Quantitative analysis of a new model for the sintering of columnar thermal barrier coatings

Abstract

Sintering of thermal barrier coatings adversely affects their long-term reliability by changing their key attributes. In recent work, we developed a novel modeling approach to study coating structure evolution due to the sintering of topcoat columns and predicted the formation of large clusters, and a network of elongated pore channels separating these [R. Krishnamurthy, D.J. Srolovitz, Acta Mater., in press]. Here we extract statistical measures, such as the pair correlation function, the in-plane porosity and pore size distribution from the predicted sintered microstructures, and systematically analyze their variation as a function of coating system parameters. The variables that have the greatest effect on these measures are the column density and the extent of the ‘feathery’ structure of the coating. At early times, low column densities, and where the ‘feathery’ protrusions extend only to a small distance, small clusters containing mainly neighboring columns are formed. On the contrary, when these variables assume large values, clusters many columns wide are formed. We also predict the formation of in-plane pores of sizes comparable to the width of the ‘mud-cracks’ seen in experiment [V. Lughi, V.K. Tolpygo, D.R. Clarke, Mater. Sci. Eng. A 368 (2004) 212–221]. Estimates for cluster size based on this pore size also agree with experiment.