Corrosion Behavior Of 17-4PH Martensitic Stainless Steel Under Hydrostatic Pressure And Tribocorrosion

In response to the "National Marine Power Strategy",the development of deep-sea resources and the development of the marine economy are inseparable from the support of advanced deep-sea equipment.As a power element for the development of marine resources,hydraulic seawater plunger pumps have been used in deep-sea environments for a long time and suffered severe corrosion,reducing their service life and restricting the development of the deep-sea field.Therefore,the research on the corrosion behavior of metal materials in the deep sea environment is of great significance.In this paper,we select 17-4PH martensitic stainless steel as the research object.The effect of hydrostatic pressure and tribocorrosion on pitting corrosion behavior of 17-4PH martensitic stainless steels was investigated in 3.5%NaCl solution using electrochemical measurements and stochastic theory.Researched the polarization curve by the statistical analysis models under different hydrostatic pressures of 0.1 MPa and 15MPa.Potentiostatic measurements revealed that the corrosion resistance of 17-4PH martensitic stainless steel with the hydrostatic pressure increased.The frequency of metastable pitting events and the probability of metastable pitting to stable pitting are suppressed under high hydrostatic pressure conditions;Hydrostatic pressure changed the steady-state pitting formation mechanism of 17-4PH martensitic stainless steel.;The growth rate of steady-state pitting corrosion is promoted under high pressure.The improvement of the corrosion resistance of 17-4PH martensitic stainless steel was that hydrostatic pressure inhibited the process of metastable pitting corrosion.The effect of the hydrostatic pressure on the performance of the passive film of 17-4PH martensitic stainless steel was investigated by electrochemical measurements,XPS,Mott-Schottky curves.The analysis results revealed that hydrostatic pressure had four effects on the passive film of 17-4PH martensitic stainless steel:Hydrostatic pressure increased the charge transfer resistance;The experimental results revealed that the hydrostatic pressure didn't change the semiconductor performance of the passive film,which was shown as n-typesemiconductor characteristics.Besides,the carrier density of passive film and the oxygen vacancy coefficient decreased and the thickness of the space charge layer increased under high hydrostatic pressure;The ability of 17-4PH martensitic stainless steel to absorb Cl-decreased under high hydrostatic pressure conditions;XPS results show that the passivation film is composed of Fe and Cr oxides and hydroxides.The increase of Cr(?)oxide content as an important reason for the improvement of the corrosion resistance of 17-4PH martensitic stainless steel under high hydrostatic pressure.The effect of tribocorrosion on the pitting behavior of 17-4PH martensitic stainless steel in tribocorrosion environment was investigated by the in-situ electrochemical test and SEM micromorphology.The results showed that wear accelerates the corrosion and the corrosion resistance of 17-4PH martensitic stainless steel decreased in tribocorrosion environment;Wear changed the metastable pitting behavior and the pitting formation mechanism of 17-4PH martensitic stainless steel.The most important thing was that the pitting formation rate increased,which leads to the corrosion rate of 17-4PH martensitic stainless steel increased.In addition,the wear mechanism of 17-4PH martensitic stainless steel is mainly abrasive and adhesive wear.