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

Abstract

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.

Keywords:

• strain-rate dependence
• brittle fracture
• Mo-Re alloy
• misorientation
• dynamic embrittlement

Acknowledgement

This research was supported through a NSF CAREER AWARD (DMR-0645246). The TEM work reported in this paper was conducted as part of the Oak Ridge National Laboratory's SHaRE User Facility, which is sponsored by the US Department of Energy, Office of Energy Efficiency and Renewable Energy, Industrial Technologies Program, Industrial Materials for the Future and the Division of Materials Sciences and Engineering, under contract DE-AC05-00OR22725 with U.T. Battelle, LLC. The authors would like to thank Michael Effgen from Semicon Associates for providing the 50Mo–50Re alloys used in this work.