Cyclic tensile response of Mo-27 at% Re and Mo-0.3 at% Si solid solution alloys

Abstract

Stress-controlled uniaxial cyclic tensile tests were conducted on binaryMo-27 at.% Reand Mo-0.3at.% Si solid solutions as a function of temperature and comparedagainst the previously reported cyclic response of pure Mo. The Mo-27at.%Re alloy with a recrystallized grain size of ~30 m was evaluated in the temperature range 25 o C to 800°Cat R=0.1 and stress range that was 80% of the ultimate tensile strength (UTS);a peak in fatigue life was observed between 300°C and 500°C. The decrease in fatigue life at the higher temperatures of 700°C and 800°C is attributed to dynamic strain aging.Transmission electron microscopy of the cyclically-deformed alloy revealed parallel bands of dislocation at room temperaturethat transitioned to a uniform cell structure at 500 o C and back to orthogonal planar arrays at800 o C. The as-extruded Mo-0.3at.%Si alloy was evaluated from 25 o C to 1200°C and showed superior fatigue life and ratcheting strain resistance as compared to pure Mo and the Mo-27at.% Re alloy(within the temperature range where data were available for comparison). The superior resistanceis attributed to the high density of dislocations within the material in this mostly unrecrystallized state rather than Si in solid solution. Above 800 o C, the ratcheting strain increases and fatigue lifedecreases rapidly with increasing temperature and is associated with dynamic recovery.