抄録
The influence of high hydrostatic pressure on the flow stress of zinc and zirconium polycrystals has been investigated at room temperature. Pressurizing under a pressure of 12000 kg/cm2, tensile tests using the differential pressure method between atmospheric pressure and 12000 kg/cm2, and tensile tests under a constant hydrostatic pressure of 12000 kg/cm2 have been carried out. The tensile load has been measured by a magnetostrictive load cell in the high pressure chamber. The results obtained are as follows : (1) Both materials belong to the hexagonal close-packed system and are anisotropic in their elastic constants. Therefore, it is expected that shear stresses are generated at grain boundaries when they are subjected to high hydrostatic pressure and cause the pressurizing effect. The effect of pressurizing, however, is very small and is within the error of measurement for both materials at atmospheric pressure. The reason seems to be that for zinc the most part of work-hardening caused by pressurizing disappears rapidly due to recovery before tensile test is carried out while for zirconium the shear strain caused by pressurizing is within the elastic region. But it is presumed that a pressurizing effect would remain latently under high hydrostatic pressure if the annealed material is not returned to atmospheric pressure. (2) In the differential pressure method, the change of flow stress with ambient pressure includes the latent pressurizing effect. At large strains where the latent pressurizing effect decreases and becomes negligibly small, the change of flow stress between 12000 kg/cm2 and atmospheric pressure is shown to be about 8% for zinc and about 3% for zirconium. These values coincide with the variation in shear modulus of the materials with hydrostatic pressure which is estimated theoretically. (3) The work-hardening is enhanced for these materials under hydrostatic pressure. In the case of zirconium, the tendency of enhancement is similar to that observed with cubic metals. That is, at first it increases and then becomes saturated. For zinc, the enhancement continues to increase with increasing strain in the strain range tested. This seems to be due to the fact that recovery is suppressed under hydrostatic pressure, while it takes place actively at atmospheric pressure.
