EDM surface characteristics and shape recovery ability of Ti _35.5Ni_48.5Zr₁₆ and Ni₆₀Al _24.5Fe_15.5 ternary shape memory alloys

Electro-discharge craters and recast materials are observed in the electro-discharge machining (EDM) surface of Ti_35.5Ni _48.5Zr₁₆ and Ni₆₀Al_24.5Fe _15.5 alloys. The recast layer is composed of TiO, NiO, ZrO ₂, Fe₂O₃, Al₂O_3. 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 Ti_35.5Ni _48.5Zr₁₆ 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 Ti_35.5Ni _48.5Zr₁₆ alloy is less than that of Ni₆₀Al _24.5Fe_15.5 alloy because of the larger θ × k_α 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(I_P × τ_P)^β. Having a larger θ × K_α value, Ti_35.5Ni_48.5Zr₁₆ alloy has a lower Ra value than that of Ni₆₀Al_24.5Fe _15.5 alloy after electro-discharge machining.