Introduction

Plasma spray deposition of both metallic and ceramic thermal barrier coatings is widely used for oxidation protection and increased component temperature capability in aircraft gas turbines. Ceramic coatings are of particular interest because of the substantial improvements in engine efficiency which are achieved through increases in turbine inlet temperature. Corresponding advantages result from use of thermal barrier coatings in diesel engines.

The performance and durability of a ceramic coating are determined by the inherent properties of the coating material and the nature of the microstructure which results from processing of the coating. Although progress has been made in the former area (i.e. understanding of composition effects, optimization of microstructure, and development of new coating chemistries), the more significant advances of the past decade have probably involved process automation. A fully automated plasma spray cell coating production system, for example, is currently being operated by the US Air Force at the San Antonio Air Logistic Center, and process qualification for selected engine components has been achieved. The successful implementation of this system contributes to the ■ data and experience base for transfer of thermal barrier coating technology to diesel engine applications.

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