Effect of corrosive environment on the delamination strength of WC-Co coating deposited by high velocity flame spraying
Nakasa Keijiro; Kato Masahiko; Zhang Dongkun; Egawa Fumiaki
Abstract:WC-Co cermet was coated on the smooth tensile specimens of annealed tool steel(JIS:SKD5) by high velocity flame spraying. For some specimens, the pores in the coating were sealed by Zn-plating. After the specimens were immersed into tap water or 3%NaCl water, the tensile tests, where the load was applied parallel to the coating, were carried out in air to examine the change of interfacial energy by corrosive environments. With increasing tensile load, the coating is divided by several cracks and the interval of cracks is decreased by the repeating process of division, and the delamination of coating occurs after the crack division has finished. The interfacial energy decreases with an increase in immersion time, and the degree of decrease is larger in the specimen immersed in 3%NaCl water than in tap water. The interfacial energy of the Zn-plated specimen is almost the same as the no immersed specimen up to the immersion time of about 1000ks in 3%NaCl water, but it quickly decreases to reach the same value as the no plated specimen when the immersion time exceeds 1500ks. The interfacial energy is almost inversely proportional to the crack interval. Key Words:WC-Co coating, high-velocity flame spraying, tool steel substrate, corrosion, delamination strength