Initial Cavitation Corrosion of Ti-6Al-4V Alloy in LiBr Solution

The evolution of cavitation corrosion of Ti-6Al-4V alloy in LiBr solution was discussed by SEM, roughness profiler, three-dimensional video microscope and electrochemical measurement. The results of the variation of surface roughness value (Rq), mean cavitation corrosion depth and morphological features indicate that there are three stages of cavitation corrosion process of Ti-6Al-4V alloy. At the initial stage, the value of Rq increases linearly with time; at the transition stage, the growth rate of Rq decreases; at the steady-state stage, the value of Rq tends to stabilize. Plastic deformation of the low intensive α phase of Ti-6Al-4V alloy occurs preferentially due to absorption of impact energy generated by bubble collapse, causing uneven deformation of material surface. Passive film on the surface of α phase in local area is easily attacked and fresh titanium alloy substrate is exposed. Small anode and large cathode form due to relatively low electric potential of α phase in comparison with β phase; meanwhile corrosives and corrosion products diffuse fast with the aid of agitation of cavitation, leading to the acceleration of the corrosion dissolution. The growth of pits causes the concentration of local internal stress, which strengthens the mechanical factor, accordingly increases the degree of surface concave and convex. The synergetic effect of mechanics and electrochemical corrosion results in the development of the existing pits and emergence of new pits. Eventually β phase distributed at the boundary of pits falls off and the degree of surface concave and convex becomes small. At the initial stage, electrochemical corrosion promotes mechanical effect of cavitation. © 2017, Northwest Institute for Nonferrous Metal Research. Published by Elsevier BV. All rights reserved.