Study On Microstructure And Property Of Boride Carbide Reinforced Ni-based Composite Coatings Produced By Laser Cladding

Surface properties of machine parts need to be promoted increasingly because of the rapid development of modern industry.Composite coatings developed on common metal benefit for improving surface properties of materials,prolonging the working life of machine parts and decreasing environment pollution.Using laser cladding,applied B₄C reinforced nickel-based alloy coatings,applied B₄C coated nickel reinforced nickel-based alloy coatings and in-situ synthesis B₄C reinforced nickel-based alloy coatings are prepared on carbon steel.The microstructure and wear properties of the composite coatings were investigated by scanning electron microscopy(SEM),X-ray diffractometer(XRD) and skimming wear machine.The experiment results show that,the coating is build up by fine dendrites and black grain phase.The black grains show a trend that more under the less,because of the floating and melting of the B₄C particles.The cracks appears when the thermal stress exceeds the yield limit of the material.Applied B₄C reinforced nickel-based alloy coatings with good formation,flawless,high performance can be obtained under 2000～2200W laser power,120～150mm/min scanning velocity,4～5mm spot diameter and the content of B₄C less than 15%wt.Although most of B₄C were resolution,arborescent structure was refining in coating.Due to the function of second phase and solid solution of B₄C ceramic particles,The microhardness and wear resistance of nickel-based alloy+B₄C coatings are improved.The wear resistance of the applied B₄C reinforced nickel-based alloy cladding layers is four times than that of matrix.The applied B₄C can be peeled off when the coating under the high load.To reduce the differences in the thermophysical properties between the B₄C particles and nickel-base alloy and reduce the decomposition of B₄C particles,using sulfuric acid activation,a layer of nickel at the surface of B₄C particles has been plated.By scanning electron microscopy,B₄C particle surface obtains a uniform, dense coating of nickel alloy.In the coating of applied B₄C coated nickel reinforced nickel-based alloy the types of borides are increased,B₄C particles coated nickel increase the wettability of particles,and decrease the decomposition of particles under high-energy laser beam volume.The diffusion distribution of a large number of B₄C particles and boride in the cladding layer,makes the coating micro-hardness and wear resistance has greatly improved,the average microhardness is around HV_0.11200.The wear resistance of the in-situ synthesis B₄C reinforced nickel-based alloy cladding layers is six times than that of matrix.The experiment results show that the in-situ synthesis B₄C reinforced nickel-based alloy cladding layers with good formation,flawless,high performance can be obtained under 1600W laser power,120mm/min scanning velocity,5mm spot diameter and the content of(B₂O₃+C) less than 25%wt.the coating is build up by fine dendrites and black grain phase.The microhardness of the coating is improved along with the content of(B₂O₃+C) growing.When the content of(B₂O₃+C) reaches 25%,the average microhardness is around HV_0.11000.In situ B₄C particles dispersed in the cladding layer,because of which,the micro-hardness and wear resistance of the in-situ synthesis B₄C reinforced nickel-based alloy cladding layers has markedly improved than that of matrix.The wear properties of cladding layers which are obtained by three different ways are analyzed.The anti-wear properties of three cladding layer are much higher than that of the matrix.The wear property of applied B₄C coated nickel reinforced nickel-based alloy cladding layer is the best;The wear property of in-situ synthesis B₄C reinforced nickel-based alloy cladding layer is the second.Along the time,the anti-wear property of the cladding layer is obvious,The wear property of applied B₄C reinforced nickel-based alloy cladding layer is the worst.