Anisotropy and Clausius-Clapeyron relation for forward and reverse stress-induced martensitic transformations in polycrystalline NiTi thin walled tubes

•The tensile behavior of samples cut in a NiTi tube shows that the slopes of the forward and reverse transformation stress-temperature lines are orientation dependent.•The product of the slopes by the transformation strain is not orientation independent.•It is proposed that frictional and stored irreversible energies depend on temperature and orientation.•Temperature dependence of irreversible energies is taken into account in a modified Clausius-Clapeyron equation.