Study On The Cavitation Erosion Resistance Of Plasma Jet Surface Metallurgy Layer

Cavitation erosion could cause serious consequences and implications because of the reason that it may reduce the using efficiency of the equipments or even lead to the damage of them.The effective way to increase the equipment parts' service life is to protect the surface of them from being cavitation erosion.The technique of plasma jet surface metallurgy can be classified into two aspects:plasma jet surface remeting and plasma jet surface cladding. Metallurgy layer which has an excellent property of heat resistance,wear resistance and low-cost could be obtained by this kind of technology on the surface of the metal,and it has been applied into the fields of mine,metallurgy and military.This technology will attain enormous economic and social benefits if it could be used to improve the cavitation-resistant property of the materials.Study of the process of cavitation damaging of the metallurgical layer has a good theoretical value because of the reason that it can help people to understand the mechanism of cavitation erosion clearly.In the paper,remeted layer which has an excellent property of cavitation erosion resistance has been produced by the technique of plasma jet surface remeting on the basis of the working station of marine cast iron cylinder engine.In view of the hydraulic machines working station,several plasma jet surface coating which has an excellent property of cavitation erosion resistance produced by Fe-based alloy have also been produced by the technique of plasma jet surface cladding.Making use of optical microscope,X-ray diffraction,microhardness tester etc.,the microstructure and conformation of the metallurgy layer were studied in detail.Results showed that,high rigidity and fine tissue were obtained on the surface of cast iron samples through the technique of plasma jet surface remeting,the form and distribution of graphite have also been changed absolutely;coatings of Fe,Cr,C,Ni and B obtained by the technique of plasma jet surface metallurgy on the surface of Q235 steel have fine macro-morphology,which have also achieved metallurgical combination.After adding different components of rare earth oxides,fine tissue was obtained,lacuna and impurity of the cladding layer were also reduced.But it didn't mean that the more quantity of the addition was,the better the property is.The best quantity of rare earth oxides was 0.1%La₂O₃ +0.1%Ce₂O₃.Microhardness profile of the plasma jet surface coating presents graded distribution.Microhardness of the subsurface of the coating is a little higher than that of the surface,which was the highest of the coating.Cavitation erosion resistance of iron remeting layer,untreated samples and samples treated by nitriding were studied by the ultrasonic sonic oscillation magnetostriction strain gage and analytical balance.Changes of the microstructures of the samples during the process of cavitation erosion were also observed by the techonique of scanning electron microscope. Results showed that cast iron samples remelted by plasma jet surface metallurgy had the least mass loss after cavitation erosion and the least cumulative mass loss after cavitation erosion of 12h.Its' property of cavitation erosion resistance was 4.48 times of the untreated samples, and also preceded to the nitriding,which shows good cavitation erosion resistance.With the prolonging of the cavitation erosion time,the superiority of the cavitation erosion resistance of the sample remelted by plasma jet surface remeting is even more obvious than that of the untreated samples and samples treated by nitriding.Main reason of this phenomenon was that the technique of plasma jet surface remeting caused the changement the existence state of the graphite and lead to the refinement of the remeting layers' tissue which has a certain depth. Making use of the same kind of equipment to sduty the cavitation erosion resistance of different kinds of Fe-based alloy coatings obtained by plasma jet surface cladding and compared with the stainless steel of 0Cr13Ni6Mo.Results showed that with the addition of Fe,Cr,C,Ni,B and Si as raw materials,the surface coating had a certain cavitation erosion resistance which was about 0.841 times of the stainless steel of 0Cr13Ni6Mo,which was mainly because of the reason that the existence of the hard grain boundary baffled the plastic deformation of theγ-(Fe,Ni) phase,which also stress-induced theγ-(Fe,Ni) phase transformed into martensite.After the addition of rare-earth,the cavitation erosion resistance of the coating was improved obviously because of the reason that the existance of the rare-earth made the structure of the coating purified,dendritic structure refined,the distance of the secondary dendritic structure reduced and the structure become uniformly dense.But the addition of the rare-earth should be appropriate.Under the experimental condition,with the addition of 0.1Ce₂O₃+ 0.1La₂O₃,surface coating has the best cavitation erosion resistance,which was nearly two times of the stainless steel of 0Cr13Ni6Mo.