Effects of Thermal and Mechanical Processing on Microstructures and Desired Properties of Particle-Strengthened Cu-Cr-Nb Alloys

摘要

Ternary Cu-Cr-Nb alloys,particularly Cu-8 Cr-4 Nb (in at.%),have demonstrated good thermal stability as well as high strength and high conductivity at low and high temperatures.This behavior-due to the insoluble and strong Cr_2Nb intermetallic phase that forms from the 2:1 Cr/Nb ratio-has put Cu-Cr-Nb alloys at the forefront as the next-generation particle-strengthened Cu alloys for aerospace applications.The initial powder material,produced by Ar-gas atomization,has a bimodal size distribution of Cr_2Nb precipitates.Primary Cr_2Nb precipitates,formed congruently from the melt,are typically approx 1 mum in size,and secondary Cr_2Nb particles,precipiated from atomized solid solution,are typically 30-200 nm in size.This study provides the first detailed examination of the stability and strengthening effects of these particles in Cu-Cr-Nb alloys.Extruded Cu-8 Cr-4 Nb exposed to temperatures of up to 1323 K for up to 100 hr sustained a drop in strength of only 25-30%.Such behavior was mainly a manifestation of Cu grains stabilized by primary and secondary Cr_2Nb dispersoids,which remained in their initial size range due to their inherently sluggish coarsening.The modest particle coarsening was analyzed in terms of and found to follow LSW-type behavior.