对改性800合金(800M)在沸腾的50%NaOH+03%SiO2+03%Na2S2O3溶液中 不同电位下恒电位极化2 h后的表面膜进行了俄歇电子能谱(AES)分析，发现在所选择的电位 条件下(-500 mV～80 mV)，表面膜中Ni的富集因子比Fe、Cr的大一个数量级，表面 膜富Ni而贫Fe、Cr.在-500 mV，800M合金C形环试样发生晶间腐蚀(IGA)是由于表面膜中S富 集、Cr的相对百分含量很低，S2-在晶界偏析及晶界形成严重贫铬区.富集因子随电位 的变化曲线有一拐点电位(Ecr=-40 mV).在-40 mV时，C形环试样发生IGA是由于 生成不稳定的Ni的氧化产物xNi2+yNi3+Oy(OH)2x+y，表面膜保护性 能下降，应力撕破表面膜，活性晶界优先发生溶解形成的.在-30 mV～40 mV时，C形环试样 发生沿晶应力腐蚀破裂( IGSCC)则可能是由于xNi2+yNi3+Oy(OH) 2x+y不稳定，活性晶界分数大于裂纹扩展所需临界分数的缘故.
The surface films formed on modified alloy 800(all oy 800M)polarized potentiostatically at different potentials in boiling 50%NaOH +0.3%SiO2+0.3%Na2S2O3 solution for two hours were analyzed by means of A uger electron spectroscopy(AES).At the potentials between -500 mV and 80 mV ,the enrichment factor of Ni was an order of magnitude higher than that of Fe and Cr in the surface films.General intergranular attack(IGA)at -500 mV occurred due to S enrichment and Cr depletion in the surface films.The curves of enrichment factor vs.potential had a critical potential(Ecr=-40 mV)where the al loy suffered from IGA due to the dissolution of active grain boundaries when str ess ruptured the surface film whose protective ability decreased by the transfor mation of Ni(OH)2 into a new unstable oxide of xNi2+yNi3+O y(OH)2x+y.At E=-30 mV～40 mV,intergranular stress corrosion cracking (IGSCC)was attributed to the formation of xNi2+yNi3+Oy·(O H) 2x+y and the percentage of active grain boundaries over a critical percentag e.
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