Study On Preparation, Structure And Properties Of Nanostructured ZrO₂/Y₂O₃ Coatings Prepared By Solution Precursor Plasma Spray

In the dissertation, ZrOCl₂ · 8H₂O and YCl₃ were regarded as materials to prepare zirconium hydroxide sol by way of positive titration method of NH₃ · H₂O. Solution precursor plasma spray (SPPS) had been used for the formation of yttria partially stabilized zirconia(ZrO₂/Y₂O₃) nanostructured coatings from the solution precursor feedstock instead of reconstituted nanopowder feedstock. The structures and properties of colloids and coatings were characterized by XRD, SEM, EDS,TG-DSC, VIDAS imagine analyzer, 71model micro-hardness, granularity analyzed etc.ZrOCl₂ · 8H₂O and YCl₃ were solved in water and occurred hydrolyzation reaction and polymerization reaction simultaneously under the precipitator of NH₃ · H₂O. With hydrolyzation reaction and polymerization reaction processing, colloid particles formed nucleus and increased. pH value, surfactant PEG (600+20000) and solution concentration were important parameters which affect colloid particles size. pH value controlled formed-nucleus and increment of colloid grains by influencing hydrolyzation reaction and polymerization reaction processing. Surfactant PEG (600+20000) dispersed agglomeration colloids by electrostatic effect and space location-obstruct effect. Solution concentration controlled critical crystal size and crystal increasing. The sol heat-weight process had losing-weight process and no losing-weight process. The colloid losing adsorption water, combine water, structure water, surfactant evaporation and NH₄Cl decomposing processes belonged to losing-weight process. However, metastable tetragonal transformation belonged to no losing-weight process.Surface morphologies of coatings prepared by SPPS presented obvious layer structure. Spray distance and atomization air pressure had important effects on microstructures and properties of coatings. The experiments indicated that nanostructured coatings had preferable microstructures and properties when spray distance was controlled between 80mm and 90mm, atomization air pressure 0.5MPa under other process parameters at certain values. If the amount of Y₂O₃ was adulterated differently in ZrO₂ coatings, pHase stability of coatings was different. Bycontrast to Y2O3 adulterated 4mol% in ZrO2 coatings, the amount of tetragonal pHase in coatings was more than that of monoclinic pHase when the content of Y2O3 was adulterated 9mol% in ZrO2 coatings. With spray distance increasing, the porocity of coatings reduced at first, then increased. The micro-hardness had relation with the porocity, the larger porocity being, the smaller micro-hardness. Since Ni/Al bond coatings between coatings and substrates could relax heat stress, the existence of them enhanced thermal cycling performance of coatings. At the same time, the larger porocity, the smaller bore, the evener porocity and the more tetragonal pHase amounts of coatings were, the more excellent thermal cycling performance was.