutectic composition happen at a fixed temperature eutectic temperature Chapter 9-11