Microstructural evolution and corrosion resistance property of in-situ Zr–C(B, Si)/Ni–Zr reinforced composite coatings on zirconium alloy by laser cladding

Abstract

In-situ reinforced coatings were prepared by laser cladding Ni60A + WC powder on R60702 zirconium. The microstructural evolution, microhardness, and corrosion resistance of in-situ reinforced composite coatings were analyzed. The reinforcements in the coatings were mainly composed of cross and fishbone-like α-Zr dendrites, block ZrC(B, Si)2, and slender needle-like NiZr. The results show that ZrC/ZrB2 reinforcements grew on the transition layer on the molten WC's surface, fell off, and connected. Some small particles acted as preferential nucleation points and preferentially grew into cross-shaped dendrites in the direction of greater supercooling. The cross-shaped dendrites were closely arranged in the direction of the main axis, and the axial growth rate was smaller than that of the side arms. During the growth process of the cross-shaped dendrites, Zr precipitated towards the side arms, forming α-Zr. Finally, the dendrites interconnected, forming fishbone-like reinforcements. As the laser power increased, the microhardness and corrosion resistance increased significantly. The microhardness (700 HV0.5) and corrosion resistance were highest when the laser power was 2.5 kW and the powder used was Ni60A + 25% WC.

Keywords

• Zirconium
• Laser cladding
• In-situ reinforcements
• Microstructural evolution
• Corrosion resistance