Research On Laser Nitriding Process,Microstructure And Properties Of Novel TiZrAlV Alloy

TiZr alloys have many excellent properties compared to other metals,and have low density,high specific strength,excellent corrosion resistance and high temperature resistance.It is therefore widely used in the military industry,nuclear industry,chemical industry and automotive industry.However,TiZr alloy systems all have engineering problems such as low surface hardness and poor wear resistance leading to surface failure.In this paper,a high hardness and wear resistance ceramic coating was prepared on the surface of TiZrAlV alloy by laser surface nitriding technique.The stability and formation ability and formation conditions of TiN and ZrN phases were analyzed by thermodynamics.The phase composition,surface morphology and element distribution,nanohardness and wear resistance of laser nitrided zone,heat affected zone and substrate at different scanning speeds by X-ray diffractometer,scanning electron microscope,electron probe,nano indenter and wear tester are tested.In order to obtain better surface coating effect,this study used orthogonal experiment to analyze the influence of laser nitriding process parameters on coating hardness and wear resistance.The research show that the surface nitriding zone after laser nitridation forms dendritic Ti₂N,ZrN,TiN nitride dendrites and fine-grained structures,and the central heat affected zone is mainly?'martensite formed by rapid cooling.The lower the laser scanning speed,the more ceramic phases are formed,the higher the hardness,the smaller the corresponding friction coefficient,and the less the wear weight loss.The results show that the laser nitriding treatment can refine the surface grains and form the hard nitride ceramic phase to prepare a ceramic coating with high surface hardness and high wear resistance.Among them,the laser scanning speed is reduced,the dissolved nitrogen content in the nitriding layer is increased,the volume fraction of the nitriding phase is increased,and the hardness and the friction and wear resistance are increased.Further orthogonal analysis of the nitriding parameter combination shows that the change of the hardness of the coating is basically uniform with the wear resistance,and the laser scanning speed is the most critical parameter affecting the hardness and wear resistance of the nitrided coating.The optimum combination of hardness or wear resistance of the laser nitrided zone and the heat affected zone are 180W of laser power,10mm/s of scanning speed,2mm of spot diameter and 135W of laser power,10mm/s of scanning speed,2mm of spot diameter.