Microscopic and macroscopic interfacial studies of NbC reinforcement layer on GCr15 bearing steel surface prepared by in-situ reaction method

Abstract

In this study, a micro/nano NbC reinforcement layer was prepared on a bearing steel surface by in-situ reaction method using GCr15 bearing steel and high purity niobium plate as raw materials. The rapid diffusion of C, strong carbide formation of Nb, and both melting and mass transfer of the matrix at certain temperatures easily controlled the gradient structure in the reinforcement layer. X-rays diffraction and X-ray photoelectron spectroscopy data revealed the presence of NbC, Fe3C, α-Fe, and Cr7C3 as the main phases in the reinforcement layer. The reinforcement layer can be divided into dense and gradient layers. SEM determined the volume fraction of NbC ceramic particles in the dense layer above 90%, with structure morphology close to that of a completely dense ceramic structure. The gradient layer was composed of two long-strip structures arranged alternately, with structure I consisting of dispersed NbC ceramic particles and structure II containing NbC ceramic particles embedded in the steel matrix. At the microscopic phase interface, the enhanced phase NbC particles were in direct contact with Fe3C without producing other transition phases, and NbC/Fe3C interface presented a non-coherent interface. The macroscopic interface characterized by Electron backscatter diffraction (EBSD) analysis showed consistent crystal orientation characteristics of NbC grains in the reinforcement layer. Also, the reinforcement layer was closely combined with the steel matrix without impurity holes. The macroscopic interfacial bonding strength displayed load scoring values from 0N to 100N without serious deformation failure behavior of the reinforcement layer.