RU2807944C2 - Method for manufacturing composite with ceramic matrix - Google Patents

Abstract

FIELD: composite with a ceramic matrix.

SUBSTANCE: method for producing a composite with a ceramic matrix is proposed. The method includes: providing an injection mould with a cavity therein; placing the workpiece in the cavity of the injection mould; impregnating the preform internally in the cavity of the injection mould with a slurry containing a solvent, a matrix binder and solid particles, removing at least a portion of the solvent without curing the matrix binder by heating the injection mould and thereby heating the preform to a temperature above the boiling point of the solvent and below the boiling point of the matrix binder to evaporate the solvent and by removing the evaporated solvent. The solid particles are an oxide ceramic material and have a size distribution ranging from 1 nm to 1000 nm. If the required characteristics of the workpiece (density, porosity or volume fraction of fibres) are not achieved, repeat the impregnation operations with the same or different suspension composition and remove the solvent. Next, the matrix binder is cured by heating the workpiece in an injection mould to a temperature sufficient to cure the matrix binder in the workpiece, removing the workpiece from the mould and sintering.

EFFECT: better control of the strength, density and volume fraction of fibres in the composite.

15 cl, 3 dwg

Description

Field of technology

The present invention relates to a method for producing a ceramic matrix composite. In particular, the invention relates to the impregnation of a matrix material into a composite preform.

State of the art

Ceramic matrix composites (CMC) are a subgroup of composite materials, as well as a subgroup of ceramic materials. CCMs contain ceramic fibers embedded in a ceramic matrix to form a ceramic fiber reinforced ceramic material. The matrix and fibers may include any ceramic material or carbon and carbon fibers.

Oxide ceramic materials are divided into two categories: monolithic oxide ceramic materials and oxide ceramic matrix (OCM) composites. Monolithic oxide ceramic materials consist of powders of pure oxide ceramic materials that have been hot pressed and sintered at temperatures above 1600°C. Oxide CMCs consist of an oxide ceramic matrix reinforced with oxide ceramic fibers. Oxide fibers provide improved mechanical properties compared to monolith. Due to the delicate nature of the fiber reinforcement, oxide CCMs are typically made either using liquid suspensions that are applied to the oxide fiber/fabric, such as pre-impregnation (“prepreg”), or by liquid infiltration of the oxide fiber preform, such as a sol-gel treatment.

For PCM, fibers made of carbon (C), silicon carbide (SiC), aluminum oxide (Al ₂ O ₃ ) and mullite (Al ₂ O ₃ →SiO ₂ ) are usually used. Particles (called whiskers or platelets) are embedded in the matrix. Matrix materials include C, SiC, alumina and mullite.

Manufacturing processes typically consist of three steps: (1) layering and fixation of fibers to produce a preform of the desired shape, (2) impregnation of the matrix material, and (3) final machining and, if required, additional processing such as coating or impregnation to reducing porosity.

Most oxide PFCs are two-dimensional (2D) multilayer stacks. They are usually prepared by pre-impregnating dry fabric with a suspension of a solvated alumina matrix that contains a binder. That is, the suspension contains a solvent, a matrix binder and particles. The matrix is thermosetting and is only partially cured to ensure easy handling during subsequent processing. The pre-impregnated CCM is later exposed to temperature, causing the matrix material to fully cure.

Oxide CCM layers are then cut from pre-impregnated fabric and vacuum bagged (for autoclaving) or pressed to compact. After this, a process step of curing and sintering is carried out in an oven to complete the processing. In cases where additional compaction is required, vacuum impregnation is usually carried out with various diluted suspensions containing 20-60 wt. % solids to improve the impregnation of hardened oxide CMC.

Another common method is to lay a stack of dry two-dimensional layers or a three-dimensional (3D) preform and impregnate it with an alumina slurry. In this approach, dry layers are stacked between two clamping plates (press plates) and impregnated in a slurry bath with a high solids content oxide slurry composition, often 75 wt. % or more solids. This is followed by a curing stage and a sintering stage. The oxide PFC is then hardened and it becomes “free-standing”, meaning it no longer needs to be held in a fixture.

The cured/sintered "free-standing" oxide CMC can be re-impregnated by the additional steps of (one or more) immersing the oxide CMC in a slurry bath of an oxide slurry composition containing a low mass fraction of solid oxide. This is again followed by a curing stage and sintering. The re-impregnation and curing/sintering steps are then repeated with more dilute slurries (to improve impregnation) until the required density and porosity are achieved.

Producing oxide CMCs using these methods can be time consuming and it can be difficult to produce composites having complex geometries. There are a number of significant challenges to the approach of fabricating a 2D material from pre-impregnated alumina. They include the following.

Layering complex shapes with pre-impregnated oxide CCM can be difficult, as the pre-impregnated oxide material often has poor drapability and often has poor rheological properties (due to the impregnated submicron particles).

Forming layers around sharp edges or sharp edges, especially using axially offset layers, can be very difficult to achieve without wrinkles or other anomalies in the layers.

Layer stacks for complex parts, especially when using axially offset layers, can be very large (many layers of different sizes and configurations). May take a long time to assemble and may result in operator errors when laying layers.

Layering, vacuum bagging and autoclaving can be slow and labor intensive.

Additionally, slurry impregnation also poses difficulties, which include the following.

Additional impregnation with a suspension can lead to “clogging” of external surfaces and make the internal porosity of the CCM inaccessible. That is, the suspension particles may not penetrate the center of the CCM well in subsequent processing cycles. The outer surfaces of the CMC may become dense with low porosity and prevent matrix from penetrating into the center of the CMC, where porous areas still exist. Additional processing steps, such as machining, may be required to make internal porous regions accessible.

Additional slurry impregnation in baths can result in matrix buildup in undesirable locations, requiring final machining to maintain oxide CCM dimensional tolerances.

SUMMARY OF THE INVENTION The present invention provides a method for producing a ceramic matrix composite which comprises impregnating a woven preform with a slurry containing a solvent, a matrix binder and particles. At least a portion of the solvent is removed without curing the matrix binder. Impregnation and removal of the solvent are repeated until the required characteristics of the workpiece are achieved. The desired property is typically at least one property selected from the group consisting of density, porosity, and fiber volume fraction. Once the required performance is achieved, the suspension is cured and the workpiece is sintered.

In one embodiment, at least a portion of the solvent is removed by exploiting differences in a chemical or physical property between the solvent and the matrix binder, such as, but not limited to, boiling point or vapor pressure.

In one embodiment, the preform is heated to a temperature that is above the boiling point of the solvent and below the boiling point of the matrix binder to evaporate the solvent, then the preform is impregnated with the slurry and the evaporated solvent is removed. In a specific embodiment, the solvent is isopropyl alcohol or acetone, the matrix binder is aluminum silicate or silane, and the solid particles are an oxide ceramic material.

In some embodiments, the solvent may be water and the particles may be silica in combination with a matrix binder. More specifically, in some embodiments, the particles may be fumed silica.

In some embodiments, the solid particles have a size distribution ranging from 1 nm to 1000 nm. In some embodiments, the suspension contains from 50 to 85 wt. % solid particles and from 15 to 50 wt. % solvent. In particular, in some embodiments the suspension contains from 75 to 81 wt. % solids and from 19 to 25 wt. % solvent.

In some embodiments, the oxide ceramic material is selected from the group consisting of alumina, zirconia, and yttria-stabilized zirconia.

Brief description of drawings

The accompanying drawings, which are included to provide a further understanding of the invention, are incorporated into and constitute a part of this technical specification. The drawings provided herein show various embodiments of the invention and, together with the description, serve to explain the principles of the invention. On the drawings:

in fig. Figure 1 shows a diagram of a system for compacting CCM by impregnation with a suspension,

in fig. 2 shows a flowchart of the described method, and

in fig. Figure 3 shows different types of 3D fiber architectures.

Detailed description

The terms “comprising” and “comprising” as used in this specification may mean “including” and “includes” or may have the meaning generally given to the terms “comprising” and “comprising” in US patent law. The terms "essentially consisting of" or "essentially consisting of" when used in claims have the meaning ascribed to them under United States patent law. Other aspects of the invention are described in the description that follows, or are obvious from the following description (and within the scope of the invention).

The terms “filaments,” “fibers,” “fiber tows,” and “yarns” are used interchangeably in the following description. "Yarns", "fibers", "fiber tows" and "yarn" as used herein may refer to monofilament yarn, multifilament yarn, spun yarn, multifilament tow, high volume yarn, woven tow, coated yarn, bicomponent yarn , as well as yarn made from elastic torn fibers from any materials known to a person skilled in the art. The yarn can be made from carbon, nylon, rayon, fiberglass, cotton, ceramic, aramid, polyester, metal, polyethylene glass and/or other materials that exhibit the desired physical, thermal, chemical or other properties.

"Suspension" means a dispersion of solids, eg particles such as ceramic particles, in a liquid carrier (solvent), which may also contain additives such as binders, surfactants, dispersants and the like.

“CMC” means ceramic matrix composite. The CCM subclass includes “oxide CCM”.

For a better understanding of the invention, its advantages and the objects achieved by its use, reference is made to the attached description, wherein non-limiting embodiments of the invention are shown in the accompanying drawings and corresponding components are designated by the same reference numerals.

The present invention is directed to a method of producing a ceramic matrix composite by slurry impregnation of a preform, such as a two-dimensional woven laminate, a rod-guided fiber placement preform, a three-dimensional woven preform, or a woven preform (types of fiber preforms are hereinafter covered by the term "preform" or "fiber preform" "), in a blank mold (also called interchangeably "tooling" and "injection mold"). The hallmark of this method is the removal of the slurry solvent from the injection mold without allowing the binder to fully cure or harden.

This method takes advantage of differences in the chemical or physical properties of the solvent and the binder. By taking advantage of the difference in properties, the method of removing solvent and incompletely curing the binder can provide better control of the density, porosity and fiber volume fraction of the resulting CCM. The uncured binder provides fluidity of the particles/binder in the mold, which allows control of design parameters such as design parameters of the final CCM such as density, porosity, fiber volume fraction, etc.

Infiltrate

In some embodiments, the injection slurry used in this method contains oxide ceramic materials including particles of aluminum oxide or yttria-stabilized zirconia (YSZ or ZrO ₂ ), a matrix binder (“binder”), and a solvent. The particles in this suspension are typically submicron-sized particles having a size distribution of 1 nm to 1000 nm. In one embodiment, the particles may be silica and, in a particular embodiment, fumed silica particles. The suspension may contain solids in an amount of 50-85 wt. % and solvent in an amount of 15-50 wt. %. A suspension containing solids in an amount of 55-85 wt. % and solvent in an amount of 15-45 wt. %, may be more time efficient than when using solids in an amount of 50-54 wt. %. You can use suspensions containing 60-75 wt. % solids and 25-40 wt. % solvent. In a specific embodiment, the alumina suspension contains solids in an amount of 75-81 wt. % and solvent in an amount of 19-25 wt. %.

The binder used may be aluminum silicate, silane, or other commonly known matrix binder. The solvent used is a highly volatile solvent such as isopropyl alcohol (IPA), acetone and the like. "Volatile" means more volatile than the matrix binder. In some embodiments, the solvent may be water.

As such, CCM contains three components: (1) solvent, (2) matrix binder, and (3) particles. KKM contains any combination of three components. For example, the solvent may be any of isopropyl alcohol, acetone, or water, the matrix binder may be any of aluminum silicate, silane, or other conventional matrix binder, and the particles may be a ceramic material including particles of alumina or yttria-stabilized zirconia. (YSZ or ZrO ₂ ), or may be silica (which includes fumed silica). Each of these components can be characterized as described above in this document.

Fiber preform

A two-dimensional woven dry (or pre-impregnated) laminated fiber stack, a three-dimensional woven preform, a rod-guided fiber placement preform, a braided preform, or other preform(s) can be made using alumina fiber. The 2D architecture may have a layered stacking mode structure, including 0°/90°, 0°/-45°/90°/45°, or any combination thereof. The “0°/90°” layering mode means alternating warp fibers at an angle of 0° and 90° relative to an arbitrary initial value in successive layers. The layer laying mode "0°/-45°/90°/45°" provides the specified angle of the warp fibers in relation to an arbitrary initial value in successive layers. Layers of 0°/-60°/90°/60° can be used similarly.

In some cases, the workpiece has a shape close to the technology specified for the product being manufactured. That is, the workpiece is very close to the final required shape, which can reduce the need for final surface finishing, machining or grinding and/or reduce scrap. Moreover, processing time can be reduced.

The three-dimensional fiber architecture can be either orthogonal 310, layer-to-layer 320, or angled interlocking 330, as shown in FIG. 3. The fiber volumes in the warp and weft directions may vary depending on the application. The alumina fiber may be, for example, any of the 3M® Nextel® fiber grades and have any denier, or other similar fibers.

Tooling and equipment

In FIG. 1 shows a simplified diagram of a matrix impregnation system that can be used to practice this method for producing oxide CCM. The system includes a die inlet 105 for supplying a matrix slurry and a die outlet 110 for removing the matrix slurry, and in particular the slurry solvent, from the workpiece (not shown). The workpiece is placed in the cavity of the injection mold 115, the cavity having a shape conjugate with the shape of the workpiece. The injection mold has at least two parts so that the cavity can be opened to accommodate the workpiece.

The injection mold parts 115 may be held together by a press comprising an upper press plate 120a and a lower press plate 120b. The press platens 120a, 120b serve to hold the injection mold parts together under the die slurry impregnation pressure. Heaters (not shown) for heating the injection mold may be part of the press or separate from the press.

The die inlet 105 includes a cylindrical injector 125 for delivering a die slurry under positive pressure through a pipe 130 into one or more inlets 135 of the injection mold 115. A valve 160 may be provided to suppress flow into the preform when solvent is removed during compaction of the preform. The die outlet 110 includes a vacuum pump 150 to provide negative pressure through the die trap 145 and pipe 155 to one or more outlet ports 140 of the injection mold 115.

Positive pressure applied to the matrix slurry at one or more inlets 135, in combination with negative pressure applied at one or more outlets 140, may help to even out the distribution of the matrix slurry throughout the workpiece during impregnation. The matrix trap 145 may capture excess slurry that exits one or more outlets 140 during slurry impregnation. Negative pressure applied at one or more outlets 140 may also allow solvent to be diverted to compact the preform.

In operation, valve 160 is open to allow positive pressure injection of matrix slurry from the cylindrical injector into the workpiece contained in the injection mold. Using a vacuum pump, negative pressure can be applied to help force the die slurry throughout the workpiece. Slurry coming out of the injection mold may indicate that the slurry has saturated the workpiece. Excess slurry exiting the injection mold can be captured by a trap.

The valve 160 can be closed during compaction of the workpiece. In this part of the method, the solvent is separated from the matrix slurry and drawn out of the injection mold using negative pressure applied at one or more outlets. The solid oxide particles and binder in suspension remain in the voids of the workpiece, thereby making the workpiece more dense.

Way

In fig. 2 shows a flow diagram 200 of a method for producing an oxide CFC according to the present invention. A two-dimensional woven laminate, a three-dimensional woven preform, a puncture-guided preform, a braided preform, or another preform (generally a "preform") is prepared 210 according to techniques known to one of ordinary skill in the art.

The preform is positioned in an injection mold, such as a polymer injection mold, in step 220, and then the injection mold is loaded 230 into the injection mold press with which the pressure to the injection mold to hold the tooling together during the subsequent application of pressure to the tooling.

The injection mold blank and press are first infiltrated with slurry at steps 240, 242, 244, 246, 248, and 250. At step 240, the slurry is pumped under positive pressure into the injection mold inlet and into the blank. inside the instrument. Negative or vacuum pressure 242 can be applied to promote uniform distribution of the slurry throughout the workpiece.

In a specific embodiment, the suspension is an IPA solvated mixture consisting of submicron alumina particles and a silane coupling agent. The preform may be, for example, an aircraft antenna window casing having a nominal size of 21.7 cm × 21.7 cm × 2.4 cm (8.56" × 8.56" × 0.938"). The slurry can be pumped into a mold for injection molding at a pressure of 1.38-1.72 MPa (200-250 psi; 10340-12930 mmHg) and a flow rate of approximately 50 cc/min. In addition to the aircraft casing example above Antenna Window Oxide PFCs are used in other applications including turbine exhaust stack structures, radar radomes, missiles, satellites and other hot environment applications.

The pressure of the slurry on the injection mold is then released and heat is applied 244 to the slurry in the preform by heating the injection mold. When the slurry reaches a predetermined temperature, a solvent removal step 246 is initiated to remove the solvent from the preform. A vacuum pump can be used to apply negative pressure at the injection mold outlet to assist solvent removal. After the solvent is removed, heating is stopped and the injection mold is allowed to cool at step 248. As the solvent is removed from the slurry, the solid oxide particles of the slurry remain in the voids of the preform, thereby making the preform denser.

Solvent removal without complete curing of the matrix binder is made possible by exploiting the differences in the physical properties of the solvent and the binder. Differences in physical properties include different boiling points, phase diagrams, vapor pressure equations and curves, reactivity, etc. That is, the binder is in the "B stage" state. Bringing the binder to "Stage B" is a method of removing at least a portion of the solvent from the binder, allowing the structure to be in an intermediate stage, meaning a solid that is only partially cured.

In a specific embodiment, the difference in boiling point between the solvent and the matrix binder can be used to evaporate the solvent, avoiding curing of the matrix binder. In one example, the suspension is an IPA solvated mixture consisting of submicron alumina particles and a silane coupling agent. In this example, heat is applied to raise the temperature of the slurry to the boiling point of the IPA solvent at atmospheric pressure of 82.5°C (180°F), which is below the cure temperature of the silane coupling agent of 121.1°C (250°F). As such, raising the temperature of the slurry to about 82.5°C (180°F) causes the IPA solvent to boil off or evaporate without curing the silane coupling matrix. Vacuum suction pressure can be applied to the injection mold to suck out the evaporated solvent. For example, a suction pressure of 67.7 kPa (20 inHg; 508 mmHg) could be used.

Removing the solvent creates free/open porosity in the workpiece. That is, an open volume in the preform is created by removing solvent from the binder in the preform. For example, if the suspension contains 80 wt. % solids and 20 wt. % solvent, then the removed solvent causes some porosity to remain in the workpiece.

At step 250, it is determined whether the CCM has the desired density, porosity, and/or fiber volume fraction. If the oxide CCM does not have the required density, porosity and/or fiber volume fraction, a second slurry impregnation can be performed according to steps 240-250 with the same or a different slurry composition.

During the second impregnation, the open volume in the workpiece created by the first removal of the solvent is filled with a suspension. The second impregnation then evaporates the solvent, creating free/open porosity for additional impregnation if required. This is repeated until the required density, porosity and/or volume fraction of the CCM fibers are achieved.

In a specific embodiment, the same suspension composition is used as during the first impregnation. In this embodiment, no dilution or alternative suspension formulations are required. As in the first impregnation embodiment discussed above for an aircraft antenna window housing, the slurry can be pumped into the injection mold at a pressure of 1.38-1.72 MPa (200-250 psi; 10340-12930 mm . Hg) and a flow rate of approximately 50 cubic meters. cm/min. The volume of suspension during the second impregnation is usually less than during the first impregnation.

After the impregnations are completed, the injection mold and the preform are heated 252 to the curing temperature of the matrix binder in the preform. After the matrix binder has cured, heating of the injection mold is stopped and the tooling is allowed to cool in step 254. The injection mold is removed from the press 256. The CMC is then removed 258 from the injection mold and sintered 260. Typical sintering temperatures are 1000°C-1200°C.

Other embodiments are within the scope of the appended claims.

Claims (25)

1. A method for manufacturing a composite with a ceramic matrix, including: providing an injection mold with a cavity therein; placing the workpiece in the cavity of the injection mold; impregnating the workpiece inside the cavity of the injection mold with a suspension containing a solvent, a matrix binder and solid particles, removing at least a portion of the solvent without curing the matrix binder by heating the injection mold and thereby heating the preform to a temperature above the boiling point of the solvent and below the boiling point of the matrix binder to evaporate the solvent and by removing the evaporated solvent; determining whether the required characteristics of the workpiece have been achieved; if the required characteristics of the workpiece are not achieved, repeat the impregnation operations with the same or different suspension composition and remove the solvent until the required characteristics of the workpiece are achieved; curing the matrix binder in the injection mold by heating the injection mold and the preform to a temperature sufficient to cure the matrix binder in the preform; removing the blank from the injection mold, and sintering, wherein the desired characteristic is at least one selected from the group consisting of density, porosity and fiber volume fraction, and the solid particles are an oxide ceramic material and have a size distribution ranging from 1 nm to 1000 nm. 2. The method of claim 1, wherein removing at least a portion of the solvent involves taking advantage of the difference in vapor pressure between the solvent and the matrix binder. 3. The method of claim 1, wherein removing at least a portion of the solvent involves applying a vacuum. 4. The method according to claim 1, in which the solvent is isopropyl alcohol or acetone, the matrix binder is aluminum silicate or silane. 5. The method according to claim 4, in which the suspension contains from 50 wt. % up to 85 wt. % solid particles and from 15 wt. % up to 50 wt. % solvent. 6. The method according to claim 5, in which the suspension contains from 75 wt. % up to 81 wt. % solid particles and from 19 wt. % up to 25 wt. % solvent. 7. The method of claim 5, wherein the oxide ceramic material is selected from the group consisting of alumina, zirconia and yttria-stabilized zirconia. 8. The method of claim 1, wherein the solvent is water, the matrix binder is aluminum silicate or silane, and the solid particles are silica. 9. The method according to claim 8, in which the suspension contains from 50 wt. % up to 85 wt. % solid particles and from 15 wt. % up to 50 wt. % solvent. 10. The method according to claim 9, in which the suspension contains from 75 wt. % up to 81 wt. % solid particles and from 19 wt. % up to 25 wt. % solvent. 11. The method of claim 8, wherein the solid particles are fumed silica. 12. The method according to claim 1, in which the suspension contains from 50 wt. % up to 85 wt. % solid particles and from 15 wt. % up to 50 wt. % solvent. 13. The method according to claim 12, in which the suspension contains from 55 wt. % up to 85 wt. % solid particles and from 15 wt. % up to 45 wt. % solvent. 14. The method according to claim 13, in which the suspension contains from 75 wt. % up to 81 wt. % solid particles and from 19 wt. % up to 25 wt. % solvent. 15. The method of claim 1, wherein the preform type is selected from the group consisting of a two-dimensional (2D) dry or pre-impregnated fiber stack, a 2D woven laminate stack created by rod-guided placement of preform fibers, a three-dimensional (3D) woven preform, and a woven blanks.

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