Internal friction during martensitic transformations in ultra-high temperature Ru-Nb shape memory alloys

In the present work we have studied a high temperature Ru-50Nb (at.%) shape memory alloy using a mechanical spectrometer able to work in the temperature range from 473 to 1723 K. We have investigated two internal friction peaks, as well as the dynamic modulus variation, linked to the martensitic transformations in the range from 573 K to 1473 K. In addition, we have evidenced another internal friction peak P-LT at lower temperature than the transformation peaks, which apparently exhibits the behaviour of a thermally activated relaxation peak. However, we show that this peak is not a relaxation one because it exhibits a strongly time-dependent behaviour. We have carefully analysed this peak and discussed its microscopic origin, concluding that it is related to the interaction of some structural defects with martensite interfaces. (C) 2015 The Authors. Published by Elsevier Ltd.