Abstract
Ti 50 Ni 50 shape memory alloy was gas nitrided to modify the surface conditions. The surface hardness, wear characteristic, transformation temperature and shape memory ability of gas-nitrided Ti 50 Ni 50 alloy were investigated. Experimental results indicate that the surface hardness is increased owing to the formation of TiN and Ti 2 NiH 0.5 compounds. The Ti 50 Ni 50 specimens nitrided at 700–900°C show improved wear characteristics, but those nitrided at 600°C cannot be effectively improved owing to surface cracks appearing in nitrided layers. Martensitic transformation temperatures are depressed slightly owing to the constraining effect originating from the nitrided layers, and/or the penetration of N and H atoms into the Ti 50 Ni 50 matrix. The shape recovery is also slightly reduced because the nitrided layers do not exhibit a shape memory effect, and the constraining effect will also depress the shape recovery of the Ti 50 Ni 50 matrix.
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