The Mechanical Behaviour of an Iron-11 at% Molybdenum Alloy in the Temperature Range 295 to 1100 °K

The effect of precipitation of an intermetallic compound on the mechanical behaviour of an Fe—11 at% Mo alloy has been studied by means of compression tests in the temperature range 295 to 1100 °K. At temperature up to 700 °K for the well‐aged conditions of the alloy and 875 °K for the solution‐treated and slightly aged states, the temperature dependence of the yield and 0.2% proof stresses can be accounted for by the change in the elastic modulus with temperature. For the well‐aged conditions in the temperature range 700 to 950 °K the yield strength was temperature and strain‐rate sensitive. It is concluded that in this temperature range, deformation is determined by the diffusion‐controlled motion of dislocations past the precipitate barriers. Above about 950 °K all conditions of the alloy exhibited a similar, and large, temperature dependence of the yield strength; in addition, secondary creep occurred at the imposed strain rate and the creep stress was found to be independent of the size and distribution of the precipitate. The very high values of the apparent activation energy for yield and secondary creep found above 950 °K are considered to be due to an anomalous change in the activation energy for diffusion during the Curie transformation.