Irreversible effect of hydrostatic pressurization on yielding in niobium

Abstract

The irreversible effects of hydrostatic pressurization on the mechanical properties of polycrystalline Nb were studied. It was found that for prior pressures up to and including 3.45 MPa, there is no detectable change in the yield stress. Prior pressurization at 6.9 MPa eliminates the yield drop and sharp yield point at room temperature and reduces the yield stress at all temperatures. Pressurization at higher pressures causes a correspondingly greater decrease in yield stress. The fractional change in yield stress for a given prior pressure is greater at lower temperatures. The mechanical behavior of pre-pressurized niobium differs from that of other bcc metals such as iron and chromium mainly in that the critical pressure to induce an irreversible effect on mechanical properties is about two orders of magnitude lower than those previously observed. (auth)