Effect of calcination temperature on the microstructure, composition and properties of nanometer agglomerated 8YSZ powders for plasma spray-physical vapor deposition (PS-PVD) and coatings thereof

Homemade nano-agglomerated powders 8YSZ powders for PS-PVD were prepared by the spray drying, then calcination processes at four different temperatures (500 degrees C, 700 degrees C, 900 degrees C and 1100 degrees C) were carried out on the spray-dried powders. Checked by laser particle sizer, scanning electron microscope (SEM) and X-ray diffraction (XRD), the physical properties, microstructure and phase constitutions of the calcined powders were investigated. The results show that the size of powders calcined at 500 degrees C is increased relative to the spray-dried powder, whereas the powders calcined at 700 degrees C, 900 degrees C and 1100 degrees C possess smaller size. The binding force of the primary particles tend to rise with the increase of calcination temperature. When the temperature was up to 900 degrees C and above, it was found that the sintering neck indicating with strong binding was formed between the primary particles. In parallel, the powders underwent an m-ZrO2 to t-ZrO2 transition as the calcination temperature rose. It is also found that the PS-PVD prepared coatings which were obtained by using the above powders undergo a transformation from a feather-like to a dense laminate structure as the calcination temperature rises. It is noteworthy that the coating obtained by the powders calcined at 700 degrees C have a special threelayer composite structure of near dense surface layer, columnar intermediate layer and dense sub-layer. The composite structural coating has excellent adhesion and thermal shock resistance, with a bonding strength of 81MPa and no major spalling when water quenched 100 cycles at 1100 degrees C.

Automated summary

Higher calcination temperatures result in smaller powder sizes and increased binding force between primary particles, leading to the formation of a three-layer composite coating with excellent adhesion and thermal shock resistance.