Ceramic-metallic composites with improved performance and methods for their manufacture

Abstract

To provide a ceramic-metallic composite material having an improved performance and a production method of the same.SOLUTION: Disclosed is a ceramic-metallic composite material together with a process for producing the same. High temperature strength of an Al2O3-Al composite material is improved by replacing aluminum in a final product with another substance that increases the high temperature strength. The respective processes are started by using a preform originally constituted of silicon dioxide of at least 5 wt.%, and the final product includes Al2O3, aluminum, and other substances.SELECTED DRAWING: Figure 16

Description

[Technical Field]

[0001] The present invention comprises embodiments of ceramic-metallic composites with improved performance and methods for their manufacture. Ceramic-metallic composites, especially those containing aluminum and aluminum compounds as constituents, have numerous applications, including brake components, including brake rotors, degassing rotors, riser tubes, molding dies and molds, heater dip tubes, thermocouple protection tubes, ladles, stirring devices, bearings, nozzles, bushings, valve components, clutches, engine components, turbine components, electrical conductors, heat sinks, radiators, metal working dies, ballistic armor, cutting tools, components for sporting goods (e.g., golf club heads and ice skate blades), impellers, and the like. [Background technology]

[0002] The melting point of aluminum is 660.3°C (1,221°F). Applicants have discovered that ceramic-metallic composites containing aluminum lose their inherent strength, even when heated to temperatures as low as 200°C, to half of the material's room temperature strength. The less aluminum in the ceramic composite, the less strength loss there is. Therefore, an important objective of the present invention is to reduce the percentage of aluminum in the final ceramic composite, thereby correspondingly reducing the strength loss at elevated temperatures. As described in more detail below, this objective is achieved in three separate embodiments by fabricating ceramic-metallic composites with significantly reduced percentages of aluminum.

[0003] Embodiments of the present invention are improvements over the inventions described in U.S. Patent Nos. 5,629,999; 5,629,999; and 5,629,999, which are cited below. Preferred embodiments from these three prior art patents include two main process steps:

[0004] 1. A preform shape comprising a sacrificial oxide ceramic, typically silicon dioxide (SiO2), is prepared according to conventional techniques. The preform shape may consist entirely of the sacrificial oxide or may contain an inert ceramic additive, typically silicon carbide (SiC).

[0005] 2. The preform shape is preheated to an operating temperature, typically between about 1000 and 1250°C, and then completely immersed in a molten aluminum (Al) bath maintained at the same temperature range. The aluminum bath may be pure or may contain trace amounts of impurities, inert alloying elements, or 20-30 wt. % silicon (Si) to completely suppress any reaction between SiC and Al (if SiC is present in the preform). During the preform immersion, the sacrificial oxide reacts with aluminum via a substitution reaction. If silicon dioxide is used, the following reaction occurs: 4Al + 3SiO2 = 2Al2O3 + 3Si. The shape is held in the molten aluminum bath long enough for the substitution reaction to reach completion, converting all of the sacrificial oxide to aluminum oxide (Al2O3). Once the reaction is complete, the shape is removed from the molten aluminum bath. If no silicon was initially present in the bath, the silicon produced by the reaction will be sufficiently diluted to produce an Al2O3-Al composite. If silicon carbide is included in the preform, an Al2O3-Al-Si-SiC composite will be produced. The weights of aluminum and silicon in the final composite will depend on the porosity in the original preform.

[0006] Composite materials produced by conventional techniques have a variety of useful properties, especially near room temperature, but at temperatures above 200°C, the strength of these composites decreases significantly due to the free aluminum phase; that is, aluminum alloys typically lose more than half of their strength when the metal is heated from room temperature to temperatures above 200°C.

[0007] The following prior art is known to the applicant.

[0008] U.S. Patent No. 4,629,999 (George) discloses a method for making aluminum oxide (Al2O3)-aluminum (Al) by a displacement reaction in a molten metal Al bath at a preferred temperature of 700-900°C. The present invention differs from the teachings of George in that the present process is carried out at significantly higher temperatures (typically 1000-1200°C) than George's. Composite materials produced by that patent would exhibit a significant decrease in mechanical performance (e.g., strength) if the material were heated above 200°C because the aluminum would soften as the temperature increased, whereas the present invention results in composite materials with improved high temperature performance.

[0009] U.S. Patent No. 5,999,629 (Breslin) discloses a method for making aluminum oxide (Al2O3)-aluminum (Al) ceramic-metallic composites by a displacement reaction in a molten metal bath at a suitable temperature at least 300°C above the melting point of aluminum (Al) (660°C). The process disclosed in that patent is carried out at temperatures of 960°C or higher. Composites produced according to that patent would exhibit a significant decrease in mechanical performance (e.g., strength) if the material were heated above 200°C because the aluminum would soften with increasing temperature, whereas the present invention provides composites with improved high temperature performance.

[0010] U.S. Patent No. 5,629,999 (Strange) discloses an improvement over the invention disclosed in U.S. Patent No. 5,629,999 (Breslin) by incorporating an inert metal additive that results in improved performance. However, as with U.S. Patent No. 5,629,999 (Breslin), composite materials produced according to that patent will exhibit a significant decrease in mechanical performance (e.g., strength) when the material is heated above 200° C., whereas the present invention results in composite materials with improved high temperature performance.

[0011] U.S. Patent No. 5,629,999 (Breslin) discloses an improvement over the invention disclosed in U.S. Patent No. 5,629,999 (Breslin) by incorporating an inert ceramic additive, such as silicon carbide, which results in improved performance. However, as with U.S. Patent No. 5,629,999 (Breslin), composite materials produced according to that patent will exhibit a significant decrease in mechanical performance (e.g., strength) when the materials are heated above 200° C., whereas the present invention results in composite materials with improved high temperature performance.

[0012] U.S. Patent No. 6,269,493 (Breslin), U.S. Patent No. 6,269,493 (Strange), and U.S. Patent No. 6,269,493 (Breslin) all discuss how to intentionally or unintentionally include substances other than aluminum and silicon in a molten metal bath, such as other metals, dopants, alloying agents, or contaminants, all of which are techniques that have been discussed in various prior art for improving the performance of aluminum. While U.S. Patent No. 6,269,493 (Breslin) and U.S. Patent No. 6,269,493 (Strange) focus on Al2O3-Al composites, and U.S. Patent No. 6,269,493 (Breslin) focuses on Al2O3-Al-SiC composites, neither of them recognizes that the free aluminum in these composites will lose strength at temperatures above 200°C, ignoring how the aluminum was alloyed using conventional techniques or that this is a significant limiting factor in whether the composite can be used in high-temperature applications.

[0013] Patent Document 3 (Breslin) discloses that the composite must contain at least 50 volume percent silicon carbide in a specific particle size range (5 to 5,000 micrometers) to optimize the amount of contact between the SiC particulates and thereby improve the performance of the final composite. Specifically, Breslin states that this will achieve significant improvements in strength, thermal and electrical conductivity, thermal shock resistance, hardness, and wear resistance compared to composites containing less than 50 volume percent SiC, but no data are presented to support these claims.

[0014] Furthermore, Breslin (US Pat. No. 3,629,499) argues that when SiC is incorporated into a composite, a minimum amount of silicon must be present in the molten metal bath to prevent the SiC from being attacked by the aluminum, thereby forming aluminum carbide (an undesirable compound). This phenomenon is well known and is also discussed in White (US Pat. No. 5,629,499). Breslin states that the minimum amount is 18 wt. % Si, at which point the reaction between aluminum and silicon carbide is no longer thermodynamically favorable, and further states that a Si content of between about 20 and about 30 wt. % is preferred.

[0015] Breslin further claims that the process can be carried out at Si levels as high as 95 wt. % in the molten metal bath, but contradicts that too much silicon may prevent the aluminum from reacting with the silica in the molten metal because there may not be enough aluminum to support the substitution reaction. There is no disclosure or knowledge in U.S. Patent No. 5,929,999 (Breslin) that free aluminum may be a limiting factor in the strength of the final composite, especially at high temperatures above 200°C.

[0016] In contrast, the present invention demonstrates that reducing free aluminum by adding silicon or intermetallic compounds has several advantages: 1) the strength of both Al2O3-Al and Al2O3-Al-SiC composites at elevated temperatures above 200°C is improved; 2) in some cases, the room temperature strength may be improved; and 3) Applicants have found that as the amount of silicon is increased, the microstructure of the resulting composite is modified to become more homogeneous, which may be beneficial in optimizing performance other than strength. In none of these cases does the addition of SiC need to be present, nor is it limited to the requirement of 50% by volume SiC, for these benefits to be realized.

[0017] Non-Patent Document 1 discloses data sufficient to support the applicant's claims regarding the improvements of the present invention.

[0018] (Non-Patent Document 2) This reference documents the performance of ceramic grades produced using techniques covered in U.S. Patent No. 5,629,999 (Breslin), U.S. Patent No. 5,629,999 (Strange), and U.S. Patent No. 5,629,999 (Breslin), and supports the claims of improvements obtained by practicing the present invention.

[0019] U.S. Patent No. 5,629,999 (White et al.) discloses a method for making improved aluminum oxide (Al2O3)-aluminum (Al) ceramic-metallic composites by a method completely different from that disclosed in U.S. Patent No. 5,629,999 (George), U.S. Patent No. 5,629,999 (Breslin), U.S. Patent No. 5,629,999 (Strange), and U.S. Patent No. 5,629,999 (Breslin). Composites produced according to this patent would exhibit a significant decrease in mechanical performance (e.g., strength) if the material were heated above 200°C because the aluminum would soften with increasing temperature, whereas the present invention provides composites with improved high temperature performance.

[0020] (Non-Patent Document 3) This reference documented the performance of aluminum and aluminum alloys, including the loss of strength as these metals are heated above 200°C.

[0021] (Non-Patent Document 4) These two references contain thermodynamic data that are used to support the details of this invention.

[0022] (Non-Patent Document 5). This reference investigates substitution reactions suitable for producing ceramic-metallic composites, including improved aluminum oxide (Al2O3)-aluminum (Al) composites, using a variety of starting materials. The data in this document support the present invention. [Prior art documents] [Patent documents]

[0023] [Patent Document 1] U.S. Patent No. 5,214,011 [Patent Document 2] U.S. Patent No. 5,728,638 [Patent Document 3] U.S. Patent No. 7,267,882 [Patent Document 4] U.S. Patent No. 2,702,750 [Patent Document 5] U.S. Patent No. 4,828,008 [Non-patent literature]

[0024] [Non-Patent Document 1] Breslin, MC, Ringnalda, J., Xu, L., Fuller, M., Seeger, J., Daehn, GS, Otani, T., and Fraser, HL, "Processing, Microstructure and Properties of Co-Continuous Alumina-Aluminum Composites", Materials Science & Engineering, A195, pp. 113~119, 1995. [Non-patent document 2] TCON® Data Sheet (2006) [Non-patent document 3] ASM Specialty Handbook: “Aluminum and Aluminum Alloys”, Edited by JRDavis, 1993 [Non-patent document 4] "NIST-JANAF Thermochemical Tables, Fourth Edition, Parts 1 and 2", Edited by MWChase, Jr., 1998 [Non-patent document 5] Liu, W. and Koester, J., "Criteria for Formation of Interpenetrating Oxide / Metal-Composites by Immersing Sacrifical Oxide Preforms in Molten Metals", Scripta Masterialia, Vol. 35, No. 1, pp. 35~40, 1996 Summary of the Invention [Problem to be solved by the invention]

[0025] The present invention comprises embodiments of ceramic-metallic composites with improved performance and methods for their manufacture. Ceramic-metallic composites containing aluminum or aluminum alloys are materials with a variety of useful properties, especially near room temperature. However, at temperatures above 200°C, the strength of these composites decreases significantly due to the aluminum phase, and aluminum alloys typically lose less than half their strength when the metal is heated from room temperature to above 200°C, despite the melting point of aluminum being 660°C. [Means for solving the problem]

[0026] To address this problem, the present invention contemplates three unique methods for controlling the ceramic microstructure and improving the high-temperature performance of ceramic-metallic composites, particularly aluminum oxide (Al2O3)-aluminum (Al) composites fabricated by displacement reactions in a molten metal bath.

[0027] The first method is achieved by adding significant amounts of silicon (Si) into the molten Al metal bath, resulting in a unique Al2O3-Al-Si composite material.

[0028] The second method is achieved by creating an intermetallic compound in the final composite by adding certain elements to the molten Al metal bath, which then form intermetallic compounds through a primary substitution reaction, resulting in a unique Al2O3-Al intermetallic compound composite.

[0029] The third method is achieved by creating intermetallic compounds in the final composite through various approaches, where primary substitution reactions are paralleled by secondary reactions that produce elements that then form intermetallic compounds, again resulting in unique Al2O3-Al-intermetallic composites.

[0030] These novel methods are not obvious from existing technology reflected in the prior art discussed above, particularly the Breslin and Strange patents, and are currently used by applicants to make composite materials sold under the trademark TCON®. Applicants further use the term "transformation process" to describe their method of making, which involves a displacement reaction in a molten metal bath.

[0031] The displacement reaction between the metal and the sacrificial oxide results in a composite material with a co-continuous ceramic-metal phase, which has unique properties. Applicant's preferred method uses a preform shape containing silicon dioxide (SiO2) and performs these displacement reactions by completely immersing the preform in a bath of molten metal; this method for performing displacement reactions is known as the "transformation" process. To avoid reactant starvation, it is best to have the bath contain more than the minimum amount of molten metal required. Furthermore, the preform shape is maintained in the bath until all of the sacrificial oxide has reacted.

[0032] In one variation of this process, the following reaction is used to produce an aluminum oxide ceramic-aluminum metal (Al2O3-Al) based composite: (4+x)Al+3SiO2=2Al2O3+xAl+3[Si] Al

[0033] Note that silicon (Si) by-product dissolves in the molten aluminum (Al); most of this flows into the Al bath, and some remains in the final composite. This results in a material with a composition of 74 wt. % Al2O3, 26 wt. % Al, and traces of Si reaction by-product. The structure of a material typically produced using this process is seen in Figures 1, 2, and 3.

[0034] In another variation of this transformation process, silicon carbide (SiC) particulate matter can be added to these Al2O3-Al-based composites to affect final performance, for example, to improve the thermal shock resistance of the material. Under appropriate processing conditions, the SiC additive is inert and does not participate in substitution reactions. More specifically, to prevent SiC from reacting with Al, the molten aluminum bath contains excess Si to suppress the reaction 4Al + 3SiC = Al4C3 + 3Si. The reaction can then be expressed as: (4+x)Al+3SiO2+y[Si] Al +zSiC=2Al2O3+xAl+(3+y)[Si] Al +zSiC

[0035] The resulting material retains the basic Al2O3-Al structure, bound together with the SiC additive, similar to that seen in Figures 2 and 3. The compositions of these types of composites, commercially manufactured by the assignee of the present application, Fireline, Inc., and sold under the trademark TCON®, are listed in Figure 4, and a typical photomicrograph is shown in Figure 5.

[0036] This transformation process is typically carried out at temperatures above 900°C for the purpose of forming alpha aluminum oxide (α-Al2O3) in the substitution reaction. Special furnaces and equipment are used to maintain the molten aluminum bath at the desired temperature, plus fully immerse the preform and later extract the final TCON® composite shape from the bath. As previously mentioned, while these composites possess unique performance capabilities, their usefulness is limited by a significant decrease in their strength as the temperature increases. Figure 6 shows that heating an Al2O3-Al composite from room temperature to 800°C results in a 73% decrease in strength (from 750 MPa to 200 MPa), and Figure 7 shows that increasing the temperature from room temperature to 700°C results in a 56-72% decrease in strength for two TCON® grades.

[0037] To improve the high temperature mechanical performance of these bicontinuous metal oxide-metal composites, applicants have developed three methods to reduce the amount of free aluminum in the material. The first two methods involve alloying the molten aluminum bath to affect the final material produced via the transformation process, while the third method implements a parallel reaction that occurs during the primary transformation process.

[0038] 1. The first method involves significantly increasing the amount of silicon in the molten metal. This approach was chosen because silicon has a higher melting point than aluminum and will precipitate as discrete crystals. The aim of this method is to replace the amount of aluminum in the composite with silicon crystals, improving high-temperature performance.

[0039] 2. The second method uses selected elements because they readily form high-temperature intermetallic compounds (compounds formed between two or more metals and metalloids), both with aluminum alone and with aluminum and silicon. These intermetallic compounds typically have higher melting points than aluminum. Again, the goal of this method is to replace the amount of aluminum in the composite with the intermetallic compound, improving high-temperature performance.

[0040] 3. The third method achieves the same end result as the second method, but in a different way. It involves adding a secondary type of sacrificial oxide to the preform in addition to the primary sacrificial oxide used to create the composite. These secondary substitution reactions liberate elements that then readily form intermetallic compounds, either with aluminum alone or with aluminum and silicon.

[0041] A number of potential industrial applications for these improved ceramic-metallic composites are outlined in the prior art patents disclosed and discussed above. A focus of current product and market development for the assignee of the present application, Fireline, Inc., is automotive brake rotors, and the composites of the present invention provide significant performance improvements in that application.

[0042] Accordingly, it is a primary object of the present invention to provide ceramic-metallic composites with improved performance, and methods for making them.

[0043] A further object of the present invention is to provide such a composite material which recognizes that the strength of aluminum in the composite material decreases when exposed to temperatures above 200°C.

[0044] A further object of the present invention is to provide improvements to ceramic-metallic composites specific to those incorporating aluminum oxide and aluminum produced by displacement reactions in a molten metal bath.

[0045] A still further object of the present invention is to create a composite material, in one embodiment, by adding a significant amount of silicon into a molten aluminum metal bath, resulting in a unique Al2O3-Al-Si composite material.

[0046] A still further object of the present invention is to create a composite material such that, in a further embodiment thereof, a unique Al2O3-Al-intermetallic composite material is obtained.

[0047] A still further object of the present invention is to carry out a secondary reaction in parallel with the primary substitution reaction, thereby forming a unique Al2O3-Al-intermetallic composite, creating the intermetallic compounds in the final composite.

[0048] It is a still further object of this invention not only to provide such composite materials, but also to disclose and claim methods for their manufacture.

[0049] These and other objects, aspects and features of the present invention will be better understood from the following detailed description taken in conjunction with the accompanying drawings. [Brief explanation of the drawings]

[0050] [Figure 1] Figure 1 shows two stereo-optical micrographs at 10x magnification of a prior art sample of Al2O3-Al composite produced from Melt A. The top half of Figure 1 is a transverse cross section of a 10 mm diameter rod, and the bottom half of Figure 1 is its longitudinal cross section. [Figure 2] 1 is a polarized light micrograph at 1,000x magnification of a prior art sample of Al2O3-Al composite made from Melt A. The red line in the upper right corner of the micrograph indicates a distance of 50 μm. [Figure 3] 1 is a scanning electron microscope (SEM) photograph at 1,500x magnification of a prior art sample of Al2O3-Al composite made from Melt A. [Figure 4] 1 is a table showing details of the grades of composite materials for the compositions of FIGS. 1 to 3 and 5 to 7. [Figure 5] Two stereo optical micrographs at 50x magnification of prior art samples of Al2O3-Al-SiC composites. The left micrograph is of grade TC1, and the right micrograph is of grade TC2. [Figure 6] 1 is a graph of compressive strength versus temperature for prior art Al2O3-Al composites. [Figure 7] FIG. 1 shows three-point bend modulus of rupture versus temperature for two standard prior art TCON grades, with the % strength loss listed for each. [Figure 8] 1 is a table showing three types of molten Al—Si alloy melts that were tested. [Figure 9]Two stereo optical micrographs at 10x magnification of an Al2O3-Al composite sample produced from Melt B from Figure 8. The top half of Figure 9 is a transverse cross section of a 10 mm diameter rod, and the bottom half of Figure 9 is its longitudinal cross section. [Figure 10] 9 is a polarized light micrograph at 1,000x magnification of a sample of Al2O3-Al composite made from Melt B from Figure 8. The red line in the upper right corner of the micrograph indicates a distance of 50 μm. [Figure 11] 9 is an SEM micrograph at 1,500x magnification of a sample of Al2O3-Al composite made from Melt B from FIG. 8. [Figure 12] 12 is a stereo optical micrograph at 10x magnification of an Al2O3-Al composite sample produced from Melt C from Figure 8. The top half of Figure 12 is a transverse cross section of a 10 mm diameter rod, and the bottom half of Figure 12 is its longitudinal cross section. [Figure 13] 9 is a polarized light micrograph at 1,000x magnification of a sample of Al2O3-Al composite made from Melt C from Figure 8. The red line in the upper right corner of the micrograph indicates a distance of 50 μm. [Figure 14] 1 is an SEM micrograph at 1,500x magnification of a sample of Al2O3-Al composite fabricated from Melt C. [Figure 15] 1 is an SEM micrograph at 1,000x magnification of a sample of Al2O3-Al composite produced from Melt B. [Figure 16] 9 is a table of three-point bend modulus of rupture for Al2O3-Al-Si composites produced from melts A, B, and C identified in FIG. 8 and run with and without SiC. [Figure 17] 9 is a table of three-point bending modulus of rupture for experimental material TQ1X (Al2O3-Al-Si composite) produced from melts A, B, and C identified in FIG. 8. [Figure 18] 9 is a table of the three-point bending modulus of rupture of experimental material TC2X (SiC-Al2O3-Al-Si composite) produced from melts B and C identified in FIG. 8. [Figure 19] 1 is a table showing the properties of experimental melts D and E containing molten Al—Fe alloy and Al—Si—Fe alloy. [Figure 20] 20 is a stereo optical micrograph at 10x magnification of an Al2O3-Al-intermetallic composite sample produced from Melt D identified in Figure 19. The top half of Figure 20 is a transverse cross section of a 10 mm diameter rod, and the bottom half is its longitudinal cross section. [Figure 21] 10 is a polarized light micrograph at 1,000x magnification of an Al2O3-Al-intermetallic composite sample produced from Melt D identified in Figure 19. The red line in the upper right corner of the micrograph indicates a distance of 50 μm. [Figure 22] 19A-19C are two SEM micrographs at 1,500x magnification of an Al2O3-Al-intermetallic composite sample produced from Melt D identified in Figure 19. The top image is an SE signal image, and the bottom image is a mixed SE / BSE image. [Figure 23] 10 is a stereo optical micrograph at 10x magnification of a sample of Al2O3-Al-intermetallic composite produced from Melt E identified in Figure 19. The top half is a transverse cross section of a 10 mm diameter rod, and the bottom half is its longitudinal cross section. [Figure 24] 10 is a polarized light photomicrograph at 1,000x magnification of a sample of Al2O3-Al-intermetallic composite produced from Melt E identified in Figure 19. The red line in the upper right corner of the photomicrograph indicates a distance of 50 μm. [Figure 25] 19A-19C are SEM micrographs at 1,500x magnification of an Al2O3-Al-intermetallic composite sample produced from Melt E identified in Figure 19. The top micrograph is an SE signal image, and the bottom micrograph is a mixed SE / BSE image. [Figure 26] 19 is a table of three-point bend modulus of rupture information for experimental composites produced from Melt B identified in FIG. 8 and Melt E identified in FIG. 19 (SiC-Al2O3-Al-Si vs. SiC-Al2O3-Al-Intermetallic). [Figure 27]19 is a table of three-point bend modulus of rupture for experimental composites TC1X and TC2X produced from Melt B identified in FIG. 8 and Melt E identified in FIG. 19 (SiC-Al2O3-Al-Si vs. SiC-Al2O3-Al-intermetallic composites). DETAILED DESCRIPTION OF THE INVENTION

[0051] The three embodiments of the present invention described below provide a significant change to the composition of the molten aluminum (Al) bath in the prior art embodiments, resulting in unique composite materials with reduced amounts of free aluminum and therefore improved performance over that obtained from the prior art embodiments.

[0052] Embodiment #1 - High Silicon Content In a first embodiment of the present invention, a molten aluminum-silicon (Al-Si) bath containing a significant amount of silicon (2-95 wt%) is used to produce Al2O3-Al-Si and Al2O3-Al-Si-SiC composites. The composites so obtained have a lower amount of free aluminum and greater strength at high temperatures than composites produced in preferred embodiments from prior art patents.

[0053] Aluminum-silicon alloy melts containing greater than 2 wt. % Si will precipitate Si crystals upon cooling and solidification. Increasing the silicon content in the Al-Si alloy will replace the Si crystals, reducing the amount of free aluminum in the solidified alloy. As a result, composites produced according to this embodiment can achieve greater high-temperature strength due to this reduction in free aluminum in the final material.

[0054] Even more surprisingly, we found that adding large amounts of Si to the molten Al bath had a dramatic effect on the microstructure of the aluminum oxide in the final composite, changing it from a heterogeneous microstructure to a much more homogeneous one. By employing this processing method, we were able to tailor the microstructure of the material to the requirements of its use, with a more homogeneous structure being desirable in some applications and a more heterogeneous structure being more suitable in others.

[0055] In a preferred embodiment of the patent document 3, an operating temperature between about 1000-1250°C and a molten Al-Si bath containing 20-30 wt% silicon (Si) is used to generally suppress any reactions between the silicon carbide (SiC) in the preform and the aluminum in the bath. The processing temperature range of 1000-1250°C in embodiments of the present invention is also similarly extended to a maximum of about 60 wt%. % It is acceptable for molten aluminum-silicon alloys containing up to 100% Si, and the resulting Al2O3-Al-Si-SiC composites will have higher high temperature strength than composites produced using conventional techniques.

[0056] However, because silicon has a higher melting point than aluminum (1414°C for Si vs. 660°C for Al), the melting temperature of the Al-Si alloy increases with increasing Si content. % At higher silicon concentrations, the temperature may be too low to practice this embodiment, and therefore the preferred processing temperature will generally be between 1250 and 1650°C for silicon concentrations in the range of 60 to 95 wt%.

[0057] In summary, this first embodiment is an improvement over prior art embodiments as a result of using the following conditions: a) a molten Al-Si bath containing 30-60 wt. % silicon at a processing temperature of about 900-1250°C; or b) a molten Al-Si bath containing about 60-95 wt. % silicon at a processing temperature of about 1250-1650°C. [Example]

[0058] Example of Embodiment #1 - High Silicon Content Example 1 Three preform rod shapes containing 100% silicon dioxide (SiO2) were conventionally prepared. Three different molten metal aluminum-silicon (Al-Si) alloy baths were prepared (FIG. 8) and heated to a temperature of 1200°C, where Melt A contained 0% Si, Melt B contained 25% Si by weight, and Melt C contained 50% Si by weight.

[0059] One of the preform rods was preheated to 1200°C and then completely immersed in one of three molten metal baths. to After immersion and removal upon completion of the displacement reaction, the process was repeated with the other two rods and melts to obtain either Al2O3-Al or Al2O3-Al-Si composites. The microstructures of these composites were examined; the composites produced from Melt A (0% Si) are shown in Figures 1, 2, and 3, the composites produced from Melt B (25% Si) are shown in Figures 9, 10, and 11, and the composites from Melt C (50% Si) are shown in Figures 12, 13, 14, and 15.

[0060] The Al2O3-Al composite produced from melt A (0% Si) had a highly radially oriented microstructure with no visible silicon present, the Al2O3-Al-Si composite from melt B (25% Si) had a somewhat homogeneous microstructure, and the composite from melt C (50% Si) had a somewhat homogeneous microstructure, but both had visible silicon clusters present.

[0061] The Si clusters are readily visible in both Figures 9 and 12 and appear to be proportional to the amount of silicon in the melt; i.e., the microstructure in Figure 12 (50% Si) is much more uniform and has twice the amount of clusters than that visible in Figure 9 (25% Si). In the scanning electron microscope (SEM) photographs of Figures 2, 11, and 14, the silicon crystallites provide insufficient contrast to stand out from the aluminum metal. When the composite made from Melt B (25% Si) was reexamined using a different SEM with higher sensitivity, the silicon crystallites became more visible, as can be seen in Figure 15.

[0062] "We found that adding large amounts of Si to the molten Al bath was sufficient to complete the transformation reaction and significantly affected the microstructure of the resulting material, transforming it from a non-uniform radially oriented structure (as in the 0% Si case) to a much more uniform structure. This processing method allowed us to tailor the microstructure of the material to the requirements of the application: a more uniform structure was desirable in some applications, and a more easily oriented structure was suitable in others."

[0063] Example 2 Three sets of preform test bar shapes containing 100% silicon dioxide (SiO2) were conventionally fabricated (TQ1X). Three different molten metal aluminum-silicon (Al-Si) alloy baths were also prepared (FIG. 8) and heated to a temperature of 1200°C, where Melt A contained 0% Si, Melt B contained 25 wt% Si, and Melt C contained 50 wt% Si.

[0064] The three sets of TQ1X preform test bars were preheated to 1200°C, and one set was then fully immersed in one of three molten metal baths, then removed once the displacement reaction was complete, and the process was repeated with the other set of bars and melt, resulting in either Al2O3-Al or Al2O3-Al-Si composites.

[0065] The modulus of rupture was measured for all three sets of test bars at both room temperature (20°C) and elevated temperature (700°C), and the results are shown in Figures 16 and 17. The silicon content in the molten metal alloy bath was found to have a significant effect on the strength of the composite. Comparing TQ1X-A and TQ1X-B, it was found that increasing the silicon from 0 to 25 wt% had virtually no effect on the room temperature strength, but substantially increased the strength at 700°C (182%). Comparing TQ1X-A and TQ1X-C, it was found that increasing the silicon from 0 to 50 wt% reduced the room temperature strength, but substantially increased the strength at 700°C (73%).

[0066] Example 3 Two sets of preform test bar shapes containing 36 wt% silicon dioxide (SiO2) and 64 wt% silicon carbide (SiC) were conventionally fabricated (TC2X). Two different molten metal aluminum-silicon (Al-Si) alloy baths were also prepared (FIG. 8) and heated to a temperature of 1200°C, where Melt B contained 25 wt% Si and Melt C contained 50 wt% Si.

[0067] The two sets of TC2X preform test bars were preheated to 1200°C, and then one set was fully immersed in Melt B (25% Si) and the other set was fully immersed in Melt C (50% Si). Both sets were extracted after the substitution reaction was complete, yielding Al2O3-SiC-Al-Si composites.

[0068] The modulus of rupture was measured for all two sets of test bars at both room temperature (20°C) and elevated temperature (700°C), and the results are shown in Figures 16 and 18. Again, the silicon content in the molten metal alloy bath was found to have a significant effect on the strength of the composite. Comparing the data for TC2X-B and TC2X-C, it was found that increasing the silicon from 25 to 50 wt% substantially increased the room temperature strength (69%) and the high temperature strength at 700°C (83%).

[0069] Embodiment #2 - Intermetallics via the Melt In a second embodiment of the present invention, intermetallic compounds are utilized to produce one of the Al2O3-Al-intermetallic, Al2O3-Al-Si-intermetallic, or Al2O3-Al-Si-SiC-intermetallic composites, where the intermetallic compounds are binary, composite, or a mixture of both. The composites so obtained have low amounts of free aluminum and are similar to those produced by the preferred embodiment from the prior art patents. difference It has greater strength at high temperatures than the composite material.

[0070] This embodiment involves the direct addition of elements into the aluminum melt to form preferred intermetallic compounds, which are compounds formed between two or more metals or metalloids (e.g., silicon, antimony, and tellurium). The elements can form binary intermetallic compounds when only one element is added to the aluminum melt, or can form complex intermetallic compounds when two or more elements are present in the aluminum melt.

[0071] In this embodiment, preferred elements and intermetallic compounds are selected starting from two criteria: 1) the boiling point of the element is about 1250°C (since the preferred processing temperature range is 900-1250°C); and 2) the resulting binary intermetallic compound has a boiling point higher than that of pure aluminum (660°C) but less than or equal to 1250°C. Review of published aluminum phase diagrams has revealed that at least 23 elements are capable of forming binary intermetallic compounds that meet these two criteria: Antimony: AlSb Barium: Al4Ba, Al 13 Ba7, Al5Ba4 Calcium: Al4Ca, Al2Ca Cerium: Al 11 Ce3, Al3Ce, AlCe Chromium: Al7Cr, Al13 Cr2, Al 11 Cr2, Al5Cr, Al4Cr, Al9Cr4, Al8Cr5, AlCr2 Cobalt: Al9Co2, Al 13 Co4, Al3Co, Al5Co2 Copper: Al4Cu9 Erbium: Al3Er, AlEr, Al2Er3, AlEr2 Gadolinium: Al3Gd, AlGd, Al2Gd3, AlGd2 Holmium: Al3Ho, AlHo, Al2Ho3, AlHo2 Iron: FeAl2, Fe2Al5, FeAl3 Manganese: Al6Mn, Al4Mn, Al 11 Mn4 Molybdenum:Al 12 Mo, Al5Mo, Al4Mo Neodymium:Al 11 Nd3, Al3Nd, AlNd, AlNd2, AlNd3 Nickel: Al3Ni, Al3Ni2, Al3Ni5 Platinum: Al 21 Pt5, Al 21 Pt8 Praseodymium:Al 11 Pr3, Al3Pr, AlPr, AlPr2 Strontium: Al4Sr, Al2Sr, Al7Sr8 Tellurium: Al2Te3 Thorium: ThAl2, ThAl, ThAl3, Th2Al7 Vanadium:Al 21 V2, Al 45 V7, Al 23 V4 Yttrium: Al3Y, AlY, Al2Y3, AlY2 Zirconium: Zr3Al, Zr2Al, Zr3Al2, Zr4Al3

[0072] Furthermore, numerous complex intermetallic compounds (containing three or more elements) can be formed by combining aluminum with two or more metals or metalloids (e.g., silicon). In addition to the binary intermetallic compounds based on the preferred elements from the above list, the following complex intermetallic compounds can be formed when two or more of these elements are present: Cr4Si4Al 13 , Cu2FeAl7, Cu2Mn3Al 20 , Cu3NiAl6, (Fe,Cr)Al3,(Fe,Mn)Al3 FeSiAl5 (Fe,Cu)Al6,(Fe,Mn)Al6,(Fe,Mn,Cr)Al6 (Fe,Mn,Cr)Al7 FeNiAl9 Fe2Si2Al9, Fe3SiAl 12 ,Mn3SiAl 12 ,(Fe,Cr)3SiAl 12 ,(Fe,Cu)3SiAl 12 ,(Fe,Mn)3SiAl 12 , (Fe,Mn,Cr)3SiAl 12 . Fe3Si2Al 12 ,

[0073] In summary, this second embodiment is an improvement over prior art embodiments as a result of using a molten aluminum alloy bath (which may or may not contain silicon) containing one or more of the preferred compounds listed above in a concentration of about 1-95 wt % and at a processing temperature of about 900-1250° C. The resulting composite material contains intermetallic compounds that are binary, composite, or a mixture of both, thereby reducing the amount of free aluminum and improving high temperature strength compared to the prior art.

[0074] Example of Embodiment #2 - Intermetallics via the Melt Example 4 A preform rod shape containing 100% silicon dioxide (SiO2) was fabricated in a conventional manner. A molten metallic aluminum-iron (Al-Fe) alloy bath was prepared (Melt D in Figure 19) and heated to a temperature of 1200°C. Melt D contained 85% aluminum and 15% iron by weight. The preform rod was preheated to 1200°C, fully immersed in the bath of Melt D, and then removed upon completion of the displacement reaction. The result was an Al2O3-Al-intermetallic composite.

[0075] The microstructure of this composite was examined. Low-magnification (10x) stereo optical micrographs of the composite, as well as high-magnification polarized light micrographs (1,000x) and scanning electron microscope (SEM) photographs (1,500x) were taken, and are shown in Figures 20, 21, and 22. As seen in Figure 20, the Al2O3-Al-intermetallic compound composite had a heterogeneous microstructure with a strong radial orientation. Chemical analysis of the composite revealed that the intermetallic compound (IMC) seen in Figures 20-22 was FeAl3, with no silicon crystals or free iron observed.

[0076] Example 5 A preform rod shape containing 100% silicon dioxide (SiO2) was fabricated in a conventional manner. A molten metallic aluminum-silicon-iron (Al-Si-Fe) alloy bath was prepared (Melt E in Figure 19) and heated to a temperature of 1200°C. Melt E contained 66.5 wt% aluminum, 26 wt% silicon, and 7.5 wt% iron. The preform rod was preheated to 1200°C, fully immersed in the bath of Melt E, and then removed upon completion of the displacement reaction. The result was an Al2O3-Al-intermetallic composite.

[0077] The microstructure of this composite was examined. Low-magnification (10x) stereo optical micrographs of the composite, as well as high-magnification polarized light micrographs (1,000x) and scanning electron microscope (SEM) photographs (1,500x) were taken, and are shown in Figures 23, 24, and 25. As seen in Figure 23, the Al2O3-Al-intermetallic compound composite had a uniform microstructure. Chemical analysis of the composite revealed that the intermetallic compound (IMC) seen in Figures 23-25 ​​was FeSiAl5, with no silicon crystals or free iron observed.

[0078] Example 6 Two sets of preform test bar shapes were conventionally prepared (TC1X) containing 40 wt. % silicon dioxide (SiO2) and 60 wt. % silicon carbide (SiC). Two different molten metal aluminum alloy baths were also prepared and heated to a temperature of 1200°C; Melt B (FIG. 8) contained 75 wt. % aluminum and 25 wt. % Si, and Melt E (FIG. 19) contained 66.5 wt. % aluminum, 26 wt. % silicon, and 7.5 wt. % iron.

[0079] The two sets of TC1X preform test bars were preheated to 1200°C, and then one set was fully immersed in Melt B (25% Si) and the other set was fully immersed in Melt E (26% Si, 7.5% Fe). Both sets were extracted upon completion of the substitution reaction to yield Al2O3-SiC-Al-intermetallic composites.

[0080] The modulus of rupture was measured for all two sets of test bars at both room temperature (20°C) and elevated temperature (700°C), and the results are shown in Figures 26 and 27. Comparing the data for TC1X-B and TC1X-E, it was found that the formation of intermetallic compounds reduced the strength at room temperature, but increased the strength at 700°C by a substantial 29%.

[0081] Example 7 Two sets of preform test bar shapes were conventionally prepared (TC2X) containing 36 wt. % silicon dioxide (SiO2) and 64 wt. % silicon carbide (SiC). Two different molten metal aluminum alloy baths were also prepared and heated to a temperature of 1200°C; Melt B (FIG. 8) contained 75 wt. % aluminum and 25 wt. % Si, and Melt E (FIG. 19) contained 66.5 wt. % aluminum, 26 wt. % silicon, and 7.5 wt. % iron.

[0082] The TC2X preform test bars were preheated to 1200°C, and then one set was fully immersed in Melt B (25% Si) and the other set was fully immersed in Melt E (26% Si, 7.5% Fe). Both sets were extracted upon completion of the substitution reaction to yield Al2O3-SiC-Al-intermetallic composites.

[0083] The modulus of rupture was measured for all two sets of test bars at both room temperature (20°C) and elevated temperature (700°C), and the results are shown in Figures 26 and 27. Comparing the data for TC2X-B and TC2X-E, it was found that the formation of intermetallic compounds resulted in a substantial improvement in strength at room temperature, with a 64% increase and a 34% increase in strength at 700°C.

[0084] Embodiment #3 - Intermetallic Compounds via Secondary Reactions According to a different method from the second embodiment, the third embodiment of the present invention also uses intermetallic compounds to produce one of the following composites: Al2O3-Al-intermetallic compound, Al2O3-Al-Si-intermetallic compound, or Al2O3-Al-Si-SiC-intermetallic compound, which intermetallic compounds are binary, complex, or a mixture of both. The composites thus obtained also have a low amount of free aluminum and are not as good as those produced by the preferred embodiment from the prior art patent. difference It has greater strength at high temperatures than the composite material.

[0085] A third embodiment involves the indirect addition of the preferred elements into the aluminum melt to form intermetallic compounds. This is accomplished by incorporating oxides of the preferred elements into a preform shape which is then processed in an aluminum bath, where a displacement reaction of the oxides releases the preferred elements into the bath, which then forms the intermetallic compounds in the same manner as described for the second embodiment.

[0086] Using the list of preferred compounds from the second embodiment and reviewing the publications cited above, at least seven elements were found whose oxides can be reduced by molten aluminum via displacement reactions: chromium, cobalt, copper, iron, manganese, molybdenum, and nickel. The following lists the displacement reactions that may occur when a preform shape is immersed in a molten metal bath at a preferred processing temperature range of 1000-1250°C: 6Al+3Cr2O3=3Al2O3+6Cr 2Al+3CoO=Al2O3+3Co 2Al+3CuO=Al2O3+3Cu 8Al+3Fe3O4=4Al2O3+9Fe 2Al+3MnO=Al2O3+3Mn 4Al+3MoO2=2Al2O3+3Mo 2Al+3NiO=Al2O3+3Ni 8Al+3NiCr2O4=4Al2O3+6Cr+3Ni 8Al+3FeCr2O4=4Al2O3+6Cr+3Fe 2Al+3NiAl2O4=4Al2O3+3Ni 2Al+3CoAl2O4=4Al2O3+3Co

[0087] In summary, this third embodiment is an improvement over prior art embodiments as a result of using preform shapes containing the preferred oxides listed above in concentrations of about 1-95 wt % and then processing the preform shapes in a molten aluminum alloy bath (which may or may not contain silicon) at processing temperatures of about 900-1250° C. The resulting composite material contains intermetallic compounds that are binary, composite, or a mixture of both, thereby reducing the amount of free aluminum and improving high temperature strength compared to the prior art.

[0088] Example of Embodiment #3 - Intermetallic Compounds via Secondary Reactions Example 8 Preform test bar shapes containing 90 wt. % silicon dioxide (SiO) and 10 wt. % iron oxide (FeO) were fabricated according to conventional methods. A molten aluminum-iron (Al-Fe) alloy bath was prepared and heated to a temperature of 1200°C, containing 85 wt. % aluminum and 15 wt. % iron (Melt D in FIG. 19). The preform test bar was preheated to 1200°C, fully immersed in the bath of Melt D, and then removed upon completion of the displacement reaction. The result was an AlO-Al intermetallic composite with a microstructure similar to that of Example 4 (FIGS. 21 and 22), containing the intermetallic compound FeAl but no silicon crystals or free iron.

[0089] Example 9 Preform test bar shapes containing 90 wt. % silicon dioxide (SiO2) and 10 wt. % iron oxide (Fe3O4) were conventionally prepared. A molten aluminum-silicon-iron (Al-Si-Fe) alloy bath was prepared and heated to a temperature of 1200°C, containing 66.5 wt. % aluminum, 26 wt. % silicon, and 7.5 wt. % iron (Melt E in Figure 19).

[0090] The preform test bar was preheated to 1200 °C, fully immersed in a bath of Melt E, and then removed once the displacement reaction was complete. The result was an Al2O3-Al-intermetallic composite with a microstructure similar to that in Example 5 (Figures 24 and 25), containing the intermetallic compound FeSiAl5 but no silicon crystals or free iron.

[0091] The substitution reactions disclosed above are most efficiently carried out at temperatures of at least 1200° C., although they may nonetheless be carried out more slowly at temperatures as low as 900° C. or higher. When the silicon content of the bath is 60% or higher, the processing temperature will generally be between 1250 and 1650° C.

[0092] The preform preferably contains 5% to 100% by weight of SiO2.

[0093] [Table 1]

[0094] Thus, having disclosed an invention with each of its objectives as set forth above, and preferred embodiments thereof which satisfy each and every one of them, the present invention provides new and useful ceramic-metallic composite materials with improved performance, and methods for their manufacture which are of great novelty and utility.

[0095] Obviously, various changes, modifications and variations of the teachings of this invention will occur to those skilled in the art without departing from the intended spirit and scope of the invention.

[0096] Accordingly, the present invention should be considered limited only by the terms of the appended claims.

Claims

1. A process for making ceramic-metallic composites employing a displacement reaction in a molten metal bath, wherein the ceramic-metallic composites have the general formula Al ２ O ３ -SiC-Al, and the modification is Al to improve strength at high temperatures. ２ O ３ - carrying out a process for forming a ceramic-metallic composite material comprising SiC-Al at a low, free aluminum concentration, comprising the following steps: a) First, 5% to 60% by weight of silicon dioxide (SiO ２ ) and providing a preform comprised of 40% to 95% by weight silicon carbide (SiC); b) providing a molten metal bath composed of molten aluminum and 32% to 60% by weight of at least one additional molten substance, said at least one additional molten substance being present in said bath either initially or via a subsequent substitution reaction of oxides incorporated in said preform; c) immersing the preform in the bath for a time sufficient to complete the substitution reaction between the preform and the bath; d) removing the preform from the bath; e) the preform, when extracted from the bath, ２ O ３ and a ceramic-metallic composite final product comprising silicon carbide (SiC), free aluminum, and a fourth material, wherein the concentration of free aluminum in the final product is reduced compared to the concentration of aluminum in the bath without the additional molten material, whereby the final product contains a reduced concentration of Al. ２ O ３ - exhibiting higher high temperature strength compared to the high temperature strength of a final product comprising SiC-Al but not comprising said fourth material.

2. 10. The process of claim 1, wherein the bath is maintained at a temperature of at least 900°C.

3. The process of claim 1 , wherein the additional molten material comprises silicon.

4. 4. The process of claim 3, wherein the bath comprises 50% by weight silicon.

5. The final product is Al ２ O ３ The process of claim 3, comprising -SiC-Al-Si.

6. The preform contains 36 wt. % SiO ２ and 64 wt.% silicon carbide (SiC).

7. The final product is Al ２ O ３ The process of claim 6, comprising -SiC-Al-Si.

8. The process of claim 1 , wherein the preform comprises a rod or bar.

9. A process for making ceramic-metallic composites employing a displacement reaction in a molten metal bath, wherein the ceramic-metallic composites have the general formula Al ２ O ３ -SiC-Al, and the modification is Al to improve strength at high temperatures. ２ O ３ - carrying out a process for forming a ceramic-metallic composite material comprising SiC-Al at a low, free aluminum concentration, comprising the following steps: a) First, 5% to 60% by weight of silicon dioxide (SiO ２ ) and providing a preform comprised of 40% to 95% by weight silicon carbide (SiC); b) providing a molten metal bath composed of molten aluminum and 32% to 60% by weight of at least one additional molten substance, the at least one additional molten substance containing at least one element that forms an intermetallic compound with aluminum and has a boiling point above 1250°C, either initially present in the bath or present via a subsequent substitution reaction of oxides incorporated in the preform; c) immersing the preform in the bath for a time sufficient to complete the substitution reaction between the preform and the bath; d) removing the preform from the bath; e) the preform, when extracted from the bath, ２ O ３ and a ceramic-metallic composite final product comprising silicon carbide (SiC), free aluminum, and a fourth material, wherein the concentration of free aluminum in the final product is reduced compared to the concentration of aluminum in the bath without the additional molten material, whereby the final product contains a reduced concentration of Al. ２ O ３ - exhibiting higher high temperature strength compared to the high temperature strength of a final product comprising SiC-Al but not comprising said fourth material.

10. 10. The process of claim 9, wherein the element is selected from the group consisting of antimony, barium, calcium, cerium, chromium, cobalt, copper, erbium, gadolinium, holmium, iron, manganese, molybdenum, neodymium, nickel, platinum, praseodymium, silicon, strontium, tellurium, thorium, vanadium, yttrium, and zirconium.

11. 10. The process of claim 9, wherein the elements include a plurality of elements that form a complex intermetallic compound comprised of at least two or more elements.

12. The process of claim 9 , wherein the preform comprises a rod or bar.

13. 10. The process of claim 9, wherein the at least one additional molten material comprises about 26 wt.% Si and about 7.5 wt.% Fe.

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