Microstructural evolution in a Ti – Ta high-temperature shape memory alloy during creep

Abstract

Alloys based on the titanium–tantalum system are considered for application as high-temperature shape memory alloys due to their martensite start temperatures, which can surpass 200 °C. In the present work we study the evolution of microstructure and the influence of creep on the phase transformation behavior of a Ti ₇₀Ta ₃₀ (at.%) high-temperature shape memory alloy. Creep tests were performed in a temperature range from 470 to 530 °C at stresses between 90 and 150 MPa. The activation energy for creep was found to be 307 kJ mol ⁻¹ and the stress exponent n was determined as 3.7. Scanning and transmission electron microscopy investigations were carried out to characterize the microstructure before and after creep. It was found that the microstructural evolution during creep suppresses subsequent martensitic phase transformations.