Microstructural characterisation and properties of quaternary Ni50Mn29Ga20Gd1 ferromagnetic shape memory alloy

A Heusler Ni50Mn29Ga20Gd1 ferromagnetic shape memory alloy is obtained by substituting 1 at%-Gd for Ga in a ternary Ni50Mn29Ga21 alloy. The microstructure, phase transformation, magnetic and mechanical properties of Ni50Mn29Ga20Gd1 alloy are investigated. It is shown that the Ni50Mn29Ga20Gd1 alloy has the best overall mechanical properties among the Ni50Mn29Ga21-xGdx (x=0, 0.1, 0.5, 1, 2, 5) alloys. Compression tests show that a compressive strength of 1124.42 MPa with a compressive strain up to 16.25% can be achieved in this alloy. The mechanism of the improved mechanical properties is also discussed. The results demonstrate that the grains are refined obviously by the addition of 1 at-% Gd. The microstructure of the Ni50Mn29Ga20Gd1 alloy consists of the matrix and the hexagonal Gd(Ni, Mn)(4)Ga phase distributing mainly along the grain boundaries. Martensitic structure changes from five-layered martensite with 0 at-% Gd to seven-layered modulated martensite with 1 at-% Gd. One-step thermoelastic martensitic transformation occurs in this quaternary alloy. The martensitic transformation temperatures of the Ni50Mn29Ga20Gd1 alloy increase and its Curie temperature keeps unchanged compared with that of ternary Ni50Mn29Ga21 alloy. Coupling of the magnetic and structural transitions is observed in the Ni50Mn29Ga20Gd1 alloy.