Microstructure and Magnetic Field-Induced Strain of a Ni-Mn-Ga-Co-Gd High-Entropy Alloy

Abstract

The effect of a high-entropy design on martensitic transformation and magnetic field-induced strain has been investigated in the present study for Ni-Mn-Ga-Co-Gd ferromagnetic shape-memory alloys. The purpose was to increase the martensitic transition temperature, as well as the magnetic field-induced strain, of these materials. The results show that there is a co-existence of β, γ, and martensite phases in the microstructure of the alloy samples. Additionally, the martensitic transformation temperature shows a markedly increasing trend for these high-entropy samples, with the largest value being approximately 500 °C. The morphology of the martensite exhibits typical twin characteristics of type L10. Moreover, the magnetic field-induced strain shows an increasing trend, which is caused by the driving force of the twin martensite re-arrangement strengthening.

Structure and magnetic properties of Ni–Mn–Ga shape memory alloys

“…Most of Ni-Mn-Ga Heusler alloys exist in both the martensitic and austenitic phases [12,[16][17][18][19][20][21][22]. The martensitic phase that relates to antiferromagnetic or weak ferromagnetic orders occurs at lower temperatures [29][30][31].…”

“…Nowadays, one of the SMAs that increasingly attract interest in research is Ni-Mn-Ga Heusler alloy because of their application in the field of actuators and sensors [1][2][3][4][5][6][7][8]. These alloys have giant magnetic-field-induced strains which allow their use as magnetic actuators, and fast response by application of a magnetic field [12][13][14][15][16][17][18][19][20]. The main cause of the large strains is the martensitic-austenitic (M-A) transformation from a high-temperature ordered cubic austenite phase to a low-temperature orthorhombic, monoclinic, or tetragonal disordered martensite phase, or vice versa.…”

“…Since then, many studies on the magnetic properties, SME, and magnetocaloric effect (MCE) of the Ni-Mn-Ga alloy with various compositions have been carried out [9,[16][17][18][19][20][21]. Most of the Ni-Mn-Ga Heusler alloys have two magnetic phase transitions, the first-order phase transition (FOPT) and the second-order phase transition (SOPT) [12,[16][17][18][19][20][21]. Xu et al reported the magnetic transformation temperatures, Néel, and Curie temperatures of the Ni 50 Mn 50-x Ga x bulk alloys [22].…”

Development of High-Entropy Shape-Memory Alloys: A Review

“…In addition, there appears the original research on high-entropy ferromagnetic shape-memory alloys. Ju et al [76] designed Ni-Mn-Ga-Co-Gd high-entropy ferromagnetic shape-memory alloys. The results show that β, γ, and martensitic phases exist in the microstructure of A1-A4 alloy, with the change in Co and Gd elements, the γ phase gets smaller, and the martensitic phase gradually replaces the matrix β phase; secondly, with the change in Co and Gd elements, the valence electron concentration of the alloy gradually increases, which leads to a gradual increase in the martensitic phase transition temperature to 300 • C, which increases the possibility of ferromagnetic shape-memory alloys for high-temperature applications.…”

Cobalt Content Effect on the Magnetic Properties of Ni50-xCoxMn35.5In14.5 Annealed Ribbons

“…Even slight changes in lattice site occupation result in noticeable changes in both magnetic and structural properties of these materials. Such modification can be done in two ways, firstly by substitution of appropriate atoms, as in the case of , which was obtained by substitution of atoms in the ternary alloy with [ 1 , 2 , 3 , 4 ]. The second, simpler method is by applying well-defined heat treatment to the base alloy [ 5 , 6 ].…”