Mechanical and elastocaloric effect of Fe and Co co-doped Ni–Mn–Al ferromagnetic shape memory alloys

Highlights: • The elastocaloric effects of Ni₄₀Fe_xCo_10-xMn₃₂Al₁₈ (x = 2, 4, 6 at. %) alloys have been investigated. • These alloys show superelastic property and prominent eCE at room temperature. • A temperature change of 6.1 K is obtained due to martensitic transformation in Ni₄₀Fe₄Co₆Mn₃₂Al₁₈ alloy. • The eCE of Ni₄₀Fe₄Co₆Mn₃₂Al₁₈ alloy maintains almost constant during 100 stress cycles. The martensitic transformation (MT), microstructure, mechanical properties and elastocaloric properties of Ni₄₀Fe_xCo_10-xMn₃₂Al₁₈ (x = 2, 4, 6 at.%) polycrystalline alloys were comprehensively investigated. The MT temperature of these alloys shifts to lower temperatures as Fe/Co ratio increases. The fracture strength is significantly enhanced from 905 MPa of Ni₄₀Fe₂Co₈Mn₃₂Al₁₈ to 1275 MPa of Ni₄₀Fe₆Co₄Mn₃₂Al₁₈. Among these alloys, Ni₄₀Fe₄Co₆Mn₃₂Al₁₈ exhibits the best elastocaloric properties. A large temperature change of 6.1 K was obtained by applying a uniaxial stress of 400 MPa, and the temperature change about −5.2 K maintains almost constant after 100 stress cycles in the Ni₄₀Fe₄Co₆Mn₃₂Al₁₈ alloy. The research results demonstrate an effective method to optimize elastocaloric materials used in solid-state refrigeration field.