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Dense Alumina–Zirconia Coatings Using the Solution Precursor Plasma Spray Process
Author(s) -
Chen Dianying,
Jordan Eric H.,
Gell Maurice,
Ma Xinqing
Publication year - 2008
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1551-2916.2007.02023.x
Subject(s) - materials science , coating , eutectic system , thermal spraying , cubic zirconia , yttria stabilized zirconia , thermal stability , lamellar structure , chemical engineering , grain size , porosity , phase (matter) , composite material , microstructure , metallurgy , ceramic , chemistry , organic chemistry , engineering
For the first time, dense coatings have been made by the solution precursor plasma spray (SPPS) process. The conditions are described for the deposition of dense Al 2 O 3 –40 wt% 7YSZ (yttria‐stabilized zirconia) coatings; the coatings are characterized and their thermal stability is evaluated. X‐ray diffraction analysis shows that the as‐sprayed coating is composed of α‐Al 2 O 3 and tetragonal ZrO 2 phases with grain sizes of 72 and 56 nm, respectively. The as‐sprayed coating has a 95.6% density and consists of ultrafine splats (1–5 μm) and unmelted spherical particles (<0.5 μm). The lamellar structure, typical of conventional plasma‐sprayed coatings, is absent at the same scale in the SPPS coating. The formation of a dense Al 2 O 3 –40 wt% 7YSZ coating is favored by the lower melting point of the eutectic composition, and resultant superheating of the molten particles. Phase and microstructural thermal stabilities were investigated by heat treatment of the as‐sprayed coating at temperatures of 1000°–1500°C. No phase transformation occurs, and the grain size is still in the nanometer range after the 1500°C exposure for 2 h. The coating hardness increases from 11.8 GPa in the as‐coated condition to 15.8 GPa following 1500°C exposure due to a decrease in coating porosity.