Young's moduli of sputter-deposited NiTi films determined by resonant ultrasound spectroscopy: Austenite, R-phase, and martensite

Young's moduli of 3 μm thick NiTi films sputter-deposited on silicon wafers are determined by resonant ultrasound spectroscopy. Three samples with different transition temperatures are studied; for each sample, the evolution of Young's modulus is obtained in a thermal cycle covering the austenite → R-phase → martensite transition sequence. The results prove that the smallest Young's modulus is attained for the R-phase, and both austenite and martensite exhibit pronounced softening towards the transition temperatures.