Microstructure And Tribological Properties Of Laser Cladding Cr₃C₂-NiCr Coating

Cr₃C₂-NiCr has the characteristics of high hardness,high strength,high temperature oxidation resistance and high wear resistance.It is widely used in bearings,seals and die parts working at high temperature.Among Cr₃C₂-NiCr,Cr₃C₂ has better thermal stability and wear resistance,while NiCr has lower thermal stress and high toughness.Therefore,Cr₃C₂-NiCr is often used in the surface treatment of workpiece,which can not only maintain the plastic toughness of the substrate,but also improve the wear resistance of the workpiece.In this paper,Cr₃C₂-NiCr cladding layer was prepared on Q235 steel surface by using different laser cladding process parameters.The effects of laser output power,scanning speed,lap rate and number of layers on the forming quality,dilution rate,microstructure and hardness of cladding layer were studied,so as to determine the best process parameters.On this basis,the influences of load,rotation speed,friction pair and medium conditions on the friction and wear properties of Cr₃C₂-NiCr cladding layer were investigated,and the wear mechanism under different working conditions was revealed.The main research results of this paper are as follows:The optimized process parameters in this experiment are as follows:laser output power is1500W,scanning speed is 6mm/s,overlap rate is 40%,layer number is 1.The Cr₃C₂-NiCr cladding layer prepared by this process has good interface flatness,good bonding between coating and substrate,and no cracks,pores and other defects at the interface.At the same time,an obvious transition layer is formed at the interface between Cr₃C₂-NiCr cladding layer and Q235 matrix,and the transition layer forms a fine structure and is perpendicular to the interface.There are obvious diffusion phenomena of Fe,Cr and Ni elements at the interface,indicating that the Cr₃C₂-NiCr cladding layer has a good metallurgical bond with the matrix.The height and width of Cr₃C₂-NiCr cladding layer increase with the increase of laser power,while the dilution rate decreases with the increase of laser power.The maximum thickness of the transition layer of 6mm/s sample is about 50μm,and the interface heat affected zone is small,which can effectively improve the productivity.The sample with 40%bonding rate has the best flatness.Under dry friction conditions,the friction coefficient of hard materials on Q235 steel in the disk（GCr15 steel after heat treatment,Vickers hardness of about 600HV）increases with the increase of load,the friction coefficient of Cr₃C₂-NiCr cladding layer increases first and then decreases with the increase of load,and decreases with the increase of rotational speed.The wear mechanism is mainly abrasive wear.The friction coefficient of Cr₃C₂-NiCr cladding layer increases with the increase of load,and the wear mechanism is mainly adhesive wear.Under the condition of 3.5%Na Cl solution,the friction coefficient of cladding layer first increases and then decreases with the increase of load.As the rotational speed increases,the friction coefficient increases.The wear mechanism is abrasive wear and corrosion wear.Under dry friction conditions,the wear rate of Cr₃C₂-NiCr cladding layer decreases by 98.8%,95.6%,98.2%and99.1%compared with that of Q235 steel substrate at 25N,50N,75N and 100N loading,respectively.The wear resistance of Q235 steel substrate is significantly improved by Cr₃C₂-NiCr cladding layer.