阻氚用Fe-Al渗铝层表面稳态相Al2O3膜生长机理研究

Investigation of Stable Al2O3 Scale on Fe-Al Aluminized Coating for Tritium Barrier

为阐释Fe-Al渗铝层表面暂态相Al2O3膜向稳态相α-Al2O3膜的转变机理,探索稳态相α-Al2O3膜制备的氧化工艺参数范围,采用掠入射角X射线衍射仪、辉光放电光谱仪、聚焦离子束、透射电镜等,结合热重分析对CLAM钢基体Fe-Al渗铝层在940~980℃、1 Pa^20 kPa参数下的氧化生长行为进行了深入表征与机理分析。研究结果表明,在1 Pa^20 kPa氧分压范围内Al2O3膜生长初期反应速率常数随着氧分压的升高而增大,而后期反应速率常数反而随之下降;采用掠入射角X射线衍射仪对3~180 min氧化不同时期表面Al2O3膜的相结构进行了掠入射角分析,推测Al2O3膜的生长经历了从氧化初期形成暂态相γ-Al2O3(15 min)→过渡态相α-(Al 0.948 Cr 0.052)2O3(30 min)→稳态相α-Al2O3(120~180 min)的演变过程,最短相转变时间约60~90 min,连续Al2O3膜厚度约2000 nm;同时,结合聚焦离子束对30、120 min形成的Al2O3膜表面进行了精确定向切割制样,并采用透射电镜选区电子衍射分析验证了相转变前Al2O3膜结构为过渡态相α-(Al 0.948 Cr 0.052)2O3(113),转变后为稳态相α-Al2O3(113),证实了Cr作为第三组元促进暂态相向稳态相α-Al2O3的转变规律。

It is well known that α-Al2O3 phase has stablility performance,high permeation reduction factor and good resistance performance in liquid LiPb,which is considered as the reference tritium barrier coating in future fusion reactor.In order to study the formation mechanism of stableα-Al2O3 scales on fusion structure material,the oxidation behavior of Fe-Al aluminized coating on China Low Activated Martensitic(CLAM)steel was investigated under the oxygen partial pressure from 1 Pa to 20 kPa at the temperature of 940-980℃.The Al2O3 scales were analyzed by thermogravimetric analysis meter,grazing angle X-ray diffractometer,glow discharge spectrometer,focused ion beam and transmission electron microscope.A single continuous Al2O3 scales with the maximum thickness of about 2000 nm was formed on the diffusion Fe-Al aluminized layer.Thermogravimetric analysis results show that the higher oxidation rate constant is achieved while increasing the oxygen partial pressure,and then oxidation rate constant decreases.The phase transformation of Al2O3 scales on the surface of Fe-Al aluminized coating was studied during different oxidation time ranges from 3 min to 180 min.The metastableγ-Al2O3 andα-(Al 0.948 Cr 0.052)2O3 phases is formed in the earlier oxidation process and finally transformed to stableα-Al2O3 phase.The features of the transientα-(Al 0.948 Cr 0.052)2O 3(113)andα-Al2O3(113)were detected by GXRD and then confirmed by focused ion beam and transmission electron microscope.