Abstract
Ni-Mn-Ga Heusler alloys exhibit high functional performance, particularly a significant magnetocaloric effect, making them promising candidates for solid-state magnetic refrigeration. However, their high thermal cycling brittleness in the as-cast state hinders practical applications. This paper presents the comprehensive results of a study focusing on the magnetic and magnetocaloric properties of the Ni50Mn18.5Ga25Cu6.5 alloy in both the as-cast and recrystallized structural states. It is shown that hot strain hardening of the initial as-cast structure followed by subsequent recrystallization annealing at 1123 K for 2 hours successfully leads to the formation of an equiaxed grain structure with an average crystallite size of approximately 200 μm. In both investigated structural states, differential scanning calorimetry data and the temperature dependence of magnetization demonstrate a coupled martensitic and magnetic (Curie point) phase transition. As a result of the transformation of the as-cast structure, the magnetic properties do not undergo significant changes. The peak value of the magnetocaloric effect (ΔTad.) in an alternating magnetic field of 0.6 T at a frequency of 2 Hz is 0.27 K in the as-cast state and 0.25 K in the recrystallized state, which clearly shows that this thermomechanical treatment does not lead to a significant change in the functional properties of the alloy.
Funding
1. Institute for Metals Superplasticity Problems, Russian Academy of Sciences -