Harnessing nanolaminate coatings for high temperature applications

基于MAX或MAB相(其中M是早期过渡金属，A是A族元素，X是碳或氮，B是硼)的纳米层状涂层结合了独特的陶瓷和金属材料特性，在高温环境中提供了巨大的应用潜力。在该项目中，将验证通过各种PVD技术沉积的形成MAX和MAB(具有M=Cr或Ti和A=Al)纳米层的氧化铝涂层的制造，并将阐明它们在干燥和潮湿大气中的高温性能。波兰和德国的合作机构将首次比较三种不同的PVD技术，包括高功率脉冲磁控溅射、直流和反应磁控溅射以及封闭式空心阴极PVD。比较和结合这些技术的可能性为了解各种沉积参数对纳米层涂层性能的影响提供了独特的机会。该涂层将应用于金属间化合物TiAl和陶瓷碳化硅上。该项目将专注于开发一种由氧化铝组成的保护性热生长氧化层及其在长期高温暴露期间的演变。由于富铝衬底提供的补充作用稳定了氧化铝层，从而防止了由于Al向内扩散进入衬底材料而导致的MAX/MAB相涂层的退化，TiAl合金的寿命有望得到改善。此外，众所周知，TiAl的力学性能恶化是通过保护性的、但脆性的涂层可以通过沉积延性MAX或MAB相的纳米层来防止的。对于碳化硅，必须防止水蒸气腐蚀。最先进的环境屏障涂层系统以稀土硅酸盐为基础，最多可有4层不同的涂层。为此，评估了它们被单层和氧化铝形成MAX或MAB相基涂层替代的可能性，提供了可持续的原材料使用。重点研究了纳米层在高温暴露时的附着力，以及涂层与惰性陶瓷碳化硅的界面设计。纳米层状物和碳化硅之间的互扩散过程将通过实验和使用CALPHAD方法的热力学模拟来评估。此外，基于这些计算，将研究与CTE匹配的富Al中间层的可选实现，其中AlN是由于碳化硅和MAX或MAB相之间的CTE而预定的。最后，对不同纳米涂层TiAl和碳化硅衬底材料进行了长期的循环氧化试验和在水蒸气中的等温暴露。涂层和未涂层TiAl合金的力学行为将在高温环境下通过拉伸、疲劳和蠕变试验进行评估。

Nanolaminate coatings based on MAX or MAB phases (where M is an early transition metal, A is an A-group element, X is carbon or nitrogen, and B is boron) combine unique ceramic and metallic material properties, providing significant potential for applications in high temperature environments. Within the project the manufacturing of the alumina forming MAX and MAB (with M = Cr or Ti and A = Al) nanolaminate coatings deposited by various PVD techniques will be validated and their performance at high temperature under dry and wet atmospheres will be elucidated. For the first time, three different PVD techniques available at the partnering institutions in Poland and Germany will be compared, including High Power Pulsed Magnetron Sputtering, DC and reactive magnetron sputtering and Closed Hollow Cathode PVD. The possibility to compare and combine these techniques enables a unique opportunity to understand the influence of various deposition parameters on the performance of the nanolaminate coatings. The coatings will be applied on intermetallic TiAl and ceramic SiC. The project will focus on the development of a protective thermally grown oxide layer composed of alumina and its evolution during long-term high temperature exposures. A promising lifetime improvement is expected for TiAl alloys due to stabilization of the alumina layer by the replenishing effect provided by the Al-rich substrate, thereby preventing the degradation of the MAX/MAB phase coatings due to Al-depletion by inward diffusion into the substrate material. Moreover, the well-known deterioration of the mechanical properties of TiAl by protective, but brittle coatings could be prevented by the deposition of ductile MAX or MAB phase based nanolaminates. In case of the silicon carbide, the necessity for protection against water vapor corrosion is mandatory. The state-of-the art environmental barrier coating systems are based on rare earth silicates with up to 4 different layers. For this reason, their potential replacement by single layered and alumina forming MAX or MAB phase-based coatings is evaluated, providing a sustainable raw material usage. Special attention will be paid to the adhesion of the nanolaminates during high temperature exposure as well as the interface design between coatings and the inert ceramic SiC. Interdiffusion processes between the nanolaminates and SiC will be evaluated by experiments and thermodynamic simulations using CALPHAD methods. Moreover, the optional implementation of a CTE-matched, Al-rich interlayer will be investigated based on these calculations, where AlN is predestined due to a CTE between SiC and MAX or MAB-phases. Finally, long-term cyclic oxidation tests and isothermal exposures in water vapor atmospheres of the different nanolaminate coated TiAl and SiC substrate materials will be performed. The mechanical behavior of the coated and uncoated TiAl alloy will be evaluated by tensile, fatigue and creep tests in high temperature environments.