| In order to repair the failed tank drive shaft gears,this paper takes the failed tank drive shaft gears as the main research object and selects Ni60 alloy powder and WC-TiO2 alloy powder for the first time using a multi-factor,multi-level and multi-objective experimental design method.The Ni60 alloy and its WC-TiO2 composite coating were prepared on a 40Cr Mn Mo alloy steel substrate using laser melting and plasma melting remanufacturing processes,and the following results were obtained by using scanning electron microscopy（SEM）,X-ray diffractometer（XRD）and ultra-deep field optical microscopy to characterize the tissue composition and structure of the coating,and to test the mechanical properties of the coating such as hardness and wear resistance.Ni60 alloy coating was prepared by plasma cladding technology,and the current selected by analysis was 170A;Powder feeding rate 6r/min;Ion gas flow4L/min;The scanning speed is 2.5mm/s,and the hardness of the coating is449HV0.2,which is 1.5 times higher than that of the substrate.The friction and wear coefficient of the coating is about 0.76,which is about 18.4%lower than that of the substrate.The wear mechanism is mainly abrasive wear and surface fatigue wear.The average impact energy of the coating increases to 62.9J,about 33.8%higher than that of the substrate,and the impact toughness of the coating is improved.The fracture is uneven in shape,with obvious tearing edges.There are a lot of large dimples between the tearing edges,and small dimples around the large dimples.The distribution of dimples is relatively uniform,which is a typical ductile fracture.The laser cladding process was used to prepare Ni60 alloy coating.The laser power of 1600W,gas flow rate of 11L/min,powder delivery rate of 10r/min and scanning speed of 4mm/s were selected for optimization test.The hardness of coating was 727.8HV0.2,which was 2.03 times higher than that of matrix hardness.No obvious cracks,holes and other defects are found on the cross section of the coating.The friction and wear coefficient of the coating is about 0.61,which is about 14.8%and 12.5%lower than that of the matrix and plasma cladding Ni60alloy coating,respectively.The wear mechanism is mainly abrasive wear.The average impact energy of the coating is increased to 53.75J,which is about 14.4%higher than that of the substrate and about 17%lower than that of the plasma cladding Ni60 alloy coating.The impact toughness of the coating is improved compared with that of the substrate.The fracture surface is very undulating and uneven,and consists of cleavage planes of different sizes and white tearing edges.The quasi-cleavage fracture mechanism has a large gully region,and some spherical materials with low binding force are attached to the gully wall,which are mainly ductile fracture accompanied by a small amount of brittle fracture.Comparing the results of coating organisation and properties between plasma and laser melting,the laser melting process was selected as the optimal remanufacturing process for repairing the drive shaft gears.The average value of the laser clad Ni60/WC-TiO2 composite coating was 842.7 HV0.2,which is 1.09times harder than the laser clad Ni60 alloy coating.The microstructure shows the presence of a large number of WC particles and hard carbides in the coating,which play a role in strengthening the coating.The average friction coefficient of the composite coating is 0.51,which is 19.6%lower than that of the laser-coated Ni60alloy coating.The main wear mechanism is abrasive wear.The average impact absorbed energy of the composite coating rises to 52 J,which is approximately3.4%lower than that of the laser-coated Ni60 alloy coating,but the impact absorbed work is greater than that of the matrix,so the impact toughness of the composite coating is improved.The fracture surface is very undulating and uneven,with a large number of WC particles,tearing ribs and deconstruction surfaces,so the fracture mode is mainly brittle fracture. |
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