Optimization of Mullite Based Coating Using Slurry Spray Technique

Ceramic-metal functionally graded materials (FGMs) have been attracting a great deal of attention as environmental barrier coatings (EBCs) for aerospace structures and turbine blades working under elevated temperatures and chemically harsh environment. A relatively new, simple and low cost manufacturing method of environmental barrier coatings based on the slurry spray technique (SST) has been developed. In this research, it is desired to develop this technique to achieve the coating quality comparable to the existing manufacturing methods, which are often expensive. This paper describes the development and optimization of mullite-nickel based coating using Slurry Spray Technique analysing the effect of MgO as liquid phase sintering (LPS) additive. Taguchi's experimental design based on L9 orthogonal array was employed for optimizing the tech- nique and analyzing the effect of selected process parameters (sintering temperature, sintering time and percentage of additives). The response parameter of the coating so produced is measured in terms of coating interface adhesion strength. The test results have been used to downselect the significant process parameters and help demonstrate the feasibility of coatings produced by slurry spray technique. The test results demonstrate satisfactory adhesion strength of the developed coating, which is comparable with that pro- duced from traditional techniques such as flame spray method.