The phase stability, martensitic transformation, and magnetic and mechanical properties of (Ni2- xCo xMn1.5Ti0.5)1- yB y (0 ≤ x ≤ 0.625; y = 0.03 and 0.06) alloys are systematically studied through the first-principles calculations method. The Co and B atoms are inclined to be aggregated distribution in the Ni2Mn1.5Ti0.5 alloy, and the phase stability of the austenite and non-modulated (NM) martensite decreases by co-doping. The ferromagnetic activation effect in the austenite occurs when x = 0.03 and y = 0.625. The magnetism of the austenite changes from an antiferromagnetic to a ferromagnetic state, which is ascribed to the elongation of the nearest neighboring distance of Mn–Mn, the nearest Mn–Mn distance increases from 2.50–2.79 to 2.90–2.94 Å, while the NM martensite always shows antiferromagnetism. Additionally, the doped B accelerates the change from antiferromagnetic to ferromagnetic for the austenite, but B-doping decreases the stability of the whole alloy system. The Co and B co-doping increases the stiffness of the NiMnTi alloy but decreases toughness and plasticity. However, the toughness and plasticity of the NiCoMnTiB alloy are better than those of the NiMnTiB alloy, indicating that the Co doping increases the d-orbital hybridization in the NiMnTiB alloy. The above results are expected to support the performance design of the NiMnTi-based alloy.
Ni-Mn-Ti-based all-d-metal Heusler alloys have become a hot research topic in the field of metal functional materials due to their excellent mechanical properties and elastocaloric effect. However, the relatively large critical stress and transition hysteresis limit its practical application. Some researchers found that doping Fe in Ni-Mn-based alloys can not only reduce hysteresis, but also greatly improve the mechanical properties of alloys. Based on this, the effects of Fe doping on phase stability, martensitic transformation and magnetic properties of Ni<sub>50-<em>x</em></sub>Mn<sub>37.5</sub>Ti<sub>12.5</sub>Fe<em><sub>x</sub></em> (<em>x</em> = 3.125, 6.25, 9.375) Heusler alloys have been systematically studied by first principles calculation. The corresponding magnetic states of the austenite and martensite of the alloy systems were determined according to the results of the formation energy. The variations of the lattice constants and the phase stability of the austenite and martensite with increasing Fe content in the alloy systems were revealed, and the related mechanism was elucidated. The atomic and total magnetic moments of the austenite and martensite in the Ni<sub>50-<em>x</em></sub>Mn<sub>37.5</sub>Ti<sub>12.5</sub>Fe<em><sub>x</sub></em> (<em>x</em> = 3.125, 6.25, 9.375) systems were calculated. Based on the results of electronic structure, the essential reasons for the magnetic state changes of the alloys were further explained. In Ni<sub>50-<em>x</em></sub>Mn<sub>37.5</sub>Ti<sub>12.5</sub>Fe<em><sub>x</sub></em> alloy system, the lattice constant of austenite decreases gradually with the increase of Fe doping amount. The stability of both austenite and martensite phase decreases with the increase of Fe doping amount. Under the different composition, the formation energy of martensite is always lower than that of austenite, indicating that the alloy can undergo martensite transformation. The energy difference Δ<em>E</em>, electron concentration <em>e/a</em> and density of electrons <em>n</em> of the alloy show a decreasing trend, indicating that the driving force of martensitic transformation decreases, and the corresponding martensitic transformation temperature decreases with the increase of Fe atom doping. The austenite of the alloy is ferromagnetic and the martensite is antiferromagnetic. After the martensitic transformation, the distance between Mn-Mn atoms decreases, and the magnetic moments of Mn<sub>Mn</sub> and Mn<sub>Ti</sub> atoms are arranged antiparallel, resulting in the total magnetic moments being almost zero. The magnetic properties of the two phases are little affected by the amount of Fe atom doping. The peak density of electronic states in the Fermi surface of martensite phase is lower than that of austenite phase, indicating that martensite phase has a more stable electronic structure than austenite phase. During the transition from austenite to martensite, there is a Jahn-Teller splitting effect at the peak of the down-spin density of states near the Fermi surface. The aim of this paper is to provide guidance for the composition design and property optimization of the Ni-Mn-Ti-Fe alloy.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.