Transformation Volume Strain in Ni-Mn-Ga Thin Films
The temperature dependences of the lattice parameters and residual stress have been measured for a fine-grained Ni52.2Mn26.8Ga21.0 (at. %) thin film fabricated by sputter deposition onto a heated silicon wafer with SiNx buffer layer. The transformation volume strain in the film was found to be a lattice expansion during the forward martensitic transformation which is opposite to a volume contraction exhibited by bulk Ni-Mn-Ga alloys. This unusual effect can be explained by the substrate-induced residual stresses in the film and the difference in the elastic modulus of austenite and martensite.
Aseguinolaza, I. R.; Reyes-Salazar, I.; Svalov, A. V.; Wilson, K.; Knowlton, W. B.; Müllner, P.; Barandiárn, J. M.; Villa, E.; and Chernenko, V. A.. (2012). "Transformation Volume Strain in Ni-Mn-Ga Thin Films". Applied Physics Letters, 101(24), 241912-1 - 241912-4. http://dx.doi.org/10.1063/1.4772005