Strain-Rate and Temperature Dependence of Plastic Deformation in White Tin Single Crystals

Abstract

Tensile tests at high and intermediate temperatures [200 K (0.4 Tm)–500 K (0.99 Tm), where Tm is the melting temperature] have been performed on single crystals of high-purity white tin with low dislocation density and with the tensile axis along the [100] direction. It is found that the stress-strain curves at temperatures below 300 K show two yield points. The first yield point phenomenon appears when a sudden multiplication of mobile dislocations occurs due to the deformation. The second yield point phenomenon appears when the dislocations forming the cell structure become mobile and the cell structure disappears. The activation energy of the second upper and lower yield stresses has the transition temperature, about 480 K (0.95 Tm). Above the transition temperature the activation energy was found to be almost equal to the lattice diffusion energy. Below the transition temperature the activation energy is about half of the lattice diffusion activation energy and has a value expected for dislocation pipe diffusion.