Reinforcements/matrix micro-interface evolution and properties of in-situ Ni60A/WC coatings prepared by laser cladding

Abstract

Ni60A/WC in-situ reinforced composite coatings are prepared on Inconel 718 alloy by laser cladding. The reinforcements/matrix micro-interface evolution, microhardness, and corrosion resistance are investigated. The phases in the coatings are mainly composed of γ-Ni, M23C6, M7C3 and NbC. The reinforcements/matrix micro-interfaces concerned in the coatings mainly include WC/matrix micro-interface and M23C6/matrix micro-interface. The WC/matrix micro-interface evolution is divided into five stages, namely, WC enters the molten pool, the micro-interface begins to grow, the reinforcements enriched at the tip, the reinforcements fall off and the formation of the stable micro-interface. The microhardness of the coatings increases with increasing WC content. On one hand, the increase in WC content promotes the generation of in-situ reinforcements, and the large lattice mismatch between dispersed reinforcement particles and matrix hinders dislocation motion. On the other hand, the two-dimensional mismatch degree of WC and γ-matrix calculated by Bramfitt's two-dimensional mismatch degree formula is 9.77 %, indicating that WC particles can serve as particles for γ heterogeneous nucleation. The increase of WC particles plays the role of fine grain strengthening, so the microhardness of the coating increases. The effect of WC on the corrosion resistance is also analyzed. The reinforcements are mainly distributed in the grain boundaries, and the HRTEM results indicate that a large degree of lattice mismatch exists in the micro-interface of reinforcements and γ-matrix. The large degree of mismatch shows that the interface between the two phases is relatively weak, and the weak interface is easy to become the channel for corrosive ion (Cl−) diffusion.