Case studies

Abstract: High-porosity thermal barrier coatings are utilized on gas turbine components wheremaximizing the coating thermal insulation capability is the primary design criteria. Though suchcoatings have been in industrial use for some time, manufacturing high-porosity coatings quickly and efficiently has proven challenging. With the industry demand to increase productivity and reduce waste generation, there is a drive to look at improved coating manufacturing methods. This article looks at high-porosity coatings manufactured using a high-power plasma system in comparison with a current industrial coating. A commercial spray powder is compared with an experimentalLow-Density powder developed to maximize coating porosity without sacrificing coating deposition efficiency. The resultant coatings have been assessed for their microstructure, adhesion strength,furnace cyclic lifetime, thermal conductivity and sintering behavior. Finally, the impact of sprayprocessing on coating economics is discussed. The use of a Low-Density powder with a high-power plasma system allows a high-porosity coating to be manufactured more eciently and more cost effectively than with conventional powder feedstock. The improvement in thermal properties for the experimental coating demonstrates there is scope to improve industrial coatings by designing with specific thermal resistance rather than thickness and porosity as coating requirements.

Keywords: thermal barrier coating; high porosity; thermal cyclic fatigue; thermal conductivity; adhesion strength; sintering; deposition efficiency; plasma spraying