Microstructures And Wear Resistance Of Coatings Produced By Laser Melt Injecting WC On Q235 Steel Surface

Laser Melt Injection (LMI) technology has great potential in the field of material surface hardening. In order to produce excellent coatings, WC powders were injected into the surface of Q235 steel by LMI process. The influence of process parameters on the form of LMI coatings were studied completely. The microstructure and composition of the coatings were analyzed by means of SEM, XRD, and EDS. Wear-resistant property of the coatings and Q235 steel was investigated comparatively.The results show that excellent coatings with no macroscopic defects can be acquired by injecting WC powders into the surface of Q235 steel. Metallurgical bonding between the coatings and Q235 substrate is realized. Microstructure in the coatings is complex, which consist of WC, W2C, and M6C(Fe3W3C- Fe4W2C) phases. The differences of microstructure in different zones of the coatings are obvious. Kinds of petaloid and dendrite precipitiation carbides are formed in the upper zone of the coatings, while fishbone-like eutectics are formed in the bottom. Besides, reaction layers are formed around WC particles. It is found that compositions of the reaction layers around particle and dendrite precipitiation carbides in the upper coating are both Fe3W3C. Surfaces of WC particles will melt when they are heat by laser beam. After being injected into laser pool, liquid WC droplets which break away from WC particles will decompose into W and C atoms. They react with Fe atoms and form crystal nucleus in the liquid pool. During the solidification of laser pool, kinds of petaloid and dendrite precipitiation carbides Fe3W3C are formed in the upper coating. The liquid WC droplets which continuely adhere to surfaces of WC particles will also decompose into W and C atoms. This lead to W-rich zone around WC particles. W reacted with Fe atoms in W-rich zone. Fe3W3C layers clinging to WC particles was grown up.The hardness results show that microhardness of coatings fluctuate from 1100HV to 1400HV, with average hardness of 1354HV, which is about six times of Q235 steel. The abrasion results show that the friction coefficient of coatings keep around 0.2 in the primal 400s, and then rise up slowly to 0.6 until 1000s. The results show that the wear resistance of coatings enhances sharply comparing with Q235 steel. The granule abrasion dominate the abrasion process of coatings, while the adhesive abrasion is the primary abrasion mechanism of Q235 steel. The good performance of coatings is not only due to high hardness of WC particles, but also thanks to the peculiar studdeding structure. WC particles play a role of framework, endure load and decrease the abrasion of coating substrates, meanwhile dendrite precipitation carbide of M6C nail and strengthen the coating substrate, avoiding the metamorphose of it, so that the coating substrate could support WC particles more tightly.