EDM surface characteristics and shape recovery ability of Ti35.5Ni48.5Zr16 and Ni60Al24.5Fe15.5 ternary shape memory alloys

• The recast layer of the EDMed SMAs is composed of TiO, NiO, ZrO2, Fe2O3, Al2O3.
• The hardening effect of the EDMed surface originates from the surface oxides.
• The material removal rate of TiNiZr alloy is less than that of NiAlFe alloy.
• The Ra values of the EDMed SMAs obey the empirical equation of Ra = C(IP × τP)β.
• The EDMed Ti35.5Ni48.5Zr16 alloy still exhibits good shape recovery.

Electro-discharge craters and recast materials are observed in the electro-discharge machining (EDM) surface of Ti35.5Ni48.5Zr16 and Ni60Al24.5Fe15.5 alloys. The recast layer is composed of TiO, NiO, ZrO2, Fe2O3, Al2O3. The hardening effect near the outer surface for EDMed TiNiZr alloy originates from the surface oxides of the recast layer. The thickness of the recast layer increases upon growing pulse energy. The EDMed Ti35.5Ni48.5Zr16 alloy still exhibits a good shape recovery, but the shape recovery is slightly reduced due to the depression of the recast layer. The material removal rate (MRR) of Ti35.5Ni48.5Zr16 alloy is less than that of Ni60Al24.5Fe15.5 alloy because of the larger θ × kα value. A high discharge energy should have a larger and deeper craters, and a rougher surface. The surface roughness of the EDMed TiNiZr and NiAlFe SMAs is found to obey the empirical equation of Ra = C(IP × τP)β. Having a larger θ × Kα value, Ti35.5Ni48.5Zr16 alloy has a lower Ra value than that of Ni60Al24.5Fe15.5 alloy after electro-discharge machining.