Patent Application
20100136296
This invention relates to coatings and, more particularly, to consolidating coatings to reduce porosity.
Coatings are widely known and used across a variety of fields for numerous different purposes. For example, one or more coatings are often used to impart a particular property or protect an underlying section from abrasion, high temperatures, or other environmental factors. Typically, the coating is deposited onto the substrate in a known manner. However, after deposition, the coating may include pores that compromise the coating and expose the substrate to a surrounding environment.
One solution to exposure from the pores is to consolidate, or densify, the coating to close the pores. For example, the coating is shot peened using media such as steel or ceramic particles. The particles impact and compress the coating to close the pores. Although effective, it is rather difficult to uniformly consolidate the coating using the media, particularly near corners or other geometric features. Due to a relatively close proximity and geometry of surfaces forming a corner, the media deflects into the path of the shot peening and interferes with consolidation in the corner. Thus, portions near the corner may remain unconsolidated.
Therefore, what is a needed is a method that permits uniform consolidation in tight areas to produce articles with uniformly consolidated coatings. This invention addresses these needs while avoiding the shortcomings and drawbacks of the prior art.
An example method of treating a coating includes the steps of providing the coating on a substrate and laser peening the coating to consolidate it. Consolidation of the coating reduces the porosity. In one example, the power of a laser used to peen the coating is controlled to consolidate the coating to a desired degree, but is not too powerful to dislodge the coating from the substrate.
One example article, such as a gas turbine engine component, includes a substrate and a laser peened coating on the substrate. Laser peening to produce a laser peened coating permits uniform coating consolidation near corners, on curved surfaces, and in other tight spaces.
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows.
Referring to
In the disclosed example, a laser 20 is directed through the tamping layer 18 and impinges on the ablative layer 16. The laser 20 vaporizes the ablative layer 16, thereby causing a localized high pressure wave.
Referring to
In one example, the power of the laser 20 is controlled to a selected range. In one example, the selected range is between 2 gigawatts (GW) and 20 GW. Selecting a power at or near 20 GW produces a relatively larger force that consolidates the coating 12 to a corresponding larger degree. Selecting a power at or near 2 GW produces a force that consolidates the coating 12 to a corresponding lesser degree. Depending on the type of the coating 12 and bonding strength between the coating 12 and the substrate 10, selecting a power above about 20 GW may dislodge the coating 12 from the substrate 10. However, selecting a power less than about 2 GW may not provide enough force to consolidate the coating 12 to a desired degree. Given this description, one or ordinary skill in the art will be able to select a suitable power to consolidate the coating 12 to meet their particular needs.
The types of materials of the substrate 10 and the coating 12 may vary, depending on the intended use. In one example, the substrate 10 is a metal or metal alloy, such as a Nickel superalloy. In another example, the coating 12 includes Nickel, Chromium, Cobalt, Aluminum, Yttrium, or combinations thereof. It is to be understood that the disclosed examples contemplate using laser peening consolidation for any type of coating 12 that would benefit from consolidation. The coating 12 is deposited onto the substrate 10 in a known manner, such as by low pressure plasma deposition, physical vapor deposition, arc deposition, spray, or other known deposition method.
Using laser peening as described above provides the benefits of enabling uniform consolidation of the coating 12. In one example, laser peening permits uniform consolidation near corners, curved surfaces, or other relatively tight areas where it was previously difficult to achieve uniform consolidation using peening media particles.
Additionally, using laser peening instead of media particles to consolidate the coating 12 eliminates a risk of contaminating the gas turbine engine component 30 with the media particles. For example, gas turbine engine components 30 typically include internal cooling passages that open to outside surfaces of the component 30. The passages must be plugged for conventional peening to prevent media particles from entering the passages. Gas turbine engine components 30 are typically scrapped if even a few media particles infiltrate into the passages. By using laser peening, the scrap rate can be reduced because of elimination of the media particles, in addition to reducing expenses associated with plugging the openings.
Although a combination of features is shown in the illustrated examples, not all of them need to be combined to realize the benefits of various embodiments of this disclosure. In other words, a system designed according to an embodiment of this disclosure will not necessarily include all of the features shown in any one of the Figures or all of the portions schematically shown in the Figures. Moreover, selected features of one example embodiment may be combined with selected features of other example embodiments.
Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
