Thickness Effect of Interlayer on Fatigue Behavior and Fatigue Fracture Mechanisms in A5052 Aluminum Alloy with DLC/Thermally Sprayed WC-12Co Hybrid Coatings
Toshifumi KAKIUCHI, Yoshihiko UEMATSU, Makoto TAKEKAWA, Takema TERATANI, Yoshifumi KOBAYASHI and Yoshio HARADA
Abstract:WC-12Co was thermally sprayed by a high velocity oxygen fuel (HVOF) method on A5052 aluminum alloy as an interlayer with the thicknesses of 25, 70 and 120 ƒÊm and subsequently diamond-like carbon (DLC) film was deposited with the thickness of 15 ƒÊm to fabricate DLC/WC-12Co hybrid coating. Rotary bending fatigue tests were conducted using the specimens with DLC/WC-12Co hybrid coating, DLC single coating, WC-12Co single coating and without coating, and the thickness effect of interlayer on the fatigue behavior was investigated. The fatigue strengths of the specimens with DLC single coating and WC-12Co single coating were higher than those of the substrate specimens. The fatigue strengths in the specimens with WC-12Co single coating increased with increasing the thickness of WC-12Co layer. The specimens with hybrid coating exhibited higher fatigue strengths than the specimens with WC-12Co single coating when the thickness of WC-12Co layer was the same. However the thicker WC-12Co interlayer led to the lower improvement of fatigue strength by hybrid coating. In the specimens with WC-12Co layer, the boundary between WC-12Co layer and substrate was rough and uneven due to the thermal spray process and a fatigue crack initiated at the concave site of substrate on the boundary. In the specimens with hybrid coating, cracking in DLC film and WC-12Co interlayer occurred simultaneously and suddenly near the end of fatigue life. A fatigue crack in the substrate had grown up to a large size and the specimen fractured soon after a crack appeared on the surface. Key Words:Fatigue, DLC, WC-12Co, Hybrid coating, Aluminum alloy