等离子喷涂-物理气相沉积7YSZ热障涂层形成机制

Deposition mechanism of 7YSZ thermal barrier coatings prepared by plasma spray-physical vapor deposition

采用等离子喷涂-物理气相沉积(PS-PVD)技术,以纳米团聚的ZrO2-7%Y2O3(7YSZ)粉末为原料在镍基高温合金为基体的CoCrAlSiY黏结层表面制备了羽毛柱状7YSZ涂层.通过透射电子显微镜(TEM)观察并分析了柱状涂层的显微结构,发现涂层的最小组成单元为纳米柱状晶,众多柱状晶在空间随喷涂遍数累积气相原子依次形核长大形成了微观上的树枝状结构,在宏观上呈现羽毛状结构涂层.基于7YSZ羽毛柱状涂层的形成过程,本文首先从热力学原理分析了7YSZ气相原子的形核机制,阐述了裹挟高浓度气相原子的高温等离子体与基体相互作用形成的温度梯度和气相原子浓度梯度规律,探讨了温度梯度下纳米柱状7YSZ晶体的长大和分枝过程,分析了等离子焰流气相原子沉积过程中过冷度变化对气相原子形核、长大和宏微观涂层结构的影响,研究了PS-PVD喷涂过程中涂层柱状结构内部和柱状结构间隙形成的内在规律和机制.

Feather-like 7YSZ coating has been prepared by plasma spray-physical vapor deposition(PS-PVD)on CoCrAlSiY bond coating with Ni-based superalloy,by using aggllomerated ZrO2-7%Y2O3(7YSZ)powders.The microstrucutres of 7YSZ coating were analyzed by transmission electron microscope(TEM),where the coating was made up with nano-colomnar grain.Those nano-columnar grains change into dendritc microstruture through multi-layer spray.Thus,feather-like 7YSZ coating can be observed in the 7YSZ coating.Considering the formation process of 7YSZ coating,the 7YSZ vapor nucleation mechanism was presented based on thermodynamic principle.The temperature gradient and vapor concentration gradient were investigated induced by interaction by plasma jet and substrate.The nucleation,growth and branching process of grain were discussed under temperature gradient and vapor concentration gradient.Besides,coating mircrosturcture with diffirent undercooling was investigated.The gap fromation mechanism in feather-like 7YSZ coating was also studied.