Development and application of ultra-high strength titanium alloy thin sheet and fine-diameter wire coated with TiN

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A high strength titanium thin sheet or fine diameter wire are needed for various medical implant devices or materials such as a metallic stent or a functional electrical stimulation (FES) electrode. This study originated from new discovery that ultra-high strength could he obtained by TiN coating on heavily cold drawn wire with a 25mm diameter. The results were summarized as followed(1) New β type titanium alloy, Ti-14%Mo-3%Nb-1.5%Zr-0.08%[O], fully satisfying target properties was developed, and biocompatibility of this alloy was found to be superior over the Type 316L steel and comparable to Ti-6A1-4V alloy, and in cold workability wan much improved over the practical titanium alloys.(2) A thin sheet with a thickness down to 33mm and a fine diameter wire with 50mm were manufactured in this new alloy. These limiting dimensions of a sheet or wire were due to restriction of rolling mill used and manufacturing technology. In fact, surface oxidation by anodizing process in place of atmosp … More heric heating for prevention from sticking phenomena during hole dies drawing was confirmed to improve markedly cold workability, indicating possibility of manufacturing a finer thickness sheet or a finer diameter wire of this alloy.(3) It was found that an extremely higher strength up over 3100 MPa in the Type 316L steel wire was obtained by very thin TiN coating by PVD, white strength of as-cold drawn wire without TiN coating was 2400 MPa. Because of non-achievement of manufacturing a 25mm diameter wire of new Ti alloy, it was unable to confirm similar strengthening in TiN coating on this alloy wire. An industrial PVD process enabling to practice continuous coating on a fine diameter wire and the optimized conditions for processing parameters of surface coating were proposed.(4) The effect of TiN coating on the Type 316L steel wire rope woven with 19 strands on rotating-bend fatigue property was examined in 0.9% NaCl physiological salt solution at 310K and fatigue strength in the high cycle range was much improved due to suppression of erosion which took place among wires during test for non coated wires. This indicates a fine diameter wire coated by TiN can be utilized as a material for FES electrode. Manufacturing test of a composite material by cladding a fine diameter wire coated with TiN and thin sheet of super-plastic Zn-Al alloy was also performed, but it remained in a preliminary test stage. Less