Study On Surface Microstructure And Friction And Wear Behavior Of High Speed Laser Cladding Fe-based Coating Strengthened By Ultrasonic Rolling

As a large manufacturing country,China ranks first in the world in terms of carbon steel output and usage for consecutive years.At the same time,due to poor service conditions,it will cause a lot of material waste every year.For example,Shanxi,as a major coal province,a large number of hydraulic supports are damaged due to corrosion failure,wear failure and fatigue failure every year.Laser cladding technology is used to prepare a layer of coating on the surface of carbon steel to improve the service life of carbon steel,while high-speed laser cladding technology can prepare higher quality coatings,realize automation and high cladding efficiency,which is more suitable for contemporary industrial applications.However,it still has the problems of low machining dimensional accuracy,low surface effect quality,and uncontrollable internal and thermal stress in the coating,which affects the performance of the coating.In this paper,the surface defects of the coating are eliminated by ultrasonic rolling and laser cladding technology.A single-layer Fe based coating was prepared on the surface of 45#steel substrate by high-speed laser cladding technology.After finishing the surface,the surface was strengthened by ultrasonic rolling technology,and the effects of ultrasonic rolling technology and rolling passes on the microstructure and properties of the coating were compared and analyzed.Through the synergistic effect of dynamic impact and static extrusion,ultrasonic rolling technology can significantly improve the coating surface quality and reduce the coating surface roughness,from Ra=8.420μm reduced to Ra=0.548μm.The surface presents a mirror effect.Through plastic cumulative deformation and severe plastic deformation,the surface grain of the coating can be significantly refined to form gradient nanocrystalline structure.From the surface of the coating to the interior of the coating,there are fine grain layer,plastic flow layer,deformed grain layer and original coarse grain layer.At the same time,the coating surface will undergo martensitic transformation,and the coating surface will change from austenite and martensite to single-phase martensite.Element analysis shows that ultrasonic rolling process will not change the element distribution on the coating surface.Through the strengthening of ultrasonic rolling,the microhardness of the coating surface is changed from 495.0 HV_0.5after high-speed laser cladding to 818.7 HV_0.5after ultrasonic rolling 6 passes.Due to the synergistic strengthening of various strengthening mechanisms such as fine grain strengthening,dislocation strengthening and work hardening,the hardness of the whole coating is improved,and the hardness of the joint between the coating and the substrate is also improved.Through the analysis of micro nano mechanics,the elastic modulus of the thick coating surface after 6 passes of ultrasonic rolling is increased to232.783 GPa,which is 39.5%higher than 166.905 GPa before rolling;After 6 passes of ultrasonic rolling,the surface hardness is the largest,reaching 6.782 GPa,which is 76.2%higher than 3.848 GPa of finish turning coating surface.Ultrasonic rolling technology can also transform the residual tensile stress in the coating into residual compressive stress after laser cladding,which can effectively inhibit the initiation and propagation of cracks and greatly improve the service life of the coating.Ultrasonic rolling technology can also reduce the friction coefficient and wear volume of the coating surface.The wear form changes from abrasive wear and adhesive wear to layered wear.The above results show that ultrasonic rolling technology,as a post-treatment technology of high-speed laser cladding,can not only eliminate the defects such as poor surface quality and residual tensile stress caused by high-speed laser cladding technology,but also significantly refine the grains,improve the hardness,elastic modulus and friction and wear properties of the coating surface,and significantly improve the forming quality of the coating surface.