Patent Description:
Airfoils and other articles in the engine, particularly the turbine section, are typically formed of a superalloy and may include thermal barrier coatings to extend temperature capability and lifetime. Ceramic materials, such as ceramic matrix composites ("CMC"), are also being considered for such articles. An example for repairing a region of CMC component is disclosed in the <CIT>.

Among other attractive properties ceramic materials have high temperature resistance. Despite this attribute, however, there are unique challenges to implementing ceramics.

A method according to an example of the present disclosure includes machining a closed-pore surface of a silicon-containing gas turbine engine article to produce a feature. The machining causes removal of the closed-pore surface to produce an open-pore machined surface. The open-pore machined surface is then laser-treated to cause formation of an oxide in the silicon-containing gas turbine engine article that seals the open-pore machined surface to produce a closed-pore treated surface.

In a further embodiment of any of the foregoing, the silicon-containing gas turbine engine article is a ceramic matrix composite (CMC).

In a further embodiment of any of the foregoing, the CMC includes silicon carbide.

In a further embodiment of any of the foregoing, the CMC includes silicon nitride.

In a further embodiment of any of the foregoing, the CMC is selected from the group consisting of silicon carbide, silicon nitride, and combinations thereof.

In a further embodiment of any of the foregoing, the machining and the laser-treating are conducted concurrently.

In a further embodiment of any of the foregoing, the machining is conducted along a first direction, and the laser-treatment includes scanning a laser beam across the open-pore machined surface in a second direction that is non-parallel to the first direction.

In a further embodiment of any of the foregoing, the second direction is transverse to the first direction.

In this disclosure, like reference numerals designate like elements where appropriate and reference numerals with the addition of one-hundred or multiples thereof designate modified elements that are understood to incorporate the same features and benefits of the corresponding elements.

The engine parameters described above and those in this paragraph are measured at this condition unless otherwise specified. The low fan pressure ratio as disclosed herein according to one non-limiting embodiment is less than about <NUM>, or more narrowly greater than or equal to <NUM>. The "Low corrected fan tip speed" as disclosed herein according to one non-limiting embodiment is less than about <NUM> ft / second (<NUM> meters/second), and can be greater than or equal to <NUM> ft / second (<NUM> meters/second).

<FIG> illustrates an article <NUM> from the engine <NUM>. To demonstrate an example implementation in accordance with this disclosure, the article <NUM> is depicted as a turbine vane from the turbine section <NUM> of the engine <NUM>. A plurality of the turbine vanes are arranged in a circumferential row about the engine central longitudinal axis A. It is to be understood, however, that the article <NUM> is not limited to vanes or airfoils and that the examples herein may also be applied to blade outer air seals, combustor liners, support rings, or other engine articles that are formed from ceramic material, particularly those along the core gas path C.

The turbine vane is comprised of several sections, including first and second platforms <NUM>/<NUM> and an airfoil section <NUM> that extends between the platforms <NUM>/<NUM>. The airfoil section <NUM> generally defines a leading edge, a trailing edge, and pressure and suction sides. In this example, the first platform <NUM> is a radially outer platform and the second platform <NUM> is a radially inner platform.

The article <NUM> is formed of a ceramic material. For example, the ceramic material may be a monolithic ceramic, a ceramic matrix composite ("CMC"), or configurations that include both monolithic ceramic and CMC. Example ceramic materials include silicon-containing ceramic, such as but not limited to, silicon carbide (SiC) and/or silicon nitride (Si<NUM>N<NUM>). A CMC is formed of ceramic fiber tows that are disposed in a ceramic matrix. As an example, the CMC may be, but is not limited to, a SiC/SiC composite in which SiC fiber tows are disposed within a SiC matrix. The fiber tows are arranged in a fiber architecture, which refers to an ordered arrangement of the tows relative to one another. A monolithic ceramic does not contain fibers or reinforcement and is formed of a single material.

The article <NUM> includes one or more features <NUM> that are formed in the ceramic material by machining, as opposed to features that may be formed during ceramic processing. The features <NUM> may be, but are not limited to, cooling through-holes, blind holes, slots, ledges, divots, and the like. The ceramic material of the article <NUM> is porous. Such porosity at the surface of the article <NUM> may permit facile infiltration of oxygen, moisture, or other substances that can participate in, or accelerate, undesired reactions with one or more elements in the ceramic material. The article <NUM>, however, may include an oxide surface barrier that seals the pores to provide a closed-pore surface. This oxide may be formed during ceramic processing or during a post treatment process, or may be present in a protective coating that is applied to the article <NUM>. The machining is a subtractive manufacturing process. Therefore, at the locations of the features <NUM> where the article <NUM> is machined, the oxide may be locally removed, thereby revealing open-pore machined surfaces. In this regard, as further discussed below, the article <NUM> is subjected to a post-treatment to re-seal the open-pore machined surfaces.

<FIG> depicts an example of the post-treatment method to re-seal the article <NUM>. In the region of the feature <NUM> shown, there is a closed-pore surface <NUM> that is yet-to-be machined. The closed-pore surface <NUM> includes an oxide that is formed during ceramic processing or during a post treatment process, or that is present in a protective coating that is applied to the article <NUM>. For example, the oxide is a silicon oxide, such as silica that is derived from the silicon of the silicon-containing ceramic from which the article <NUM> is formed.

In the example shown, a tool <NUM> machines the closed-pore surface <NUM> to remove material and thus form the feature <NUM>. The tool <NUM> may be, but is not limited to, a milling tool or a grinding tool. In this example, the machining is conducted along a first direction 74a by moving the tool <NUM> relative to the article <NUM>. In this regard, the machining may be conducted in a manner known to those of ordinary skill in the art by mounting the article <NUM> in a fixture of a computer numerical control (CNC) machine. The machining causes removal of the closed-pore surface <NUM> to produce an open-pore machined surface <NUM>. The open-pore machined surface <NUM> has an open pore volume that is substantially greater than the open-pore volume of the closed-pore surface <NUM>. For example, the open-pore volume of the open-pore machined surface <NUM> is greater than the open pore volume of the closed-pore surface <NUM> by <NUM> % or more.

If left untreated, the open-pore machined surface <NUM> may permit infiltration of oxygen, moisture, or other substances that can participate in, or accelerate, undesired reactions that may reduce durability of the article <NUM>. To re-seal the article <NUM>, the open-pore machined surface <NUM> is laser-treated. In the illustrated example, a laser head <NUM> emits a laser beam 76a onto the open-pore machined surface <NUM>. The laser beam 76a heats the open-pore machined surface <NUM> to facilitate the formation of an oxide that plugs and thus seals the pores of the open-pore machined surface to produce a closed-pore treated surface <NUM>. While not wishing to be bound, it is believed that the heat mobilizes silicon or silicon-containing phases in the silicon-containing ceramic to move to the pores where the silicon readily oxidizes to silicon oxide (e.g., silica) and immobilizes to plug the pores. The closed-pore treated surface <NUM> thus has an open pore volume that is substantially less than the open pore volume of the open-pore machined surface <NUM>. For example, the open-pore volume of the closed-pore treated surface <NUM> is less than the open pore volume of the open-pore machined surface <NUM> by <NUM> % or more.

The laser-treatment may be conducted concurrently with the machining. For instance, as shown, the laser beam 76a follows closely behind the tool <NUM> to treat the open-pore machined surface <NUM> as it is produced from the tool <NUM>. In this regard, the laser-treatment and machining are conducted concurrently, i.e. overlapping in time, such that the feature <NUM> of the article <NUM> is machined and re-sealed in a single, continuous process. As the diameter of the laser beam 76a is smaller than the path machined by the tool <NUM>, the laser beam 76a is scanned over a scanning path across the open-pore machined surface <NUM>. For example, the laser beam 76a is scanned in one or more second directions 76b that are non-parallel to the first direction 74a along which the machining is conducted. That is, the laser beam 76a may be scanned back-and-forth across the machined path in order to treat the full area of the open-pore machined surface <NUM> as it is produced from the tool <NUM>. In one further example, the second direction or direction is/are transverse (<NUM> degrees) to the first direction 74a.

The parameters of the laser-treatment may be adapted to the particular process implementation to minimize material removal. That is, the machining provides bulk removal to substantially form the desired geometry of the feature <NUM>, while the laser-treatment re-seals the surface and removes little or no material.

The disclosed re-sealing may facilitate the elimination of a post-machining seal coating processes. For instance, chemical vapor infiltration and other deposition processes may be used to form dense surface seal coatings on machined surfaces. Such post-machining processes, however, may add cost and choke production process throughput. Thus, by sealing It is to be appreciated that the disclosed examples may also be used where there is little or no initial sealing from an oxide. For instance, the laser-treatment may be used on machined surfaces as discussed above but may then also be used on adjacent non-machined surfaces to provide sealing.

Claim 1:
A method comprising:
machining a closed-pore surface (<NUM>) of a silicon-containing gas turbine engine article (<NUM>) to produce a feature (<NUM>), the machining causing removal of the closed-pore surface (<NUM>) to produce an open-pore machined surface (<NUM>); and
laser-treating the open-pore machined surface (<NUM>), the laser-treating causing formation of an oxide in the silicon-containing gas turbine engine article (<NUM>) that seals the open-pore machined surface (<NUM>) to produce a closed-pore treated surface (<NUM>).