Effect Of Oxide Film On Cavitation Erosion-corrosion Behavior Of Engineering Alloys

Seawater is a kind of corrosive medium.Marine equipments used in the marine environment,such as marine propellers,water pump impellers,hydro turbines and offshore machines,face the severe problem of cavitation erosion-corrosion.Therefore,studying the mechanism of cavitation erosion-corrosion of marine engineering materials,especially the influence of oxide film on the cavitation erosion-corrosion behavior,and providing important theoretical support for the development of surface anti-cavitation erosion-corrosion protection technology is very necessary.In this paper,mild steel 1050,nickel-aluminum bronze alloy(NAB)and 316 L stainless steel were selected as the research materials.The pulse and continuous cavitation erosion experiments combined with weightless analysis were used to compare the differences of cavitation erosion-corrosion behavior of alloys between the two experimental modes.The in-situ electrochemical test was used to analysis electrochemical behavior and surface change of alloys during pulse cavitation erosion-corrosion.In addition,electrochemical atomic force microscope(EC-AFM)was used to observe the initial formation process of the oxide film on the surface of the alloy in 3.5 wt.% Na Cl solution.Scanning electron microscopy(SEM),energy-dispersive spectroscopy(EDS),X-ray photoelectron spectroscopy(XPS)and X-ray diffraction(XRD)semi-quantitative analysis technologies were carried out to analyze the composition of the oxide film and to observe the morphology of samples after cavitation erosion.The research showed that the oxide film formed on the surface of mild steel 1050 was porous and couldn't form rapidly when the absence of cavitation.However,the oxide film could form rapidly on the surface of NAB alloy and 316 L stainless steel.Besides the oxide film was relatively dense and protective.Cavitation erosion-corrosion damage includes cavitation,corrosion as well as the synergy between cavitation and corrosion.In the pulse mode,the total weight loss and synergistic weightlessness of mild steel 1050 were greater than that of continuous mode.That was because the porous corrosion film of the mild steel 1050 was not protective and couldn't protect the matrix from cavitation erosion.In contrast,the oxide film on the surface of NAB alloy and 316 L stainless steel quickly repaired,which was dense and was of good mechanical properties.Therefore,in the pulse mode,the cavitation erosion-corrosion weight loss and synergistic weight loss were less than that under continuous mode.Among them,in the process of pulse cavitation erosion-corrosion of 316 L stainless steel,the oxide film formed via corrosion reaction was of good resistance to cavitation damage,and the value of synergistic weight loss was negative.Namely the synergy between cavitation and corrosion was negative.The oxide film formed on the surface of the NAB alloy in pulse mode reduced the positive synergistic effect compared with that of the continuous cavitation corrosion process.In the pulse cavitation corrosion process of the mild steel 1050,the positive synergy between corrosion and cavitation was intensified.