Mechanics Study And Modeling Of Low Stress Repeated Impact Deformation Of Laser Cladding Coat

Low stress repeated impact load is ubiquitous in engineering. Under the effect of this kind of load, there are microscopic deformations and various disfigurements appear on the contact surface of the parts, and then lead to damage and failure. Compared with other technologies of surface peening, laser cladding coat has better performance of anti-repeated impact. The microcosmic mechanics of plastic deformation of laser cladding coat under low stress repeated impact load is studied, and the model of its microscopic deformations is build.The experiment is carried out on self-making repeated impact machine, and the coating material are the cobalt-base self-fusible alloy and nickel-base self-fusible alloy. Against the plastic deformation of the coat under repeated impact load, which is the main reason of crack, depression, upset, pit on the surface and breakout, metallographic analysis and stereoscan analysis are taken on the structure of coats before and after deformation. It is found: ①the grains of surface and subsurface have obvious deformation after repeated impact, and the direction of deformation have an angle about 30° -45° with the force axis; ②after repeated impact, there are obvious destruct phenomenon of grain boundary and the broken phenomenon of grain; ③the change of bottom structure is inconspicuous.According to the results of metallographic analysis and stereoscan analysis, on the assumption that under the repeated impact load, the plastic strain of coat surface and subsurface is big, the dislocations are active gradually, and than the formed glide bands meet the obstruction of grain boundary. Because of this obstruction, when the impact number get to some value, and the dislocation number blocked in the obstruction reach to enough numbers, the total stress will cause the grain to be sheared and refined. The phase analysis of cladding coat by X diffractometer show: there are many kinds of multiple eutectic compounds in the laser cladding coat, such as, chride, etc. And the laser cladding coat structure has more complex phase structure. It is concluded that the obstruction should be the grain boundary; and the carbide and boride which have high hardness and high-yield...