Influence of substrate and sintering temperature on the thickness and number of layers of 3YSZ multilayer sol-gel coatings

Abstract

A study was made of the influence of the substrate (fused quartz, sapphire, soda-lime glass, and stainless steel AISI-310) and sintering temperature (300 °C, 500 °C, and 800 °C) on the thickness and number of layers of 3YSZ multilayer sol-gel coatings that can be deposited by dip-coating without the coating cracking. It was found that the thickness and the number of layers increase with the higher sintering temperature and the greater substrate's thermal expansion coefficient. These trends were explained as resulting from the residual in-plane stresses generated in the sol-gel coating when cooled from the sintering temperature down to room temperature due to its thermal expansion coefficient differing from that of the substrate. Thus, the smaller the residual in-plane tensile stress or the greater the residual in-plane compressive stress, the greater can be the thickness and number of layers of the sol-gel coating. The same is the case for higher sintering temperatures because the densification of the layers either predominates over the increased in-plane tensile stresses or combines synergistically with the greater in-plane compressive stresses.