Control of Microstructures and Properties of a Phosphorus-Containing Cu-0.6 Wt.% Cr Alloy through Precipitation Treatment

Abstract

A phosphorus-containing Cu-0.6 wt.% Cr alloy was solution treated and then aged using various combinations of time and temperature. The influence of aging time and temperature on microstructures and properties of this alloy was investigated by means of an analytical transmission electronic microscope (TEM) and measurements of hardness and electrical conductivity. It was found that neither underaging nor overaging could harden the alloy significantly. The microstructure corresponding to peak hardness was characterized by very fine and coherent precipitates. Increasing aging time and temperature caused the precipitates to grow into rodlike incoherent Cr particles having body-centered cubic (bcc) crystal structure, but aging temperature influenced the microstructures and properties more intensively than did aging time. Undissolved body-centered tetragonal (bct) Cr3P particles, which were found in both assolution-treated and as-aged structures, were not harmful to electrical conductivity and might act as obstacles impeding dislocation motion. As compared to a Cu-0.65 wt.% Cr alloy not containing phosphorus, the studied alloy needs aging at a higher temperature to reach peak hardness.