The Study Of Stresscorrosion Cracking Behavior And Corrosion Electrochemical Behavior Of Titanium Alloys

Titanium alloy is the most promising new metal material in our country even the world and has been widely applied in some pillar industries such as aerospace, military equipment and industrial production, etc. However, Ti alloy can still suffer from the environmental corrosion despite that it belongs to the high strength corrosion-resistant metal materials. In this paper, the corrosion behaviors of three kinds of Ti alloys (TC4、TC18、TC21) in NaCl solution environment were observed by means of real-time potential monitoring, cyclic voltammetry scanning, wedge loaded WOL pre-crack sample method combined with the method of scanning electron microscope and the resistant properties to pitting and stress corrosion in NaCl solution environment were evaluated. The main research contents and results are showed as follows:1、The electrochemical behaviors of three different types of Ti alloys in the environment of constant temperature of35℃and NaCl solution with mass fraction of3.5%were measured by electrochemical methods. The data of CV indicates that all three kinds of Ti alloys show better resistant property to pitting corrosion in this experiment. The broken potential are1.625V,1.671V and1.842V for TC4, TC8and TC21respectively representing the excellent corrosion resistance over steel and aluminum alloy or other metal materials. Furthermore, TC21has the highest broken potential and the best self-healing ability of passive film when pitting happens among the three types, while TC4has a similar pitting corrosion resistance similar to TC8, but the self-healing ability of TC4is a little better than that of TC8.2、The stress corrosion behaviors were measured by wedge loaded WOL pre-crack sample method. As the result shows, all three kinds of Ti alloys have better stress corrosion resistance and the regularity of the growing rate of cracks is stable that it is fast initially as time extension, while a to Ki shows an approximate linear relationship with a negative slope. As time goes on a increases with the decrease of Ki, which means with the extension of cracks the stress reduces. The curve of the extension rate of cracks (da/dt) to stress intensity factor (KI) indicates generally the stress intensity factor and the growth rate of cracks are both decrease as time extends. And the curve meets an apparent platform where the rate changes gently as KI within certain limits, meaning the stress corrosion rate reaches a steady state when stress intensity factor is in this limits. Ki for TC4, TC8and TC21is62-64MPa.m-5,67-69MPa.m-0.5,and72-75MPa.m-0.5respectively, the three kinds of Ti alloys have better stress corrosion resistance and the TC21is the best in stress corrosion resistance.