CLAM钢表面Fe-Al合金渗层的制备

Preparation of Fe-Al alloy layer on CLAM steel

FeAl/Al2O3阻氚涂层具有高阻氚因子、耐腐蚀和耐高温等优良性能,是ITER首选的阻氚涂层.Fe-Al合金渗层对Al2O3膜层的形成质量有重要的影响.本文采用了AlCl3-EMIC离子液体电镀法在CLAM钢表面镀铝,然后利用热处理使Al与基体相互扩散制备Fe-Al合金渗层.采用X射线衍射仪、扫描电子显微镜和能量散射谱仪研究了热处理时间和温度对渗层组织结构的影响.结果表明:渗层厚度随着热处理温度和时间的提升而增大,试样表面逐渐由富铝相向贫铝相转化.在不同热处理条件下获得的渗层与CLAM钢基体结合紧密,无孔洞等缺陷.热处理时间一定时,热处理温度对渗层生长速率的影响符合Arrhenius关系,拟合计算出CLAM钢的渗铝Arrhenius活化能为78.48 kJ/mol.在640℃和760℃时,渗层中金属间化合物的生长受晶界扩散速率与体扩散速率的共同影响.在综合考虑合理的渗层厚度、表面Fe-Al合金相、热处理成本的情况下,较优的热处理工艺为700℃/10 h.

Reduced activation ferritic/martensitic steel is one of the candidate materials for tritium breeding module in the fusion reactor.In order to control the permeability of tritium in an acceptable range,coating with low hydrogen isotope permeability,known as tritium permeation barrier,is usually prepared on the surface of such structural materials.The FeAl/Al2O3 is the first choice of tritium permeation barrier for many countries,because of its fine performance of high permeation reduction factor,corrosion resistance and high-temperature resistance.The surface morphology and microstructure of Fe-Al infiltrated layer have important influence on the quality of Al2O3 coating.In this study,Al coating on the surface of CLAM steel is prepared by electroplating of aluminum from AlCl3-EMIC.Then the Fe-Al infiltrated layer is obtained by diffusion between Al and substrate by annealing.The effects of annealing time and temperature on the microstructure of Fe-Al infiltrated layer are studied by X-ray diffraction,scanning electron microscope and energy dispersive spectrometer.The results show that 20-μm-thick aluminum coating is obtained on the CLAM steel surface by electroplating.The Al coating is uniform and compact,and the size of its surface columnar grain decreases with electroplating current density increasing.Annealing results show that neither hole nor gap is observed between the Fe-Al infiltrated layer and the substrate.In addition,the infiltrated layer is found to be tightly bound to the substrate with a thickness ranging from 7μm to 45μm,depending on the annealing parameters.At the initial stage of annealing,Cr enriched Fe-Al alloy is formed evidently.However,such a Cr enrichment disappears at higher annealing temperature or longer annealing time due to diffusion.The surface of infiltrated layer changes from aluminum-rich phase to aluminum-poor phase,and its thickness increases with annealing time or temperature rising.The temperature dependence of the growth rate of Fe-Al infiltrated layer can be described by Arrhenius equation.At this time,the Arrhenius activation energy of aluminization on CLAM steel is calculated to be 78.48 kJ/mol.At 640℃ and 760℃,the growth of Fe-Al infiltrated layer is controlled by the grain boundary as well as the volume diffusion.When the reasonable thickness and microstructure of Fe-Al alloy layer are used and annealing time or temperature keeps as low as possible,the optimal annealing temperature and time are 700 ℃/10 h,respectively.