Fatigue Property of Functionally Graded Plasma-Carburized Ti and Ti-Alloy

Titanium and titanium-alloy (Ti-6A1-4V) have recently been used as bolt and nut materials of jet engines. But the bolts and nuts often seize up with a material to be fixed because Ti and Ti-6A1-4V alloy have high friction coefficient and low thermal conductivity. In order to prevent seizing, the surfaces of the bolts and nuts of titanium and titanium alloy are treated by plasma carburizing process. Plasma-carburizing that uses the glow-discharged hydrocarbon gases produces a high concentration of carbon in the surface layer within a short period of time. It has thus been frequently applied to industrial materials to concentrate carbon content in their surface region. However, the carburized materials often lose fatigue strength. In this study, the fatigue property of titanium and titanium-alloy after carburization was investigated. The following results have been obtained. (1) No significant differences in the fatigue property have been found between the carburized and non-carburized materials. (2) Fatigue property depends on the structure of base metal.