Study On Crack Sensitivity And Control Method Of Laser Cladding Coating

Laser cladding is an advanced green additive manufacturing technology that integrates light,powder,and gas.It has attracted much attention in the industrial field due to its low dilution rate,small heat affected zone,and controllable forming accuracy.But since the birth of laser cladding technology,the high crack sensitivity of the cladding layer has been a very difficult problem,especially the preparation of high-hardness coating is more prone to cracks,which seriously hinders the development of laser cladding technology.This paper studies the problem of laser coating cracks.The following are the major study ways and verdicts:(1)The macro morphology of cracks in laser cladding Ni60 coating and the formation conditions,location,causes and influencing factors of cold cracks and hot cracks(including solidification cracks in cladding layer,liquefying cracks in heat affected zone and liquefying cracks in cladding metal)were studied.The effect of the stress produced during and after laser cladding on the substrate and cladding layer is analyzed.The crack source and the propagation direction of the main crack are determined by the secondary micro cracks.By using the laser cladding method with variable substrate thickness,the deformation law of substrate with different thickness and the crack sensitivity of coating were studied.The crack sensitivity of the coating under different parameters was studied by orthogonal test,the primary and secondary order of the influence of each factor on the crack sensitivity was analyzed by visual analysis,and the significance of each factor on the crack sensitivity was studied by variance analysis.(2)Based on the sample data collected by the orthogonal test,the genetic algorithm optimization neural network model between the powder feeding amount,overlap rate,scanning speed and the crack density of the Laser Cladding Nickel Base cladding layer is established.The nonlinear mapping relationship between process parameters and crack density of Ni60 cladding layer is established.After testing,the Forecast errors of the network model are less than 9.8%,which proves the reliability of the model.Thirdly,genetic algorithm is used to optimize the prediction results of neural network model.The process parameters with the lowest crack density are:powder feeding 15.0726g/min,overlap ratio 49.7997%,scanning speed 5.9275mm/s.This has great reference significance for the research on the intelligent control of coating cracks.(3)Ni60 and Fe60 coatings were prepared on 45 steel with and without ultrasonic vibration.The effects of ultrasonic vibration on the cracks and microstructure of laser cladding Ni60 and Fe60 coatings were studied from the micro and macro perspectives.The results show that under ultrasonic vibration conditions,the surface roughness of Ni60 and Fe60 cladding layers is smaller,the crack sensitivity is lower,the internal grains of the coating are smaller,and the overall morphology and structure are better than those without ultrasonic vibration intervention.The average hardness of the nickel-based and iron-based cladding layers with ultrasonic vibration is about 3.94times and 3.91 times that of the substrate,respectively,which is about 117HV_0.2 and106HV_0.2more than the average hardness of the nickel-based and iron-based cladding layers without ultrasonic vibration.Ultrasonic vibration has little effect on the wear resistance of Ni60 and Fe60 coatings,only slightly improved.