Effect of Shock Pressure on the Ductile-Brittle Transition Behavior of Polycrystalline Molybdenum.

Abstract

An explosive shock pressure treatment at 930 MPa was given to polycrystalline molybdenum (99.9 mass % purity) in water to examine the change in the tensile behavior of the metal. Findings in the present study are summarized as follows. (1) No sharp yielding appeared in the specimen in the annealed state and its yield stress was increased with decreasing temperature and increasing strain rate. Increasing strain rate raised the ductile-brittle transition temperature of the specimen. (2) The transition temperature of the annealed specimen remained unchanged even after the specimen was prestrained by 6% in tension at a warm temperature of 673 K. (3) Neither deformation twins nor detectable macroscopic plastic deformation were observed in the specimen shock-loaded at 930 MPa. The shock loading at this pressure lowered not only the yield stress but also the transition temperature. As interpreted from the behavior of iron, steel and chromium, it is supposed that the free dislocations generated at the elastic discontinuities in the shock-loaded specimen are responsible for the decrease in the yield stress, by which the ductile-brittle transition temperature is lowered.