Examination of some high-strength, high-conductivity copper alloys for high-temperature applications

摘要

Copper fvlloys with high strength and high thermal and electrical conductivily have received a lot of attention over the last decades. Most of such efforts have concentrated on the development of alloys contain I rig fine, dispersed particles (1-9), and using rapid solidification techniques to ensure a sufficient volume fraction and sufficient fineness of the dispersed phase. One of the limitations of most such alloys is the lack of strength at temperatures above 500"C, related generally to the excessive coarsening ol particles. Good stability of fine dispersed particles at high temperature is especially necessary since the 'material is typically exposed to elevated temperatures during fabrication, for example for hot extrusion, and may encounter high temperatures during secondary processing, for example during brazing of components into their working situation, or during operation itself. Under such conditions the microstructure of the alloys will change, especially the distribution of the fine particles, degrading the mechanical properties. In a recent study (10), a .Cu-8Cr-4Nb alloy was developed which shows relatively good strength up to 700°C, a result which was explained by the resistance to coarsening of I he fine Cr2Nb intermelallic particles in this materials. The amount of intermelallic CisNb second phase in this alloy was about 14vol% (11) and it was claimed that the special compound-nature of the inlcrmetyllic phase was responsible for the good stability and retention of strength to high temperature. In order to examine the influence of the nature of the fine particles present and their stability against coarsening, as well as to examine the influence of volume fraction of second phase on tensile strength, three different alloys have been chosen for study: Cu-2Nb and Cu-4Cr for examining the role of second phase chemistry (Nb or Cr) on structural and property stability, and a Cu-14Cr alloy, for comparison with the- Cu-4Cr alloy, to examine the role of volume fraction of the second phase. The stability of these alloys will then be compared with that, reported (10) for the Cu-RCr-4Nb. alloy.