Ceramic-metallic composites with improved properties and their methods of manufacture

Abstract

Ceramic-metallic composites are disclosed along with the processes for their manufacture. The present invention improves high temperature strength of Al.sub.2O.sub.3—Al composites by displacing aluminum in the finished product with other substances that enhance the high temperature strength. Each process commences with a preform initially composed of at least 5% by weight silicon dioxide, and the finished product includes Al.sub.2O.sub.3, aluminum and another substance.

Claims

1. In a process for making a ceramic-metallic composite employing a displacement reaction in a molten metal bath, wherein the ceramic-metallic composite has the general formula Al.sub.2O.sub.3—SiC—Al, the improvement comprising conducting a process in which a ceramic-metallic composite including Al.sub.2O.sub.3—SiC—Al is formed with reduced concentration of free aluminum to enhance high temperature strength, including the steps of: a) providing a preform initially composed of from 5% to 60% by weight silicon dioxide (SiO.sub.2) and 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 within said bath either initially or via a subsequent displacement reaction of an oxide incorporated into said preform; c) immersing said preform in said bath for a sufficient time period to complete said displacement reaction between said preform and said bath; d) removing said preform from said bath; e) said preform when removed from said bath comprising a ceramic-metallic composite finished product consisting of Al.sub.2O.sub.3 as well as Silicon Carbide (SiC), free aluminum and a fourth substance, concentration of free aluminum in said finished product being reduced as compared to concentration of aluminum had said bath not included said additional molten substance, whereby said finished product exhibits enhanced high temperature strength as compared to high temperature strength of a finished product comprising Al.sub.2O.sub.3—SiC—Al but devoid of said fourth substance.

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

3. The process of claim 1, wherein said additional molten substance comprises silicon.

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

5. The process of claim 3, wherein said finished product comprises Al.sub.2O.sub.3—SiC—Al—Si.

6. The process of claim 1, wherein said preform comprises 36% by weight SiO.sub.2 and 64% by weight silicon carbide (SiC).

7. The process of claim 6, wherein said finished product comprises Al.sub.2O.sub.3—SiC—Al—Si.

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

9. In a process for making a ceramic-metallic composite employing a displacement reaction in a molten metal bath, wherein the ceramic-metallic composite has the general formula Al.sub.2O.sub.3—SiC—Al, the improvement comprising conducting a process in which a ceramic-metallic composite including Al.sub.2O.sub.3—SiC—Al is formed with reduced concentration of free aluminum to enhance high temperature strength, including the steps of: a) providing a preform initially composed of from 5% to 60% by weight silicon dioxide (SiO.sub.2) and 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 comprising at least one element forming an intermetallic compound with aluminum having a boiling point greater than 1,250° C. and being within said bath either initially or via a subsequent displacement reaction of an oxide incorporated into said preform; c) immersing said preform in said bath for a sufficient time period to complete said displacement reaction between said preform and said bath; d) removing said preform from said bath; e) said preform when removed from said bath comprising a ceramic-metallic composite finished product consisting of Al.sub.2O.sub.3 as well as Silicon Carbide (SiC), free aluminum and a fourth substance, concentration of free aluminum in said finished product being reduced as compared to concentration of aluminum had said bath not included said additional molten substance, whereby said finished product exhibits enhanced high temperature strength as compared to high temperature strength of a finished product comprising Al.sub.2O.sub.3—SiC—Al but devoid of said fourth substance.

10. The process of claim 9, wherein said element is chosen 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. The process of claim 9, wherein said element comprises multiple elements which create complex intermetallic compounds composed of at least two or more elements.

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

13. The process of claim 9, wherein said at least one additional molten substance comprises about 26% by weight Si and about 7.5% by weight Fe.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 shows two stereo optical photomicrographs at 10× magnification of Al.sub.2O.sub.3—Al composite prior art samples produced from Melt A. The top half of FIG. 1 is the lateral cross-section and the bottom half of FIG. 1 is the longitudinal cross-section of a 10 mm diameter rod.

(2) FIG. 2 shows a polarized optical photomicrograph at 1,000× magnification of Al.sub.2O.sub.3—Al composite prior art sample produced from Melt A. The red bar in the upper right hand corner of the photomicrograph shows the distance 50 μm.

(3) FIG. 3 shows a scanning electron microscope (SEM) photomicrograph at 1,500× magnification of an Al.sub.2O.sub.3—Al composite prior art sample produced from Melt A.

(4) FIG. 4 shows a chart detailing composite grades for compositions of FIGS. 1-3 and FIGS. 5-7.

(5) FIG. 5 shows two stereo optical photomicrographs at 50× magnification of an Al.sub.2O.sub.3—Al—SiC composite prior art sample. The left hand photomicrograph is of grade TC1 and the right hand photomicrograph is of grade TC2.

(6) FIG. 6 shows a graph of compression strength versus temperature of a prior art Al.sub.2O.sub.3—Al composite.

(7) FIG. 7 shows 3-point bend modulus of rupture of two standard prior art TCON grades versus temperature with % strength loss noted for each.

(8) FIG. 8 shows a chart of three Melts of experimental molten Al—Si alloys.

(9) FIG. 9 shows two stereo optical photomicrographs at 10× magnification of Al.sub.2O.sub.3—Al composite sample produced from Melt B from FIG. 8. The top half of FIG. 9 is the lateral cross-section and the bottom half of FIG. 9 is the longitudinal cross-section of a 10 mm diameter rod.

(10) FIG. 10 shows a polarized optical photomicrograph at 1,000× magnification of Al.sub.2O.sub.3—Al composite sample produced from Melt B from FIG. 8. The red bar in the upper right hand corner of the photomicrograph shows the distance 50 μm.

(11) FIG. 11 shows an SEM photomicrograph at 1,500× magnification of Al.sub.2O.sub.3—Al composite sample produced from Melt B in FIG. 8.

(12) FIG. 12 shows stereo optical photomicrographs at 10× magnification of Al.sub.2O.sub.3—Al composite sample produced from Melt C from FIG. 8. The top half of FIG. 12 is the lateral cross-section and the bottom half of FIG. 12 is the longitudinal cross-section of a 10 mm diameter rod.

(13) FIG. 13 shows a polarized optical photomicrograph at 1,000× magnification of Al.sub.2O.sub.3—Al composite sample produced from Melt C from FIG. 8. The red bar in the upper right hand corner of the photomicrograph shows the distance 50 μm.

(14) FIG. 14 shows an SEM photomicrograph at 1,500× magnification of Al.sub.2O.sub.3—Al composite sample produced from Melt C.

(15) FIG. 15 shows an SEM photomicrograph at 1,000× magnification of Al.sub.2O.sub.3—Al composite sample produced from Melt B.

(16) FIG. 16 shows a chart of the 3-point bend modulus of rupture of experimental Al.sub.2O.sub.3—Al—Si composites with and without SiC produced from Melts A, B, and C identified in FIG. 8.

(17) FIG. 17 shows the 3-point bend modulus of rupture of experimental materials TQ1X (Al.sub.2O.sub.3—Al—Si composites) produced from Melts A, B, and C identified in FIG. 8.

(18) FIG. 18 shows the 3-point bend modulus of rupture of experimental materials TC2X (SiC—Al.sub.2O.sub.3—Al—Si composites) produced from Melts B and C identified in FIG. 8.

(19) FIG. 19 shows a chart depicting properties of Melts D and E which comprise experimental molten Al—Fe and Al—Si—Fe alloys.

(20) FIG. 20 shows stereo optical photomicrographs at 10× magnification of Al.sub.2O.sub.3—Al-intermetallic composite samples produced from Melt D as identified in FIG. 19. The top half of FIG. 20 is the lateral cross-section and the bottom half is the longitudinal cross-section of a 10 mm diameter rod.

(21) FIG. 21 shows a polarized optical photomicrograph at 1,000× magnification of an Al.sub.2O.sub.3—Al-intermetallic composite sample produced from Melt D identified in FIG. 19. The red bar in the upper right hand corner of the photomicrograph shows the distance 50 μm.

(22) FIG. 22 shows two SEM photomicrographs at 1,500× magnification of Al.sub.2O.sub.3—Al-intermetallic composite sample produced from Melt D identified in FIG. 19. The top image is an SE signal image and the bottom image is a mixed SE/BSE image.

(23) FIG. 23 shows a stereo optical photomicrograph at Ix magnification of Al.sub.2O.sub.3-A-intermetallic composite sample produced from Melt E identified in FIG. 19. The top half is the lateral cross-section and the bottom half is the longitudinal cross-section of a 10 mm diameter rod.

(24) FIG. 24 shows a polarized optical photomicrograph at 1,000× magnification of Al.sub.2O.sub.3—Al-intermetallic composite sample produced from Melt E identified in FIG. 19. The red bar in the upper right hand corner of the photomicrograph shows the distance 50 μm.

(25) FIG. 25 shows SEM photomicrographs at 1,500× magnification of Al.sub.2O.sub.3—Al-intermetallic composite sample produced from Melt E identified in FIG. 19. The top photomicrograph is an SE signal image and the bottom photomicrograph is a mixed SE/BSE image.

(26) FIG. 26 shows a chart consisting of 3-point bend modulus of rupture information of experimental composites produced from Melt B identified in FIG. 8 and Melt E identified in FIG. 19 (SiC—Al.sub.2O.sub.3—Al—Si versus SiC—Al.sub.2O.sub.3—Al-intermetallic).

(27) FIG. 27 shows a chart of 3-point bend modulus of rupture of experimental materials TC1X and TC2X produced from Melt B identified in FIG. 8 and Melt E identified in FIG. 19 (SiC—Al.sub.2O.sub.3—Al—Si versus SiC—Al.sub.2O.sub.3—Al-intermetallic composites).

SPECIFIC DESCRIPTION OF THE PREFERRED EMBODIMENTS

(28) The following three embodiments for this invention make significant changes to the composition of the molten aluminum (Al) bath in the prior art embodiment, resulting in unique composites with lower amounts of free aluminum and subsequently improved properties over those resulting from the prior art embodiment.

Embodiment #1—Elevated Silicon Contents

(29) The first embodiment of this invention utilizes a molten aluminum-silicon (Al—Si) bath containing significant amounts of silicon (2 to 95 weight %) to produce Al.sub.2O.sub.3—Al—Si and Al.sub.2O.sub.3—Al—Si—SiC composites. These resulting composites have lower amounts of free aluminum and greater high temperature strengths than the composites produced via the preferred embodiment from the prior art patents.

(30) Aluminum-silicon alloy melts that contain greater than 2 weight % Si will precipitate out Si crystals upon cooling and solidification. As the silicon content is increased in Al—Si alloys the amount of free aluminum will decrease in the solidified alloy, having been displaced by Si crystals. As a result, the composites produced from this embodiment can achieve greater high temperature strengths with this reduction of free aluminum in the final material.

(31) It was also surprising to learn that adding large amounts of Si to the molten Al bath has a very significant impact on the resulting microstructure of the aluminum oxide in the final composite material, going from a heterogeneous microstructure to a much more uniformly homogeneous structure. This processing technique allows the material microstructure to be tailored to fit the application requirements, whereby a more homogeneous structure may be desirable for certain applications and a less homogeneous structure appropriate for others.

(32) The preferred embodiment in U.S. Pat. No. 7,267,882 utilizes an operating temperature between about 1000 to 1250° C. and a molten Al—Si bath containing 20 to 30 weight % silicon (Si) to totally suppress any reaction between silicon carbide (SiC) in the preform and the aluminum in the bath. A process temperature range of 1000 to 1250° C. in the present invention's embodiment is also acceptable for molten aluminum-silicon alloys containing Si up to approximately 60 weight percent, and the resulting Al.sub.2O.sub.3—Al—Si—SiC composite will have a higher temperature strength than the composite produced utilizing the prior art.

(33) However, because silicon has a higher melting point than aluminum (1414° C. for Si versus 660° C. for Al), the melting temperature of Al—Si alloys increase as the Si content increases. Subsequently 1250° C. would be too low of a temperature to carry this embodiment at concentrations greater than 60 weight percent silicon. Therefore, the preferred processing temperature would generally be between 1250 to 1650° C. for silicon concentrations from 60 to 95 weight %.

(34) In summary, this first embodiment is an improvement over the prior art embodiment as a result of utilizing: a) a molten Al—Si bath containing 30 to 60 weight % silicon at a process temperature of about 900 to 1250° C.; or b) a molten Al—Si bath containing about 60 to 95 weight % silicon at a process temperature of about 1250 to 1650° C.

Examples of Embodiment #1—Elevated Silicon Contents

Example 1

(35) Three preform rod shapes containing 100% silicon dioxide (SiO.sub.2) were conventionally fabricated. Three different molten metal aluminum-silicon (Al—Si) alloy baths were prepared (FIG. 8) and heated to a temperature of 1200° C., with Melt A containing 0% Si, Melt B containing 25 weight % Si, and Melt C containing 50 weight % Si.

(36) One of the preform rods was preheated to 1200° C.; it was fully immersed in one of the three molten metal baths and then extracted upon completion of the displacement reaction, with the process repeated with the other two rods and melts, resulting in either an Al.sub.2O.sub.3—Al or Al.sub.2O.sub.3—Al—Si composite. The microstructures of those composites were examined; the composite produced from Melt A (0% Si) is seen in FIGS. 1, 2, and 3, the composite produced from Melt B (25% Si) is shown in FIGS. 9, 10, and 11, and the composite from Melt C (50% Si) is seen in FIGS. 12, 13, 14, and 15.

(37) The Al.sub.2O.sub.3—Al composite material produced from Melt A (0% Si) resulted in a very radially oriented microstructure and no visible silicon. The Al.sub.2O.sub.3—Al—Si composite from Melt B (25% Si) resulted in a somewhat homogenous microstructure, and the composite from Melt C (50% Si) resulted in a somewhat homogenous microstructure, both with visible clusters of silicon.

(38) The Si clusters are readily visible in both FIGS. 9 and 12, and appear to be proportional to the amount of silicon in the melt, i.e., the microstructure in FIG. 12 (50% Si) is much more homogeneous and has twice the amount of clusters than what is visible in FIG. 9 (25% Si). The contrast of the silicon crystals was not high enough to make them stand out against the aluminum metal in the scanning electron microscope (SEM) photomicrographs of FIGS. 2, 11, and 14. Using a different SEM with higher sensitivity, the composite produced from Melt B (25% Si) was re-analyzed, allowing the silicon crystals to be much more observable in FIG. 15.

(39) It was surprising to learn that adding large amounts of —Si to the molten Al bath still allows the transformation reaction to go to completion yet has a very significant impact on the resulting microstructure of the material, going from a heterogeneous, radially oriented structure (at 0% Si) to a much more uniformly homogeneous structure. This processing technique allows the material microstructure to be tailored to fit the application requirements, whereby a more homogeneous structure may be desirable for certain applications and a more radially oriented structure appropriate for others.

Example 2

(40) Three sets of preform test bar shapes were conventionally fabricated (TQ1X), containing 100% silicon dioxide (SiO.sub.2). Three different molten metal aluminum-silicon (Al—Si) alloy baths were also prepared (FIG. 8) and heated to a temperature of 1200° C., with Melt A containing 0% Si, Melt B containing 25 weight % Si, and Melt C containing 50 weight % Si.

(41) The three sets of the TQ1X preform test bars were preheated to 1200° C. and then one set was fully immersed in one of the three molten metal baths and then extracted upon completion of the displacement reaction, with the process repeated with the other sets of bars and melts. This resulted in either an Al.sub.2O.sub.3—Al or Al.sub.2O.sub.3—Al—Si composite.

(42) The modulus of rupture was measured on all three sets of test bars at both room temperature (20° C.) and at high temperature (700° C.), and the results are displayed in FIGS. 16 and 17. It was found that the silicon content in the molten metal alloy baths have a significant effect on the strength of the composite materials. In comparing TQ1X-A to TQ1X-B, it was found that increasing the silicon from 0 to 25 weight % had practically no effect on the room temperature strength, but substantially increased the strength at 700° C. (by 182%). In comparing TQ1X-A to TQ1X-C, it was found that increasing the silicon from 0 to 50 weight % did reduce the room temperature strength, but substantially increased the strength at 700° C. (by 73%).

Example 3

(43) Two sets of preform test bar shapes were conventionally fabricated (TC2X) containing 36 weight % silicon dioxide (SiO.sub.2) and 64 weight % silicon carbide (SiC). Two different molten metal aluminum-silicon (Al—Si) alloy baths were also prepared (FIG. 8) and heated to a temperature of 1200° C., with Melt B containing 25 weight % Si and Melt C containing 50 weight % Si.

(44) Two sets of the TC2X preform test bars were preheated to 1200° C., then one set was fully immersed in Melt B (25% Si) and the other set fully immersed in Melt C (50% Si). Both sets were then extracted upon completion of the displacement reaction, resulting in Al.sub.2O.sub.3—SiC—Al—Si composites.

(45) The modulus of rupture was measured on the two sets of test bars at both room temperature (20° C.) and at high temperature (700° C.), and the results are displayed in FIGS. 16 and 18. Again, it was found that the silicon content in the molten metal alloy baths have a significant effect on the strength of the composite materials. Comparing the data from TC2X-B to TC2X-C, it was found that increasing the silicon from 25 to 50 weight % substantially increase the room temperature strength (by 69%) and the high temperature strength at 700° C. (by 83%).

Embodiment #2—Intermetallics Via the Melt

(46) The second embodiment of this invention utilizes intermetallics to produce one of the following composites: Al.sub.2O.sub.3—Al-intermetallics, Al.sub.2O.sub.3—Al—Si-intermetallics, or Al.sub.2O.sub.3—Al—Si—SiC-intermetallics, whereby the intermetallics are binary, complex, or a mixture of both. These resulting composites have lower amounts of free aluminum and greater high temperature strengths than the composites produced via the preferred embodiment from the prior art patents.

(47) This embodiment involves the direct addition of elements into the aluminum melt in order to form preferred intermetallic compounds, which are compounds formed between two or more metals or metalloids (such as silicon, antimony, and tellurium). These elements can form binary intermetallic compounds when just one element is added into an aluminum melt, while complex intermetallic compounds can form when two or more elements are present in an aluminum melt.

(48) In this embodiment preferred elements and intermetallic compounds are selected starting with two criteria: 1) the boiling point of the element is above 1250° C. (since the preferred processing temperature range is 900 to 1250° C.); and 2) the resulting binary intermetallic compound has a melting point higher than that for pure aluminum (660° C.) but no higher than 1250° C. A review of published aluminum phase diagrams found at least twenty three elements that form the binary intermetallics that meet these two criteria: Antimony —AlSb Barium —Al.sub.4Ba, Al.sub.13Ba.sub.7, A.sub.5Ba.sub.4 Calcium —Al.sub.4Ca, Al.sub.2Ca Cerium —Al.sub.11Ce.sub.3, Al.sub.3Ce, AlCe Chromium —Al.sub.7Cr, Al.sub.13Cr.sub.2, Al.sub.11Cr.sub.2, A.sub.5Cr, A.sub.4Cr, Al.sub.9Cr.sub.4, Al.sub.8Cr.sub.5, AlCr.sub.2 Cobalt —Al.sub.9Co.sub.2, Al.sub.13Co.sub.4, Al.sub.3Co, A.sub.5Co.sub.2 Copper —Al.sub.4Cu.sub.9 Erbium —Al.sub.3Er, AlEr, Al.sub.2Er.sub.3, AlEr.sub.2 Gadolinium —Al.sub.3Gd, AlGd, Al.sub.2Gd.sub.3, AlGd.sub.2 Holmium —Al.sub.3Ho, AlHo, Al.sub.2Ho.sub.3, AlHo.sub.2 Iron —FeAl.sub.2, Fe.sub.2Al.sub.5, FeAl.sub.3 Manganese —Al.sub.6Mn, Al.sub.4Mn, Al.sub.11Mn.sub.4 Molybdenum —Al.sub.2Mo, Al.sub.5Mo, Al.sub.4Mo Neodymium —Al.sub.11Nd.sub.3, Al.sub.3Nd, AlNd, AlNd.sub.2, AlNd.sub.3 Nickel —Al.sub.3Ni, Al.sub.3Ni.sub.2, Al.sub.3Ni.sub.5 Platinum —Al.sub.21Pt.sub.5, Al.sub.21Pt.sub.8 Praseodymium —Al.sub.11Pr.sub.3, Al.sub.3Pb, AlPr, AlPr.sub.2 Strontium —Al.sub.4Sr, Al.sub.2Sr, A.sub.7Sr.sub.8 Tellurium —Al.sub.2Te.sub.3 Thorium —ThAl.sub.2, ThAl, ThA.sub.3, Th.sub.2Al.sub.7 Vanadium —Al.sub.21V2, Al.sub.45V7, Al.sub.23V.sub.4 Yttrium —Al.sub.3Y, AlY, Al.sub.2Y3, AlY.sub.2 Zirconium —Zr.sub.3Al, Zr.sub.2Al, Zr.sub.3Al.sub.2, Zr.sub.4Al.sub.3

(49) Also, numerous complex intermetallics (containing three or more elements) can be formed by combining aluminum with two or more metals or metalloids (such as silicon). Based on the preferred elements from above list and in addition to the binary intermetallic compounds, the following complex intermetallics can form when more than one of those elements is present: Cr.sub.4Si.sub.4Al.sub.3, Cu.sub.2FeAl.sub.7, Cu.sub.2Mn.sub.3Al.sub.20, Cu.sub.3NiAl.sub.6, (Fe, Cr)Al.sub.3, (Fe, Mn)Al.sub.3 FeSiAl.sub.5 (Fe, Cu)Al.sub.6, (Fe, Mn)Al.sub.6, (Fe, Mn, Cr)Al.sub.6 (Fe, Mn, Cr)Al.sub.7 FeNiAl.sub.9 Fe.sub.2Si.sub.2Al.sub.9, Fe.sub.3SiAl.sub.12, Mn.sub.3SiA.sub.12, (Fe, Cr).sub.3SiAl.sub.2, (Fe, Cu).sub.3SiAl.sub.12, (Fe, Mn).sub.3SiAl.sub.2, (Fe, Mn, Cr).sub.3SiAl.sub.12. Fe.sub.3Si.sub.2Al.sub.12,

(50) In summary, this second embodiment is an improvement over the prior art embodiment as a result of utilizing a molten aluminum alloy bath, which may or may not contain silicon, containing one or more of the preferred compounds listed above in concentrations of approximately 1 to 95 weight %, at a process temperature of about 900 to 1250° C. The resulting composites contain intermetallic compounds that are binary, complex, or a mixture of both, thereby reducing the amount of free aluminum and increasing the high temperature strengths as compared with the prior art.

Examples of Embodiment #2—Intermetallics via the Melt

Example 4

(51) A preform rod shape containing 100% silicon dioxide (SiO.sub.2) was conventionally fabricated. A molten metal aluminum-iron (Al—Fe) alloy bath was prepared (Melt D in FIG. 19) and heated to a temperature of 1200° C. This Melt D contained 85 weight % aluminum and 15 weight % iron. The preform rod was preheated to 1200° C. and was fully immersed in the Melt D bath and then extracted upon completion of the displacement reaction. The result was a Al.sub.2O.sub.3—Al-intermetallic composite.

(52) The microstructure of this composite was examined. Low magnification (10×) stereo optical photomicrographs, plus high magnification polarized optical photomicrographs (1,000×) and scanning electron microscope (SEM) photomicrographs (1,500×) were taken of this composite material and are shown in FIGS. 20, 21, and 22. As seen in FIG. 20, this Al.sub.2O.sub.3—Al-intermetallic composite material had a very radially oriented, inhomogeneous microstructure. Chemical analysis of the composite found that the intermetallic compound (IMC) visible in FIGS. 20 through 22 was FeAl.sub.3, and that no silicon crystals or free iron was observed.

Example 5

(53) A preform rod shape containing 100% silicon dioxide (SiO.sub.2) was conventionally fabricated. A molten metal aluminum-silicon-iron (Al—Si—Fe) alloy bath was prepared (Melt E in FIG. 19) and heated to a temperature of 1200° C. This Melt E contained 66.5 weight % aluminum, 26 weight % silicon, and 7.5 weight % iron. The preform rod was preheated to 1200° C. and was fully immersed in the Melt E bath and then extracted upon completion of the displacement reaction. The result was a Al.sub.2O.sub.3—Al-intermetallic composite.

(54) The microstructure of this composite was examined. Low magnification (10×) stereo optical photomicrographs, plus high magnification polarized optical photomicrographs (1,000×) and scanning electron microscope (SEM) photomicrographs (1,500×) were taken of this composite material and are shown in FIGS. 23, 24, and 25. As seen in FIG. 23, this Al.sub.2O.sub.3—Al-intermetallic composite material had a homogeneous microstructure. Chemical analysis of the composite found that the intermetallic compound (IMC) visible in FIGS. 23 through 25 was FeSiAl.sub.5, and that no silicon crystals or free iron was observed.

Example 6

(55) Two sets of preform test bar shapes were conventionally fabricated (TC1X) and contained 40 weight % silicon dioxide (SiO.sub.2) and 60 weight % 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 weight % aluminum and 25 weight % Si, and Melt E (FIG. 19) contained 66.5 weight % aluminum, 26 weight % silicon, and 7.5 weight % iron.

(56) Two sets of the TC1X preform test bars were preheated to 1200° C., then one set was fully immersed in Melt B (25% Si) and the other set fully immersed in Melt E (26% Si, 7.5% Fe). Both sets were then extracted upon completion of the displacement reaction, resulting in Al.sub.2O.sub.3—SiC—Al-intermetallic composites.

(57) The modulus of rupture was measured on the two sets of test bars at both room temperature (20° C.) and at high temperature (700° C.), and the results are displayed in FIGS. 26 and 27. Comparing the data from TC1X-B to TC1X-E it was found that formation of the intermetallic compound did reduce the room temperature strength, but substantially increased the strength at 700° C. (by 29%).

Example 7

(58) Two sets of preform test bar shapes were conventionally fabricated (TC2X) and contained 36 weight % silicon dioxide (SiO2) and 64 weight % 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 weight % aluminum and 25 weight % Si, and Melt E (FIG. 19) contained 66.5 weight % aluminum, 26 weight % silicon, and 7.5 weight % iron.

(59) The TC2X preform test bars were preheated to 1200° C., then one set was fully immersed in Melt B (25% Si) and the other set fully immersed in Melt E (26% Si, 7.5% Fe). Both sets were then extracted upon completion of the displacement reaction, resulting in Al.sub.2O.sub.3—SiC—Al-intermetallic composites.

(60) The modulus of rupture was measured on the two sets of test bars at both room temperature (20° C.) and at high temperature (700° C.), and the results are displayed in FIGS. 26 and 27. Comparing the data from TC2X-B to TC2X-E it was found that formation of the intermetallic compound substantially improved the room temperature strength (by 64%) as well as the strength at 700° C. (by 34%).

Embodiment #3—Intermetallics Via Secondary Reactions

(61) By following a different method than the second embodiment, the third embodiment of this invention also utilizes intermetallics to produce one of the following composites: Al.sub.2O.sub.3—Al-intermetallics, Al.sub.2O.sub.3—Al—Si-intermetallics, or Al.sub.2O.sub.3—Al—Si—SiC-intermetallics, whereby the intermetallics are binary, complex, or a mixture of both. These resulting composites also have lower amounts of free aluminum and greater high temperature strengths than the composites produced via the preferred embodiment from the prior art patents.

(62) The third embodiment involves forming intermetallic compounds by indirectly adding the preferred elements into the aluminum melt. This is accomplished by incorporating oxides of those preferred elements into the preform shape and then processing it through the aluminum bath; the result displacement reactions of those oxides releases the preferred elements into the bath, subsequently forming intermetallics in the same way as described in the second embodiment.

(63) Using the preferred compounds list from the second embodiment, a review of published literature cited supra found at least seven of those elements whose oxides can be reduced by molten aluminum via a displacement reaction: chromium, cobalt, copper, iron, manganese, molybdenum, and nickel. The following lists the displacement reactions that will take place when the preform shape is immersed in the molten metal bath at the preferred processing temperature range of 1000 to 1250° C.:
6Al+3Cr.sub.2O.sub.3═3Al.sub.2O.sub.3+6Cr
2Al+3CoO═Al.sub.2O.sub.3+3Co
2Al+3CuO═Al.sub.2O.sub.3+3Cu
8Al+3Fe.sub.3O.sub.4═4Al.sub.2O.sub.3+9Fe
2Al+3MnO═Al.sub.2O.sub.3+3Mn
4Al+3MoO.sub.2═2Al.sub.2O.sub.3+3Mo
2Al+3NiO═Al.sub.2O.sub.3+3Ni
8Al+3NiCr.sub.2O.sub.4═4Al.sub.2O.sub.3+6Cr+3Ni
8Al+3FeCr.sub.2O.sub.4═4Al.sub.2O.sub.3+6Cr+3Fe
2Al+3NiAl.sub.2O.sub.4═4Al.sub.2O.sub.3+3Ni
2Al+3CoAl.sub.2O.sub.4═4Al.sub.2O.sub.3+3Co.

(64) In summary, this third embodiment is an improvement over the prior art embodiment as a result of utilizing preform shapes that contain the preferred oxides listed above in concentrations of approximately 1 to 95 weight %, and then processing those preform shapes in a molten aluminum alloy bath which may or may not contain silicon at a process temperature of about 900 to 1250° C. The resulting composites contain intermetallic compounds that are binary, complex, or a mixture of both, thereby reducing the amount of free aluminum and increasing the high temperature strengths as compared with the prior art.

Examples of Embodiment #3—Intermetallics Via Secondary Reactions

Example 8

(65) A preform test bar shape was conventionally fabricated containing 90 weight % silicon dioxide (SiO.sub.2) and 10 weight % iron oxide (Fe.sub.3O.sub.4). A molten metal aluminum-iron (Al—Fe) alloy bath was prepared and heated to a temperature of 1200° C., which contained 85 weight % aluminum and 15 weight % iron (Melt D in FIG. 19). The preform test bar was preheated to 1200° C. and was fully immersed in the Melt D bath and then extracted upon completion of the displacement reaction. The result was a Al.sub.2O.sub.3—Al-intermetallic composite that contained the intermetallic compound FeAl.sub.3 and no silicon crystals or free iron, similar to the microstructures for Example 4 (FIGS. 21 and 22).

Example 9

(66) A preform test bar shape was conventionally fabricated containing 90 weight % silicon dioxide (SiO.sub.2) and 10 weight % iron oxide (Fe.sub.3O.sub.4). A molten metal aluminum-silicon-iron (Al—Si—Fe) alloy bath was prepared and heated to a temperature of 1200° C., which contained 66.5 weight % aluminum, 26 weight % silicon, and 7.5 weight % iron (Melt E in FIG. 19).

(67) The preform test bar was preheated to 1200° C. and was fully immersed in the Melt E bath and then extracted upon completion of the displacement reaction. The result was a Al.sub.2O.sub.3—Al-intermetallic composite that contained the intermetallic compound FeSiAl.sub.5, and no silicon crystals or free iron, similar to the microstructures for Example 5 (FIGS. 24 and 25).

(68) While the displacement reactions disclosed above are most efficiently carried out at bath temperature of at least 1200° C., they may be carried out, albeit more slowly, at temperatures as low as 900 and greater. In cases where the silicon content in the bath is 60% or greater, then the processing temperature would generally be between 1250 to 1650° C.

(69) The preform may preferably include from 5% to 100 weight % SiO.sub.2.

(70) TABLE-US-00001 TABLE 1 Range of Variables Embodiment # 1 Embodiment # 2 Embodiment # 3 Preform 5-100% SiO.sub.2 5-100% SiO.sub.2 5-95% SiO.sub.2 compositions 0-95% SiC 0-95% SiC 0-90% SiC 5-95% preferred oxides Al Bath - 2-95% Si with no SiC 0-90% Si with no SiC 0-90% Si with no SiC compositions or or or 25-95% Si with SiC 18-90% Si with SiC 18-90% Si with SiC Balance Al (5-98%) +5-95% preferred +5-95% preferred elements, elements, added during added by secondary reactions bath preparation of preferred oxides Balance Al (5-95%) Balance Al (5-95%) Al Bath - 900-1250° C. (Si ≤ 60%) 900-1250° C. 900-1250° C. temperatures or 1250-1650° C. (Si > 60%) Final part Al.sub.2O.sub.3-Al-Si Al.sub.2O.sub.3-Al-intermetallics Al.sub.2O.sub.3-Al-intermetallics compositions Al.sub.2O.sub.3-Al-Si-SiC Al.sub.2O.sub.3-Al-intermetallics-Si Al.sub.2O.sub.3-Al-intennetallics-Si Al.sub.2O.sub.3-Al-intermetallics-Si-SiC Al.sub.2O.sub.3-Al-intermetallics-Si-SiC

(71) As such, an invention has been disclosed in terms of preferred embodiments thereof which fulfill each and every one of the objects of the invention as set forth hereinabove, and provides new and useful ceramic-metallic composites with improved properties and their methods of manufacture of great novelty and utility.

(72) Of course, various changes, modifications and alterations in the teachings of the present invention may be contemplated by those skilled in the art without departing from the intended spirit and scope thereof.

(73) As such, it is intended that the present invention only be limited by the terms of the appended claims.