Uniaxial, load-controlled cyclic deformation of recrystallized molybdenum sheet

Abstract

► Cyclic deformation of Mo was studied using R = 0.1 in the range 25–500 °C. ► At 25 °C, unrecrystallized Mo shows more ratcheting than recrystallized Mo. ► Ratcheting rate increases, then decreases and then increases prior to failure. ► Ratcheting strain at 25 °C increases with increases in mean stress. ► Ratcheting strain is higher at higher temperatures for given loading conditions. Monotonic tensile tests and uniaxial load-controlled tension–tension cyclic tests were performed on commercial purity (99.99%) molybdenum in the recrystallized state in the temperature interval spanning RT (25 °C) to 500 °C range. Cyclic deformation behavior was characterized by analyzing the ratcheting strain, cyclic hardening response, and fatigue life. The response of unrecrystallized and recrystallized Mo was compared at room temperature; the influence of test variables including mean stress, stress amplitude and R ratio on ratcheting strain in recrystallized Mo at room temperature was also examined. The magnitude and rate of ratcheting strain evolution with cycles appear to depend on both the mean stress and the stress amplitude. Microstructural evolution during cyclic loading was characterized by conducting interrupted tests at room temperature as well as at 400 °C. Observations confirm dislocations cell structure formation during cyclic plastic deformation at room temperature and at 400 °C, the process occurring more rapidly at the higher temperature; in addition, at the higher temperature some of the cell walls appeared to have transformed into subgrain boundaries, suggesting partial recovery.