Abstract
Tensile tests were conducted on 50Mo-50Re alloys, in fully-recrystallized and recovery heat-treated conditions respectively, at a very low strain rate of 10-6 s-1 and room temperature in air. It was found that both these alloys exhibited predominantly cleavage fracture with significant intergranular secondary cracking, compared to the predominantly ductile fracture found in the alloys at a higher strain rate. Cracks were often initiated at grain boundary triple junctions at the low strain rate. Electron back scatter diffraction (EBSD) measurements revealed significantly high misorientation gradients at grain boundaries, especially in the vicinity of some grain boundary triple junctions in the deformed alloys. Transmission electron microscopic (TEM) results verified the existence of significant misorientation taking place at grain boundaries in these alloys. Stress-assisted dynamic embrittlement, possibly due to trace interstitials, was the possible cause for the occurrence of brittle fracture in the 50Mo-50Re alloys at the low strain rate.