X-ray diffraction study of subgrain misorientation during high temperature creep of tin single crystals

Abstract

Creep tests in the high temperature range (0.68 Tm-0.94 Tm, where Tm is the melting temperature) have been performed on high purity tin single crystals with the [100] direction as the tensile axis. Above the transition temperature, about 0.84 Tm (150 °C), the creep activation energy was found to be almost equal to the self diffusion energy. Below the transition temperature the creep activation energy is about half of the self diffusion energy and has a value of the order expected for dislocation pipe diffusion. A method based on X-ray rocking curves was developed to measure subgrain misorientation angles of crept specimens. The average subgrain misorientation angles for specimens crept at 70 °C and 100 °C increased continuously with creep strain at rates a factor of 20 to 40 smaller than that predicted by a cross-slip controlled process. The average subgrain misorientation angles at a given strain decrease slightly with increasing temperature. However, no abrupt change of the angle was observed at the transition temperature. It was concluded that a cross-slip controlled mechanism cannot control below the transition temperature. Instead, our results lend support to Sherby and Weertman’s argument that dislocation climb controls creep over the entire high temperature regime.