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This study investigated the effects of the types and length of nonmetallic inclusions on fatigue properties in rotating bending fatigue testing of Ti-Ni alloy fine wire. It was fabricated to include titanium carbides Ti(C,O) and titanium oxides Ti4Ni2Ox as either single phases or a mixture of both phases as nonmetallic inclusions in Ti-Ni alloy. The fatigue strength of Ti-Ni alloy depended on the number of nonmetallic inclusions of a length of ≥2 μm. Compared with Ti(C,O), Ti4Ni2Ox is coarse. It also exhibited a trend of readily forming particles and void assemblies, which are a defect morphology that originates from nonmetallic inclusions and readily act as crack origins of fatigue fractures.

The effects of carbon/oxygen concentrations in Ti-51 at.% Ni on the morphology and phase changes of inclusions in a commercial wire manufacturing process were investigated. Whereas cast material fabricated with a carbon to oxygen mass concentration ratio (C/O ratio) of 1.0-1.5 were found to contain single-phase Ti(C,O), when hot working was performed, some of the Ti(C,O) exhibited a phase change to Ti 2 Ni(O), and a mixed phase structure was found in specimens with a C/O ratio of less than 1.5. On the other hand, single-phase Ti(C,O) was found to remain in the wire produced from the specimens with a C/O ratio of 1.5.

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