Effect of Sn substitution and heat treatment on microstructure and microhardness of Co38Ni34Al28–xSnx magnetic shape memory alloys

Abstract

Sn was used to replace Al in Co38Ni34Al28 alloy. The microstructure and microhardness of Co38Ni34Al28–xSnx (x=0, 1, 2, 3) magnetic shape memory alloys were investigated at different heat treatment temperatures (1373 K, 1473 K, and 1573 K) for 2 h. The results show that more Sn substitution reduces the content of γ-phase and a partial phase of martensite can be obtained in Co38Ni34Al28–xSnx (x=1, 2, 3) alloys after treatment at 1573 K for 2 h. The maximum martensite phase appears when 2% Al is substituted by Sn. The reverse martensitic transformation temperature of Co38Ni34Al28–xSnx alloys increases at x=1 and 2, then decreases as x=3. As the content of Sn and the temperature increase, the microhardness will increase.