Study On Plastic Deformation Law And Model Of Laser Cladding Coat Under Low Repeated Impact Load

This article makes a study of the plastic deformation law of laser cladding coat under low repeated impact load and dicusses its microcosmic mechanism. Base on the research, a mathematical model that is relevent to the plastic deformation is builded.This article firstly chooses two laser cladding parts to accomplish twice deformation tests with the self-made repeated impact machine. Through the comparison of the parts in different test periods, it is found that the two parts coat and substrate generate appreciable accumulated plastic deformation when the impact surface stress is 100 Mpa to 300 Mpa(The value is only ten percent of yield strength of coat material and one second to one third of yield strength of basis material), impact stroke is 20mm and impact frequency is 4Hz. This kind of accumulated deformation with the characters of normal temperature and low stress is defined as repeated impact creep. The deformation data shows that the coating parts under repeated impact have characters of skin effect problem, time nonlinearity and space nonlinearity, which explains that the coats surface deformation rate has the maximum value and it dereases as a manner of exponential function with the impact times and layer depth increasing and at last it will be zero.The basis strain rate dereases with the impact times and depth from lunction plane increasing and the variety tendency coincides to that of coats. It is also found that the growth rate of accumulated deformation amount of basis and coat takes on a trend of decrement as impact time increases and eventually creep keeps on the stable state. The accumulated creep amount increase with impact load increasing. But the creep stabilization period will not continue for a long time and it will be stationary after generally 150 thousands to 250 thousands times impact.The TEM and X ray of coated parts before impact and after imapct shows that the material generates grain boundary sliding and migration under low repeated impact load.The metallurgical phase analysis shows that coats material microstructure generates variation under low stress repeated impact load The formation of substrcture and twin crystal accelerates the progress of repeated creep and the formation of substrcture and twin crystal accelerates the progress of repeated impact creep. The first cause of low stress repeated impact creep is impact energy drive. The continual input of impact energy makes the vibration partical overpass the potential energy hill and accelerates the kinking formation and crystal gliding, which causes the generation accumulated plastic deformation. The necessary condition of repeated impact creep generation is that the material must reach the minimum stress of inducing microdeformation and the partical has effective turbulent energy. The article summarizes up the conception of repeated inpact creep equivalent stress threshold value and also builds creep model framework. It is thought that in the analysis of repeated impact, energy input is also one of essences and it should not be ignored.The main damaged failure of laser cladding coated parts under repeated impact is analysed. The coated parts generate the phenomena of deformation hardness, deformation softening and impacted mass loss. The concrete performance of surface damage is cracking, spalling, corrosion pit and subsidence and the first cause of all the damaged failure can be resloved into the repeated elastic-plastic deformation of material.