Investigation On Microstructure And Properties Of Stellite6/TiCN Composite Coating By Laser Cladding

Based on the high energy density of the laser beam,3D printing (namely material additive manufacturing) is innovation of the way that the product are manufactured, which has become a central issue at home and abroad. For polymer materials like plastics,3D printing tends to mature, while it makes a slow progress for metals and ceramic materials due to cracking caused by thermal stress. Stellite6/TiCN mixed powder selected as raw material, is fabricated composite coating by laser cladding technology through the optimization of laser processing parameters and improving the composition ratio of Stellite6/TiCN to investigate microstructure and performance of composite coatings, so that it could offer scientific basis and technical support for selection of raw materials for3D printing.Good self-deoxy performance and slagging of Stellite6help to get the cladding layers of low oxide and less porosity; its excellent wettability is favorable to the liquidity and surface tension of alloys. TiCN combines the advantages of TiC and TiN, such as high melting point, high hardness, good resistance to wear, thermal stability, good wettability, thermal and electrical conduction, chemical stability and biocompatibility.The microstructure, phase composition, hardness, resistance to wear and corrosion are detected or characterized by optical microscopy, scanning electron microscopy, X-ray diffraction, electron probe microanalysis, microhardness tester, wear test and salt spray corrosion box.In contrast to multiple processing parameters of composite coating of Stellite6/TiCN, combining with microstructure and performance of the cladding layer, the laser processing parameters in this experiment are optimized as follows:the optimal laser output power P=4kW, spot diameter D=2mm, scanning speed V=7mm/s, overlap rate is1mm, in Ar gas shield. Cladding layer consist of cladding region, heat-affected zone and the base zone. Different solidification morphology appears in the cladding layer from the interface between the pool and substrate to the surface of substrate, which are plane crystal (at the interface), cellular dendrite and dendrites.The composition ratios of alloy powder (Stellite6+(0-50%wt.)TiCN) in cladding layers appear to be gradient. Experimental results show that the content of TiCN has a significant effect on the microstructure of coating. The microstructure of coating distributes evenly and is coarse without adding TiCN powder; while the microstructure obviously turn fine with adding, which suggest that TiCN powder is helpful to grain refinement of cladding layers. In addition, the solidification rate of cladding layer and the concentration of TiCN in molten pool have some influence on the morphology of TiCN secondary phase due to the laser beam with rapid heating and cooling. When the content of TiCN is less (0-20%w1.), TiCN completely dissolves in the eutectic microstructure without the precipitated TiCN secondary phase, and the microstructure consists of primary dendrite (y-Co phase) and the interdendritic eutectic ((Cr, Mo)23C6,(Cr, Fe)7C3) composition; with the increase in the content(more than30%wt.) of TiCN, the fusion-precipitation mechanism of TiCN in cladding layer dominates, and the precipitated TiCN appears in microstructure.The content of TiCN in Stellite6/TiCN composite cladding layers has a significant effect on the average microhardness. When the content of TiCN reaches30%wt., the average microhardness of composite layers reaches a maximum of1027HVo.2, and increases by about560%in comparison with that of the substrate (183.3HV0.2).Abrasive wear test at room temperature indicates that the cladding layers have improved resistance to wear of the substrate, and the hard phase TiCN particles and their decomposed product at elevated temperature largely bear the loads in cladding layers and significantly reduce the surface wear.The specimens with Stellite6/TiCN cladding layers and the substrate40CrNiMo are placed in the salt spray corrosion box for8h continuous spray (5%sodium chloride solution) to measure its resistance to corrosion by simulating the accelerated corrosion of marine environment. Corrosion rate:30%wt.(TiCN)<20%wt.(TiCN)<50%wt.(TiCN)<10%wt.(TiCN)<40%wt.(TiCN)<0%wt.(TiCN)<40CrNiMo. The cladding layers are clearly superior in resistance to corrosion in comparison with the substrate, benefiting from the precipitated TiCN with good resistance to corrosion.