Microstructure And Properties Of Laser Cladding 304L+La₂O₃ Coating

Currently,low carbon steel is widely used in various industrial production fields.It has excellent comprehensive performance and low price.However,due to the limitations of the nature of the steel itself,and working in specific working conditions and harsh environments,the surface will wear out and fail.In recent years,laser cladding technology has been developed.As a new surface modification technology,laser cladding can ensure the original mechanical properties of the matrix,and it has excellent properties of high hardness,high temperature resistance,wear resistance and oxidation resistance on the surface of low carbon steel parts.Coating to extend part life and reduce replacement costs.In this paper,laser cladding technology is used to prepare low-cost composite coatings on the surface of 45 steel,304L powder is selected as the cladding material,and three auxiliary means of rare earth,ultrasonic vibration and vacuum environment are used to further improve the performance of the coating and repair the worn surface of the parts.First,the optimal process parameters of laser cladding were determined by observing and analyzing the macro-morphology and cross-sectional morphology of the cladding layer through multiple sets of experimental laser cladding 304L coatings.Then,the rare earth La₂O₃ was added to the cladding powder to prepare a 304L+La₂O₃ composite coating,the influence of different rare earth contents on the cladding layer was studied,the structure and properties of the cladding parts were observed,and the optimal powder ratio was obtained.Follow-up tests are carried out.Next,ultrasonic vibration and vacuum environment were applied as auxiliary processes in the laser cladding test process,and the phase composition,macroscopic appearance,microstructure,microhardness and wear resistance of the cladding layer were detected to explore The performance improvement of 304L+La₂O₃ composite coating by two auxiliary processes.The test results show that the optimal process parameters for laser cladding 304L powder on the surface of 45 steel are:laser power 1800W,scanning speed 4 mm/s,spot diameter 4 mm,and multi-pass overlap ratio of 50%.With the addition of different contents of rare earth La₂O₃,the fluidity of the molten pool was significantly improved,and no cracks occurred on the surface of the coating;the phase composition of the coating was basically the same,which was composed of Cr0.5,but the addition of La₂O₃ reduces the peak value of the diffraction peak of Cr0.19Fe0.7Ni0.11 and increases the peak value of CFe2.5;the microstructure of the cladding layer with a La₂O₃ content of 1%is composed of cellular crystals and columnar crystals,and the microstructure is also arranged.It is the most uniform,dense,and has obvious structure refinement;the microhardness is 703.6 HV,which is 20.6%higher than that of the cladding layer without La₂O₃.The wear mechanism is adhesive wear and fatigue wear,and the wear scar is the shallowest.The analysis shows that 1%La₂O₃ is the optimal addition amount.After applying ultrasonic vibration,the difference between the first cladding height and other secondary cladding heights on the surface of the 304L+La₂O₃ composite coating was significantly reduced;the microstructure was refined due to the cavitation of the liquid metal in the molten pool by the ultrasonic wave;cladding The phase of the layer is composed of Cr0.19Fe0.7Ni0.11,CFe2.5,Cu0.81Ni0.19,which is more Cu0.81Ni0.19than the phase without ultrasonic vibration;the acoustic flow under ultrasonic vibration accelerates the molecular The movement makes the Cu element in the matrix enter the cladding layer to form a new phase,and also makes the distribution of each element uniform;the average microhardness is 758.2 HV,the average friction coefficient is 0.388,and the wear amount is 12.12×10^-3 mm³.The amount of wear was reduced by 12.9%,and the hardness and wear resistance were enhanced.The surface of the 304L+La₂O₃ coating prepared in a vacuum environment is almost not oxidized due to the isolation of oxygen,and there is a certain metal brightness;for cladding in a vacuum environment,the pressure difference between the molten pool and the vacuum can be used to fully release the alloy in the alloy.The gas increases the fluidity of the molten pool.The microstructure in the middle of the coating is composed of a large number of cellular crystals;the distribution of Fe,Cr,Ni,C and other elements in the cladding layer is also more uniform;the average microhardness is 797.9 HV,the average microhardness of the cladding layer is increased by 13.4%compared with the non-vacuum environment;the wear amount of the coating is 11.56×10^-3 mm³,and the wear amount is reduced by 16.9%;the wear form is mainly slight adhesive wear.