Brittle fracture in 50Mo-50Re alloys during slow strain rate tensile testing

Tensile tests were conducted on 50 wt% Mo-50 wt% Re alloys in both fully recrystallized and recovery heat-treated conditions at a low strain rate of 10-6 s-1 and room temperature in air. It was found that both material conditions 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 backscatter diffraction (EBSD) measurements revealed significantly high misorientation gradients (i.e. highly localized change in orientation) at grain boundaries, especially in the vicinity of some grain boundary triple junctions in the deformed alloys. Transmission electron microscopy (TEM) results verified the existence of significant misorientations near grain boundaries in these alloys. Stress-assisted dynamic embrittlement, possibly due to trace interstitials, was the possible cause of brittle fracture in the 50Mo-50Re alloys at the low strain rate.