稀土六铝酸盐涂层中无定形相的晶化机理及涂层的改性研究

Lanthanum magnesium hexaaluminate (LaMgAl11O19, LMA) with high thermal expansion coefficient, low thermal conductivity and high fracture toughness is a promising competitor to yttria partially stabilized zirconia (YSZ) as a new ceramic material for thermal barrier coatings (TBCs). A large amount of amorphous phase often presents in the plasma sprayed LMA coating. The following recrystallization of the amorphous phase during high temperature service is adverse to the thermal cycling lifetime of the coating. In this project, the crystallization kinetic of the amorphous and the compositions of the crystals are researched comprehensively to reveal the crystallization mechanism, which provides a theoretical basis for the modification of the coating. The crystallization of the amorphous is induced by controlling heat treatment conditions prior to its using, which has no any damage to the coating structure and weakens the bad effects of the crystallization for the coating during service. The effects of the rare-earth ions on the amorphous phase content and the thermosphysical properties of the coating are studied by adjusting its compositions. The rare earth hexaaluminate coatings with low amorphous phase, high thermal insulation and long thermal cycling life can be prepared, which will promote the industrial application of the kind of the coating.

六铝酸镁镧（LaMgAl11O19, LMA）具有高的热膨胀系数、低的热导率和高的断裂韧性，是最有希望取代氧化钇部分稳定的氧化锆（YSZ）的新型热障涂层（TBCs）陶瓷材料。等离子喷涂制备的LMA涂层中存在大量的无定形相，高温服役过程中无定形相的晶化严重影响涂层的热循环寿命。本项目将系统研究无定形相的晶化动力学和析出晶粒的元素组成，揭示无定形相的晶化机理，为涂层改性提供理论依据。通过对涂层服役之前热处理过程的调控，在不破坏涂层自身结构的前提下诱导无定形相析晶，减弱涂层服役过程中无定形相晶化的不利影响。通过组成设计，研究稀土离子类型和含量与涂层无定形相含量以及热物理性能的规律，制备低无定形含量、高隔热、长寿命的稀土六铝酸盐涂层，促进该类涂层的工业化应用。

等离子喷涂技术制备的稀土六铝酸盐涂层中存在大量的无定形相，在以往的研究中始终将无定形相产生的原因归于较快的冷却速度。本项目通过对无定形相的晶化过程进行了系统研究，发现磁铅石结构的稀土六铝酸盐中稀土离子对其它原子扩散的抑制作用是此类物质喷涂后容易产生无定形相的主要原因，通过掺杂半径较小的稀土离子可以有效降低涂层中无定形相含量。此外，我们发现无定形相分别在900℃和1200℃附近分步析晶，析出晶粒中稀土元素含量的差异是导致其分步析晶的原因。鉴于无定形相的晶化会导致涂层的体积收缩对涂层使用的可靠性产生影响，因此，在本项目中我们尝试将LaPO4和YSZ等与LaMgAl11O19（LMA）制备成复合材料。