Study Of Structural Characterization And Local Corrosion Of Ti_0.3（CoCrFeNi）_0.7 High Entropy Alloy

With the rapid development of the economy,human society’s growing demand for energy,oil and gas extraction environment was becoming more and more severe.Corrosion failure of metals had become a great threat to the safe development of oil and gas.At present,the development of novel corrosion-resistant alloys urgently became the goal to cope with the severe service conditions.High entropy alloys had received wide attention due to a series of excellent mechanical properties such as high strength,high hardness,high wear resistance and special functional properties such as irradiation resistance,catalytic properties and hydrogen storage properties.However,the corrosion resistance of high-entropy alloys was still in the experimental research stage,and there was a general lack of corrosion behavior and mechanism research in the actual service environment,and the research on the corrosion behavior of high-entropy alloys in the acidic environment containing H₂S was in a vacant state.In this paper,the Ti_0.3（CoCrFeNi）_0.7 high-entropy alloy was prepared by vacuum arc melting of 5 elements,Co,Cr,Fe,Ni and Ti,and its structure and physicochemical properties were analyzed by investigating the relevant literature on the corrosion behavior of high-entropy alloys.The microstructure of Ti_0.3（CoCrFeNi）_0.7 high-entropy alloy is dendritic and interdendritic,FCC,BCC and Laves phase structures were formed.Corrosion properties were investigated by linear polarization resistance（LPR）potentiodynamic polarization and electrochemical impedance spectroscopy（EIS）in H₂S-HCl-H₂O simulated solution.The experimental results showed that the corrosion behavior of Ti_0.3（CoCrFeNi）_0.7 high-entropy alloy was influenced by the p H and temperature.With the decrease of solution p H,the self-corrosion potential of Ti_0.3（CoCrFeNi）_0.7 high-entropy alloy decreased and the self-corrosion current density increased,and the decrease of p H had an accelerating effect on the corrosion of high-entropy alloy.The increase in solution temperature affects the corrosion behavior of the alloy through two aspects,on the one hand,the increase in temperature ionic activity increased,the rate of chemical reaction increased;on the other hand,the temperature affected the solubility of H₂S in solution,reducing the possibility of stress corrosion cracking,the two aspects synergistically affected the corrosion of the alloy.60℃～80℃,the reaction was affected by the solubility of H₂S,90℃,corrosion behavior was mainly controlled by temperature.The corrosion behavior of Ti_0.3（CoCrFeNi）_0.7 high-entropy alloy in H₂S-HCl-H₂O simulated solution was investigated by simulation experimental method,and the corrosion morphology and corrosion products of the alloy were analyzed by XRD,SEM,EDS,and super-field depth microscopy.The experimental results showed that the corrosion rate of Ti_0.3（CoCrFeNi）_0.7 high-entropy alloy shows a trend of decreasing and then increasing with the increase of ambient temperature,which is consistent with the electrochemical research results on the corrosion resistance of the alloy by temperature.In the H₂S-HCl-H₂O environment,H⁺,Cl^-,HS^-,S^2-and other corrosive ions act in concert,and the alloy is susceptible to stress corrosion cracking,leading to a serious localized corrosion phenomenon.In this comparative study,the corrosion behavior of Ti_0.3（CoCrFeNi）_0.7 high-entropy alloy and 316L stainless steel was investigated by immersion test in H₂S-HCl-H₂O simulated solution.The results showed that the corrosion rate of the high-entropy alloy has a negative temperature gradient,and the corrosion rate of the alloy decreases with increasing temperature and is significantly lower than that of 316L stainless steel,indicating that the corrosion resistance of Ti_0.3（CoCrFeNi）_0.7 high-entropy alloy is better than that of 316L stainless steel.