Stress Corrosion Behavior Of Ti-6Mo-5V-3Al-2Fe-2Zr Alloy

Titanium alloys have been widely used in marine engineering equipment because of its excellent mechanical properties and corrosion resistance.With the vigorous development of ocean engineering,the mechanical properties of titanium alloy used in ocean engineering are demanded in greater and greater.The mechanical properties of near-βtitanium alloy can be improved greatly after heat treatment,and it has great application prospect in marine engineering.However,there are few kinds of near-βtitanium alloys developed for marine engineering in China,and there are relatively few studies on their stress corrosion behavior in marine corrosion environment.Therefore,the stress corrosion behavior of Ti-6Mo-5V-3Al-2Fe-2Zr（wt.%）,with different phase composition in 3.5wt.%Na Cl solution was studied in this paper,in order to provide reference for the service of near-βtitanium alloy in marine engineering equipment application.The electrochemical test results showed that the alloys with different phase composition had different corrosion resistance in 3.5wt.%Na Cl solution.The singleβphase（M2）alloy had the highest corrosion resistance,followed byβ+αphase（M1）alloy,and theβ+coarseαphase（M3）alloy had the worst corrosion resistance.The M2alloy had the highest self-corrosion potential of-0.35 V,the lowest self-corrosion current density of 3.59×10^-7 A/cm²,the lowest passivation current density of 3.30×10^-6A/cm²,and the highest polarization resistance value of 1.58×10⁵Ω·cm².After the tensile test of slow strain rate in dry air and in 3.5wt.%Na Cl solution,the stress corrosion sensitivity index of the alloy in 3.5wt.%Na Cl solution was calculated based on the plastic loss of the alloy.The stress corrosion sensitivity index with different phase composition all increase with the increase of strain rate,indicating that the increase of strain rate increases the stress corrosion tendency of the alloys.At the same strain rate,M3 alloy had the highest stress corrosion sensitivity index,followed by M1alloy,M2 alloy had the lowest stress corrosion sensitivity index,indicating that M3alloy has a relatively higher stress corrosion tendency.The presence ofαphase increases the stress corrosion tendency of the alloy,and the size ofαphase has a significant effect on the stress corrosion tendency of the alloy.Based on the results of constant stress loading in 3.5wt.%Na Cl solution for 15days,the tensile strength,yield strength and reduction in area of the alloy all decreased after different stress loading.Compared with the smaller loading stress,when the loading stress value reached a larger level of 900 MPa,the tensile strength,yield strength and reduction in area decreased the highest.