Effect of Initial Annealing Temperature on Microstructural Development and Microhardness in High‐Purity Copper Processed by High‐Pressure Torsion

Abstract

The effect of the initial annealing temperature on the evolution of microstructure and microhardness in high purity OFHC Cu is investigated after processing by HPT. Disks of Cu are annealed for 1 h at two different annealing temperatures, 400 and 800 C, and then processed by HPT at room temperature under a pressure of 6.0 GPa for 1/4, 1/2, 1, 5, and 10 turns. Samples are stored for 6 months after HPT processing to examine the self-annealing effects. Electron backscattered diffraction (EBSD) measurements are recorded for each disk at three positions: center, mid-radius, and near edge. Microhardness measurements are also recorded along the diameters of each disk. Both alloys show rapid hardening and then strain softening in the very early stages of straining due to self-annealing with a clear delay in the onset of softening in the alloy initially annealed at 800 C. This delay is due to the relatively larger initial grain size compared to the alloy initially annealed at 400 C. The final microstructures consist of homogeneous fine grains having average sizes of 0.28 and 0.34 mm for the alloys initially annealed at 400 and 800 C, respectively. A new model is proposed to describe the behavior of the hardness evolution by HPT in high purity OFHC Cu.

Microstructure, mechanical properties and aging behaviour of nanocrystalline copper–beryllium alloy

“…It is known that grain refinement during SPD of fcc metals such as copper and aluminium is very sensitive to the level of impurity. Thus, high purity copper processed by SPD typically exhibits an average grain size in the range of 380 -470 nm which depends on preliminary thermal treatment condition [30], while a typical value of about 150 nm is reported for coarse-grained copper with 1.49 wt.% Si deformed in similar conditions [31]. The Si impurity remain in the solution with Cu at this composition [32].…”

Microstructure and Microhardness Evolution in Pure Molybdenum Processed by High‐Pressure Torsion

“…[21] For refractory metals, reports are now available on the processing of W by ECAP or HPT over a range of temperatures from 673 to 1273 K, [22][23][24][25] the processing of Ta by ECAP at RT [26][27][28][29][30][31] or at 1173 or 1473 K [32] and HPT at RT, [33][34][35][36][37] the processing of V by HPT at RT, [38][39][40] and the processing of Mo by ECAP or HPT at temperatures from 623 to 1073 K [41][42][43][44][45][46][47][48] and HPT at both RT [38,[49][50][51][52][53][54][55][56][57] and a cryogenic temperature of 80 K. [54,56] Although several reports are now available on the processing of Mo by HPT, there have been no systematic studies of the concurrent evolution of microstructural refinement and hardness in pure molybdenum as are available, for example, in conventional fcc metals such as aluminum, [15] Al-based alloys, [16,58] and highpurity Cu. [59,…”

“…Although several reports are now available on the processing of Mo by HPT, there have been no systematic studies of the concurrent evolution of microstructural refinement and hardness in pure molybdenum as are available, for example, in conventional fcc metals such as aluminum, Al‐based alloys, and high‐purity Cu . Accordingly, the present research was initiated to provide detailed information on the microstructure and hardness evolution when processing pure Mo through numbers of HPT turns using transmission electron microscopy (TEM), electron backscatter diffraction (EBSD), and measurements of the Vickers microhardness.…”