Preparation And Properties Studies Of Laser Cladding Al₂O₃@Ni Composite Coating

The effects of different cladding powders on the preparation of coatings were studied and analyzed.The results show that the forming effect of Al₂O₃@Ni composite coating is better than that of pure Al₂O₃ powder and Al₂O₃-Ni mixed powder.The Al₂O₃@Ni composite coating has fine and uniform structure,thick thickness and good bonding with the matrix,which improves the agglomeration and reduces loss of Al₂O₃ particles in the cladding layer.The structure of the composite coating is composed of cellular crystals,columnar crystals with directional growth and equiaxed crystals.The changes of macro-size and dilution rate of composite coatings under different process parameters were discussed.With the increase of laser power,the height of cladding layer decreases,the width increases,the molten pool deepens and the dilution ratio increases,and the number of pore increases,and cracks appear.With the increase of scanning speed and coating height,the width of cladding layer,the depth of molten pool and the dilution rate will decrease,and the porosity will change.Thickening the pre-prepared powder,the height of coating increases,the width of cladding layer,the depth of molten pool,the dilution rate decreases,and the porosity varies.The hardness increases first and then decreases from the surface of the cladding layer to the substrate,and the maximum reaches 917.0HV at 0.35mm away from the surface of the cladding layer.The corrosion rate of the matrix and cladding layer increases first and then decreases with time,but the corrosion rate of the cladding layer is much lower than that of the matrix.With the change of time,it is found that the corrosion degree of the matrix is more serious than that of the cladding layer,there are more corrosion pits,and the bright color of the metal is lost,and the thickness is obviously thinner than that of the cladding layer.The Tafel curve analysis shows that the i_corr of the cladding layer is 1.5×10^-7A far less than 8.9×10^-6A of the matrix,and the E_corr is increased by nearly 100 mV.The hardness and corrosion resistance of laser composite coating are greatly improved,which is very helpful for surface modification of 304 stainless steel.