Phase Formation and Transformation in Alumina/YSZ Nanocomposite Coating Deposited by Suspension Plasma Spray Process

Abstract

Phase formation and transformation in alumina/YSZ nanocomposite coating deposited by suspension plasma spray process Tarasi, F.; Medraj, M.; Dolatabadi, A.; Oberste-Berghaus, J.; Moreau, C.Contact us / Contactez nous: nparc.cisti@nrc-cnrc.gc.ca. Suspension Plasma Spray process was used for deposition of pseudo-eutectic composition of aluminayttria-stabilized zirconia as a potential thermal barrier coating using Mettech axial III torch. Process variables including feed and plasma parameters were altered to find their effects on the formation of phases in the composite coating. The in-flight particle velocity was found to be the crucial parameter on phase formation in the resulting coatings. Low particle velocities below 650 m/s result in the formation of stable phases i.e., a-alumina and tetragonal zirconia. In contrast, high particle velocities more than 750 m/s favor the metastable c-alumina and cubic zirconia phases as dominant structures in as-deposited coatings. Accordingly, the plasma auxiliary gas and plasma power as influential parameters on the particle velocity were found to be reliable tools in controlling the resulting coating structure thus, the consequent properties. The noncrystalline portion of the coatings was also studied. It was revealed that upon heating, the amorphous phase prefers to crystallize into pre-existing crystalline phases in the as-deposited coating. Thus, the ultimate crystalline structure can be designed using the parameters that control the particle velocity during plasma spray coating.

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

“…It can be appreciated that coatings were mainly crystalline with α-Al2O3 and metastable t'-ZrO2 as main phases. γ-Al2O3, usual in Al2O3 and Al2O3/YSZ coatings, was not observed due probably to two different reasons: unmelted regions kept the crystalline phases of the starting powders while an overheating of the coating together with the reheating of the coating by the subsequent deposition passes can explain the phase transformation from metastable γ-to α-Al2O3 in the melted zones [17]. Nevertheless these observed phases in the coatings are characterised by high thermal stability in a wide range of temperatures which include those of operational turbines [2], In addition, melted α-Al2O3 and t'-ZrO2 display better mechanical properties than those exhibited by the other possible crystalline phases [17].…”

“…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.…”

Solution and Suspension Plasma Spraying of Nanostructure Coatings

“…Al 2 O 3 -ZrO 2 composite coatings showed higher wear resistance than pure Al 2 O 3 coatings, Tingaud et al (2010) . Tarasi et al (2010) investigated the phase formation in Al 2 O 3 -YSZ sprayed with an Axial III plasma torch. They found that the particle velocity was the key parameter to achieve stable or metastable phases.…”

Microstructure evolution and thermomechanical properties of plasma‐sprayed Yb2SiO5 coating during thermal aging

“…The wide peak between 200°C and 800°C may be interpreted as the relaxation area that is a feature of amorphous materials. This relaxation involves changes in some physical properties caused by the reduction in the free volume to a closer‐to‐equilibrium condition that was not possible during rapid solidification . The sharp exothermic peak at 1018°C is related to crystallization of Yb 2 SiO 5 from amorphous phase into crystals, which is expected to spontaneously generate.…”