等离子喷涂-物理气相沉积的气相沉积机理

Deposition Mechanism Based on Plasma Spray-Physical Vapor Deposition

以等离子喷涂-物理气相沉积(PS-PVD)喷涂团聚的Zr O_2-7wt%Y_2O_3(7YSZ)粉末在五个喷距下制备了热障涂层。通过场发射-扫描电镜(FE-SEM)和X射线衍射(XRD)分析了五个涂层样品的微观结构和相成分差异。另外,通过发射光谱(OES)诊断研究了射流中7YSZ粉末气相浓度随喷距的变化。最后,阐述了3种不同的气相沉积涂层生长机制,说明了射流中粉末的状态和气相浓度对涂层结构的影响。研究表明:(1)350 mm和1800 mm喷距下形成的均是致密结构涂层,而650~1250 mm喷距下形成的是典型的PS-PVD柱状结构涂层。(2)350 mm喷距下制备的涂层由四方相(t’)和单斜相(m)氧化锆构成;当喷距大于650 mm时,涂层以四方相(t’)氧化锆为主。(3)350 mm喷距下涂层是由高浓度气相过饱和自发形核形成的新核和液/固粒子共同作用形成的;喷距650~1250 mm下,涂层生长以气相沉积于基体进行非自发形核为主,气相在射流中的自发形核为辅;喷距1800 mm下涂层由气相过冷凝固的粒子堆积而成。

Thermal barrier coatings （TBCs） were prepared via plasma spray-physical vapor deposition （PS-PVD） technique at five spray distances by using agglomerated ZrO2-7wt%Y2O3 （7YSZ） powders. The microstructure and phase composition of these coatings under different spray distances were analyzed by field emission-scanning electron microscope （FE-SEM） and X-ray diffraction （XRD）. Besides, gas concentration of the powders in plasma jet was diagnosed with stand-off distances by Optical Emission Spectroscopy （OES）. Eventually, three formation mechanisms of the PS-PVD coatings based on vapor deposition were proposed, and the relationship between the concentration of gas phase and the microstructure of the coatings was explained. The results reveal that： （1） the coatings prepared at spray distance of 350 mm and 1800 mm exhibit dense structure, while typical PS-PVD 7YSZ columnar coatings were formed at spraying distance of 650-1250 mm; （2） the coating formed at 350 mm spraying distance is composed of t＇- and m-ZrO2, and others are mainly composed of t＇-ZrO2 at over 650 mm stand-off distance; （3） At 350 mm spray distance, the coating is developed under the combination effect of the supersaturated spontaneous nucleation from high concentration of the gas phase and liquid/solid particles. At spraying distance of 650-1250 mm, the growth of colum- nar coatings are dominated by the non-spontaneous nucleation after the deposition of gas phase on the substrate, and supplemented by spontaneous nucleation in plasma jet. At spraying distance of 1800 mm, the coating is accumulated from spontaneous re-solidified gas phase particles.