Strength of Cu-Zr-Cr Alloy Relating to the Aged Structures

Abstract

The reasons why the strength of Cu-Zr-Cr alloys is superior to those of Cu-Zr and Cu-Cr alloys were investigated in relation to their aged structures by transmission electron microscopy. Three sorts of alloys, i.e., Cu-0.54%Zr-0.50%Cr, Cu-0.30%Zr and Cu-0.26%Cr alloys, were used in this study. In each alloy, specimens in the state of solution-treatment at 950°C and of cold-working by 83% after solution-treatment were prepared. Each specimen was vacuum-aged at various temperatures up to 700°C.The results obtained were as follows:(1) Under the same aging condition, two sorts of precipitates in Cu-Zr-Cr alloy, i.e., Cu3Zr and Cr, were finer and more densely distributed than the individual precipitate in each binary alloy, leading to the higher strength of the ternary alloy.(2) The sequense of precipitation of the two sorts of precipitates corresponded to that of the precipitate in the binary alloys. Modes of precipitation were heterogeneous and homogeneous in the Cu-Zr and Cu-Cr alloys, respectively.(3) In cold-worked state, the precipitate of Cu3Zr stabilized the worked structure of the Cu-Zr-Cr alloy due to preferential precipitation on the cell-walls in the same way as in the Cu-Zr alloys.