T. Haenschke, Y. Li, Y. Y. Tse, X. Wu, University of Birmingham, Birmingham, United Kingdom; J. Webster, R. Hobbs, P. Newton, Rolls-Royce, Derby, United Kingdom
TiNi-based alloys are famous for their outstanding shape memory (SM) properties. In this study experiments were carried out using plates of a Ti rich NiTi SMA. DSC measurements were performed to understand the influence of different heat treatment conditions on austenitic and martensitic transformation temperatures. Thermo-mechanical fatigue tests, i.e. stress and temperature are cycled simultaneously, were carried out to assess the performance and stability of the NiTi SMA under a range of stresses and a range of temperatures. The influence of minimum stress, maximum stress and peak temperature on the performance stability of the NiTi SMA is assessed. SEM and TEM analyses are used to understand the influence of the starting microstructure, texture, dislocation and particle distribution on the mechanical behaviour. The evolution of texture during thermo-mechanical fatigue is also investigated. Furthermore, synchrotron tests were performed and analysed using rietveld refinement to clarify the mechanism for the instability of SMA during thermo-mechanical fatigue under some testing conditions, including texture evolution and variable volume fraction of the previous phase retained during phase transformation under cycling.
Summary: Understanding the thermo-mechanical fatigue behaviour of the NiTi SMA under service conditions for aeroengine applications. The instability of the material under the simultaneous cycling of stress and temperature has been investigated and its mechanism has been studied, together with the information from the in-suit testing in Synchrontron.
