Tailoring martensitic transformation and martensite structure of NiMnIn alloy by Ga doping In

Abstract

The martensitic transformation and the martensite crystal structure of alloys Ni50Mn34In16−xGax (x=0, 2, 4, 6, 8, 10, 12, 14, 16) have been investigated in this study. The studied alloys, with cubic L21 phase (x=0, 2), seven-layered modulated (14M) martensite phase (x=4, 6, 8), and non-modulated (NM) martensite phase (x=10, 12, 14, 16), exhibit martensitic transformation with critical temperature increasing linearly from 238K for x=0 to 486K for x=16. The linearity coefficient is estimated to be ∼15K per at.% of Ga. With regards to the lattice parameters, a elongates, whereas b and c contract as the austenite phase transformed to 14M martensite phase. While, it turns to c elongates, a and b contract as austenite transformed to NM martensite phase. It is found that the unit cell volume decreases with increasing Ga content, which contributes to the increase of transformation temperature with Ga content. A maximum strain of 12% is predicted through the lattice distortion in 14M martensite. Magnetic measurement shows the Curie temperature for martensite increases with Ga content.