Effect of laser irradiation condition on bonding strength in laser plasma hybrid spraying

The effect of the laser irradiation condition on the bonding strength of a coating made by the laser-plasma-hybrid-spraying (LPHS) method was studied. LPHS is able to improve the bonding strength as the interfaces are melted and joined by the laser simultaneously with plasma spraying. However, the c orrelation between strength and interfacial properties has not been previou sly studied in detail. In this study, the relationship between bonding stre ngth and laser irradiation intensity was evaluated using the shearing test for the NiTi-LPHS-coating made from a mixture powder of nickel and titanium . The main results are summarized as follows: The shearing strength was inc reased to 6 times that of the VPS-coating upon using LPHS. This is because diffusion between the coating and the substrate was promoted and a diffusio n layer approximately 30-mum thick was formed by laser heating and melting. The shearing strength decreased as the power density increased over 4x10(8 ) W m(-2) because an intermetallic compound which was brittle anti had a lo w yielding point was formed at the interface. We proposed to spray an inser t layer, such as chromium and molybdenum, on the substrate, to avoid the fo rmation of brittle intermetallic compounds at the interface. By this method , both high bonding strength and high erosion resistance were achieved. (C) 2001 Published by Elsevier Science B.V. All rights reserved.