Surface modification and machining of TiNi/TiNb-based alloys by electrical discharge machining

Ti50Ni50 and Ti50Ni49.5Mo0.5 shape memory alloys and Ti30Nb1Fe1Hf alloy with a low elastic modulus were prepared for biomedical implant applications. Effects of the composition of the TiNi/TiNb-based alloys and electrical discharge machining (EDM) parameters on the properties of the materials were investigated. The addition of Mo to TiNi or of Nb to Ti clearly reduced the material removal rate (MRR), electrode wear rate, surface roughness, and recast layer thickness, which was attributed to the increased melting temperature and thermal conductivity of the materials. The surface roughness (Ra) of the electrical discharge machined (EDMed) alloys obeyed the empirical equation Ra = β(Ip × τp)α. A higher discharge current Ip combined with an appropriate pulse duration τp can achieve the highest MRR and lowest thickness of the recast layer. However, under low current and a small pulse duration, the recast layer has a surface roughness of 1 μm, which is favorable for oral implants. In addition, the EDMed surface contains Ti and Nb oxides, which are well-known biocompatible materials.