| In"Made in China 2025",China puts forward the basic policy of"green development".Compared with manufacturing new construction machinery parts,remanufacturing and repairing the failed parts could not only save a lot of resources for the country,but also have great economic and social benefits.To solve the problem of friction,wear and corrosion failure of 42Cr Mo steel for marine crankshafts,Co-based alloy composite coating was prepared on the surface of 42Cr Mo steel by laser cladding technology.Laser cladding technology contributed to realize the remanufacturing of marine crankshafts and prolong the service life of marine crankshafts.The main research contents were as follows.(1)The influence of laser power and scanning speed on the properties of Co-based coating was studied.The average microhardness,wear rate and electrochemical impedance were used to evaluate the performance of the coating.The influence of the process parameters on the coating was analyzed by adjusting the laser power and scanning speed in the laser process parameters.The average microhardness of Co-based coating could reach 619HV0.2,the wear rate was 0.598×10-4mm3/N·m and electrochemical impedance was 13061.1?/cm2while the laser power was 1800W.At the scanning speed of 400mm/min,the average microhardness of Co-based coating was 615HV0.2,the wear rate was 0.554×10-4mm3/N·m,and the electrochemical impedance was 13850.7?/cm2,which meaned that the performances were also better.(2)The effect of CeO2 on the properties of Co-based coating and the strengthening mechanism were studied.Different mass fractions of rare earth oxide CeO2 were added into Stellite-6 powders.The effect of CeO2 content on the microstructure and properties of Co-based coating was investigated.The mechanism of CeO2 enhanced microhardness,wear resistance and corrosion resistance of Co-based coating was analyzed.The results showed that3wt.%CeO2/Co-based composite coating consisted of uniform and fine equiaxed crystal,and the average friction coefficient was only 0.326.After CeO2 mixed with Co-based powder,a large number of hard phases M7C3 and M23C6 appeared in the coating,and the stability of M23C6 was greater than that of M7C3.The results showed that the wear mechanism of the coating without CeO2 was oxidation wear,while the wear resistance of the coating with CeO2powder was greatly improved,showing a slight groove.In the electrochemical detection,the passive film Cr2O3 formed on the surface of the coating could isolate the corrosion solution,eventually slow down the oxidation reaction,and improve the corrosion resistance of the coating.(3)Multi objective optimization of CeO2/Co-based composite coating by laser cladding.Based on the response surface method,the laser power,scanning speed and CeO2 content were optimized to obtain the best combination of processing parameters.The results showed that the optimization range of process parameters could be greatly reduced by using multi-objective genetic algorithm optimization.In order to obtain better coating quality,the laser power was mainly distributed between 1600?1650W,the scanning speed was between425?440mm/min,and the mass fraction of CeO2 was between 2.6?2.8wt.%.The results showed that the average microhardness was 690HV0.2,the wear rate was about0.52×10-4mm3/N·m,and the electrochemical impedance was about 69000?/cm2.In the process of verifying the reliability of Pareto solution set,the error between each index and the actual detection results could be controlled within 5.4%,which indicated that the multi-objective optimization has high reliability.(4)Remanufacturing repair multi-channel multi-level planning.The influence of laser power,scanning speed and CeO2 mass fraction on the geometric characteristics of single pass cobalt based coating was analyzed.And the geometric prediction model of coating width and height was established.The macro morphology and microstructure of the coating under20,30,40,50,60%overlap ratio were obtained,and the overlap ratio suitable for Co-based coating was further determined to be 50%.On the basis of determining the process parameters,the reasonable overlap ratio was selected.The repair of typical"inverted trapezoid"sample was realized by the connection rate,and the planning of multi-channel and multi-layer coating was realized. |
PDF Full Text Request