T225NG钛合金在高温高压水介质中应力腐蚀行为的研究

Stress Corrosion of T225NG Alloy in Loop Water of High Temperature and Pressure

研究T2 2 5NG钛合金在高温高压水中的应力腐蚀情况 ,通过将双悬臂梁试样预加应力后放入高温高压的回路水中 ,试样经过 2 0 0 0h的试验 ,观察试样应力腐蚀和裂纹扩展情况。结果发现 ,双悬臂梁试样的预制裂纹经试验后发生了很小的扩展。经过计算 ,在 5 0 0h内裂纹扩展速度da/dt<1× 10 - 9m·s- 1 ,而且KISCC/KIC>0 .75 ,说明T2 2 5NG钛合金在高温高压的回路水中具有良好的耐应力腐蚀性能。同时也发现在试样表面生成了氧化膜 ,研究表明 ,表面氧化膜主要是由白色的TiO2 颗粒组成 ,由于表面氧化膜的存在 ,阻碍了阴极析氢产生的氢进入钛合金中 ,防止了氢在钛合金中的聚集而产生的氢化物及氢脆 ,这进一步证明了T2 2 5NG钛合金在高温高压水溶液中具有良好的耐应力腐蚀性能。

The stress corrosion of cracking of T225NG alloy was researched in loop water. At first, DCB specimens were stressed, then they were put into loop water and finally the stress corrosion and crack expansion of specimens after 2000 h were observed. The results show that small expansion occurrs on the DCB along the direction of pre-cracking. According to calculation, in 500 h the speed of cracking expansion (da/dt) is lower than 1×10 -9 m·s -1 and K ISCC/K IC is higher than 0.75, which prove that T225NG alloy does not have the susceptivity of the stress corrosion in loop water. There is oxide film on the surface of specimens. The result shows that oxide film mainly consists of many white particles of TiO 2. Because of the existence of the oxide film, hydrogen which separates out from cathode is blocked to go into Ti-alloy so that hydrogen is not collected, hydride is not created and hydrogen embrittlement is not occurred. These prove further that T225NG alloy does not have the susceptivity of the stress corrosion in loop water.