Study On Laser Cladding And Zirconium Coating Of SP-700 Titanium Alloy For Steam Turbine Blade

SP-700 titanium alloy is outstanding for its high strength,corrosion resistance and heat resistance,especially in hot working,cold working and fatigue properties,it is widely used in automobile parts,ships,trains,high-speed trains,sports tools and so on.In the research of steam turbine blades,SP-700 titanium alloy has gained wide attention and recognition,which is expected to replace Ti-6Al-4V alloy as the material of steam turbine blades,the Zr-infiltrated layer formed on the surface of pure titanium,Ti-6Al-4V and TC11 titanium alloy can strengthen the surface of the three alloy substrates.The hardness of the cladding layer is higher than that of the substrate,and the oxidation resistance and wear resistance of the cladding layer are enhanced greatly,therefore,laser cladding Zr treatment on SP-700 titanium alloy is the best way to improve the surface strengthening effect.In this paper,Ti-based Zr laser cladding layer was prepared on the surface of SP-700 titanium alloy,which was used as the base material of steam turbine blade The effects of scanning speed and powder feeder revolution on the macromorphology,layer width,layer thickness,dilution rate,crack rate,microstructure,layer composition,microhardness,friction coefficient,wear morphology and wear resistance of the cladding layer were studied The optimum process was determined.It provides a scientific basis for the improvement of SP-700 titanium alloy blade and its application in steam turbine,and provides an experimental reference and theoretical support for metal surface modification.The main research work of this thesis is as follows:(1)The effects of scanning speed and powder feed speed on the surface,cross section,fusion width,fusion height,fusion depth,dilution,lap width,fusion thickness and crack rate of the cladding layer were investigated.With the increase of the rotating speed of the powder feeder,the surface of the cladding layer changes from shallow to dark,the roughness increases,the fish lines increase and the surface effect becomes worse,the melting width is the smallest at F4 rotating speed,the melting height is on the rise,the dilution rate is on the decline,the lap width is on the level,the melting thickness is on the increase after F4 rotating speed,the crack rate is on the rise,and the crack rate is the biggest at F8 rotating speed.As the scanning speed increases,the Surface roughness increases and the effect becomes worse;the boundary smoothness decreases and defects are more likely to occur;and the number of cracks increases.(2)The effects of scanning speed and powder feeder speed on the hardness and friction and wear properties of the cladding layer were analyzed.In the aspect of hardness performance:The hardness of the cladding zone is the highest,the further away from the cladding layer,the lower the hardness is,and the hardness of the Matrix is reduced rapidly in the heat affected zone,the hardness of the cladding zone is the highest in the V6/F4 process,the average hardnes s of the single channel is 674.5 HV,which is 1.6 times higher than that of the Matrix It’s better on multiple tracks,697.8HV,up to 1.8 times higher,and has a lower hardness at F8.Friction and wear performance:With the increase of powder feeder speed,the friction coefficient of the sample increases.In the"stable" stage,the friction coefficient at F6 and F8 speeds exceeds the Matrix Coefficient,and the wear morphology of the cladding layer at F8 speeds has powdery debris,the Matrix is torn on both sides,and there are a few areas of F6 rotation With the increase of scanning speed,the rougher the wear appearance is,the wider the friction mark is,the higher the wear resistance is at F2-F4 speed,the higher the wear resistance is at V6/F4 process,and the worse the wear resistance is at F6-F8 speed,this is due to the uneven structure of the junction and the propagation of its own cracks.The higher the scanning speed,the worse the wear resistance.(3)The optimum parameters of laser cladding layer are:the scanning speed is 6mm/min,the powder feeder revolution is 4rpm;the surface forming quality is better at this time,with medium thickness and width,average dilution rate and crack rate of the clad layer;uniform tissue distribution,clear crystals and low dispersion in the clad layer;high microhardness,with an overall increase of about 1.8 times relative to the substrate;good friction wear morphology No obvious defects and good wear resistance.