Fatigue property improvements of Ti-6Al-4V by thin film coatings of metallic glass and TiN: a comparison study

Thin film metallic glasses (TFMGs) with unique physical and mechanical properties have attracted interest in the past decade. With the aim of taking their advantages to their applications, a 200-nm-thick TFMG (Zr50Cu27Al16Ni7) film with a 10 nm titanium adhesion layer and a hard coating TiN film were coated on a substrate. Effects of these two types of films on the four-point fatigue property improvements of Ti-6Al-4V substrate were investigated. The fatigue life improved from 2.2 × 105 cycles of uncoated sample to 3.7 × 106 cycles, ~ 17 times, and 1.0 × 106 cycles, ~ 4.5 times, by TFMGs and TiN coatings, respectively, all under a stress of 675 MPa. It is demonstrated that both TFMG and TiN films with high strength retarded the cracks propagated during fatigue cycles, resulting in increased fatigue life. The especially significant improvement from TFMGs was largely attributable to improved ductility and flexibility and to increased adhesion strength from the titanium adhesion layer.