EFFECTS OF THERMAL-MECHANICAL VARIABLES ON THE TEXTURE AND BEND DUCTILITY OF HIGH PURITY BERYLLIUM SHEET.

Abstract : The purpose of this research program was to assess the improvements which might be obtained in the bend ductility of beryllium sheet by using powder of higher purity than that of standard commercial practice and by consolidating this powder into sheet using low order deformation. The starting powder was prepared from Pechiney SR grade beryllium and the fabrication procedures consisted of compression (polydirectional) rolling, hot upsetting, and hot forging with reduction ratios of from 2:1 to 12:1 and at temperatures from 750 C to 1050 C. It was found that as the plastic bend ductility increased (up to 4% with a w/t of 10:1) the yield strength decreased and that the higher bend ductility corresponded to lower reduction ratios, lower degrees of preferred orientation and a larger sub-grain size as determined by transmission electron microscopy. The ductile-to-brittle transition temperature in bending decreased from about 200 C to about 150 C as the degree of preferred orientation and the impurity content decreased from that represented by Brush S200 commercial cross rolled sheet (low purity and strong texture) to hot upset SR sheet (high purity and weak texture). The transition temperature of SR compression rolled sheet (high purity and strong texture) was intermediate at about 170 C.