High-Performance Dispersion-Strengthened Cu-8 Cr-4 Nb Alloy

摘要

A new high-temperature-strength, high-conductivity Cu-Cr-Nb alloy with a Cr.Nb ratio of 2:1 was developed to achieve improved performance and durability. The Cu-8 Cr-4 Nb alloy studied has demonstrated remarkable thermal and microstructural stability after long exposures at temperatures up to 0.98 T_m. This stability was mainly attributed to the slow coarsening kinetics of the CrJNb precipitates present in the alloy. At all temperatures, the micro structure consists of a bimodal and sometimes trimodal distribution of strengthening Cr_2Nb precipitates, depending on precipitation condition, i.e., from liquid or solid solution, and cooling rates. These precipitates remain in the same size range, i.e., large precipitates of approximately 1mu m and small precipitates less than 300 run, and effectively pin the grain boundaries, thus retaining a fine grain size of 2.7 /am after 100 hours at 1323 K. This grain-boundary pinning and sluggish coarsening of Cr_2Nb particles explain the retention of good mechanical properties after prolonged holding at very high temperatures, e.g., two-thirds of the original yield strength after aging for 100 hours at 1273 K. The main sources of strengthening are the Hall-Petch and Orowan mechanisms due mostly to small particles. The coarsening kinetics of the large precipitates are most likely governed by grain-boundary diffusion and, to a lesser extent, volume diffusion mechanisms.