Effect of laser power on the microstructure and property of ZrB2/ZrC in-situ reinforced coatings on zirconium alloy by laser cladding

ZrB2/ZrC in-situ reinforced coating was fabricated by laser cladding Ni60A + WC powder on zirconium alloy. The effect of laser power on the formation of coating, microstructure, reinforcements and microhardness was investigated. The results show that the good appearance of the coating was obtained and no defects such as pores and cracks were found. As the laser power increased, the width and height of the coating increased significantly. Reinforcements in the coating were mainly composed of fine alpha-Zr dendrites, granular and block ZrC and Zr(B, C)2. ZrB2/ZrC eutectic was formed inside the unmolten WC. The similar values of Gibbs free energy for forming ZrB2 and ZrC at elevated temperature made it easy to form lamellar eutectic. With increasing laser power, the growth of the secondary arm of dendrites was suppressed and the granular reinforcements gradually transformed to block reinforcements. The microhardness of coating increased significantly as increasing laser power. The highest value of microhardness (about 720HV0.5) was obtained when the laser power is 2.8 kW.