本论文综述了氧化铝阻氚涂层、热浸镀铝技术、热浸镀铝与微弧氧化复合制备技术、α-Al2O3相晶种诱导的概念、原理及研究现状，在此基础上提出了采用热浸镀铝与微弧氧化相结合的复合梯度涂层制备方法，得到具有较厚氧化铝层的复合梯度涂层，同时通过对氧化铝层进行晶型调控，提高涂层中α-Al2O3相的含量，以此作为新型阻氚涂层的研究思路。
采用热浸镀铝技术在316L不锈钢表面获得梯度涂层，用光学显微镜和扫描电镜观察了梯度涂层表面和截面的显微形貌；用能谱仪（EDS）和X射线衍射仪（XRD）分析了梯度涂层的化学成分和物相组成；综合分析了梯度涂层结构随热浸镀铝温度和时间的变化规律，并对热浸镀铝工艺进行优化；研究了梯度涂层显微硬度。结果表明：（1）316L不锈钢热浸镀铝梯度涂层结构为：基体/金属间化合物层/多相混合层/纯铝层。（2）金属间化合物层的物相组成为：FeAl3 + Fe4Al13，少量Al相富集，并嵌于铁铝金属间化合物之中，硬度最高；多相混合层的物相组成为：Al + FeAl3 + Fe4Al13，铁铝金属间化合物呈絮状均匀分散于Al相中；纯铝层只有Al相，表面存在微孔，硬度最低。（3）在700℃条件下热浸镀铝，金属间化合物层最厚。在730℃条件下热浸镀铝，多相混合层最厚。在760℃条件下热浸镀铝，纯铝层占梯度涂层比例最大。（4）优化出最合适后续微弧氧化的热浸镀铝参数为：浸镀温度760℃，浸镀时间11min。
对热浸镀铝梯度涂层进行微弧氧化，观察了微弧氧化复合梯度涂层的表面和截面形貌，分析了氧化铝陶瓷层的物相组成。结果表明：（1）微弧氧化放电仅在纯铝层表面进行，复合梯度涂层结构为：基体/金属间化合物层/多相混合层/纯铝层/氧化铝层。氧化铝层致密，与纯铝层结合良好，表面微孔尺寸小。（2）微弧氧化复合梯度涂层表面氧化铝陶瓷层由η-Al2O3相构成，没有阻氚性能最好的α-Al2O3相。
引入α-Al2O3和Cr两种晶种对氧化铝层进行晶型调控，分析氧化铝层的物相组成。结果表明：（1）基于微弧氧化α-Al2O3掺杂制备的复合梯度涂层表面的物相组成为：η-Al2O3 + α-Al2O3，掺杂α-Al2O3晶种对α-Al2O3相的生成有促进作用，同时，添加α-Al2O3颗粒后微弧放电更剧烈。（2）316L不锈钢热浸镀铝铬梯度涂层的表面纯铝层物相组成为：Al + Fe4 Al13 + Fe2 Al5 + Fe Al6 + Fe Al2 + Cr + AlCr2 + Al13Cr2。Cr元素成片状在镀层表面富集，Cr单质以颗粒的形式镶嵌在镀层中。Cr元素的掺杂促进了铝铬反应和铝铁反应的进行。（3）基于热浸镀铝Cr掺杂的微弧氧化复合梯度涂层表面的物相组成为：η-Al2O3 + α-Al2O3 + δ-Al2O3 + Cr2O3。掺杂Cr元素对α-Al2O3相的生成有促进作用，同时微弧氧化陶瓷层均匀，微孔孔径小。
 

The conception，principle and developmental  states of Al2O3 tritium permeation barriers, crystal nucleus to induce α-Al2O3 formation, and hybrid techniques combining hot dip aluminizing (HDA) with micro-arc oxidation(MAO) are reviewed. On the basis of the review, FeAl/Al/Al2O3 composite gradient coating was prepared by hot-dipping aluminum and micro-arc oxidation on the surface of 316L stainless steel to increase the thickness Al2O3 tritium permeation barriers. Furthermore, the content of α-Al2O3 was improved by doping α-Al2O3 and Cr seeds.
Firstly, gradient coatings were prepared by hot dip aluminizing on the surface of 316L stainless steel substrate. The surface morphologies and cross-sectional microstructure were investigated with optical microscope (OM) and scanning electron microscopy (SEM). The energy dispersive spectrometer(EDS) and X-ray diffraction (XRD) was used to analyze the phase composition of the gradient coatings. The evolutions of the gradient structure changing with HDA temperature and time. The cross-sectional microhardness of the HDA treated specimens were studied. The results indicate that: (1) The gradient structure obtained by HDA consist of four layers from substrate to the outside: 316L substrate / intermetallic compound layer / two-phase mixed layer / pure aluminum layer. (2) The intermetallic compound layer consists of a mixture of intermetallic FeAl3+Fe4Al13 phases. The multi-phases mixed layer consists of Al+FeAl3+Fe4Al13 phases; the pure aluminum layer contains only Al. (3) The thickness of intermetallic compound layer and pure aluminum layer have maximum values at HDA temperature of 700℃and 760℃, respectively. (4) In our experiment conditions, the suitable HDA condition for MAO is developed at the HDA temperature of 760℃ and with the time of 11min. The corresponding maximum thickness of the pure aluminum layer is about 62 μm.
Secondly，then ceramic coatings were obtained on the aluminum coatings by micro-arc oxidation. The surface and cross-sectional morphologies of the composite gradient coatings were observed with OM and SEM. The phase composition of the Al2O3 ceramic coatings was analyzed with XRD. The results show that: (1) The composite gradient structure obtained by hybrid techniques of HDA and MAO consist of five layers from substrate to the outside: 316L substrate / intermetallic compound layer / two-phase mixed layer / pure aluminum layer / Al2O3 layer. (2) The phase composition of the ceramic coatings is mainly composed of η- Al2O3, without α- Al2O3.
Finally, alumina coatings were prepared through hybrid techniques of HDA and MAO with doping α-Al2O3 seeds and Cr seeds. The results show that: (1) After doping α-Al2O3 seeds in the MAO electrolyte, the Al2O3 layer was composed of both η-Al2O3 and α-Al2O3. The α-Al2O3 seeds was effective to induce the formation of α-Al2O3 in MAO coatings. (2) Cr doped gradient coatings were successfully prepared. In the surface of the coatings, Al+ Fe4Al13 + Fe2Al5 + FeAl6 + FeAl2 + Cr+ AlCr2 +Al13Cr2 phases was obtained. After doping Cr seeds in the HDA gradient coatings, the MAO Al2O3 layer was composed of η-Al2O3 +α-Al2O3 +δ-Al2O3 +Cr2O3. The inducing effect of Cr seeds was also effective.
 

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