Study On WC/Fe Composite Coating By Laser Cladding And Its Grinding Machinability

In this paper,the WC/Fe composite coating was prepared by laser cladding technology. The effects of re-melting process, Co content, the laser cladding parameters and heat treatment as well as different particle size and content of WC on the surface smoothness, cracking susceptibility, microstructure and mechanical properties of WC/Fe cladding coating were studied. The formulas of coating and the laser cladding process for inhibiting coating crack were explored. WC/Fe composite coatings with different WC were prepared for grinding experiments to study the grinding mechanism of the composite coating and its grinding performance.The experimental results show that the re-melting process is helpful to improve the surface quality of the coating, to reduce the cracking susceptibility. The distribution of hardness of the coating is more uniform, but the hardness decreased slightly. Crack in the coating can be inhibited effectively by applying 250℃ preheat to the substrate and annealing treatment at 300℃ for 1h for the coating. But preheat to the substrate will increase the dissolution and precipitation of WC, and result in a slight decrease of the hardness of the coating. The appropriate process parameters of multi-cladding are as follow: the electric current is 120 A, scanning speed is 360mm/min, the frequency is 30 Hz, pulse width is 3ms, spot diameter is 1.5mm, and the scanning distance is 1.0mm.Smaller microstructures can be obtained and the bending strength of the coating is increased by adding Co element into the WC/Fe coating. The crack resistance of the coating increases with the increase of Co content. The hardness and the wear resistance of WC/Fe composite coatings were increased visibly with the increase of WC content. However, the bending strength decreased obviously and the cracking susceptibility increased with the increase of WC content. The bending strength of the WC/Fe coating with larger size of WC was decreased, and the cracking susceptibility was increased. The size of WC particles has not much effect on the hardness of the coating, but the coating with larger particle size of WC will has better wear resistance. The wear mechanism of WC/Fe coating against hardened 45 steel is adhesive wear and oxidation wear. The WC particles of the coating are crushed and broken down into tiny WC particles in the wear process and then pressed into the wear surface.The ratio of vertical grinding force and horizontal grinding force(Fz/Fx) is 1.7 ~2.4 when the alumina grinding wheel is used to grind the WC/Fe coating with 10 wt.% WC. The value of Fz/Fx increases with the increase of cutting depth and grinding speed. The main defects in the ground surface of WC/Fe coating include the grinding traces, cracks,debris adherence and voids in the Fe matrix, the broken WC particles, the debris of broken WC particles and cracks generated in the WC particles. With the increase of the amount of WC, The value of Fz/Fx increases and the specific energy decreases. The value of Fz/Fx increases obviously with the increase of the grinding time. Wear on the grinding wheel increases with the increase of the WC content. With the grinding time is prolonged, the chip adhesion and clogging on the surface of the grinding wheel becomes more serious, burnout and grinding vibration waviness appears on the ground surface of the coating.In conclusion, by using appropriate cladding process and adding a certain amount of Co element, the WC/Fe composite coating without cracks and with a wear resistance higher than hardened 45 steel can be fabricated. With the increase of the amount of WC, the hardness and wear resistance of the coating is increased, but its bending strength decreases and the cracking susceptibility increases. Also the ratio of Fz/Fx and the wear of the grinding wheel increases.The duration for grinding wheel to keep sharp is shortened. The dominant ground surface defects are induced due to the grinding traces of the Fe matrix and broken of WC particles.