| The seawater hydraulic pump faces severe technical problems of corrosion and wear.TheNi based ceramet self-lubrication wear and corrosion resistance coating was prepared on thekey parts of seawater pump by means of laser cladding and ion sulfurization compoundmodification to increase its service life. In this dissertation, the microstructure and property ofthe compound modified layer and its forming influencing factors were analyzed, the processwas optimized by the method of orthogonal design, and its forming process as well asmechanism was investigated.Overlaping laser cladding of self-made Ni-base ceramic layer had been prepared on45steel surfaces, the slag detachability of overlapping cladding layer is excellent, and it issmooth, dense and no crack. There are Ni-Fe solid-solution, Fe2B, WC, M7C3and M23C6carbides in the coating. The microhardness of cladding layer is about600HV0.2. Acompound modified layer was formed on the surface of Ni-based coating by low temperatureion sulfurization. The layers is consists of deposition layer which constructed of micro-nanolever sharp-island particles and diffusion layer. The thickness of sulfide layer is about4μm.The S element content of its surface is high. The S atoms have diffused into the surface ofNi-base coating and produced FeS. The compound solid lubricative layer was produced byion sulfurization which could reduce friction coefficient and relieve the wear of friction pairapparently. Under dry friction condition, the friction coefficient of Ni-base ceramic layer is0.75, while the friction coefficient decreased to0.6after ion sulfurization. And theweightlessness of wear decreases by40%.The sulphurizing temperature and surface roughness have great influence on morphologyof the compound modified layer. Neither over high temperature nor surface roughness ishelpful to its forming. The micro-morphology of the layer of same surface roughness under different sulphurizing parameters is similar. Each compound modified layer with differentparameters contains Fe, Ni, W and S, while the S element content of its surface has greatrelationship with sulphurizing parameters. The sulphurizing temperature is the main factorwhich influences the S element content. And the influence of surface roughness is secondary,while holding time has the least influence on it after holding longer than2h. When thesulphurizing parameters is230℃, holding4h and surface roughness0.07, the samples havethe highest S element content and lower friction coefficient and weightlessness of wear. Theresults show that it is the best sulphurizing parameters.The formation and growth of the compound solid lubricative layer is a transformationprocess of gas-solid, which includes dissociation of sulfur-content medium and transportationof active sulfides, adsorption and reaction on cladding layer of active sulfides, and diffusionof active S atoms. There are two kinds of effects of active sulfides decomposed fromhydrogen sulfide gas with the surface of cladding layer, sulfide ion sputter with the surfaceand neutral S atoms adsorp on it. Sulfides which are produced by reaction of sputtered Featoms and S atoms deposit, adopt and nucleate on the surface of laser cladding layer with lowsurface energy, and grow up as Volmer-Webermodel.They combine into the networkstructure and form the compound modified layer finally.The O and S element content of itssurface have great relationship with holding time. However, the atomic ratio of S and Fe isabout1：1after holding2hours. The S element content of the surface is decreased and thedeposition layer become compacter cracked and spalled after prolonged the holding time. |
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