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

Abstract

Suspension plasma spraying (SPS) deposition represents an innovative technique to produce coatings that exhibit improved properties. However, the key to obtain coatings with superior functional properties relies on the investigation of the suspensions as starting materials. For this reason, the present work deals with the suspension preparation for SPS process and its influence on the resulting coatings.Laboratory-prepared 60/40 wt% alumina-zirconia suspensions were concentrated to avoid energy loss and were then successfully deposited by SPS technique. The liquid used was water instead of ethanol due to economical, environmental and safety reasons. The preparation of the suspension plays an important role in SPS process since stable and well-dispersed water suspensions are difficult to obtain. For this reason, colloidal behaviour characterisation of the starting particles as well as rheological optimisation of the feedstock suspensions were addressed in this research.Suspensions with different solid loadings (up to 30 vol.% or 72 wt%) were deposited using several spraying distances. All coatings displayed a bimodal microstructure consisting in partially melted zones surrounded by a fully melted matrix. α-Al2O3 and t'-ZrO2 constituted the main crystalline phases, but differences in the microstructure and properties of the coatings were observed. From these results, some relations between starting suspension and spraying parameters with coating characteristics were found. Thus the optimal spraying distance becomes shorter when the suspension solid loading increases.

Effect of fructose-containing feedstocks on the microstructure of multicomponent coatings deposited by suspension plasma spraying

“…Before injection, the suspensions were filtered to remove agglomerates larger than 75 µm. Suspension plasma spraying conditions were as follows: 700 A, 37/8 slpm of argon and hydrogen flow rates respectively, 1.25 m/s torch scan speed, 22 ml/min suspensions flow rate, 40 mm stand-off distance and to further adherence enhancement the substrates were preheated at 573 K. These conditions have been stablished on the basis of previous research [6,29].…”

“…As set out in the introduction, multifunctionality of fructose in ceramic processing together with its high compatibility in aqueous suspensions allow to use this saccharide in large amounts in ceramic suspensions. However, the viscosity of the suspension must be kept below certain limits in order not to compromise the feeding of the suspension into the plasma torch as reported elsewhere [29,32]. For this reason, preliminary experimentation was carried out to determine the effect of fructose addition on water viscosity.…”

Aqueous suspension processing of multicomponent submicronic Y-TZP/Al 2 O 3 /SiC particles for suspension plasma spraying

“…. This grey-coloured, melted matrix corresponds to the pseudo eutectic mixture of zirconia and alumina [35], which is distributed throughout the coating.…”

Effects of particle dispersion on the properties of suspension-sprayed coatings

“…6)14) For example, Carpio et al 9),12), 14) reported the effects of the spraying distance and supply speed on the properties of sprayed coatings. Rampon et al 7) researched the effects of the viscosity and surface tension of the suspension medium on suspension-sprayed coatings.…”