Characterization of strengthening mechanism and hot deformation behavior of powder metallurgy molybdenum

The high-temperature deformation behavior of powder metallurgy molybdenum has been investigated based on a series of isothermal hot compression tests, which were carried out on a Gleeble-1500 thermal mechanical simulator in a wide range of temperatures (900-1450°C) and strain rates (0.01-10s^-1). Through the research on the experimental stress-strain curves, it reveals that dynamic recrystallization softening effect of powder metallurgy molybdenum occurs in the temperature range from 1200°C to 1450°C, in which the flow stress is significantly sensitive to temperature. In comparison with the value of strain hardening index n which decreases along with the temperature rising, the value of strain-rate sensitivity exponent m does not change obviously; however, it increases slowly with the increasing of temperature at first and achieves a peak value at 1350°C. Furthermore, relying on the comparison of mean value of n and m, it is suggested that deformation strengthening is the main strengthening mechanism at low temperature while the rheological strengthening changes into the primary strengthening mechanism at high temperature.