Microstructure And Properties Of Laser Cladding Ceramic Particle Reinforced Iron-Based Coating

The turbine blade is the core component of the marine hydropower system.The performance of the turbine blade in the hydropower system to resist seawater corrosion,hard particle wear and fracture will directly affect the efficiency and safety of the marine hydropower work in the complex marine environment.Therefore,it is particularly important to develop materials with low cost,corrosion resistance,wear resistance and high toughness.Iron-based alloys with high hardness and other properties can improve the ability of turbine blades to resist damage under marine service conditions.Compared with the traditional surface modification technology,laser cladding technology has the characteristics of small heat affected area and strong bonding ability between coating and substrate,which is widely used.(1)The effects of laser power and laser scanning rate on the formation,phase,hardness and microstructure of the lap cladding coating were studied by changing the laser cladding process parameters.Through the comprehensive analysis of the obtained coating thickness,crack number,section porosity and grain refinement degree,it is concluded that 1200 W and 40 mm/s are the optimal process parameters.Under the optimal process parameters,the coating is composed of hard phase and ductile phase caused by element segregation.(2)The iron-based coatings reinforced by 0 wt.%,1 wt.%,3 wt.%and 5 wt.%nickel-coated alumina were prepared by using the optimal laser cladding process parameters,and studying the effects of different nickel-coated alumina contents on the microstructure,phase,hardness,corrosion resistance,wear resistance and fracture toughness of iron-based coatings.Nickel-coated alumina can refine the structure of iron-based coating,reduce the segregation of elements in different structures,and improve the hardness of the coating.The 3 wt.%nickel-coated alumina reinforced iron-based coating has lower current corrosion density and higher impedance.The excessive 5 wt.%nickel-coated alumina content makes the alumina particles aggregate into hard particles in the coating,thereby weakening the corrosion resistance of the iron-based coating.With the increase of nickel-coated alumina content,the coating changes from severe abrasive wear to delamination wear and oxidation delamination wear of oxide film.The fracture toughness gradually increases with the increase of nickel-coated alumina content,but the 5 wt.%nickel-coated alumina-reinforced iron-based coating appears unrelated cracks.It is considered that the 3 wt.%nickel-coated alumina-reinforced iron-based coating has better fracture toughness,and the crack presents typical brittle fracture and ductile fracture of hard phase and ductile phase.(3)The 3 wt.%nickel-coated alumina reinforced iron-based coating with the best comprehensive performance was heat treated.The effects of different heat treatment temperatures on the microstructure,phase,hardness,corrosion resistance,wear resistance and fracture toughness of nickel-coated alumina reinforced iron-based coating were studied.Heat treatment makes the hard phase structure in the coating finer and more uniform.The hardness,corrosion resistance and wear resistance of the nickel-coated alumina-reinforced iron-based coating gradually increase with the increase of the heat treatment temperature.The heat treatment temperature reaches 1000℃ and weakens the coating performance.The nickel-coated alumina-iron-based coating has the best corrosion resistance and wear resistance at 800℃ heat treatment temperature.The fracture toughness of the coating increases gradually with the increase of heat treatment temperature,and the toughness increases little after 800℃.