Corrosion-resistant layered coatings

The present invention relates to corrosion-resistant coatings for metallic articles and to methods for forming the corrosion-resistant coatings on the metallic articles. More specifically, but not exclusively, the present invention is directed to multilayered coatings and to methods for forming the layered coatings on metallic articles.

In the gas turbine engine industry, high temperature corrosion- and oxidation-resistant protective coatings for nickel-based and cobalt-based alloy components, such as turbine blades and vanes, are required. These coatings are particularly useful for new generation gas turbine engines that are designed to operate at higher turbine inlet temperatures for greater engine performance and fuel efficiency.

Current methodologies use a MCrAlY-type coating (M=Co, Ni, or Fe) to provide oxidation and hot corrosion protection for many superalloy components used in, but not restricted to, turbine engine components. The MCrAlY type coatings offer protection for Type 1 hot corrosion processes which predominate at a temperature around 1650° F. (˜900° C.). However, it has been observed that, in use, some coated components exhibit corrosion patterns consistent with Type 2 corrosion processes, which typically occur around 1300° F. (˜700° C.). This result may not be entirely unexpected since many superalloy components, for example, turbine components routinely used in marine environments, operate over a wide temperature range and under widely differing conditions. It would be desirable to prepare a coated alloy component that can provide extended service life under widely varying operating conditions.

A need therefore exists for advancements in the relevant field, including improved. coatings that can protect the underlying substrate from oxidation and corrosion, particularly in high temperature environments, coated articles, and methods of coating the articles with high temperature, corrosion-resistant coatings. The present invention is such an advancement and provides a wide variety of benefits and advantages.

The present invention relates to corrosion-resistant coating systems and methods of providing the coating systems to metallic articles. Various aspects of the invention are novel, nonobvious, and provide various advantages. While the actual nature of the invention covered herein can only be determined with reference to the claims appended hereto, certain forms and features, which are characteristic of the preferred embodiments disclosed herein, are described briefly as follows.

In one form, the present invention provides a graded coating on a metallic substrate. The graded coating is derived from application of a MCrAl(Y, Hf) coating composition followed by application of a green coating composition. The resulting green coated substrate is then heat treated to form the diffused graded coating.

In another form, the present invention provides a coated article comprising: a metallic substrate; a first layer comprising an MCrAl(Y, Hf) alloy, where M is selected from Co, Ni, Fe and mixtures of these metals; and a second layer comprising one or more of the following combinations: a noble metal, silicon containing composition; a noble metal, silicon, aluminum containing composition; a noble metal, silicon, chromium containing composition; an aluminum, silicon containing composition; an aluminum, silicon, chromium containing composition and mixtures thereof. The compositions can be an alloy, a prealloy powder, or a green coating mixture. In preferred embodiments, the noble metal silicon or the aluminum silicon containing metallic compositions can include additional metallic components including: aluminum, chromium, hafnium, lanthanum, manganese, and yttrium.

In another form, the present invention provides a method of preparing a coated metallic article. The method comprises: applying to a metallic substrate a first coating composition comprising a MCrAl(Y, Hf) coating; and applying a second coating composition over the MCrAl(Y, Hf) coating composition, where the second coating composition comprises one or more of the following combinations: a noble metal, silicon containing composition; a noble metal, silicon, aluminum containing composition; a noble metal. silicon, chromium containing composition; an aluminum, silicon containing composition: an aluminum. silicon, chromium containing composition; a noble metal, silicon, aluminum, chromium containing composition; a noble metal, silicon, aluminum, chromium, manganese containing compositions; and mixtures thereof. The resulting coated article is heat treated to provide a diffused coating on the metallic substrate.

Regardless of the metals used, the inventive one-step method diffuses the metals into the underlying layer or substrate. Preferably, a multi-stage heating process is employed. With the multi-stage heating process, the powder-covered substrate is initially heated to a first temperature to begin the diffusion process and is then heated to a second temperature to complete the diffusion. In some embodiments, a pre-diffusion heat treatment is also used.

One object of the present invention is to provide corrosion-resistant layered coatings and methods of coating metallic articles.

Further objects and advantages of the present invention will be apparent from the description provided below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a scanned image of a micrograph of one embodiment of a corrosion-resistant layered coating having a CoCrAlY first layer overlaid with a diffused coating derived from a green coating composition containing platinum, silicon, chromium, and aluminum, which was prepared as discussed in Example 1 in accordance with this invention.

FIG. 2 is a scanned image of a micrograph of one embodiment of a corrosion-resistant layered coating having a CoCrAlY first layer overlaid with a diffused coating derived from a green coating composition containing platinum, silicon, chromium, and aluminum, which was prepared as discussed in Example 2 in accordance with this invention.

FIG. 3 is a scanned image of a micrograph of one embodiment of a corrosion-resistant layered coating having a CoCrAlY first layer overlaid with a diffused coating derived from a green coating composition containing platinum and silicon, which was prepared as discussed in Example 3 in accordance with this invention.

FIG. 4 is a scanned image of a micrograph of one embodiment of a corrosion-resistant layered coating having a CoCrAlHf first layer overlaid with a diffused coating derived from a green coating composition containing platinum, silicon, chromium, and aluminum, which was prepared as discussed in Example 4 in accordance with this invention.

FIG. 5 is a scanned image of a micrograph of one embodiment of a corrosion-resistant layered coating having a CoCrAlY first layer overlaid with a diffused coating derived from a green coating composition containing, silicon, chromium, and aluminum, which was prepared as discussed in Example 5 in accordance with this invention.

FIG. 6 is a scanned image of a micrograph of one embodiment of a corrosion-resistant layered coating having a CoCrAlY first layer overlaid with a diffused coating derived from a green coating composition containing platinum and silicon, which was prepared as discussed in Example 6 in accordance with this invention, followed by a second green coating of aluminum and chromium.

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