Substructure strengthening in zirconium and zirconium-tin alloys

Abstract

The substructures developed during the hot compression of α-Zr and a series of Zr-Sn solid solution alloys were examined by means of transmission electron microscopy. The materials were hot compressed in a modified Instron testing machine at constant true strain rates of 10 −4 to 3 × 10 −1 sec −1. The range of testing temperatures was 625 to 825 °C. Over the subgrain size range 0.3 to 7 μm, the high temperature flow stress and subgrain size were inversely related. The increase in flow stress due to substructure formation also obeyed this type of relation. The results are consistent with a glide model of deformation in which the build-up of internal stress is due to the substructure developed by the deformation. Room temperature yield strengths were measured on cylinders machined from the hot compressed samples. The data obeyed an equation of the modified Hall-Petch type in which the strength increases linearly with the inverse subgrain size. This relationship reflects the change in sub-boundary strength resulting from a reduction in the perfection of the sub-boundaries and an increase in their redundant dislocation content as the subgrain size decreases.