Partition coeff. at constant temp. and press. if ml < 0 k < 1. İf ml > 0 k >1
|
|
- Brittany King
- 5 years ago
- Views:
Transcription
1 Microsegregation
2 Partition coeff. k=cs/cl at constant temp. and press. if ml < 0 k < 1 İf ml > 0 k >1
3
4
5
6
7
8
9 Models for Microsegregation 1 no mixing in liquid no diffusion in solid no coarsening 2. partial mixing in liquid no diffusion in solid no coarsening 3. complete mixing in liquid no diffusion in solid no coarsening 4. complete mixing in liquid diffusion in solid no coarsening 5. complete mixing in liquid diffusion in solid coarsening 6. complete mixing in liquid complete diffusion in solid
10 1 no mixing in liquid no diffusion in solid no coarsening 2. partial mixing in liquid no diffusion in solid no coarsening 3. complete mixing in liquid no diffusion in solid no coarsening 4. complete mixing in liquid diffusion in solid no coarsening 5. complete mixing in liquid diffusion in solid coarsening 6. complete mixing in liquid complete diffusion in solid
11 (6 Model). Eq solidification (Level Rule)
12 p=1-k
13
14
15
16
17 1 no mixing in liquid no diffusion in solid no coarsening 2. partial mixing in liquid no diffusion in solid no coarsening 3. complete mixing in liquid no diffusion in solid no coarsening 4. complete mixing in liquid diffusion in solid no coarsening 5. complete mixing in liquid diffusion in solid coarsening 6. complete mixing in liquid complete diffusion in solid
18 1 model
19
20
21
22
23
24
25
26 1 no mixing in liquid no diffusion in solid no coarsening 2. partial mixing in liquid no diffusion in solid no coarsening 3. complete mixing in liquid no diffusion in solid no coarsening 4. complete mixing in liquid diffusion in solid no coarsening 5. complete mixing in liquid diffusion in solid coarsening 6. complete mixing in liquid complete diffusion in solid
27 2 model
28
29
30 1 no mixing in liquid no diffusion in solid no coarsening 2. partial mixing in liquid no diffusion in solid no coarsening 3. complete mixing in liquid no diffusion in solid no coarsening 4. complete mixing in liquid diffusion in solid no coarsening 5. complete mixing in liquid diffusion in solid coarsening 6. complete mixing in liquid complete diffusion in solid
31
32
33 CL=Co(1-fs)^(k-1) CL=Cofl^(k-1) Cs=kCofl^(k-1) fs+fl=1 k=cs/cl
34
35
36
37
38
39
40 Co= Gulliver-Scheil Eq. Cs k=0.1 k=0.2 k=0.4 k=0.6 k=0.8 k= fs
41 50 40 Gulliver-Scheil Eq. Co=4.5Cu CL k=0.1 k=0.2 k=0.4 k=0.6 k=0.8 k= fs
42 1 no mixing in liquid no diffusion in solid no coarsening 2. partial mixing in liquid no diffusion in solid no coarsening 3. complete mixing in liquid no diffusion in solid no coarsening 4. complete mixing in liquid diffusion in solid no coarsening 5. complete mixing in liquid diffusion in solid coarsening 6. complete mixing in liquid complete diffusion in solid
43
44
45 Cs=kCo(1-(1-k*beta)*fs)^((k-1)/(1-k*beta))
46 Beta=2*alpha/(1+2*alpha) Ohnaka Beta=2*alpha/(1+2*alpha+1/2k)
47
48
49
50
51 CL Beta=0 beta=0.01 beta=0.1 beta=0.4 beta=0.8 beta=1 Ohnaka Eq. Co=4.5Cu k=
52
53 T Ohnaka Eq. Co=4.5Cu k=0.166 beta=0 beta=0.01 beta=0.1 beta=0.4 beta=0.8 beta= fs
54 1 no mixing in liquid no diffusion in solid no coarsening 2. partial mixing in liquid no diffusion in solid no coarsening 3. complete mixing in liquid no diffusion in solid no coarsening 4. complete mixing in liquid diffusion in solid no coarsening 5. complete mixing in liquid diffusion in solid coarsening 6. complete mixing in liquid complete diffusion in solid
55 Beta=2*alpha/(1+2*alpha) Ohnaka
56
57
58
59
60
61
62
63 Solidification in Ternary System
64
65 Solidification in Al-Cu-Mg Alloys
66 7050 Plate Focus on one alloy (7050) and product (thick hot rolled plate) Components machined from 7050 alloy thick plate are widely used in load bearing applications e.g. wing spars 7050 composition specification
67 Processing Sequence Plate Cast Direct chill Age Homogenize ~475 o C, 24h Solution treat 475 o C, 1h spray quenched Hot roll ~ o C 20+ passes reduction~70%
68 Temperature Microstructural Changes Time RD 50nm Cast Homogenized Rolled Solutionized Aged
69 -AlMg -AlMg Temperature (C) Temperature (C) Temperature (C) Simple Phase Diagrams Even for simple 2xxx alloy (Al-Cu-Mg), need data for 3 binaries and information about ternary phases Al Al-Cu System (Al-Rich) Liquid + -Al Liquid -Al + -Al 2 Cu Liquid + -Al 2 Cu -Al 2 Cu wt.% Cu Al Al-Mg System (Al-Rich) Liquid + -Al -Al + -AlMg Liquid wt.% Mg -AlMg Cu + Laves - C15 L + -Cu Liquid + Laves - C15 Laves - C15 Ternary Phases S - Al 2 CuMg, T - Mg 32 (Al,Cu) 49, V - Al 5 Cu 6 Mg 2, Q - Al 7 Cu 3 Mg 6 Cu-Mg System CuMg2 L + CuMg wt.% Mg Liquid CuMg2 + Mg Liquid + Mg MTDATA predicted phase diagrams Real, commercial Al-alloys may contain > 10 alloying elements! Success of thermodynamic models relies on availability of sufficient, high quality, thermodynamic data
70 Mass Phase Fraction Predictions for Binary Al-Cu Alloy Al 2 Cu Eutectic Reaction Freezing Range fcc -Al Liquid Temperature (C) - Al 2 Cu eutectic fcc -Al eutectic fcc -Al dendrites
71 Predictions for Ternary Al-Cu- Mass Phase Fraction 1.0 Mg alloy Predictions for 2xxx (Al-4.5Cu-1.5wt%) Mg alloy T S fcc -Al Liquid 0.2 S - Al 2 CuMg Al 2 Cu Temperature (C) Ternary Eutectic Predicted at ~ 500ºC DT T L
72 Prediction of Freezing Range To reduce tendency for solidification cracking, need to minimize absolute freezing range Use thermodynamic model to predict freezing range for different alloy compositions DT (Freezing Range of Eutectic) Optimum composition range Effect of Mg content on freezing range of eutectic in Al-4.5Cu-x Mg alloy Binary Eutectic [ + ] Ternary Eutectic [ + S] Saddle Point [ + S] wt.% Mg
73
74 Fe-C-Mn Aloys
75 Fe-C-Mn Phase Diagram
76
77 Color Etching
78 Color Etching
79
80
81
82
83