The Study On Susceptibility To Stress Corrosion Cracking And Hydrogen Embrittlement Of Titanium And Titanium Alloy In Seawater

Titanium and its alloys are attractive choice for application in various industrial aspects because they have high strength-to-density ratio and excellent corrosion resistance. However, titanium and its alloys show the susceptibility to stress corrosion cracking and hydrogen embrittlement due to the high strength, etchant solution and easy to generate hydrogen when they are coupled with other more negative metal or excess cathodic protection happens. It is necessary to study the corrosion behavior and its protection of titanium and its alloys in seawater. It was studied in this work that effect of strain rate and cathodic polarization on the susceptibility to hydrogen embrittlement of TA2and TC4by means of slow strain rate test method and fracture morphology were taken by three-dimension microscope and SEM. The fracture mechanism of strain rate and cathodic polarization was investigated. Thus, after hydrogen charging under a certain current density and hydrogen charging time, corrosion behavior of titanium and its alloy was studied by using potentiodynamic polarization and AC impedance technique.The study on the effect of strain rate on the susceptibility to stress corrosion cracking of TA2and TC4showed that stress corrosion cracking was effected by different strain rate. When the strain rate was0.006mm/min,TC4had susceptibility to stress corrosion cracking. The strain rate was0.008mm/min. TA2had susceptibility to stress corrosion cracking. The titanium and its alloy presented the feature of brittle fracture at this two strain rate. The process of stress corrosion cracking is the results of stress and corrosion working together. This two elements make crack extension and fracture.The effect of hydrogen charing on electrochemical corrosion behavior of titanium and its alloy showed that the Ecorr of TA2and TC4were relatively positive and corrosion potential of TC4was higher than that of TA2.The cathodic polarization of TA2and TC4shifted to the right as well as the hydrogen evolution potential shifted to positive with the increase of hydrogen charing time. When the hydrogen charing current density was-6mA/cm2,the hydrogen charing time had effects on anodic polarization of TA2and TC4.The obvious influence on anodic polarization of TA2after hydrogen charing4h.But the influence on anodic polarization of TC4wasn’t obvious after increasing of hydrogen charing time.It was studied in this work that effect of cathodic polarization on the susceptibility to hydrogen embrittlement of titanium and its alloys indicated that elongation、time to fracture decreased with the shifting potential in the negative direction among Ecorr-1.5V. The SEM results showed that alloy the rupture morpholoyies changed ductile fracture from to quasi-cleavage fracture. Among Ecorr and-0.7～-1.3V, the fracture form was mainly ductility fracture. When the potential shifted to-1.5V, the fracture form transform into brittle fracture.