Effective Parameters in Axial Injection Suspension Plasma Spray Process of Alumina-Zirconia Ceramics

Abstract

Suspension plasma spray (SPS) is a novel process for producing nano-structured coatings with metastable phases using significantly smaller particles as compared to conventional thermal spraying. Considering the complexity of the system there is an extensive need to better understand the relationship between plasma spray conditions and resulting coating microstructure and defects. In this study, an alumina/ 8 wt.% yttria-stabilized zirconia was deposited by axial injection SPS process. The effects of principal deposition parameters on the microstructural features are evaluated using the Taguchi design of experiment. The microstructural features include microcracks, porosities, and deposition rate. To better understand the role of the spray parameters, in-flight particle characteristics, i.e., temperature and velocity were also measured. The role of the porosity in this multicomponent structure is studied as well.The results indicate that thermal diffusivity of the coatings, an important property for potential thermal barrier applications, is barely affected by the changes in porosity content.

Alumina-zirconia coatings obtained by suspension plasma spraying from highly concentrated aqueous suspensions

“…Using water as liquid feedstock instead of ethanol causes higher power requeriments giving rise to lower melting. Besides the presence of partially melted zones, a low solid melting degree results in a high coating porosity which can contribute to reduce thermal conductivity and improve the thermal fatigue resistance while coating hardness can be impaired [3,8]. Furthermore the higher surface tension of water with respect to ethanol also favours that the liquid drops, which are formed inside the plasma plume after suspension stream fragmentation, become larger making the heat transmission even more difficult.…”

“…One possible solution addressed in previous works consists in adding alumina to zirconia stabilized with different yttria contents. This addition enhances the thermodynamic stabilization and improves the mechanical properties and thermal fatigue [2,3].…”

“…However, no equilibrium phases form in plasma processes owing to rapid melting inside the plasma plume as well as fast cooling on the substrate surface. Some authors have found a pseudo-eutectic point for a composition of 60/40 wt% to Al2O3/ZrO2, where the temperature to melt the solid inside the plasma plume is minimum [3,16]. Hence, a reduction of plasma enthalpy requirements is achieved by depositing this pseudo-eutectic composition.…”

“…However, Al2O3/ZrO2 coatings by SPS have been less addressed. Besides when SPS coatings were researched the corresponding feedstocks suspensions were too diluted (30 wt.%) for industrial scale [3,17]. For this reason, the aim of the present work is to develop a thermal barrier coating by SPS technique from aqueous Al2O3/YSZ suspensions with low power consumption by using concentrated suspensions of an eutectic composition.…”

Thermal Plasma Processes for Production of Hollow Spherical Powders: Theory and Experiment

“…In several recent years an active interest has been shown to suspension plasma spraying (SPS), a process in which a liquid containing suspended nano-and submicrometer particles of spray material is injected under pressure into a plasma flow [22][23][24][25].…”