Patent Application
20110146576
Embodiments described herein generally relate to systems for applying a thermal barrier coating to a superalloy substrate. More particularly, embodiments herein generally relate to systems for carrying out laser assisted plasma coating at atmospheric pressure for applying a thermal barrier coating to a superalloy substrate.
Increasingly stringent demands are being imposed on the efficacy of gas turbine engines employed in the aerospace and power generation industries. This demand is driven by the requirement to reduce the consumption of fossil fuels, and in turn, operating costs. One way to improve turbine efficiency is to increase the operating temperature in the turbine section of the engine. However, with increased operating temperatures comes an increased demand on materials used in the turbine section. Not only must these materials be able to withstand the higher operating temperatures (from about 800° C. to about 1500° C.), but they must also endure increased mechanical stresses, corrosion, erosion, and other severe operating conditions, while continuing to fulfill lifetime requirements expected by the industry. This can be accomplished through the use of thermal barrier coatings (TBCs) applied to the high temperature component.
Conventional practices often utilize plasma spray or electron beam physical vapor deposition (EBPVD) to apply the high temperature TBCs, both of which can be problematic. For example, plasma spray can produce highly porous coatings having lower erosion and impact resistance than EBPVD. Such plasma sprayed coatings can be susceptible to plugging up the cooling holes of turbine components to which they are applied. While EBPVD can produce more desirable coatings, it is an expensive process because it is carried out under a high vacuum and has higher equipment costs.
Accordingly, there remains a need for systems that are capable of producing coatings that are structurally similar to those resulting from EBPVD, without the costly vacuum and equipment requirements set forth previously.
Embodiments herein generally relate to systems for applying a thermal barrier coating to a superalloy substrate comprising: at least one target for supplying a material for making the thermal barrier coating; at least one laser operably directed toward the target for liberating atomic particles from the target; and a plasma torch for generating a plasma for accelerating and depositing the atomic particles onto the superalloy substrate as the thermal barrier coating wherein the superalloy substrate is a nickel based superalloy or a cobalt based superalloy.
Embodiments herein also generally relate to systems for applying a thermal barrier coating to a superalloy substrate comprising: two targets for supplying a material for making the thermal barrier coating; two lasers, one laser operably directed toward each of the targets for liberating atomic particles from the targets; and a plasma torch for generating a plasma for accelerating and depositing the atomic particles onto the superalloy substrate as the thermal barrier coating wherein the superalloy substrate is a nickel based superalloy or a cobalt based superalloy.
Embodiments herein also generally relate to systems for applying a thermal barrier coating to a superalloy substrate comprising: two targets for supplying a material for making the thermal barrier coating, a first target comprising zirconium oxide and a second target comprising yttrium oxide; two Nd:YAG lasers, one laser operably directed toward each of the targets for liberating atomic particles from the targets; and a plasma torch for generating a plasma for accelerating and depositing the atomic particles onto the superalloy substrate as the thermal barrier coating comprising about 92% by weight zirconium oxide and about 8% by weight yttrium oxide.
These and other features, aspects and advantages will become evident to those skilled in the art from the following disclosure.
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 systems for carrying out laser assisted plasma coating at atmospheric pressure (LAPCAP) for applying a thermal barrier coating to a superalloy substrate. While the systems herein are designated “at atmospheric pressure,” they should not be limited to such. More specifically, the LAPCAP system may be utilized at near atmospheric pressure (e.g. about 0.5 Atm to about 3 Atm).
In general, the LAPCAP system involves using at least one pulsed laser to liberate atomic particles from at least one target, and then feeding those atomic particles into a plasma for deposition onto a substrate to form a thermal barrier coating. As used herein, “liberate” can refer to any of ablating, vaporizing, melting, or some combination thereof. While the coatings described herein may be used on any substrate exposed to high temperature environments (from about 800° C. to about 1500° C.), such coatings are particularly suited for use on components in the turbine section of a gas turbine engine.
In one embodiment, and as shown in
More particularly, gas stream 18 can feed into discharge tube 20 to help generate plasma 24 and can comprise any gas suitable for carrying out conventional plasma spray processes, which in one embodiment, can be selected from argon, nitrogen, hydrogen, helium, oxygen, and combinations thereof. In particular, as gas stream 18 feeds into discharge tube 20, the radio frequency field generated by ICP coils 22 can be activated. As gas stream 18 passes through discharge tube 20, adjacent to ICP coils, gas stream 18 can become electrically conductive, and form plasma 24. At low flow rates (e.g. about 0.5 L/minute, for example) the plasma can be more stationary, whereas at higher gas flow rates (e.g. about 30 L/minute, for example) the plasma can take the form of a jet. It will be understood that a variety of flow rates, both above and below those provided herein, can also be utilized to alter the surface morphology and of the thermal barrier coatings. In an alternate embodiment, plasma 24 can be created by a microwave discharge (not shown) instead of, or in conjunction with, ICP coils 22.
Target 12 may comprise any material capable of being atomized by laser 14 and suitable for use as a thermal barrier coating, such as for example, ceramic materials and metallic materials. As used herein, “ceramic materials” can include zirconium oxide, yttrium oxide, alumina and pre-alloyed combinations thereof, while “metallic materials” may include zirconium, yttrium, aluminum, and combinations thereof.
In the embodiment shown in
Several varieties of solid state pulsed lasers having sufficient energy to liberate the atomic particles from the target can be utilized, including, but not limited to, neodymium-doped yttrium aluminum garnet (Nd:YAG) lasers. Because of the adjacency of target 12 to plasma 24, atomic particles 26 are fed into plasma 24 as they are liberated. Plasma 24 can then accelerate the atomic particles, forcing them onto substrate 28, where they can deposit as TBC 30. Variation in the combination of laser operating parameters, including laser pulse length, laser pulse energy, laser intensity, and laser spot size can allow the atomic particle flux and distribution to be tailored to achieve the desired coating composition and properties. Generally, pulsed laser 14 can have a pulse length of from about 5 femtoseconds to about 100 microseconds, a pulse energy of from about 0.001 mJ to about 10 J, an intensity of from about 104 W/cm2 to about 1015 W/cm2, and a laser spot size ranging from about 1 micrometer to about 5 millimeters.
While a variety of substrates 28 can be used in conjunction with the embodiments herein, in one embodiment, substrate 28 may be selected from superalloys suitable for use in high temperature (from about 800° C. to about 1500° C.) environments, such as those present in the turbine section of a gas turbine engine. Some examples of such superalloys can include, but should not be limited to, nickel based superalloys, and cobalt based superalloys. In order to achieve the desired TBC 30 thickness, which can range from about 50 microns to about 750 microns, substrate 28 can be moved beneath a stationary LAPCAP system 10 to build up layers of TBC 30. In an alternate embodiment, substrate 28 can be stationary while the system 10 moves as needed using a pre-programmed robotic armature (not shown). The embodiments herein can result in the deposition of a TBC that has a columnar microstructure similar to that of coatings obtained using EBPVD. More specifically, the TBCs herein can have a column width of from about 0.5 microns to about 60 microns, and an intra column porosity of from about 0% to about 9%. In one embodiment, the TBC can comprise smaller diameter columns and about 0% porosity.
In an alternate embodiment, more than one target and more than one laser can be used. As used here, “lasers” can refer to either multiple independent lasers, or alternately, one laser split into multiple beams. In such instances, each target may comprise the same or different materials (such as in the exemplary embodiment below). It will be understood that one laser, i.e. either an independent laser, or a split laser beam, can be operably directed toward each target to liberate atomic particles therefrom.
By way of example and not limitation, and as shown in
The embodiments described herein differ from conventional processes. Particularly, unlike EBPVD, LAPCAP does not require the use of costly vacuum pumps, and particle generation, acceleration, and deposition can be accomplished using a single apparatus. However, in spite of these differences, LAPCAP can produce coatings having a columnar microstructure that is similar to coatings made using EBPVD. This is possible since LAPCAP deposition occurs on an atomic level. The result is a TBC that can be less susceptible to impact and erosion damage than coatings produced using conventional plasma spray processes. Additionally, the clogging of cooling holes that can occur with plasma spray can be greatly reduced or eliminated using LAPCAP.
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.
