High temperature imaging media for digital image correlation

A thermal barrier coating is provided. The thermal barrier coating is configured to remain adherent to a substrate under high strains, thus allowing the use of non-contacting strain measurement systems, using digital image correlation for example. The thermal barrier coating may include a first layer of a partially metallic material configured to adhere to a metallic substrate, and a second layer of a partially ceramic material configured to adhere to the first layer. A successful configuration has a top layer thickness that is approximately two-thirds of the first layer thickness.

FIELD OF THE DISCLOSURE

The present disclosure generally relates to thermal barrier coatings, and particularly to thermal barrier coatings for use in non-contact characterization of high temperature materials.

BACKGROUND OF THE DISCLOSURE

Thermal barrier coatings are applied to a variety of materials typically exposed to high temperature or high temperature gradient environments. Thermal barrier coatings are typically applied to the surfaces of metallic substrates to insulate and protect the general integrity of the metallic substrates from prolonged thermal loads. The unique characteristics of thermal barrier coatings allow for use in non-contact strain measurements of the metallic substrates which may be exposed to high temperature or high temperature gradient environments.

Conventional thermal barrier coatings are comprised of two or more layers, such as a bond coat, a thermally grown oxide and a top layer. The bond coat is typically formed of a metallic material or metal alloy which provides an adhering interface between the top coat and the substrate. Existing non-contact strain measurements are limited to relatively low temperatures (<1000° F.), and strain levels less than ˜10%. These limits are associated with the materials, such as ceramic paint, used to provide optical contrast.

Ceramic paints are limited both in temperature capability and strain compatibility. They are susceptible to spalling and flaking at high strain levels. Degradation of this type will preclude successful use of a non-contact strain measurement technique such as digital image correlation. The present disclosure is directed at addressing one or more of the deficiencies set forth above.

SUMMARY OF THE DISCLOSURE

In accordance with one aspect of the disclosure, a thermal barrier coating is provided. The thermal barrier coating includes a bond layer having a first thickness, and a top layer having a second thickness that is approximately two-thirds of the first thickness.

In a refinement, one or more of the bond layer and the top layer may be configured to maintain substantial adherence with a metallic substrate at temperatures of at least approximately 1400° F. and under strain levels of at least approximately 30%.

In accordance with another aspect of the disclosure, a thermal barrier coating is provided. The thermal barrier coating includes a metallic bond coat having a thickness of approximately 0.003 inches, and a second layer ceramic top coat having a thickness of approximately 0.002 inches.

In accordance with yet another aspect of the disclosure, a method of applying a thermal barrier coating onto a metallic substrate is provided. The method includes applying a first layer of a partially metallic material of a first thickness to a surface of the metallic substrate; and applying a second layer of a partially ceramic material of a second thickness to the first layer. The second layer is applied such that the second thickness is approximately two-thirds of the first thickness.

These and other aspects of this disclosure will become more readily apparent upon reading the following detailed description when taken in conjunction with the accompanying drawings.

DETAILED DESCRIPTION

Referring toFIG.1, one exemplary embodiment of a thermal barrier coating20which may be applied to a metallic substrate22is provided. As shown, the thermal bather coating20may include a plurality of layers configured to bond against one another as well as with a given surface of the metallic substrate22in a manner which substantially withstands relatively high temperatures, for example, approximately 1400 F or greater, and relatively high strain levels, for example, strain levels of approximately 30% or greater. More particularly, the thermal barrier coating20may be structured to substantially maintain the integrity thereof and thereby enable non-contact characterization of the metallic substrate22, such as by digital image correlation, or the like, under both high temperature and high strain conditions.

As shown inFIG.1, the thermal barrier coating20may include a first coat or bond layer24that is configured to adhere or bond with a surface of a metallic substrate22. More specifically, the first layer24may be applied in the form of a bond coat or layer24as is commonly used in the art. The bond layer24may be generally metallic, or at least partially composed of a metallic substance or material, such as in the form of a metal alloy, or the like. Moreover, the bond layer24may be composed of any material commonly used in the art that is suited to adhere to the metallic substrate22and provide a sufficient interface between the metallic substrate22and any one or more additional layers of the thermal barrier coating20. Furthermore, the bond layer24may be applied onto the surface of the metallic substrate22in the form of a spray or any other means conventionally used in the art.

The thermal barrier coating20ofFIG.1may additionally include a second layer26that is configured to adhere or bond with the first or bond layer24so as to generally protect the first or bond layer24. The second layer26may be applied, for example, via spray, or the like, onto the bond layer24in the form of a top coat or layer26as is commonly used in the art, and composed of a generally ceramic material. For example, the top layer26may include any one or more of yttria-stabilized zirconia (YSZ), alumina compounds, or any other material capable of sufficiently adhering with the bond layer24.

Still referring toFIG.1, the thermal barrier coating20may additionally include a third layer or a thermally grown oxide layer28that is generally disposed between the first layer24and the second layer26. In particular, the thermally grown oxide layer28may be composed of a slow-growing oxide that is formed through oxidation of the bond layer24, which may further serve to generally protect the bond layer24.

Furthermore, the bond layer24and the top layer26of the thermal barrier coating20ofFIG.1may be provided with different thicknesses to exhibit different properties under high temperatures and high strain levels. As shown inFIG.1, for example, the bond layer24may be provided with a thickness of t1, while the top layer26may be provided with a thickness of t2. Moreover, the bond layer24and the top layer26may be configured such that the second thickness t2is approximately two-thirds of the first thickness t1. For example, the bond layer24may have a thickness of approximately 0.003 inches and the top layer26may have a thickness of approximately 0.002 inches. Such thicknesses of the bond layer24and the top layer26have been found to exhibit desirable results under high temperatures (approximately 1400° F. to approximately 1600° F. or greater) and high levels of strain (approximately 30% to approximately 40% or greater).

Turning now toFIGS.2-5, one exemplary thermal barrier coating20is applied to a sample metallic substrate22and tested under high temperature and high strain conditions. For example, the thermal barrier coating20applied may include a bond layer24having a thickness of approximately 0.003 inches and two passes of a top layer26having an overall thickness of approximately 0.002 inches. As shown,FIG.2illustrates the substrate22as coated with the thermal barrier coating20as described and prior to being subjected to any high temperatures or high strain conditions. Furthermore,FIG.3illustrates the thermal barrier coating20at 1400° F. after 10% strain,FIG.4illustrates the thermal barrier coating20at 1400° F. after 20% strain, andFIG.5illustrates the thermal barrier coating20at 1400° F. after 30% strain. As more clearly shown inFIG.5, the integrity of the thermal barrier coating20may be substantially intact while exhibiting surface cracks under high temperatures and high levels of strain. Moreover, the network of surface cracks are desirable as they are indicative of coating behavior with the ability to assess or map relatively high levels of strain on the sample substrate22using non-contact characterization means, such as digital image correlation, or the like, that was otherwise not possible under such high temperatures due to flaking, spalling, or other modes of degradation.