Microstructure And Performance Of Ni-based Spherical WC Composite Coating By Laser Cladding

The current research and development trends of laser cladding r emanufacturingtechnology in surface engineering field were first reviewed in this thesis. For the technicalproblems, such as poor high-temperature wear resistance and thermal shock damage on thehigh temperature roller’s surface coating of furnace rollers and roller ring, two kinds of Nimatrix spherical WC composite coatings of NiCoCrAlY and Inconel625were prepared on the310S stainless steel surfaces by laser cladding. The effects of different process parameters(coating materials, coating thickness, laser power, and scanning velocity) on themicrostructure and crack forming were studied. The microstructure, composition and phasestructure of Ni-based WC composite coating were characterized by optical metallographicmicroscope, scanning electron microscope, X-ray diffraction, and energy dispersivespectroscopy. In addition, the room temperature abrasive wear behavior of NiCoCrAlY-15%WC cladding layer, Inconel625-20%WC cladding layer, and stainless steel werecomparatively studied. The high-temperature wear resistance of NiCoCrAlY-15%WCcladding layer, Inconel625-20%WC cladding layer and stainless steel under300℃,700℃,1000℃were also comparatively studied. Finally, the thermal shock resistance of Ni-basedWC cladding layer with stainless steel were compared.The results showed that the Ni-based spherical WC cladding layers combined with auniform microstructure and good combination with the substrate on the condition ofoptimized process parameters. From the surface to the interface, the microstructure of laserclad composite coating followed by the fine dendrites-the coarse dendrites-the cellularstructure vertical to the interface. The NiCoCrAlY-15%WC coating was consisted of Ni-basedsolid solution, eutectic AlNi3and M26C6, and the Inconel625-20%WC coating was consistedof Ni3Cr2, Ni17W3, Cr4Ni15W, Fe6W6C, Mo6Ni6C, W3C and WC hard phases. TheNiCoCrAlY-15%WC coating and the Inconel625-20%WC coating showed a good wearresistance under room temperature with the solid solution strengthening, dispersionstrengthening of intermetallics of Co, Mo, Nb alloy elements, and WC hard phases supportedto anti-wear behavior. The mainly wear mechanism of Ni-based spherical WC coatings wasabrasive wear, but the stainless steel appeared seriously abrasive wear and adhesion wear.The results of high temperature wear test showed that the friction coefficient of Ni-based spherical WC coatings and stainless steel reduced with the rise of temperature. With thestrengthening of the WC ceramic phase, the wear resistances of Ni-based spherical WC coatings were greatly improved. At300℃, the wear resistance of Inconel625based WCcladding layer was better than the NiCoCrAlY based WC cladding layer; but at700℃and1000℃, NiCoCrAlY-15%WC cladding layer showed a better well wear resistance thanInconel625-20%WC cladding layer by the protection of Al2O3and Cr2O3.The annealing state Inconel625-10%WC cladding layer showed the best anti-thermalshock resistance, the non-annealing state Inconel625-10%WC cladding layer presented thesecond best anti-thermal shock resistance, and the310S stainless steel presented rather pooranti-thermal shock resistance. The crack failure of Ni-based WC coatings was mainly due tothe thermal stress concentration, which was caused by the mismatch of thermal expansioncoefficient between materials. In addition, the high temperature oxidation phenomenonaccelerated crack growth in cladding layer. The stress annealing treatment could relax theresidual stress of Ni-based WC coating, so it effectively improved the anti-thermal shockresistance of coating.