Process maps for plasma spraying of yttria-stabilized zirconia: An integrated approach to design, optimization and reliability

Plasma-sprayed yttria-stabilized zirconia (YSZ) continues to play an important role in enhancing performance of both propulsion and land-based gas turbine engines. Tailoring the microstructure and properties of these thermal barrier coatings towards achieving both prime reliance and manufacturing reproducibility is a complex task due to the multitude of interrelated parameters that influence the plasma spray process and the deposit formation dynamics. In this article, we report on a study that connects thermal spray coatings through process science and materials science utilizing the concept of process maps. Process maps are representations of interrelationships among control parameters and measured responses. First-order process maps have been established for three YSZ powder morphologies, linking the plasma forming torch parameters to the particle state (responses) through a design of experiments approach and in-flight diagnostics. Refinements to representation of the raw particle characteristics are proposed through the use of group parameters (melting index and kinetic energy) from the experimental results. First-order process maps have been used for process parameterization and feedback control. Correlating the first-order responses with coating properties allows representation of coating properties in the form of second-order process maps and enables identification of process windows. As will be demonstrated in this paper, these advances provide a platform with which to construct comprehensive process-microstructure-property relationships with implications for coating design, process efficiency and full-field assessment of manufacturing reliability. (C) 2008 Elsevier B.V. All rights reserved.