Electrochemical Corrosion Behaviors Of Si₃N₄/1Cr18Ni9Ti Co-continuous Composites

Due to the further acceleration of the development of the high-speed rail Electric Multiple Unit under the new situation,the existing materials such as hubs and brake pads must be replaced,and the comprehensive performance of single-phase metal or alloy materials can not meet the requirements.Moreover,the high-strength,wear-resistant and corrosion-resistant materials used in mines,metallurgy,machinery and other industries are also unable to adapt to the higher requirements set forth under increasingly harsh production conditions.In response to these problems,the research team of Zhang Jinsong from the Institute of Metal Research,Chinese Academy of Sciences,developed the Si3N4/1Cr1 8Ni9Ti co-continuous composites and conducted detailed testing and comprehensive characterization of the composites in terms of fracture,wear and corrosion.This essay mainly studies the electrochemical performance,corrosion behavior and mechanism of Si3N4/1Cr18Ni9Ti co-continuous composites,provides theoretical basis and technical support for the continuous optimization of the preparation process.This essay adopts polymer pyrolysis combined with reactive sintering(organic foam impregnation)method to prepare three kinds of porous Si3N4 ceramic foam ceramics.This essay adopts pressure casting to make the 1Cr18Ni9Ti combined with Si3N4 foam ceramic and prepared three kinds of Si3N4/1Cr18Ni9Ti co-continuous composites.In contrast,this essay prepared 1Cr18Ni9Ti stainless steel specimens and Si3N4 ceramic compact specimens.After welding the back of the working face of the sample,this test sealed and embedded the non-working face,polished and cleaned the working face to prepare a sample for electrochemical test.This essay adopts Princeton Applied Research PARSTAT 4000 electrochemical test system and puts the standard salt concentration in seawater as a benchmark to measure the open circuit potential and tafel curve of the Si3N4/1Cr18Ni9Ti co-continuous composites and its matrix material in deionized water,0.6mol/L Sodium Chloride Solution,0.6mol/L hydrochloric acid,0.3mol/L,sulfuric acid,0.2mol/L boric acid 0.6mol/L nitric acid,0.6mol/L sodium hydroxide solution respectively.Increasing or decreasing the concentrations of boric acid,sodium hydroxide solution and sodium chloride solution proportionally,and tested open circuit potential and tafel curve of the Si3N4/1Cr18Ni9Ti co-continuous composites and their matrix materials.The co-continuous composites corrosion resistance in different solutions are worse than1Cr18Ni9Ti,less than Si3N4 ceramics.The corrosion rate of Si3N4/1Cr18Ni9Ti co-continuous composites increases with the increase of sodium chloride concentration,decreases and then increases with the increase of boric acid concentration,increases and then decreases with the increase of sodium hydroxide solution concentration.This essay examined the electrode surface of Si3N4/1Cr18Ni9Ti co-continuous composites and its matrix material after electrochemical testing of 0.6mol/L sodium chloride solution by scanning electron microscopy and energy spectrum analysis.This essay also etched the work surface without electrochemical testing and examined by metallographic microscope,scanning electron microscopy and energy spectrum analysis to observe and test the morphology and composition of grain and grain boundary.The electrochemical corrosion of Si3N4/1Crl8Ni9Ti co-continuous composites mainly caused pitting corrosion,pitting corrosion and crevice corrosion,and the formation of oxides and chlorides,and the precipitation of carbides.Corrosion of ceramic and metal at the junction of the more obvious,is the main part of the corrosion occurred.Small holes and mesoporous composite stainless steels are ferrite grains instead of austenite grains and the ? phase precipitates on the ferrite matrix,resulting in the reduction of the lattice densities of the stainless steel phases and the decrease of the structural stability.Content of chromium increases and the content of nickel decreases in the interface between stainless steel and silicon nitride of small holes and mesoporous composite,which results in the low chromium content of stainless steel and the corrosion resistance(especially intergranular corrosion resistance)decreases.Macro-porous composite stainless steel phase is austenite grain.There are at least two new phases between the stainless steel phase and the ceramic phase.Boundaries of each phase are obvious,and the potential difference exists between the phases to form the original cell structure,which aggravates the corrosion rate.It forms oxides in the new phase.From the stainless steel phase to the silicon nitride phase,the content of chromium and nickel in each phase gradually decreases and the corrosion resistance decreases.