Patent Description:
A prior art method of forming a ceramic matrix composite is disclosed in <CIT> and a method of forming a glass ceramic component is disclosed in <CIT>.

The present invention provides a method of fabricating a glass matrix composite according to claim <NUM>.

Other features of embodiments are recited in the dependent claims.

A method of fabricating a glass matrix composite according to an example of the present disclosure includes providing a fiber preform in a cavity of a die tooling. The fiber preform circumscribes an interior region and initially has a first size. A parison of glass matrix material is provided in the interior region, and pressurized inert gas is introduced into the parison to outwardly inflate the parison against the fiber <NUM> preform. The pressure causes the glass matrix material to compress the fiber preform to a second size against the mold tool and also flow and infiltrate into the fiber preform to thereby form a consolidated workpiece. The consolidated workpiece is cooled to form a glass matrix composite.

In a further embodiment of any of the foregoing embodiments, the fiber preform is formed of fibers selected from the group consisting of silicon carbide fibers, carbon fibers, Si<NUM>N<NUM> fibers, SiBCN fibers, SiCN fibers, SiOC, SiAlOC fibers, SiZrOC fibers, SiTiOC fibers, B<NUM>C fibers, ZrC fibers, HfC fibers, alumino silicate fibers, Al<NUM>O<NUM> fibers, ZrO<NUM> fibers, and combinations thereof.

In a further embodiment of any of the foregoing embodiments, the fiber preform has at least <NUM>-axis curvature.

In a further embodiment of any of the foregoing embodiments, the fiber-reinforced matrix composite is, by volume percent, <NUM>% to <NUM>% of the glass-containing matrix material and <NUM>% to <NUM>% of the fiber preform.

A further embodiment of any of the foregoing embodiment includes pre-heating the parison outside of the interior region and then inserting the parison into the interior region.

In a further embodiment of any of the foregoing embodiments, the fiber preform initially has a first size, and the pressure causes the glass matrix material to compact the fiber preform to a second size against the mold tool.

A further embodiment of any of the foregoing embodiment includes, prior to providing the fiber preform in the cavity of the die tooling, depositing a glass layer on the cavity of the die tooling.

A further embodiment of any of the foregoing embodiment includes holding the pressure for a period of time to saturate the fiber preform with the glass matrix material.

In a further embodiment of any of the foregoing embodiments, the fiber preform is axisymmetric.

Forming glass matrix or glass-ceramic matrix composites into complex geometries with good properties, and in a repeatable manner, can be challenging. As will be discussed herein, the disclosed methodology may be used to facilitate forming such composites into complex geometries with low porosity, although the methodology may also be applied to other geometries. For example, the method may be used to fabricate an annular combustor shell for a gas turbine engine, but it will be appreciated that the method may also be applied to other gas turbine engine components.

<FIG> schematically depict several states through the disclosed methodology. Although these states may be presented individually herein and/or by steps, it is to be understood that some of these states may be performed or may occur in combination, over the same or overlapping time frame. The method is generally a glass blow-molding technique that is conducted in a die tooling <NUM>, which is shown in <FIG>. The die tooling <NUM> in this example has two opposed die halves that form a cavity 20a there between. The cavity 20a is shaped in the geometry of the component being made. As is typical, the die halves are moveable relative to one another to open and close the cavity 20a. As an example, the die tooling <NUM> is formed of graphite, although not limited thereto. The die tooling <NUM> may be situated in a heater (not shown) with process gas (e.g., argon, nitrogen, carbon monoxide) capability or high vacuum capability (typically vacuum pressure less than <NUM>-<NUM> torr).

As also depicted in <FIG>, a fiber preform <NUM> is provided in the cavity 20a and generally lines the cavity 20a. The fiber preform <NUM> is thus located at the margins of the cavity 20a, and the portion of the cavity 20a inboard of the fiber preform <NUM> is referred to herein as an interior region. Although many different geometries may be used, the method in particular facilitates complex geometries. For instance, the fiber preform <NUM> (and also the cavity 20a) has at least <NUM>-axis curvature (curvature about <NUM> axes).

The fiber preform <NUM> is a network of fibers, such as but not limited to, one or more layers of unidirectional fibers layers (e.g., fiber tape), woven sheets, or <NUM>-dimensional fabrics. The layers, sheets, fabric, or other starting fiber material may be provided by laying-up the network of fibers in a desired configuration in the cavity 20a. In one further example, the fiber preform <NUM> is a braided tubular structure that generally conforms to the geometry of the cavity 20a. In a further example, the fiber preform <NUM> (and the cavity 20a) are axisymmetric about a central axis A. The types of fibers of the fiber preform <NUM> are not particularly limited. As an example, silicon carbide fibers, carbon fibers, Si<NUM>N<NUM> fibers, SiBCN fibers, SiCN fibers, SiOC, SiAlOC fibers, SiZrOC fibers, SiTiOC fibers, B<NUM>C fibers, ZrC fibers, HfC fibers, alumino silicate fibers, Al<NUM>O<NUM> fibers, ZrO<NUM> fibers, or combinations may be useful for combustors or other gas turbine engine components.

In some examples, the preform <NUM> may include other constituents or sub-components in addition to the fibers. For instance, the preform <NUM> may include pre-impregnated glass (e.g., a glass powder), pre-impregnated inorganic material, or polymeric binder. A pre-impregnated glass may facilitate densification or contribute to desired properties of the final product. Similarly, an inorganic material may facilitate densification or contribute to rigidization. A polymeric binder may facilitate the formation of the fibers into the geometry of the preform <NUM>. The binder may be burned off prior to lay-up in the die tooling <NUM> or during processing. Sub-components may also be included, in the preform <NUM> and/or adjacent the preform <NUM> in the die tooling <NUM>. Such sub-components may be, but are not limited to, pre-consolidated sub-components that are formed of glass-ceramic matrix composites or other materials, as long as the materials can substantially withstand the heat and pressure of the glass blow-molding process. For example, the preform <NUM> may be used in the glass blow-molding process to additively join several pre-consolidated sub-components.

As shown in <FIG>, while the cavity 20a is open, a parison <NUM> of glass matrix material is provided in the interior region in the cavity 20a. The parison <NUM> is a solid block, but may alternatively be a hollow structure. The glass matrix material is generally a glass that is composed mostly of silica but may contain other oxides, such as but not limited to, oxides of calcium, magnesium, barium, boron, aluminum, sodium, potassium, or combinations thereof. Most typically, the parison <NUM> will be made only of the glass and will exclude fillers that hinder or prevent inflation. Additional example glass may include, but is not limited to, borosilicate glass B<NUM>O<NUM> x - Al<NUM>O<NUM> y - nSiO<NUM>, Li<NUM>O x - Al<NUM>O<NUM> y - nSiO<NUM>-System (LAS-System), MgO x - Al<NUM>O<NUM> y - nSiO<NUM>-System (MAS-System), ZnO x - Al<NUM>O<NUM> y - nSiO<NUM>-System (ZAS-System), CaO x - Al<NUM>O<NUM> y - nSiO<NUM>-System (CAS), BaO x - MgO y - Al<NUM>O<NUM> z - nSiO<NUM>-System (BMAS-System), BaO x - Al<NUM>O<NUM> y - nSiO<NUM>-System (BAS-System), SrO x - Al<NUM>O<NUM> y - nSiO<NUM>-System (SAS-System), REO-x-Al<NUM>O<NUM>-nSiO<NUM>- Systems (where REO are oxides of the rare earth metals, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, including Sc, Y, and Hf), and the like, including combinations. The glass matrix material may be selected in accordance with the type of fibers used in the preform <NUM>, viscosity at the desired processing temperatures, and end-use requirements.

The parison <NUM> is at first temperature which corresponds to a first viscosity at which the parison <NUM> can be inflated. As will be appreciated, the first temperature and the first viscosity will depend on the composition of the glass used. Such temperature and viscosity will be recognized by those skilled in the art given the benefit of this disclosure, but is generally above <NUM> and below <NUM>. Viscosity can be obtained from known reference charts showing viscosity versus temperature.

The first temperature and first viscosity can be achieved by pre-heating the parison <NUM> outside of the die tooling <NUM>, as depicted at <NUM>. For example, the parison <NUM> is pre-heated in a separate heating chamber and then inserted into the die tooling <NUM>. Alternatively, the parison <NUM> is heated while in the die tooling <NUM> using the heating chamber in which the mold tool <NUM> is located. That is, the die tooling <NUM> and the parison <NUM> are heated at the same temperature. In a further alternative, the parison <NUM> is partially pre-heated in a separate heating chamber to a temperature lower than the desired first temperature and then heated the remaining amount in the die tooling <NUM>. As shown, the parison <NUM> also includes a gas tube <NUM> for inflation.

As depicted in <FIG>, the die tooling <NUM> is then closed and an inert pressurized gas <NUM> is introduced into the parison <NUM> via the gas tube <NUM> to inflate the parison <NUM> outwardly against the fiber preform <NUM>. The force of the parison <NUM> against the preform <NUM> may also serve to compress (debulk) the fiber preform <NUM>. An inert gas is one that does not substantially react with the glass or fiber preform <NUM> under the fabrication conditions. For example, the inert gas is argon, nitrogen, helium, carbon monoxide, or mixtures thereof. The flow rate and pressure of the inert gas is controlled to inflate the parison <NUM>. For instance, the flow rate and pressure are controlled to avoid puncturing the parison <NUM> during inflation and, optionally, to adjust the compressive force against the fiber preform <NUM>.

Referring to <FIG>, the glass infiltrates into the fiber preform <NUM> to form a green workpiece <NUM>. While under pressure from the inert pressurized gas, the glass begins to infiltrate into the fiber preform <NUM> and continues to compress the fiber preform <NUM>. This infiltration is enhanced, however, by heating the parison <NUM> to increase the first temperature to a second temperature, thereby decreasing the first viscosity of the glass to a second viscosity, i.e., an in-process, in-situ viscosity adjustment. At this second, lower viscosity the glass can more readily flow and infiltrate between the fibers of the fiber preform <NUM> under the continued pressure from the inert gas. Notably, this second, lower viscosity also permits the glass to more readily flow into and fill complex geometries of the fiber preform <NUM>, such as into corner regions and regions of <NUM>-axis curvature. As a result, in comparison to the first viscosity, fewer voids are expected by adjusting to the second viscosity. If the preform <NUM> includes pre-impregnated glass, the pre-impregnated glass may also soften and flow among the fibers. If the preform <NUM> includes inorganic fillers, the glass may also flow around the fillers.

In general, the first viscosity is greater than the second viscosity by a factor of <NUM> or more, or in further examples, by a factor of <NUM> or more but not typically more than a factor of <NUM>. In one example, the first viscosity is above <NUM><NUM> Poise, and the second viscosity is below <NUM><NUM> Poise. The second viscosity will practically be limited to a viscosity at which the glass becomes too thin for the pressure of the inert gas to act on over the time frame of the process.

The pressure of the inert gas may also be controlled to drive the glass into the preform <NUM>. Moreover, the pressure may be held for a period of time to saturate the fiber preform <NUM> with the glass. The hold does not necessarily imply that the pressure is constant, only that pressure is maintained above minimum levels. Therefore, as long as the pressure is above the minimum, the pressure may be increased, decreased, cycled, etc. Flow rate may also be monitored or controlled in order to maintain or effectuate a desired increase, decrease, or cycling or pressure. Those skilled in the art with the benefit of this disclosure will recognize useful flow rates and pressures. In examples, the pressure is from <NUM> MPa (<NUM> psi) to <NUM> MPa (<NUM> ksi). As will also be appreciated, the optimal pressures may differ between different compositions of the glass and/or between components of different sizes. For relatively large sizes, multiple gas tubes <NUM> may be used to provide multiple gas injection locations to facilitate more uniform inflation.

The workpiece is then cooled to form a glass matrix composite <NUM> as shown in <FIG>. For example, the cooling is conducted under an inert gas flow, such as by maintaining a flow of the inert gas from the prior steps. For instance, the glass matrix composite <NUM> is cooled to a point at which it is self-supporting and can be removed from the die tooling <NUM> without substantial damage. This cooling scheme is not limited, and it is to be appreciated that alternative cooling schemes could be used.

In further examples, the glass matrix composite <NUM> is, by volume percent, <NUM>% to <NUM>% of the glass matrix material and a remainder of <NUM>% to <NUM>% of the fiber preform <NUM>. Thus, the level of compression of the preform <NUM> is selected in conjunction with the volume of the glass of the parison <NUM> to achieve the desired glass-to-fiber volume ratio.

Subsequently, the glass matrix composite <NUM> may be subjected to one or more further processing steps. One example processing step includes a heat treatment step that causes crystallization of at least of portion of the glass matrix to convert it to a glass-ceramic matrix. Such a heat treatment may be conducted in the die tooling <NUM> as a further step in the blow-molding process or in a later, separate step before or after other post-consolidation steps.

In one further example of the process described above, two parisons <NUM> are used. A first parison <NUM> is used prior to introduction of the preform <NUM> into the die tooling <NUM> and is expanded outwards in the manner discussed above but is expanded to conform against the sides of the die tooling <NUM> (the steps as in <FIG> but without the preform <NUM>). This first parison <NUM> is thus used to deposit a layer of glass on the sides of the die tooling <NUM>. Subsequently, the preform <NUM> is introduced into the die tooling <NUM> and onto the layer of glass and the process then continues as from <FIG> described above to expand what will be a second parison <NUM>. This enables glass matrix material to infiltrate into the preform <NUM> from both sides to facilitate fewer voids.

In further examples, the glass of the first and second parisons <NUM> may be of different glass compositions in order to infiltrate the respective sides of the preform <NUM> with glasses having differing properties. In this manner, the sides of the preform <NUM>, and thus ultimately the final composite <NUM>, can be tailored for different properties. As will be appreciated, the glass compositions may require the use of different processing temperatures. In this regard, one temperature or temperature range may be used for expanding the first parison <NUM>, followed by use of a second different temperature or temperature range for the second parison <NUM>. Most typically, the second temperature or temperature range will be lower than the first so as to avoid substantially affecting the glass from the first parison <NUM>.

Claim 1:
A method of fabricating a glass matrix composite (<NUM>), the method comprising:
providing a fiber preform (<NUM>) in a cavity (20a) of a die tooling (<NUM>), the fiber preform (<NUM>) circumscribing an interior region and initially having a first size;
providing a parison (<NUM>) of glass matrix material in the interior region;
introducing pressurized inert gas into the parison (<NUM>) to outwardly inflate the parison (<NUM>) against the fiber preform (<NUM>), the pressure causing the glass matrix material to compress the fiber preform (<NUM>) to a second size against the mold tool (<NUM>) and also flow and infiltrate into the fiber preform (<NUM>) to thereby form a consolidated workpiece (<NUM>); and
cooling the consolidated workpiece (<NUM>) to thereby form a glass matrix composite (<NUM>).