Modified thermal barrier composite coatings

Abstract

A novel coating system is provided that allows for a single coating structure to exhibit properties previously considered mutually exclusive. A unique approach for tailoring specific properties of a coating structure as a function of location within the coating is provided with a specially designed undercoat having a columnar macrostructure and a second coating layer that is selected to be compatible with and complement the undercoat. The resultant composite coating system can maintain thermocomechanical compliance while improving various bulk and / or free surface properties of the composite coating system.

Description

FIELD OF THE INVENTION[0001]The present invention relates generally to the field of thermal barrier composite coatings utilized to protect substrate materials from high temperature and corrosive environments.BACKGROUND OF THE INVENTION[0002]Thermal barrier coatings (hereinafter, referred to as “TBC's”) applied onto a substrate are known to inhibit the flow of heat into the substrate. TBC's are commonly utilized to protect alloy components of gas turbine engines that are exposed to hot combustion gases.[0003]TBC's can be deposited by vapor processes, such as physical vapor deposition (PVD). Such PVD coatings typically are produced from process conditions designed to foster nucleation and growth of discrete, tightly packed, columnar grains which provides a compliant microstructure. The columnar grains are separated by small gaps that can relieve the stress in the coating. However, the gaps between the columns can provide pathways for penetration of contaminants which can induce corros...

AI Technical Summary

Benefits of technology

This patent describes a thermal barrier composite coating that is applied to a smooth substrate. The coating has a first layer with small columns and valleys that improve its adhesion to a second layer. The first layer is made from a liquid suspension of small splats that have a random orientation, while the second layer is made from a densified coating that has lower porosity and better resistance to erosion. The composite coating has improved mechanical properties and can withstand higher temperatures compared to a single layer coating.

Problems solved by technology

However, the gaps between the columns can provide pathways for penetration of contaminants which can induce corrosion of the underlying coating and / or substrate material.

The inter-splat boundaries can be tightly joined or may be separated by gaps resulting in some porosity.

However, the inter-splat gaps in the as-deposited APS microstructure tend to densify upon exposure to high temperatures.

Such densification may result in a shorter operating life in a gas turbine environment by virtue of repeated thermal cycling inducing accumulation of thermal stresses within the coating that can ultimately cause spallation.

While such a columnar structure may have some advantages when compared to the conventional as-deposited APS microstructure, these coatings have drawbacks, including low erosion resistance when tailored to have low intra-columnar densities; a direct heat path along the inter-columnar gaps; and / or potentially low resistance to chemical infiltration due to inter-columnar gaps and low intra-columnar densities.

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