In-situ Synthesis Of Modified Layers For Ceramic Reinforced Metal Matrix Composite By PTAW

Wear is an important reason causing failure of materials. Many machinery parts serve inthe harsh working environment for long, and the surfaces are under very high impact load, sothey offen fail because of wear which not only reduce the service life but also cause largeeconomic loss and waste of resource. Surface modification technology of materials can changethe microstructure, component and phase composition to improve the wear resistance ofmaterials. Particle reinforced metal matrix composites have excellent performancecharacteristics of metal materials and ceramic materials. The traditional metal matrixcomposites prepared by adding the reinforcing phase directly usually exist problems like thepoor interface wettability between enhanced particles and matrix and the uneven distributionof reinforced phases, which make the performance of materials unable to reach the expectedeffect. The in-situ synthesis method has overcome this problem. The metal matrix compositesprepared by this method have a good thermodynamic stability, the uniform distribution ofreinforced phases in the matrix, a good interface bonding, which effectively improve thesurface properties of materials and have a great application prospect.In this work, the WC reinforced Ni-based alloy modified layers by in-situ synthesis weredeposited on304L stainless steel by plasma transferred arc welding (PTAW). The processparameters and performance were optimized. The microstructure, chemical composition,constituent phases, microhardness, friction and wear characteristics of the modified layerswere investigated by optical microscope, scanning electron microscopy (SEM), energydispersive X-ray spectroscopy (EDS), X-ray diffraction (XRD), microhardness tester andpin-dish abrasion tester. At the same time, we added appropriate rare earth oxides to themodified layers and studied the effects of rare earth on the properties of the modified layers.The experimental results showed that when preparing the additional WC particlesreinforced Ni-based alloy composite modified layers, the sinking of WC particles phenomenonappeared, leading to the nonuniform microstructure in the modified layers. However, the WCphases in the in-situ synthesized WC reinforced Ni-based alloy composites presented massiveand were uniformly distributed in the modified layers. The microhardness of Ni-based alloycomposites modified layers prepared by adding WC particles directly presented gradientdistribution. The microhardness at the bottom of WC aggregation zone was significantly higher than that of the upper layer and the average microhardness was925HV. The wearmechanisms of the modified layers were mainly fatigue fracture and adhesive, and the relativewear resistance was12.0. The microhardness of in-situ synthesized WC reinforced Ni-basedalloy composites modified layers presented uniform distribution, and the highest averagemicrohardness was915HV. The wear surface of the modified layers presented furrow-like, andthe wear mechanisms was mainly abrasive wear, the relative wear resistance increasedsignificantly. After the addition of rare earth oxides, the microstructure became finer anddenser, and the morphology, size and distribution of WC particles have changed. Themicrohardness of modified layers increased in different degree, and the highest wear resistancewas up to36.0.