Processing–microstructure relationships for plasma-sprayed yttrium aluminum garnet

• Published in: Surface & coatings technology Vol. 202; no. 24; pp. 6081 - 6089
• Main Authors: Weyant, C.M., Faber, K.T.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 15.08.2008; Elsevier
• Subjects: Amorphous coating; Applied sciences; Cross-disciplinary physics: materials science; rheology; Design of experiments; Exact sciences and technology; Materials science; Metals. Metallurgy; Nonmetallic coatings; Physics; Plasma spray; Processing; Production techniques; Surface treatment; Surface treatments; Thermal barrier coating; Yttrium aluminum garnet; 81.05.Je; 82.80; Ej; Yttrium aluminum garnet; Amorphous coating; 81.15.Tv; Design of experiments; Plasma spray; Thermal barrier coating; Processing; Plasma; Hot spraying; Surface treatments; Non metal coating; Design; Experimental design; Thermal barriers; Plasma arc spraying; Microstructure
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2008.07.008

Plasma-sprayed yttrium aluminum garnet (YAG) has been considered as a component in a thermal barrier coating system to reduce oxidation of the bond coat by impeding oxygen diffusion through the coating. For this application, a fully crystalline, dense YAG coating would be advantageous to maximize lifetime and minimize oxygen diffusion. The effects of nine processing variables on the porosity and percent crystallinity in plasma-sprayed YAG were determined. Two powder types were investigated to compare a commercial, off-the-shelf, fused-and-crushed powder to a specially-processed, spherical plasma-spray powder. The resultant models suggest that plasma torch power and spray distance had the largest effect on the responses. It was determined that the processing parameters that lead to a coating with low porosity produce a coating with low crystallinity and vice versa. A possible route to producing a dense, crystalline coating was explored where a dense, amorphous coating was subsequently heat treated to produce crystalline material that retained the microstructure of the as-sprayed YAG in the bulk of the coating. However, macrocracking in the system due to thermal mismatch and crystallization stresses would need to be addressed for a viable multilayer TBC.