Improving the high temperature mechanical performance of Cu–Cr alloy induced by residual nano-sized Cr precipitates

The mechanical performance of Cu–Cr alloy severely deteriorates at high temperatures due to the Cr precipitates coarsening rapidly or dissolving in Cu matrix again. This study achieved the supersaturated solid solution Cu-5wt%Cr alloy (S1) with Cr solubility of 0.94 wt% by combining mechanical alloying and spark plasma sintering. The effect of residual Cr precipitates on the high temperature hardness, softening resistance and microstructures were investigated. The results showed that S1 alloy exhibited an excellent hardness of 106.27 HV at 500 °C, 23.14% higher than the common sample. The softening temperature of S1 alloy is 800 °C (0.74T_m), and the average grain size of S1 alloy annealed at 800 °C is 0.69 μm, which increased by only 0.11 μm. The microstructural evolution showed that the high thermal stability is mainly attributed to two kinds of residual Cr precipitates in the matrix. The larger ones act as obstacles to inhibit the motion of Cu grain boundaries, and the fine precipitates disperse in Cu matrix to fix the dislocations. Combining these two types of residual Cr precipitates act as very powerful obstacles to inhibit the motion of dislocations and grain boundaries. Also, the increment in yield strength at elevated temperature (300–700 °C) deduced from the residual Cr precipitates strengthening ranges from 320 MPa to 337 MPa.