Thermal stress and strain effects on phase transition temperatures in differential thermal analysis testing

The effects of thermal stress and strain on the solid-phase transition temperature in differential thermal analysis (DTA) were investigated both theoretically and experimentally. The thermal stress is caused by the nonuniform distribution of temperature in the sample, and the strain is caused by the phase transformation. The experimental materials included high-purity Zr, commercially pure Ti, and high-purity Fe. It was found that the effect of thermal stress on the solid-phase transformation temperature was negligible due to the small size of the sample. An equation relating the phase transition temperature and the heating rate was developed which contains both strain energy and grain boundary energy considerations. Equilibrium phase transition temperatures calculated using this equation for Zr, Ti, and Fe are in good agreement with the phase diagrams and previous work. © 1992 The Minerals, Metals and Materials Society, and ASM International.