The Effects of Precompression and Pressurization on the Ductile–Brittle Transition of Polycrystalline Cast Chromium,Molybdenum,and Tungsten

Abstract

The ductility transition temperature, T_T , of polycrystalline cast chromium, tungsten, and molybdenum was lowered by 280, 230, and > 90 K, respectively, by a 4% precompression at room temperature. Pressurization treatment at 10 kbar (1 GN/m²) had a very similar effect on chromium; pressurization of molybdenum at 20 kbar (2 GN/m²) and of tungsten at 28 kbar (2·8 GN/m²), however, did not produce any significant changes in their mechanical properties. The results are discussed in terms of the effect which the dislocations, generated during the precompression and pressurization, have on the stresses for yielding, σ _Y , crack nucleation, σ _N and crack propagation, σ _p . Precompression appears to lower σ _N in chromium, raise it in molybdenum below T_T , and leave it unaltered in tungsten, for which, however, it raises σ _p . The only significant effect of pressurization was to lower σ _N in chromium.