通过对改性800合金(800M)在沸腾的50%NaOH+0.3%SiO2+0.3%Na2S2O3溶液中发生的晶间腐蚀(IGA)和沿晶应力腐蚀破裂(IGSCC)试样的扫描电镜(SEM)观察,结合阳极极化曲线、表面膜俄歇电子能谱(AES)分析和恒电位极化的稳定溶解电流密度ist等测试研究了800M合金在碱液中的IGA形成及IGSCC破裂机理,并探讨了IGA对IGSCC的促进作用.发现在-500mV/SCE整个表面发生的IGA是表面膜中Cr的相对含量低,保护性差,以及溶液中S2O32-还原成S2-在晶界偏析,使晶界的化学活性增加,导致C形环晶界的溶解速率iIG＞晶粒的溶解速率iGCiGC所致.在电位E=-40及-20mV/SCE发生IGSCC,可能是由于Ni形成不稳定的氧化产物,使合金表面膜保护性能下降,在应力作用下,活性大的晶界溶解,形成的微裂纹沿晶界扩展而导致沿晶应力腐蚀破裂.800M合金表面形成的IGA对IGSCC的萌生与扩展有促进作用,晶界是合金发生IGSCC的活性通路.
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