Optimization of plasma spray process variables to attain the minimum porosity and maximum hardness of the LZ/YSZ thermal barrier coatings utilizing the response surface approach

Abstract

Lanthanum zirconate (LZ) has emerged as a novel thermal barrier coating (TBC) material because of its higher temperature phase stability, and low sintering ability than the current standard yttria-stabilized zirconia (YSZ). In order to combine the advantages, LZ and YSZ feedstock powders are blended with predetermined weight ratios (50:50) as composite coatings. The leading issue in developing the composite coating using the atmospheric plasma spray method (APS) is finding the optimum range of input parameters to attain the desired coating properties. This issue can be resolved by developing empirical relations to find the porosity and microhardness of the coating by the atmospheric plasma spray method (APS). Spray parameters such as input power, spray distance, and powder feed rate are vital in determining the coating quality. Three variables and five levels of central composite rotatable design (CCD) to reduce the overall run of the experiment were utilized in the research. The empirical relations were predicted to find the porosity and microhardness of the specimens with APS process parameters, and the empirical relations were examined through ANOVA. Optimizing the plasma spray parameters was done using response surface methodology (RSM), which provides the minimum porosity and maximum hardness. It is validated using surface response graphs, contour plots, and overlay plots. As a result, the input power has the greatest impact on the coating properties among the three variables, and the standoff distance and powder feed rate are the subsequent important spray parameters.

Keywords

• optimization
• design of experiments
• porosity
• hardness
• lanthanum zirconate
• yttria-stabilized zirconia