Not measured by atom-probe tomography: Pair correlation functions Inter-precipitate distance distributions (IDDs)

Transcription

1 Additional measurements possible using scanning electron microscopy (SEM) Not measured by atom-probe tomography: Pair correlation functions Inter-precipitate distance distributions (IDDs) Also measurable by SEM*: Mean radius of precipitates, <R(t)> Volume fraction of γ (L1 2 structure)-phase, f(t) Number density of precipitates, N v (t) Precipitate size distributions, PSDs, as a function of time (t). Sudbrack CK, Ziebell TD, Noebe RD, Seidman DN. Effects of a tungsten addition on the morphological evolution, spatial correlations and temporal evolution of a model Ni-Al-Cr superalloy. Acta Mater. 2008;56:448. 1

2 High Temperature Materials Motivations and Applications (a) Ni alloys (b) Ni alloys Maximum service temperature ( C) C Ti alloys Al-based "superalloy" Existing Al alloys Fe alloys Maximum service temperature ( C) Fe alloys 425 C Al-based "superalloy" Existing Al alloys Ti alloys Density (Mg m -3 ) Price ($ kg -1 ) Internal combustion engine Front section of turbine engine Brake rotor 8/21/16 2

3 Aluminum Aluminum alloys for alloys automotive for automotive applications applications Following the recommendation of the Corporate Average Fuel Economy (CAFE) standards, the automotive industry needs to reduce fuel consumption of vehicles, making more fuel efficient vehicles. One way to achieve this is by using lightweight materials. Ford F Maximum operating temperature of commercially available aluminum alloys is in the C range. - Temperature is limited due to the dissolution or rapid coarsening of the precipitate hardening phases with increasing temperatures. - Application of concern: brake rotors 3

4 Al 3 Sc Precipitation-Strengthened Alloys Al 3 Sc slow coarsening kinetics up to 300 o C (>0.6T m ) Coherent (L1 2 structure) nano-scale precipitates High strength and creep resistance Marquis et al

5 Trialuminide-forming elements 5

6 Modifications of Al-Sc Alloys 1. Replace Sc partially by Rare-Earth (RE) elements 2. Replace Sc partially by Transition-Metal (TM) elements 3. Multicomponent and multifunctional Al-Sc based alloy 4. Enhance mechanical strength by addition of inoculants (Si) 6

7 Part 1: Ternary Al-Sc-RE (RE= Rare Earth) Alloys Sc Al-0.06Sc-0.02Er at.%, aged at 300 o C/24 h Er Formation of Er-core/Sc-shell precipitates Indication that Er has a higher diffusivity than Sc in α-al Krug et al 2008 Same core-shell structure observed in all other Al-Sc-RE alloys 7

8 Microhardness Al-0.06Sc-0.02RE at.% has peak hardness similar to Al-0.08Sc at.% higher than Al-0.06Sc at.% successful replacement of Sc with RE Al-Sc-Yb alloy hardens at much earlier aging times 1 Krug et al

9 Al-Sc-RE Alloys Have a High Creep Resistance Values at 300 o C General climb model RE-core/Sc-shell precipitates, still coherent with Al matrix Krug thesis, /21/16 9

10 Al-Sc-RE Alloys Have High Creep Resistance Values at 300 o C Krug thesis, /21/16 10

11 Part 2: Ternary Al-Sc-TM (TM= Transition Metals) Alloys Formation of Sc-core/Zr-shell precipitates Indication that Zr has a smaller diffusivity than Sc in α-al Same core-shell structure observed in other Al-Sc-TM (TM = Ti or Hf) alloys Sc Zr Al-0.06Sc-0.06Zr at.% isochronally aged to 450 o C (25 o C/1h) Booth-Morrison et al

12 Coarsening Resistance of Al-Sc-Zr Alloys Isochronal aging (25 o C/3h) of Al-0.06Sc-0.06Zr at.% Isothermal aging at 400 o C of Al-0.06Sc-0.06Zr at.% Keith et al 2011 Booth-Morrison et al 2012 Zr addition Improves coarsening resistance of Al-Sc alloy Al-0.06Sc-0.06Zr at.% can be operational at 400 o C for at least 64 days 12

13 Part 3: Quaternary multifunctional Al-Sc-Er-Zr Alloys Formation of Er-core/Sc-shell/Zr-shell precipitates Core-double shell structure is due to sequential precipitation of Er, Sc, and Zr (D Er < D Sc < D Zr ) Enhanced creep resistance due to Er-core, owing to a large lattice parameter mismatch between precipitate and matrix Enhanced coarsening resistance due to Zr-shell, acting as a diffusion barrier for precipitates Al-0.04Sc-0.02Er-0.06Zr at.% isochronally aged to 450 o C (25 o C/1h) Er Sc Zr Booth-Morrison et al

14 Part 4: Effects of Si Addition in Al-Sc-Er-Zr Alloys Al-0.055Sc-0.005Er-0.02Zr-0.05Si at.% Si Er Sc Zr Si exists in master alloy à lowers alloy cost Si induces heterogeneous nucleation à increases strength Si accelerates Er and Sc diffusion kinetic à shortens homogenization and peak-aging time à decreases processing cost Booth-Morrison et al /21/16 14

15 Properties of Al-0.055Sc-0.005Er-0.02Zr-0.05Si at.% Large-grain structure Si-containing achieves higher peak-strength Si-containing achieves peakstrength faster Si-containing seems to decrease strength earlier 8/21/16 15

16 Properties of Al-0.055Sc-0.005Er-0.02Zr-0.05Si at.% Large-grain structure Samples for atom-probe tomography Si-containing achieves higher peak-strength Si-containing achieves peakstrength faster Si-containing seems to drop strength earlier 8/21/16 16

17 Atom-Probe Tomography Explains the Effect s of Si Additions Al-0.055Sc-0.005Er-0.02Zr-0.05Si at.% 0.5 h: Microhardness = 504 Mpa <R>=4.1±0.8 nm Nv = 1.11±0.37 x 1022 m-3 Al-0.04Sc-0.02Er-0.06Zr at.% 0.5 h: Microhardness = 414 Mpa <R>=3.7±0.3 nm Nv = 0.54 ±0.17 x 1022 m-3 8/21/16 66 days Microhardness = 429 Mpa <R>=6.3±0.3 nm Nv = 0.20 ±0.10 x 1022 m-3 64 days Hardness = 448 Mpa <R>=3.8±0.4 nm Nv = 0.61 ±0.19 x 1022 m-3 17

18 Precipitate Structure of Si-containing Alloy, aged at 400 o C for 66 days Followed coarsening Initial nucleated ppt 16 nm Er Sc Zr Er+Sc+Zr coarsening Large precipitates grow at the expense of small precipitates, which shrink and disappear (Ostwald ripening) from the system 8/21/16 18

19 Increasing Additional Si Concentrations Higher Si concentrations achieve higher peak hardnesses. Peak hardness of 0.18Si is 600 MPa, while peak hardness of the sample without Si is 450 MPa. This is a 60% enhancement in microhardness with the Si addition (base microhardness is 200 MPa) Al-0.055Sc-0.005Er--0.02Zr-0.XSiat.% 400 o C Higher Si concentrations achieve peak aged condition faster: 2 h for 0.18Si and 0.12Si, 80 h for 0.05Si, and 300 h for no-si Higher Si concentrations accelerates the decrease of the microhardness, implying that it reduces the coarsening resistance due to the Zr-enriched shell 8/21/16 19

20 Isothermal Aging at 400 o C: Atom-Probe Tomogrpahic Results 50 nm Si h Hardness = 504 Mpa <R>=4.14±0.81 nm N v = 1.11±0.37 x m nm Si h Hardness = 536 Mpa <R>=2.91±0.71 nm N v = 2.29±0.57 x m -3 Si h Hardness = 414 Mpa <r>=3.7±0.3 nm N v = 0.54 ±0.17 x m nm 8/21/16 20

21 Isothermal Aging at 400 o C: Precipitate Nanostructure 0.05Si-0.5h 0.18Si-0.5h 0.0Si-0.5h 8/21/16 21

22 Si Accelerates Zr Diffusion Kinetics Zr-enriched shell structure of samples aged at 400 o C for 0.5 h Edge-to-Edge Interprecipitate spacing is ~80 nm RMS Diffusion distance of Zr at 400 o C [sqrt(4dt)]- for 0.5 h is 9 nm à Zr diffuses faster as Si concentration increases 8/21/16 22

23 Summary 1. Replace Sc partially by Rare-Earth (RE) elements Decreases alloy cost Increases creep resistance 2. Replace Sc partially by Transition-Metal (TM) elements Decreases alloy cost Increases coarsening resistance 3. Multifunctional Al-Sc based alloy Creep resistance due to Er-core of precipitates Coarsening resistance due to Zr-shell of precipitates Enhanced strength by Si addition(s) Decreased alloy cost due to existence of Si in master alloys 4. Effect of higher Si concentrations (up to 0.2 at.%) Higher peak-aging strength Reduce peak-aging time at 400 o C by accelerating Er, Sc precipitation kinetics Accelerates Zr diffusion kinetics, reducing coarsening resistance 8/21/16 23

24 Additional measurements possible using scanning electron microscopy (SEM) Not measured by atom-probe tomography: Pair correlation functions Inter-precipitate distance distributions (IDDs) Also measurable by SEM*: Mean radius of precipitates, <R(t)> Volume fraction of γ (L1 2 structure)-phase, f(t) Number density of precipitates, N v (t) Precipitate size distributions, PSDs, as a function of time (t). Sudbrack CK, Ziebell TD, Noebe RD, Seidman DN. Effects of a tungsten addition on the morphological evolution, spatial correlations and temporal evolution of a model Ni-Al-Cr superalloy. Acta Mater. 2008;56:

25 High Temperature Materials Motivations and Applications (a) Ni alloys (b) Ni alloys Maximum service temperature ( C) C Ti alloys Al-based "superalloy" Existing Al alloys Fe alloys Maximum service temperature ( C) Fe alloys 425 C Al-based "superalloy" Existing Al alloys Ti alloys Density (Mg m -3 ) Price ($ kg -1 ) Internal combustion engine Front section of turbine engine Brake rotor 8/21/16 25

26 Aluminum Aluminum alloys for alloys automotive for automotive applications applications Following the recommendation of the Corporate Average Fuel Economy (CAFE) standards, the automotive industry needs to reduce fuel consumption of vehicles, making more fuel efficient vehicles. One way to achieve this is by using lightweight materials. Ford F Maximum operating temperature of commercially available aluminum alloys is in the C range. - Temperature is limited due to the dissolution or rapid coarsening of the precipitate hardening phases with increasing temperatures. - Application of concern: brake rotors 26

27 Al 3 Sc Precipitation-Strengthened Alloys Al 3 Sc slow coarsening kinetics up to 300 o C (>0.6T m ) Coherent (L1 2 structure) nano-scale precipitates High strength and creep resistance Marquis et al

28 Trialuminide-forming elements 28

29 Modifications of Al-Sc Alloys 1. Replace Sc partially by Rare-Earth (RE) elements 2. Replace Sc partially by Transition-Metal (TM) elements 3. Multicomponent and multifunctional Al-Sc based alloy 4. Enhance mechanical strength by addition of inoculants (Si) 29

30 Part 1: Ternary Al-Sc-RE (RE= Rare Earth) Alloys Sc Al-0.06Sc-0.02Er at.%, aged at 300 o C/24 h Er Formation of Er-core/Sc-shell precipitates Indication that Er has a higher diffusivity than Sc in α-al Krug et al 2008 Same core-shell structure observed in all other Al-Sc-RE alloys 30

31 Microhardness Al-0.06Sc-0.02RE at.% has peak hardness similar to Al-0.08Sc at.% higher than Al-0.06Sc at.% successful replacement of Sc with RE Al-Sc-Yb alloy hardens at much earlier aging times 1 Krug et al

32 Al-Sc-RE Alloys Have a High Creep Resistance Values at 300 o C General climb model RE-core/Sc-shell precipitates, still coherent with Al matrix Krug thesis, /21/16 32

33 Al-Sc-RE Alloys Have High Creep Resistance Values at 300 o C Krug thesis, /21/16 33

34 Part 2: Ternary Al-Sc-TM (TM= Transition Metals) Alloys Formation of Sc-core/Zr-shell precipitates Indication that Zr has a smaller diffusivity than Sc in α-al Same core-shell structure observed in other Al-Sc-TM (TM = Ti or Hf) alloys Sc Zr Al-0.06Sc-0.06Zr at.% isochronally aged to 450 o C (25 o C/1h) Booth-Morrison et al

35 Coarsening Resistance of Al-Sc-Zr Alloys Isochronal aging (25 o C/3h) of Al-0.06Sc-0.06Zr at.% Isothermal aging at 400 o C of Al-0.06Sc-0.06Zr at.% Keith et al 2011 Booth-Morrison et al 2012 Zr addition Improves coarsening resistance of Al-Sc alloy Al-0.06Sc-0.06Zr at.% can be operational at 400 o C for at least 64 days 35

36 Part 3: Quaternary multifunctional Al-Sc-Er-Zr Alloys Formation of Er-core/Sc-shell/Zr-shell precipitates Core-double shell structure is due to sequential precipitation of Er, Sc, and Zr (D Er < D Sc < D Zr ) Enhanced creep resistance due to Er-core, owing to a large lattice parameter mismatch between precipitate and matrix Enhanced coarsening resistance due to Zr-shell, acting as a diffusion barrier for precipitates Al-0.04Sc-0.02Er-0.06Zr at.% isochronally aged to 450 o C (25 o C/1h) Er Sc Zr Booth-Morrison et al

37 Part 4: Effects of Si Addition in Al-Sc-Er-Zr Alloys Al-0.055Sc-0.005Er-0.02Zr-0.05Si at.% Si Er Sc Zr Si exists in master alloy à lowers alloy cost Si induces heterogeneous nucleation à increases strength Si accelerates Er and Sc diffusion kinetic à shortens homogenization and peak-aging time à decreases processing cost Booth-Morrison et al /21/16 37

38 Properties of Al-0.055Sc-0.005Er-0.02Zr-0.05Si at.% Large-grain structure Si-containing achieves higher peak-strength Si-containing achieves peakstrength faster Si-containing seems to decrease strength earlier 8/21/16 38

39 Properties of Al-0.055Sc-0.005Er-0.02Zr-0.05Si at.% Large-grain structure Samples for atom-probe tomography Si-containing achieves higher peak-strength Si-containing achieves peakstrength faster Si-containing seems to drop strength earlier 8/21/16 39

40 Atom-Probe Tomography Explains the Effect s of Si Additions Al-0.055Sc-0.005Er-0.02Zr-0.05Si at.% 0.5 h: Microhardness = 504 Mpa <R>=4.1±0.8 nm Nv = 1.11±0.37 x 1022 m-3 Al-0.04Sc-0.02Er-0.06Zr at.% 0.5 h: Microhardness = 414 Mpa <R>=3.7±0.3 nm Nv = 0.54 ±0.17 x 1022 m-3 8/21/16 66 days Microhardness = 429 Mpa <R>=6.3±0.3 nm Nv = 0.20 ±0.10 x 1022 m-3 64 days Hardness = 448 Mpa <R>=3.8±0.4 nm Nv = 0.61 ±0.19 x 1022 m-3 40

41 Precipitate Structure of Si-containing Alloy, aged at 400 o C for 66 days Followed coarsening Initial nucleated ppt 16 nm Er Sc Zr Er+Sc+Zr coarsening Large precipitates grow at the expense of small precipitates, which shrink and disappear (Ostwald ripening) from the system 8/21/16 41

42 Increasing Additional Si Concentrations Higher Si concentrations achieve higher peak hardnesses. Peak hardness of 0.18Si is 600 MPa, while peak hardness of the sample without Si is 450 MPa. This is a 60% enhancement in microhardness with the Si addition (base microhardness is 200 MPa) Al-0.055Sc-0.005Er--0.02Zr-0.XSiat.% 400 o C Higher Si concentrations achieve peak aged condition faster: 2 h for 0.18Si and 0.12Si, 80 h for 0.05Si, and 300 h for no-si Higher Si concentrations accelerates the decrease of the microhardness, implying that it reduces the coarsening resistance due to the Zr-enriched shell 8/21/16 42

43 Isothermal Aging at 400 o C: Atom-Probe Tomogrpahic Results 50 nm Si h Hardness = 504 Mpa <R>=4.14±0.81 nm N v = 1.11±0.37 x m nm Si h Hardness = 536 Mpa <R>=2.91±0.71 nm N v = 2.29±0.57 x m -3 Si h Hardness = 414 Mpa <r>=3.7±0.3 nm N v = 0.54 ±0.17 x m nm 8/21/16 43

44 Isothermal Aging at 400 o C: Precipitate Nanostructure 0.05Si-0.5h 0.18Si-0.5h 0.0Si-0.5h 8/21/16 44

45 Si Accelerates Zr Diffusion Kinetics Zr-enriched shell structure of samples aged at 400 o C for 0.5 h Edge-to-Edge Interprecipitate spacing is ~80 nm RMS Diffusion distance of Zr at 400 o C [sqrt(4dt)]- for 0.5 h is 9 nm à Zr diffuses faster as Si concentration increases 8/21/16 45

46 Summary 1. Replace Sc partially by Rare-Earth (RE) elements Decreases alloy cost Increases creep resistance 2. Replace Sc partially by Transition-Metal (TM) elements Decreases alloy cost Increases coarsening resistance 3. Multifunctional Al-Sc based alloy Creep resistance due to Er-core of precipitates Coarsening resistance due to Zr-shell of precipitates Enhanced strength by Si addition(s) Decreased alloy cost due to existence of Si in master alloys 4. Effect of higher Si concentrations (up to 0.2 at.%) Higher peak-aging strength Reduce peak-aging time at 400 o C by accelerating Er, Sc precipitation kinetics Accelerates Zr diffusion kinetics, reducing coarsening resistance 8/21/16 46