Cavitation Erosion Behavior Of Amorphous/Microcrystalline Fe-Based Composite Coatings Prepared By Laser Cladding

TC4 titanium alloy is widely used as propeller material in Marine environment because of its high specific strength,rigidity and excellent corrosion resistance.However,cavitation erosion phenomenon usually occurs in the environment in which the equipment is used,damaging TC4 materials,resulting in mechanical vibration and noise,reducing the operating efficiency and safety of the equipment,and seriously affecting the reliability and service life of the equipment.Therefore,it is necessary to take corresponding measures to protect the surface of TC4 titanium alloy,in order to reduce the damage caused by cavitation erosion on its surface,and prolong the service life of key parts of TC4 material manufacturing.In this thesis,the laser cladding coatings of amorphous/microcrystalline Fe-based powder containing 0%,5%,10%and 15%microcrystalline Fe-based powder was used as the main research objects to study the cavitation protection effect of the composite coatings on TC4 substrate surface.Firstly,amorphous/microcrystalline Fe-based powder composite coatings were prepared on the surface of TC4 substrate by Laser Cladding technology,and the phase composition,surface morphology,density and surface porosity of the coatings were characterized.The results show that during the laser cladding process,more Fe₃C and（Cr,Mo,Fe）solid solution are formed in the amorphous/microcrystalline Fe-based powder composite coatings,which means obvious solution strengthening effect,and thus the surface hardness of the coatings is significantly improved.The surface hardness of the coatings is obviously harder than that of TC4 matrix（390Hv）,especially A/M-5 coating reaches 699Hv.At the same time,A/M-5 coating has the highest density and the least surface microdefects,showing the better mechanical properties.Secondly,the cavitation erosion tests of A/M-0,A/M-5,A/M-10,A/M-15 coatings and TC4 substrate were carried out for 6h in 3.5%Na Cl solution to analyze their material loss and surface morphology after cavitation erosion tests and explore their cavitation erosion resistance.After cavitation erosion tests,the volume loss and surface thinning thickness of the coatings are less than that of TC4 substrate.The surface roughness of coatings is significantly lower than that of TC4 substrate.It can be seen that the material loss of laser cladding coatings is obviously less than that of TC4,and the surface morphology of coatings after cavitation erosion tests is better than that of TC4.Therefore,the cavitation resistance of the coating is obviously better than that of TC4.Among the four kinds of coatings,A/M-5 coating has the least material loss and its surface morphology after cavitation erosion tests is better.It also has the longest incubation period of cavitation and the shortest ascending period of cavitation.Therefore,A/M-5 coating has the best cavitation erosion resistance among all samples.Finally,electrochemical corrosion tests and 192h salt spray corrosion tests were carried out on A/M-0,A/M-5,A/M-10,A/M-15 coatings with 3.5wt%Na Cl solution as corrosion medium.The results show that the 5%microcrystalline Fe-based powder coating has the lowest corrosion rate and the largest arc radius,showing the best electrochemical corrosion behavior.After salt spray corrosion,the surface morphology of the 5%microcrystalline Fe-based powder coating is the most flat,without too much corrosion,which also shows the best salt spray corrosion resistance.In this thesis,the cavitation erosion performance and partial corrosion performance of amorphous/microcrystalline Fe-based composite laser cladding coatings were studied,and their cavitation erosion protection effect on TC4 material was explored,which provided a certain reference for the wider application of this kind of coatings.There are 54 figures,16 tables,101 references in the thesis.