Effect of Cyclic Surface Pressure on Delamination Strength of WC-Co Coating Sprayed by HP-HVOF
Chengwei LI, Masahiko KATO, Keijiro NAKASA and Dongkun ZHANG
Abstract:Substrate specimens of mild steel (JIS: SS400) and tool steel (JIS: SKD5) were coated with WC-Co cermet by High-Pressure High-Velocity Oxygen Fuel (HP-HVOF) spraying. Repeating pressure was applied on the surface of the specimens, and tensile tests and edge-indent tests were carried out to evaluate the tensile strength and the delamination strength of the coating. The tensile strength ƒÐC of WC-Co coating increases first and then decreases with increasing surface pressure cycles N when the maximum repeating pressure ƒÐmax is 240 MPa, while ƒÐC increases with increasing N for ƒÐmax =480MPa. Both the interfacial fracture toughness Gc1/2 and the delamination strength Ed for SS400 specimens decreases with increasing N. On the other hand, Ed for SKD5 specimens does not change with N in each ƒÐmax. The SEM micrographs of cross section of coating show the existence of cracks parallel to the interface for SS400 specimens and they are developed with increasing pressure cycles, while the crack extension is small for SKD5 specimens. Key Words:WC-Co coating, Edge-indent test, Tensile test, Tensile strength of coating, Delamination energy, Interfacial fracture toughness