Research On Cladding Process And Modification Of Laser Cladding Nickel-based Alloy Coating On 304 Stainless Steel

As a huge industrial group,the pump and valve industry plays an important role in the national economic construction.Its products are widely used in petrochemical,a erospace,electric power,steel and military industries.The key components of pump v alve products,such as spool seat,impeller and shaft,work under long-term wear cond ition,which is prone to wear failure and high cost.In this paper,for the surface modification and repair of some key components in pump and valve products,the Ni60 alloy coating is prepared on the surface of 304austenitic stainless steel by laser cladding technology.The effects of different cladding parameters on the macroscopic morphology,crack sensitivity and mechanical propertie s of nickel-based coatings were systematically studied,and the cladding process was o ptimized to produce high-quality large-area laser cladding coatings.A nickel-based com posite coating layer is prepared by adding a gradient content of rare earth LaB₆ to th e Ni60 alloy powder.The microstructure,microhardness,surface wear and corrosion re sistance of the nickel-based cladding layer were analyzed and tested.The main results and conclusions are as follows:1.Comprehensive evaluation of macro-morphology,cracking sensitivity and mecha nical properties of laser cladding layer was carried out.Laser power 1500W,scanning speed 120mm/min,powder feeding voltage 7V,preheating temperature 200?,nickel-b ased laser cladding layer has good slag removal,smooth surface,no obvious ripple,lo w dilution rate,good forming quality,low crack sensitivity and high surface macro-har dness,which is the best laser cladding process parameters.2.The nickel-based laser cladding layer is a non-equilibrium rapid solidification s tructure,which is mainly composed of a relatively large dendritic structure and strip-li ke,massive,dendritic hard phase particles dispersed on the dendritic matrix.The main phases are solid solution?-?Ni,Fe?,intermetallic compound FeNi₃,Cr₄Ni₁₅W,carbide?Cr,Fe?₂₃C₆ and boride CrB,etc.3.After laser cladding treatment,the micro-hardness of the nickel-based cladding layer is significantly higher than that of the substrate,the friction coefficient and wear rate of the coating are reduced,the wear resistance is obviously improved,and the c orrosion resistance is improved.When the laser power and scanning speed are low,it's easy to obtain a nickel-based cladding coating with high microhardness.In a certain range,the hardness of the coating increases with the increase of powder feeding volt age,after the pre-heat treatment,the average hardness of the cladding layer gradually decreases;the laser power has little effect on the wear resistance of the coating;the s canning speed and the powder feeding voltage The wear resistance of the coating has a significant effect.When the scanning speed is 120 mm/min and the powder feedin g voltage is 7V,the wear rate of the cladding layer is the smallest and the wear resis tance of the cladding layer is the best.With the increase of laser power,scanning spe ed and powder feeding voltage,the corrosion resistance of nickel-based coatings is gra dually improved,and the corrosion resistance of the cladding layer is degraded due to pre-heat treatment of the substrate.4.The multi-pass bonding treatment of the single-pass cladding layer can realize the preparation of a large-area laser cladding layer,which is of great practical signific ance.Through the test and analysis of the forming quality,microhardness,wear-resistan ce and corrosion resistance of the laser cladding layer under different lapping rates,th e optimum lapping rate is 30%.5.The addition of rare earth LaB₆ improves the crack sensitivity of nickel-based coatings.When the content of LaB₆ is 0.5%,there is no crack on the surface of the cladding layer.With the increase of rare earth content,the structure of cladding layer fines gradually,the carbide phase precipitated on the dendritic matrix changes from M₂₃C₆ to M₇C₃,and the content of CrB in hard phase increases.After adding rare earth LaB₆,the hardness of the nickel-based cladding layer is improved.When the content is 0.3%,the hardness of the cladding layer is the highest(average hardness 696HV_0.2).At the same time,the friction coefficient and wear rate of the cladding layer are e ffectively reduced,which shows that the wear resistance of the coating is improved.With the increase of LaB₆ content,the pitting potential of the coating increases,the p assivation zone of the coating is obviously widened,and the corrosion resistance of th e nickel-based cladding layer is improved.