Carbide reinforced Ni–Cr–B–Si–C composite coating on 4Cr5MoSiV1 steel by comprehensive plasma melt injection method

Abstract

The present work deals with fabricating a carbide reinforced nickel matrix composite coating on 4Cr5MoSiV1 steel. Electroless nickel coated silicon carbide particles (Ni/SiCp) were injected into plasma generated nickel alloy melt pool using plasma melt injection (PMI) method and plasma transfer arc (PTA) process simultaneously. The appropriate injection angle (θ) in this comprehensive PMI method (PTA+PMI) was calculated to satisfy the specific requirement of injection position for reducing the gasification of SiC particles (SiCp). The effects of the PTA+PMI method and electroless nickel coating (ENC) on SiCp were identified in a comprehensive manner by comparing the microstructural aspects of the coatings. The results show that the appropriate value of θ ranges from 57° to 64° in the present study. The deposition of ENC on SiCp is found to be very effective in retarding the gasification of SiCp during the PTA+PMI process. Meanwhile, the improved wettability of SiCp by the ENC decreased the necessary minimal vertical velocity of SiCp, which consequently promoted the impregnation of SiCp in the PTA+PMI process. The nickel matrix composite coating reinforced by Ni/SiCp (S5) using the PTA+PMI method mainly consists of large amount of in situ chromium-rich carbides (M7C3) together with nickel silicide (Ni3Si) in a nickel iron solid solution (γ-Ni(Fe)). Microhardness and tribological tests reveal considerable improvement in surface microhardness and wear resistance properties of 4Cr5MoSiV1 steel.