Crack initiation and propagation behavior of WC particles reinforced Fe-based metal matrix composite produced by laser melting deposition

Abstract

It is generally believed that cracks in metal matrix composites (MMC) parts manufacturing are crucial to the reliable material properties, especially for the reinforcement particles with high volume fraction. In this paper, WC particles (WCp) reinforced Fe-based metal matrix composites (WCp/Fe) were manufactured by laser melting deposition (LMD) technology to investigate the characteristics of cracks formation. The section morphology of composites were analyzed by optical microscope (OM), and microstructure of WCp, matrix and interface were analyzed by X-ray diffraction (XRD) and scanning electron microscopy (SEM), in order to study the crack initiation and propagation behavior under different laser process conditions. The temperature of materials during the laser melting deposition was detected by the infrared thermometer. The results showed that the cracks often appeared after five layers laser deposition in this experiment. The cracks crossed through WC particles rather than the interface, so the strength of interface obtained by the LMD was relatively large. When the thermal stress induced by high temperature gradient during LMD and the coefficient of thermal expansion mismatch between WC and matrix was larger than yield strength of WC, the cracks would initiate inside WC particle. Cracks mostly propagated along the eutectic phases whose brittleness was very large. The obtained thin interface was beneficial to transmitting the stress from particle to matrix. The influence of volume fraction of particles, laser power and scanning speed on cracks were investigated. This paper investigated the influence of WC particles size on cracks systematically, and the smallest size of cracked WC in different laser processing parameters was also researched.