无定形相的结晶与纳米晶化对六铝酸盐热障涂层热物理性能影响的研究

Hexaluminate thermal barrier coatings with the magnetoplumbite-type structure exhibit excellent thermophysical properties and thermal shock resistance cycling lifetime. Plasma sprayed hexaluminate coatings have a large amount of amorphous phases which make these coating unreliable in high temperature service. The effects of crystallization of the amorphous phases on the microstructures,thermophysical properties and the thermal cycling failure mechanisms of the coatings are still explicit up to now. In this project, we'll make comprehensive studies on the crystallization mechanisms and kinetics of the amorphous phases among hexaluminate coatings. To explore the effects and mechanisms of action of the growths and thermal stability of the platelet-like grains, especially for the growths of nanosized platelet-like grains resulted from the crystallization of amorphous phases, on the microstructures, mechanical and thermophysical properties of the coatings. We plan to build quantitative relationships between the thermophysical properties and the microstructure evolution accompanied by crystallization and platelet-like grain growth of hexaluminate coatings, which will provide important experimental physical parameters for the theoretical prediction of the coatings' properties in service and the analyses of their failure mechanisms. These research results of this project will have important theoretical and technical significances to promote this kind of coatings for industrial applications.

磁铅石结构六铝酸盐热障涂层具有优异的热物理性能及抗热震循环寿命。等离子喷涂制备的该类涂层中存在大量无定形相严重影响服役涂层的可靠性，无定形相的结晶对涂层组织结构、热物理性能以及热循环失效机制的影响至今仍不明晰。本项目系统研究六铝酸盐涂层中无定形相的结晶机理与动力学规律，探究结晶诱导的片状晶粒（尤其是纳米片晶）的生长与热稳定性对涂层组织结构、力学与热物理性能影响的规律与作用机制。构建涂层组织结构演变与涂层热物理性能的定量关系，为涂层服役性能的理论预测与失效机制分析提供重要实验物理参数。本项目的研究成果对推动该类涂层走向工业应用具有重要的理论和技术意义。

具有磁铅石结构的六铝酸盐是一类性能优异的热障涂层材料，但是等离子喷涂(APS)该类涂层通常存在大量无定形相。由于对其高温条件下的结晶及结构稳定性对涂层热物理性能与力学性能缺乏足够的认识，一直延滞着这类涂层的工业应用。该项目主要开展了APS过程中无定形相含量的可控制备以及高温条件下无定形相重结晶对涂层热物理性能影响的研究。通过优化APS制备参数，我们成功开发了无定形相含量少于20%的系列六铝酸盐涂层，使得该类涂层的热循环寿命提高20%。同时我们发现该类涂层无定形相在900oC可以较好的结晶，而后的晶粒生长会形成片状纳米晶粒，其中LaMA与NdMA涂层重结晶后的纳米和亚微米晶粒可以在1350oC的温度下长时间保持稳定（>100 h），具有非常好的抗烧结能力。涂层重结晶导致的纳米片状晶粒及其生长会导致孔隙率的增加，可以将涂层最初的热导率由3.5 W/m K降到1 W/m K以下。同时伴随涂层杨氏模量等力学性能的降低和长时间的稳定，从而有效降低对应热障涂层体系高温服役条件下的热应力，提高涂层的热循环寿命。