Research On Metal Local Corrosion Damage Evolution Based On Cellular Automata Method

Corrosion is one of the most common failure modes of metal materials.Local corrosion is characterized by rapid corrosion destruction,strong concealment,difficulty in prediction and control.Compared with general corrosion,it is more harmful and more prone to catastrophic accidents.Therefore,it is of great value and significance to predict the corrosion morphology of metals,study the evolution process and regularity of metal local corrosion damage,and explore the local corrosion mechanism of metals.Based on the mechanism of metal corrosion and the theory of Cellular Automata(CA),the basic physical and chemical processes in local metal corrosion under corrosive environment are analyzed,and the corresponding physical models are obtained.The corrosive system is discretized into ordered cellular grids in the space of cellular automata.Local evolution rules are formulated,and the cellular automaton model corresponding to the problem is established to simulate the evolution process of metal local corrosion damage.The main research contents and conclusions are as follows:(1)According to the dissolution and passivation phenomena in the metal corrosion process,three parameters of electrolyte concentration c,dissolution probability P_d and passivation probability P_p are introduced to investigate the influence of different parameters on the corrosion evolution process of metal corrosion.The results show that the simulated results of pit morphology are consistent with the actual pit morphology;with the increase of c,P_d and the decrease of P_p,the equivalent radius,equivalent depth and the number of dissolved metal cells increase,the metal dissolution rate accelerates,and the pit expands continuously;when P_p increases to the same level as P_d,the metal dissolution and passivation are in dynamic equilibrium,and the pit hardly expands.(2)Based on the mechanism of metastable pitting corrosion of metals,a cellular automaton model of metastable pitting corrosion process was established,and the corrosion morphology of pitting pits at different dissolution probabilities was obtained.According to the simulation results,the current-time curve and current density-time curve have a relationship of I?t~2 and i?t respectively.The influence of different simulation parameters on the simulation results is analyzed.It is determined that when the grid constant q=3.5 nm and the dissolution probability d=0.1~0.25,the simulation results can reflect the real etching pit morphology and agree with the experimental results.(3)Based on the autocatalytic theory of occluded corrosion batteries,a CA model framework is proposed to simulate the steady pitting corrosion process of metals.Based on the heterogeneity of corrosion rate in space,the parametric models of corrosion probability are established by introducing parameters such as?,?and?into the model.?is used to control the overall corrosion probability in the pit;?defines the relative position of two regions with different reaction probability in the pit;and?adjusts the reaction probability in these two regions.