抄録
The effect of grain size on the increase of flow stress of polycrystalline cadmium due to hydrostatic pressure was investigated. Tensile tests and pressure change tests were carried out under 10MPa and 600MPa on various specimens with different grain sizes. The results obtained are summarized as follows.
(1) A strain softening phenomenon was observed on the specimens when hydrostatic pressure was changed from 10MPa to 600MPa. The amount of decrease of the flow stress under 600MPa decreased with increasing prestrain at 10MPa, and it was larger for the 18μm grain size specimen than for the 36μm one.
(2) The flow stress at a particular strain value was able to be related to the grain size d by the same form as the Hall-Petch equation,
σ=σοε+κεd-1/2
where the intercept σοε and the slope κε are experimental constants.
(3) σοε at 10MPa and 600MPa increased with an increase of strain, while κε decreased gradually. σοε at 600MPa was larger than that at 10MPa, while κε at 600MPa was smaller than that at 10MPa.
(4) The rate of increase Δσ/σ of the flow stress due to the pressure change to 600MPa increased with increasing strain and grain size. For the specimen with the largest grain size of 111μm, Δσ/σ became the maximum value of 20%. It is considered that this large increase of flow stress due to hydrostatic pressure is caused mainly by the pressure dependence of σοε, and the grain size dependence of Δσ/σ is brought in by the decrease of κε due to pressure.
