Patent Application
20080080978
While the specification concludes with claims particularly pointing out and distinctly claiming the invention, it is believed that the embodiments set forth herein will be better understood from the following description in conjunction with the accompanying figures, in which like reference numerals identify like elements.
Embodiments described herein generally relate to methods for forming a protective coating on a turbine engine rotor component used at an elevated operating temperature (i.e. above about 540° C.). Such methods can allow the mechanical performance of the rotor component to be optimized by using the best available alloy, and can protect that alloy against corrosion and oxidation via the application of a protective coating to the component. The protective coating is highly adhesive, does not adversely affect the properties of the underlying base metal, and is thin enough so as not to significantly alter the dimensions of the component to which it is applied. The protective coating can also be readily reconditioned and repaired if necessary. While embodiments herein may generally focus on turbine rotor components of aircraft engines, it will be understood by those skilled in the art that the description should not be limited to such.
The turbine engine rotor component may be of any type, however, methods described herein may be particularly advantageous for use with rotor components, or portions thereof, that experience a service operating temperature of from about 540° C. to about 815° C. Such components may be exposed to compressor bleed air or gas path environments containing ingested corrosive agents, such as metal sulfates, sulfites, chlorides, carbonates, and the like, which can become deposited on the surface of the component over time and result in corrosion damage. Rotor components that may benefit from the methods described herein include, but are not limited to, turbine disks, turbine seal elements and turbine blade retainers. While the entire rotor component may be protected, in many cases, it may be more advantageous and cost effective to protect only selected portions of the rotor component. For example, the mid-to-outer portion of the hub of the turbine disk may be coated, while the bore region, inner portion of the hub, and blade slots may or may not be coated.
Referring to
Referring to
Prior to applying protective coating 60 on surface 62 of metal substrate 64, surface 62 may be pretreated to make surface 62 more receptive for coating 60. One suitable pretreatment method is grit blasting, with or without masking of surfaces not subjected thereto. While those skilled in the art will understand the appropriate parameters for such pretreatment, in general, surface 62 of metal substrate 64 can be pretreated by grit blasting using abrasive particles, such as, silicon carbide, steel, alumina and the like. In one embodiment, the particles may be alumina particles having a particle size of from about 25 μm to about 500 μm. In another embodiment, the alumina particles may have a particle size of from about 35 μm to about 200 μm.
Regardless of whether pretreatment is employed, protective coating 60 may comprise at least one platinum group metal selected from the group consisting of platinum, palladium, rhodium, ruthenium, iridium, osmium, and combinations thereof. The platinum group metal may be deposited onto rotor component 30 by any method known to those skilled in the art, such as, for example, slurry coating, painting, physical vapor deposition, chemical vapor deposition, and metal plating (i.e. electroplating). In one embodiment, the platinum group metal may be deposited in a thickness of from about 0.2 μm to about 50 μm, including all subranges therebetween. However, in another embodiment the coating may have a thickness of from about 0.3 μm to about 10 μm, and in yet another embodiment, from about 0.5 μm to about 3 μm.
As previously described, in one embodiment, it may be desirable to deposit the platinum group metal on portions of surface 62 of metal substrate 64 of rotor component 30 that experience a service operating temperature of from about 540° C. to about 815° C., in another embodiment from about 640° C. to about 760° C., as the natural oxidation and corrosion resistance of such areas may be insufficient to provide the desired protection at elevated service operating temperatures. In contrast, portions of rotor component 30 that generally experience service operating temperatures of less than about 540° C. may not need protective coating 60 as the oxidation and corrosion resistance of the materials of construction alone can provide sufficient resistance. Likewise, portions of rotor component 30 that generally experience service operating temperatures in excess of about 815° C. may require more complex protective coatings, such as thicker diffusion coatings or overlay coatings, and optionally thermal barrier coatings, to help ensure adequate protection.
As referenced previously, in one embodiment, the platinum group metal may be deposited by any of a variety of metal plating techniques, all of which will be understood by those skilled in the art. However,
Referring again to
As previously described, the deposited platinum group metal coating may provide protection against corrosion and oxidation and may have a thickness of from about 0.2 μm to about 50 μm and all subranges therebetween. However, in another embodiment, the coating may have a thickness of from about 0.3 μm to about 10 μm, and in yet another embodiment, from about 0.5 μm to about 3 μm.
While embodiments set forth herein are generally directed to depositing a protective coating directly on a metal substrate, it will be understood by those skilled in the art that the previously described protective coating may similarly be deposited over any preexisting corrosion resistant coating or coatings on the metal substrate.
An electroplating tank (as illustrated in
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to make and use the invention. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal language of the claims.
