Ti-6Al-4V在溴化锂溶液中的初期空化腐蚀研究

Research on the initial cavitation corrosion of Ti-6Al-4V alloy in LiBr solution

摘要:

利用扫描电镜、粗糙度轮廓仪、三维视频显微镜和电化学测试技术研究了Ti-6Al-4V合金在溴化锂溶液中空化腐蚀的破坏过程及腐蚀和空化的协同作用。从粗糙度、平均空化腐蚀深度和微观形貌随时间的变化观察到Ti-6Al-4V合金空化腐蚀破坏的三个阶段：线性增长的初始阶段；增长速率降低的过渡阶段；粗糙度基本不变的稳定阶段。Ti-6Al-4V合金的低强度α相吸收空泡溃灭产生的冲击能优先发生塑性变形,材料表面变形不均匀,在空化作用下α相局部区域表面钝化膜破裂并暴露出钛合金基体,由于α相电位低于β相,形成小阳极大阴极,同时腐蚀物和腐蚀产物在空化的搅拌作用下能够及时扩散,加速了腐蚀溶解,产生的腐蚀坑又导致局部内应力更加集中而加强力学因素,表面凹凸程度增加。空化力学和电化学腐蚀的共同作用使腐蚀坑继续发展并促进了新腐蚀坑的生成,腐蚀坑周边的β相发生脱落,从而导致表面凹凸程度降低。初期阶段,电化学腐蚀促进了空化作用。

Abstract:

In this paper, the evolution of cavitation corrosion of Ti-6Al-4V alloy in LiBr solution was discussed by means of 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 initial stage, the value of Rq increases linearly with time; at transition stage, the growth rate of Rq decreases; when the steady-state stage reaches, 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.