Enhanced elastocaloric effect and mechanical properties of Gd-doped Ni–Mn–Sn-Gd ferromagnetic shape memory alloys

Abstract

The effect of Gd substitution for Sn on martensitic transformation (MT) temperature, microstructure, elastocaloric effect (eCE) and mechanical properties of Mn49Ni41Sn10 ferromagnetic shape memory alloy has been systematically investigated. These alloys undergo MT from L21 austenite to 5 M martensite during the cooling process. MT temperature can be tuned to the vicinity of room temperature by alloying Gd. The substitution of Gd for Sn introduces γ phase (Gd-rich second phase in Gd-doping alloys), and the volume fraction of the γ phase increases with the increase of Gd content from 0.3 at.% to 0.9 at.%. Among these alloys, Mn49Ni41Sn9.4Gd0.6 alloy shows prominent eCE and stable superelasticity, making it a promising candidate for the elastocaloric cooling application. A large adiabatic temperature change of −11.4 K is obtained by the stress (500 MPa) removal, and a constant temperature change of −9.6 K shows no apparent degradation under the compressive stress of 400 MPa during 200 cycles for this alloy. The underlying mechanism of the enhanced eCE and mechanical properties is also revealed.