Effects of Temperature and Heat Treatment on the Short-Range Order in Cu-Mn Alloys

Abstract

We have extended our neutron diffraction measurements of the short‐range atomic ordering in copper‐rich Cu‐Mn alloys over a wide temperature range (0 to 450C). The short‐range ordering is found to develop over a very large temperature range (∼ 600 to OC), but with the correlation length of only about 3, 2.5, and 2 fcc unit cells in well‐annealed single crystals of 25, 20, and 15 atomic percent Mn respectively. The effect of raising the temperature from OC to 450C in Cu‐25% Mn is to reduce the correlation distance from 3 to about 2 fcc unit cells; this is accompanied by a 4‐fold decrease in scattered intensity. The effect of rapid cooling from high temperature is to reduce the extent of the atomic correlations by about 10% both in Cu‐25% Mn and Cu‐20% Mn. This change is accompanied by a change of about 35% in the diffuse intensity.