Oxidation behavior of Hf1-xAlxB2 and (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)1-yAlyB2 coatings synthesized by high power pulsed magnetron sputtering (HPPMS) using massive subplantation of Al

抗氧化性是恶劣环境下使用的超高温陶瓷的重要设计标准之一。虽然对HfB2的氧化行为进行了研究，但对x和y在0 ~ 1.0范围内变化时Hf1-xAlxB2或（Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2）1-yAlyB2的Al溶解度和Al浓度依赖的氧化行为均未进行研究。我们之前已经证明了通过大量的Al亚镀膜，合成了前所未有的Al浓度高达x = 0.74的单相V1-xAlxN涂层。这种过饱和是通过在反应性混合高功率脉冲磁控溅射过程中，脉冲衬底偏压与高能Al离子的强烈周期通量同步，在时间和能量域分离成膜物质而获得的。在这里，我们将首次利用大量的Al离子通量来合成具有最大Al浓度（xmax, ymax）的单相Hf1-xAlxB2和（Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2）1-yAlyB2涂层，并遵循G. grezynski和申请人设想的亚种植方法。除了具有最大Al浓度的两种薄膜外，还具有5和10 at的薄膜。Al浓度低于各自最大浓度%的样品，以及不含Al（作为参考）的样品，将在两种材料体系中生长和评估。所有六种成分的氧化行为将在高达1200°C的温度下进行评估，并在炉中暴露时间长达60分钟。完整的数据集将允许直接比较亚稳Hf1-xAlxB2和（Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2）1-yAlyB2固溶体的温度依赖氧化行为，时间依赖氧化行为，al浓度依赖氧化行为。具体来说，该项目旨在回答第1部分结束时提出的研究问题，即：1。Al在单相Hf1-xAlxB2和（Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2）1-yAlyB2中的临界溶解度（xmax, ymax）是多少？2. 单相Hf1-xAlxmaxB2和（Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2）1-ymaxAlymaxB2的氧化行为与不含Al?3的相应相相比有何不同？Al掺入对单相Hf1-xAlxB2和（Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2）1-yAlyB2的氧化动力学有什么影响？基于光谱学、衍射、显微镜和层析成像的数据，我们试图提高我们对铝浓度对氧化行为的依赖性的理解。我们期望这将使未来设计具有优异抗氧化性的超高温二硼化物涂层成为可能。

Resistance against oxidation is one of the critical design criteria for ultra-high temperature ceramics utilized in harsh environment. While the oxidation behavior of HfB2 has been investigated, neither the Al solubility nor the Al concentration-dependent oxidation behavior of Hf1-xAlxB2 or (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)1-yAlyB2 with x and y varying from 0 to 1.0 has been studied.We have previously demonstrated the synthesis for single-phase V1-xAlxN coatings with unprecedented Al concentrations of up to x = 0.74 by massive subplantation of Al. This supersaturation was obtained by separating the film-forming species in time and energy domains through synchronization of the pulsed substrate bias with intense periodic fluxes of energetic Al ions during reactive hybrid high power pulsed magnetron sputtering. Here, we will utilize massive Al ion fluxes for the first time during synthesis of single-phase Hf1-xAlxB2 and (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)1-yAlyB2 coatings with maximized Al concentrations (xmax , ymax) following the subplantation approach conceived by G. Greczynski and the applicant. In addition to the two films with maximized Al concentration, also films with a 5 and 10 at.% lower Al concentration than the respective maximum concentration, as well as samples without Al (as a reference), will be grown and evaluated for both material systems. The oxidation behavior of all six compositions will be evaluated at temperatures of up to 1200 °C and exposure times of up to 60 min in a furnace. The complete data set will allow for straightforward comparisons of the temperature-dependent oxidation behavior, time-dependent oxidation behavior, Al concentration-dependent oxidation behavior of metastable Hf1-xAlxB2 and (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)1-yAlyB2 solid solutions.Specifically, the project is aimed at answering the research questions motivated at the end of section 1, namely:1. What is the critical solubility (xmax, ymax) of Al in single-phase Hf1-xAlxB2 and in (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)1-yAlyB2? 2. How does the oxidation behavior of single-phase Hf1-xAlxmaxB2 and (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)1-ymaxAlymaxB2 compare to that of the corresponding phases without Al?3. What are the consequences of Al incorporation for the oxidation kinetics of single-phase Hf1-xAlxB2 and (Hf0.2Zr0.2Ta0.2Nb0.2Ti0.2)1-yAlyB2?Based on spectroscopy, diffraction, microscopy, and tomography data obtained from the as-grown compared to the oxidized coatings, we seek to advance our understanding concerning the Al concentration dependence of the oxidation behavior. We expect that this will enable future design of ultra-high temperature diboride coatings with superior oxidation resistance.