Research On Wear Resistance And Corrosion Resistance Of Conventional Laser Cladding And Ultra-High-Speed Laser Cladding Wheel Material Coating

As a key component of the train,the state of the train wheel is directly related to the safety of the train.Due to the complex working condition of railway line,local damage of wheel rim and tread are prone to,which affects the reliability of train operation and causes hidden danger.At present,a large amount of wheel material is wasted and the life of the wheel is shortened.Laser cladding technology（LC）has evident superiority in repairing local damage of train wheels.Although the conventional laser cladding technology（CLC）can achieve surface modification and repair,its low efficiency and high dilution rate limit its application in industry.In contrast,ultra-high-speed laser cladding technology（UHSLC）has higher efficiency and lower dilution rate,making it a new surface modification technology,which can better meet the needs of industrial applications.At the same time,it has a slightly high binding with the matrix,and the matrix material has a small heat-affected area.It is expected to become an important technology in the field of surface modification and surface repair.In this paper,CLC and UHSLC of Fe-based,Co-based and 316L stainless steel alloy coatings were prepared on RE8 high-speed wheel steel,respectively.The macroscopic morphology,microstructure,phase composition,element distribution and microhardness of the coatings were characterized.The wear resistance and corrosion resistance of six kinds of laser cladding alloy coatings were studied by rolling/sliding wear test and electrochemical corrosion test respectively,in order to compare the properties of the coatings.The specific research contents and conclusions are as follows:（1）Compared to CLC,the UHSLC alloy coating thickness of the alloy coating is reduced by 800μm,and the heat affected zone（HAZ）is smaller,only 40μm.,the surface is smoother,and the dilution rate is lower.In addition,due to the high cooling rate of UHSLC,the grain structure of the coating becomes finer,the degree of segregation of elements is lower,and the distribution of elements is more uniform,thus improving the performance and service life of the coatings.There is little difference in the phase composition of the coatings prepared by the two processes.The Fe-based alloy coating is mainly composed of（Fe,Ni）solid solution and Cr₇C₃ phase,the Co-based alloy coating is mainly composed ofγ-Co phase and Cr₂₃C₆phase,and the 316L stainless steel alloy coating is mainly composed ofα-Fe phase andγ-Fe phase.There are more carbide and martensite in UHSLC alloy coatings,therefore,the coating hardness is higher than that of CLC alloy coating,and the hardness of Fe-based alloy coating is greater than that of Co-based alloy coating and 316L stainless steel alloy coating in turn.（2）By means of rolling contact fatigue wear test and sliding friction wear test,the difference of wear resistance between CLC and UHSLC of Fe-based,Co-based and 316L stainless steel alloy coatings were compared and analyzed,and the wear mechanism was expounded.Under the same test conditions,the UHSLC alloy coating shows lower friction coefficient and damage degree,and lower wear rate,which makes it have better wear resistance,thus greatly improving its service performance.The wear rates of Fe-based,Co-based and 316L stainless steel alloy coatings were 4.226×10^-5g·m^-1,0.148×10^-5g·m^-1 and 0.537×10^-5g·m^-1,respectively,which decreased by 40.7%,58.1%and 73.8%compared with CLC alloy coatings.Co-based coating showed the best wear resistance,followed by 316L stainless steel and Fe-based alloy coating.The results of sliding friction wear test and rolling wear test have the same rule,and the wear mechanism of CLC and UHSLC alloy coatings is the same,which are abrasive wear,oxidation wear and adhesive wear.（3）Electrochemical corrosion tests were carried out in acid rain solution to analyze the corrosion behavior of CLC and UHSLC coatings under the same test conditions.The experimental results show that compared with the CLC,the UHSLC alloy coating has higher self-corrosion potential and lower self-corrosion current density.At the same time,the UHSLC alloy coatings have higher charge transfer resistance Rct,and among the same alloy coating,the corrosion degree of CLC coatings is more serious.It is proved that the corrosion resistance of UHSLC alloy coating is better than that of the same alloy powder.Among them,under the same preparation process,Co-based alloy coating shows the most excellent corrosion resistance,followed by 316L stainless steel alloy coating,and Fe-based alloy coating is the worst.