Properties and recrystallization behavior of heavily worked copper
Properties and recrystallization behavior of heavily worked copper J. Springs 2, Y-T. Kao 2, A. Srivastava 1, Z. Levin 2, R. E. Barber 3, K. T. Hartwig 1, 2, 3 1 Materials Science & Engineering department, Texas A&M University, College Station, TX 2 Department of Mechanical Engineering, Texas A&M University, College Station, TX 3 Shear form, Inc. Bryan, TX 77801 Results Abstract PROBLEM Annealed copper has low strength and a superior conductivity, yet a stronger copper material is needed with still low resistivity. Could work hardening be the solution to a high strength low resistivity Cu? APPROACH CDA 101, 110, and C 182 copper were work hardened via the severe plastic deformation (SPD) process equal channel angular extrusion (ECAE). Subsequent testing revealed tensile and hardness properties, grains sizes, recrystallization behavior, conductivity, and low temperature residual resistivity. RESULTS The highest strength copper was formed via ECAE + rolling with a tensile strength of 494 MPa. The highest tensile strength for ECAE only comes from 4 pass route B at 442 MPa. Hardness and tensile strength saturates around 3 -4 ECAE passes. CDA 101 and CDA 110 both had a 5% conductivity drop maximum compared to IACS when fully worked while the C 182 has a 60% drop in conductivity. Recrystallization for pure Cu occurs at 225 C for 8 pass samples. Route Bc produced the smallest grains for both as-worked and recrystallized conditions. CONCLUSIONS • Achieving a target tensile strength of 500 MPa for copper may be possible with an improved SPD schedule and post processing treatment • Route Bc is a preferred method for creating the smallest grains • Alloying, while good for increasing mechanical properties, decreases conductivity substantially Results Table 1: Microstructure for as-worked and recrystallized for CDA 101 copper Route a) AR 1 A 2 A 4 A 4 B 4 Bc 4 E 8 Bc 8 E 16 Bc a) a) Accumulated Strain 0 1. 1 2. 3 4. 6 9. 2 18. 5 Grain Size (micron) b) b) 29. 5 0. 98 0. 75 0. 58 0. 49 0. 41 0. 47 0. 42 0. 53 0. 42 Standard Deviation (micron) 14. 4 0. 67 0. 24 0. 20 0. 11 0. 13 0. 14 0. 16 0. 20 0. 13 Recrystallized Standard Grain Size Deviation (micron) c) N/A 6. 26 4. 44 2. 22 2. 48 1. 95 2. 14 1. 40 1. 66 1. 32 N/A 4. 49 2. 72 1. 18 1. 56 0. 82 1. 23 0. 66 1. 15 0. 72 c) Table 2: Summary of tensile strength data and hardness for CDA 101 copper Route Accumulated Strain Vickers hardness (VH 300) Yield Strength (MPa) Tensile Strength (MPa) Strain to Failure AR 1 A 2 A 4 A 4 B 4 E 4 Bc 8 E 16 Bc 0 1. 1 2. 3 4. 6 9. 2 18. 5 54 ± 1 126 ± 2 132 ± 5 137 ± 2 145 ± 4 143 ± 3 144 ± 2 141 ± 4 145 ± 2 136 ± 2 181 ± 2 323 ± 5 364 ± 1 372 ± 1 399 ± 4 402 ± 1 383 ± 17 373 ± 3 382 ± 2 357 ± 3 248 ± 2 349 ± 4 383 ± 4 397 ± 2 442 ± 4 438 ± 2 421 ± 6 437 ± 6 427 ± 1 438 ± 3 0. 38 ±. 02 0. 14 ±. 01 0. 14 ±. 03 0. 16 ±. 01 0. 19 ±. 01 0. 16 ±. 02 0. 20 ±. 01 0. 15 ±. 01 0. 18 ±. 01 Table 3: Summary of conductivity for CDA 101, CDA 110, and C 182 copper as well as RR and RRR values for CDA 101 copper C 182 Figure 2: SEM images of a) annealed CDA at 400 x b) 1 A processed CDA 101 at 20000 x c) 8 Bc processed CDA 101 at 20000 x CDA 110 Processing %IACS Annealed 1 A 2 A 2 B 4 A 4 Bc 4 E 8 Bc 8 E 16 Bc 59. 6 41. 2 N/A 41. 4 N/A 40. 4 41. 8 39. 1 41. 4 N/A 100. 7 97. 0 N/A 97. 2 N/A 96. 5 97. 1 96. 5 97. 2 N/A 103. 4 98. 2 N/A 96. 9 N/A 95. 6 97. 1 95. 4 97. 0 N/A CDA 101 RR (77 K/4. 2 K) 11. 2 7. 40 6. 05 N/A 4. 94 4. 14 4. 79 3. 64 4. 28 3. 48 RRR (273 K/4. 2 K) 91. 0 51. 6 36. 4 N/A 30. 8 24. 5 30. 0 21. 1 27. 3 19. 2 Deformation Processing Figure 3: Left-Stress strain curves for AR, 1 A, 2 A, 4 A, 8 A, and rolled 4 A. Right-Conductivity of CDA 101, CDA 110, and C 182 compared to the IACS value TS=501 -2. 8*RRR R 2=0. 96 Figure 1: Example ECAE 90˚ die and billet schematic The different designation of routes in ECAE are determined by the rotation seen between successive passes. Route A has no rotation, Route B is rotated by 90º on even numbered passes and by 270º on odd numbered passes. Route C keeps the same orientation through all passes at a rotation of 180º. Route E is rotated 180º for all even numbered passes, and by 90º or 270º for the odd numbered passes. Finally route Bc, is rotated by 90º for all passes. Figure 5: Tensile strength vs RRR correlation for various selected routes Acknowledgments Figure 4: Left-Vickers hardness vs temperature of route 8 Bc CDA 101, CDA 110, and C 182 copper. Right-DSC curve for 8 pass CDA 101 samples Texas A&M University for the use of equipment and lab space Michael Elverud for help in fabrication and testing
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