2015 年 81 巻 824 号 p. 14-00590
The effect of functionally graded TiN coating on the wear and fretting fatigue behavior of titanium alloy was investigated. The two kinds of monolayer TiN coatings and three kinds of functionally graded TiN coatings were deposited on Ti-6Al-4V alloy substrate using an ion beam assisted deposition technique. Monolayer TiN coating was fabricated by an electron beam evaporation of titanium and simultaneous nitrogen ion bombardment at the acceleration voltage of 0.2 or 2.0 keV. The later consisted of top TiN layer and functionally graded layer. During the fabrication of functionally graded layer, the mixing ratio of nitrogen and argon gas that were used for the generation of ion beam increased stepwisely. The mixed layer formed by ion beam bombardment became thicker by an increase in acceleration voltage. The adhesion and wear resistance improved with an increase in the acceleration voltage. Moreover, inserting the functionally graded layer with the layer thickness of 250 nm improved them significantly. However, further increase in graded layer thickness deteriorated the adhesion and wear resistance. The fretting fatigue life was evaluated by a four-point bending fatigues test. The fretting fatigue life of specimen coated with monolayer TiN film was longer than that of uncoated specimen. The TiN coating with functionally graded layer was the most effective to improve the fretting fatigue life. It was concluded that the insert of functionally graded layer with appropriate layer thickness is effective way for improvement of wear and fretting fatigue behavior.
