Large magnetocaloric effect and excellent mechanical properties near room temperature in Ni-Co-Mn-Ti non-textured polycrystalline alloys

Exploring novel materials with large magnetocaloric effect and excellent mechanical properties near room temperature (RT) are highly desired for Ni-Mn based Heusler alloys. In this work, the martensitic transformation, magnetic properties, and mechanical properties of Ni50-xCoxMn50-yTiy (x = 13–15, y = 13–16) alloys were systematically investigated by tuning Co or Ti contents. The magnetism of austenite was enhanced with an increase in Co or Ti content. 5M and 6M martensites were observed in Ni-Co-Mn-Ti alloys by transmission electron microscopy. The Ni36Co14Mn35Ti15 alloy with a large magnetocaloric effect was found near room temperature by tuning composition. The largest magnetization change (ΔM) and magnetic entropy change (ΔSm) in the Ni36Co14Mn35Ti15 non-textured polycrystalline alloy obtained during martensitic transformation under the magnetic field of 5 T were about 106 emu/g and 19.3 J kg−1 K−1, respectively. Furthermore, the maximum compressive strength and ductility for the Ni36Co14Mn35Ti15 as-cast alloy can exceed 1220 MPa and 15%, respectively. The fracture mechanism and bonding interaction were analyzed by a scanning electron microscope and first-principles calculations.