Preparation Of Laser Modification Layer On17-4PH Stainless Steel And Study On Its Cavitation Erosion Performance

17-4PH stainless steel has been widely applied in large turbines and turbine blade forgood corrosion resistance and mechanical properties. Because of the cavitation corrosion inlong-term service process, the damaged flow passage components have severe impact onsafety of utility-type unit and work efficiency. In consideration of safety, economic benefitsand long-term development strategy, high technology means are often used to prolong theservice life of such parts to meet the needs of industrial development. Therefore, this paperreports an experiment, in which laser cladding and laser cladding NiTi alloy processingwere prepared on17-4PH stainless steel surface using YAG solid pulse laser and CO2laser.Metallographic microscope, scanning electron microscope (SEM), energy dispersive X-ray(EDX) microanalysis, X-ray diffraction analysis (XRD), microhardness tester andultrasonic cavitation instrument were employed to observe microstructure andcompositions of coatings and analyze cavitation erosion resistance.The result shows that coating with refined organization on17-4PH stainless steeltreated by YAG solid pulse laser got fine acicular martensite structure. Surface hardnessincreases by about fifty HV. After480℃aging temperature for3h, the organization ofSolid solution state17-4PH steel and laser fused sample was more even. With theprecipitation ε-Cu strengthening phase to improve surface hardness, hardness can increaseto465HV after fused aging treatment. Using the optimized process parameters of outputpower P=3kW、the scanning speed V=5mm/s、spot size D=10×1mm, the NiTi alloycladding layer with good metallurgical bond was prepared. The cladding structure wasdendritic structure, and binding region structure was typical equiaxed crystal. Through thesecond phase strengthening and the refined crystalline strengthening mechanisms, thecladding layer has been strengthened, with microhardness of about700Hv. After lasersurface melting treatment and ageing treatment, the fatigue resistance of the surfacemelting layer was improved through the refined crystalline strengthening and increased sub-structure of the melting layer. The surface plastic deformation was equally distributedwhen suffering cavitation damage. The cavitation erosion resistance was improved throughextending cavitation erosion incubation period. The NiTi alloy cladding layer showedsuperior cavitation resistance，which attributed to superelasticity and other characteristicsof the NiTi alloy. The NiTi alloy cladding layer absorbed most of the energy of thevacuolar impact by stress induced martensite phase transformation. In addition, fine grainmicrostructure of the NiTi alloy laser cladding layer improved the performance ofcavitation erosion resistance further. But the second phase particles played a negative rolefor the cavitation resistance of the cladding layer. Compared with17-4PH steel, thecavitation erosion resistance of NiTi alloy cladding layer has increased five times.