Influence of in-situ synthesized carboborides on microstructure evolution and the wear resistance of laser clad Fe-base composite coatings

Abstract

The carboboride reinforced Fe-base composite coatings were prepared to improve the abrasive wear resistance of 42CrMo by laser cladding. The compositions of the coatings were high-speed steel with high boron contents. The effects of boron content on the microstructure, hardness, and wear behaviors of the coatings were focused. The microstructure evolution and phase transformation were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe micro-analyzer (EPMA), and transmission electron microscope (TEM). The results showed that the types and morphologies of hard phases in the coatings were influenced by boron content. The MC, M2C, and M6C carbides were observed in the coating without boron addition; while M23(B, C)6 and residual M3(B, C) existed in the coating when boron was added. The eutectic structure consisted of M23(B, C)6, residual M3(B, C), and matrix appeared at the grain boundary when the boron content exceeded 0.75% (wt%). The hardness and wear resistance of the coatings improved with the increasing boron content. But when the boron content was up to 1%, cracks would occur in the coating. The hardness of the best coating with 0.75% boron addition reached 8.95 GPa, which was 2.6 times that of the 42CrMo substrate. The wear weight loss of the coating with 0.75% boron addition was 0.0965 g, which was only 10% that of the 42CrMo substrate.