改性800M合金在热浓碱溶液中生成的表面膜的AES研究

AES ANALYSIS OF THE SURFACE FILMS FORMED ON ALLOY 800M IN HOT CONCENTRATED CAUSTIC SOLUTION

对改性 8 0 0合金 (80 0M)在沸腾的 5 0 %NaOH +0 3%SiO2 +0 3%Na2 S2 O3 溶液中不同电位下恒电位极化 2h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 (- 5 0 0mV～ 80mV) ,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 - 5 0 0mV ,80 0M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=- 40mV) .在 - 40mV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 - 30mV～40mV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(alloy 800M)polarized potentiostatically at different potentials in boiling 50%NaOH+0.3%SiO 2+0.3%Na 2S 2O 3 solution for two hours were analyzed by means of Auger 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(E cr=-40 mV)where the alloy suffered from IGA due to the dissolution of active grain boundaries when stress ruptured the surface film whose protective ability decreased by the transformation of Ni(OH) 2 into a new unstable oxide of xNi 2+yNi 3+O y(OH) 2x+y.At E=-30 mV～40 mV,intergranular stress corrosion cracking(IGSCC)was attributed to the formation of xNi 2+yNi 3+O y·(OH) 2x+y and the percentage of active grain boundaries over a critical percentage.