Effect of Cu Doping on Phase Transition, Thermal Strain, and Thermal Expansion Property in Polycrystalline Ni₅₀Mn_23−xCu_xGa₂₇ Alloys

Abstract

The influence of Cu doping on phase transition, thermal strain and thermal expansion property of polycrystalline Ni50Mn23‐x Cu x Ga27(x=1, 3, 5, 6 and 7) alloys were investigated. The results show that with increasing Cu concentration the martensitic transformation gradually gets close to Curie transition. A magnetostructural transition (MST) is observed in samples with x=6 and 7. Such a MST can enhance the magnitude of transformation strain. Besides, Ni50Mn23‐x Cu x Ga27 alloys possess an isotropic, recoverable and thermally stable thermal strain. Excitedly, Cu doping can effectively tune the phase transition, thermal strain and thermal expansion properties of Ni50Mn23‐x Cu x Ga27 alloys. Adjustable coefficients of thermal expansion from positive to negative are obtained by Cu‐doped Ni50Mn23‐x Cu x Ga27 alloys. The average linear expansion coefficient (α) between ‐140.44 and ‐207.70 ppm/K is observed in samples with x=6 and 7 for a narrow temperature span of 11 – 14 K. When the temperature span is about 72 K (x=6) and 73 K (x=7), which is the largest temperature span observed in Ni‐Mn‐Ga based alloys recently, the α values decrease to about ‐36 ppm/K. These findings are beneficial for manipulating the thermal expansion property of Ni‐Mn‐Ga‐Cu alloys and their multifunctional applications.This article is protected by copyright. All rights reserved.