METHOD OF PRODUCING A PREFORM WIRE, SHEET OR TAPE FOR FIBRE-REINFORCED METALS, AND AN ULTRASONIC WAVE VIBRATION APPARATUS

Abstract: A preform wire for FRM consisting of a metal/silicon car­ bide fiber composite material is light in weight and excellent in strength and elasticity, and can be easily obtained by im­ pregnating a silicon carbide fiber bundle (2) with a molten metal which is kept vibrated by means of an ultrasonic wave vibration apparatus (9) having a cooling means.

Description: The present invention relates to a method of producing a preform wire for FRM and an ultrasonic wave vibration apparatus used in the method. More particularly, the present invention relates to a method of producing a light, elastic and strong preform wire for FRM, which wire is a silicon carbide fiber/metal composite material consisting of silicon carbide fibers and a metal fully penetrated between the fibers, and has no vacant space between the fibers; and an ultrasonic wave vibration apparatus which can vibrate efficiently a molten metal used in the method. The term "preform wire for FRM" used in the present invention includes not only preform wire for FRM, but also preform sheet or tape for FRM. A composite material consisting of a fibrous material, such as silicon carbide fiber or the like, impregnated with a metal, such as aluminum or the like, has excellent properties of both the metal and the fiber, and is tough, light and flexible. Therefore, the composite material is expected to be widely used as a material for vehicle, aircraft, rocket, spaceship and other various articles. There have been proposed various methods in the production of the metal/fiber composite material. For example, there is known a method, such as plasma jet, metalikon or vapor deposition, wherein fine metal particles or metal vapor is blown against a fiber bundle to adhere the metal to the fiber surface and to produce a metal/fiber composite material or its precursor. However, in these methods, metal fine particles or metal vapor is straight blown to a fiber bundle, and therefore these methods have the drawback that the metal does not fully penetrate the interior of the fiber bundle, and a composite material having satisfactorily high strength and elasticity cannot be obtained. It is known to use ultrasonic vibrations for the manufacture of fiber-composite materials. For instance, FR-A-1 559 942 describes the application of ultrasound to compact a fibre bundle, and DD- 142 313 uses ultrasound to ensure impregnation of carbon-reinforced polymer sheet material. Further, JP-A-54-89907 proposes a method wherein a fiber bundle is immersed in a molten metal bath and at the same time an ultrasonic wave vibration is given to the molten metal bath in order to cause the molten metal to penetrate the interior of the fiber bundle. However, in this method, the fiber bundle is disordered by the ultrasonic wave vibration; thus, although any air contained in the interior of the fiber bundle is exhausted, so that the metal fully penetrates the interior of the fiber bundle, the fibers are fixed in a randomly disordered state as a result of the vibration. Accordingly, it is difficult to produce in this method a metal/fiber composite material having the desired strength and elasticity. A further problem is that, if a hole is formed in the wall of an ultrasonic wave vibration apparatus in order to allow cooling water through the horn, the wall of the vibrator tends to crack whereupon the vibration is no longer transmitted to the horn end portion immersed in the molten metal bath. As described above, there have been known neither a method of producing a metal/fiber composite material which is light in weight and is excellent in strength and elasticity, nor an ultrasonic wave vibration apparatus to be advantageously used for the method. The present invention aims to solve the above described problems and to provide a metal/fiber composite material, particularly a preform wire for FRM, which consists of a metal, such as aluminium or the like, and silicon carbide fiber, and is lighter in weight and is more excellent in strength and elasticity than conventional metal/fiber composite materials, and to provide an ultrasonic wave vibration apparatus to be used in the method. The inventors have made various investigations in order to attain the above described object, and found out that, when a silicon carbide fiber bundle is previously drawn such that the element fibers constituting the fiber bundle are arranged in a uniform parallel fashion along their length direction, the parallel arrangement is maintained e.g. by spraying or deposition with a metal, such as aluminium or the like, and the fiber bundle is immersed in a molten metal bath which is kept vibrated by means of an ultrasonic wave vibration apparatus, an excellent preform wire for FRM can be obtained. The inventors have further found out that, in order to protect an ultrasonic wave vibration apparatus used in the above described method from high temperature, when a hole for cooling water is formed in the horn of the vibrator, or a water-cooling jacket is arranged on the horn of the vibrator, at the upper portion, which is not immersed in the molten metal bath, and at a position corresponding to a node of the half-wavelength of the ultrasonic wave, a metal/fiber composite material having a stable property over a long period of time and being free from cracks in the horn during the use can be obtained. As the result, the inventors have reached the present invention. According to one aspect of the present invention there is provided a method of producing a preform wire, sheet or tape for FRM, comprising unfastening and drawing a silicon carbide fiber bundle so that the element fibers constituting the fiber bundle are loosened and uniformly arranged in a parallel relationship along their length, and impregnating the fiber bundle, while maintaining the element fibers in their loosened and parallel arrangement, for a period of time of not longer than 50 seconds with a molten metal, which is kept vibrated by means of an ultrasonic wave vibration apparatus having a cooling means. The impregnation time is preferably not longer than 2 seconds. In the metal/silicon-carbide fiber composite material obtained by this method, metal is fully penetrated between the element fibers and there are no vacant spaces between the fibers. In the method of the present invention, the unfastened and drawn silicon carbide fiber bundle may be previously sprayed with or vapor deposited with a metal, and then the thus treated unfastened and drawn silicon carbide fiber bundle is impregnated with a molten metal while vibrating the molten metal by means of an ultrasonic wave. The metal to be used in this spraying or vapor deposition may be same as or different from the metal to be used for impregnation in the form of a molten metal. Further, the fiber bundle may be electromagnetically vibrated during the impregnation. The preform wire for FRM obtained in the above described method is light in weight and is excellent in strength, elasticity and other properties. According to a second aspect of the present invention there is provided an ultrasonic wave vibration apparatus comprising a vibrator with a horn and an ultrasonic wave oscillator, the vibrator being adapted to vibrate a molten metal bath to be used for impregnating a starting silicon carbide bundle in the production of a preform wire for FRM at a predetermined frequency f, characterised by the further provision of means for unfastening and drawing the bundle prior to impregnation so that the element fibers constituting the fiber bundle are loosened and uniformly arranged in a parallel relationship along their length, and means for maintaining the fibers of the bundle parallel during impregnation, the horn having a cooling water passage or jacket at its upper portion at a position corresponding to a node of the half-wavelength of the ultrasonic wave. The ultrasonic wave vibration apparatus having the above described structure protects the vibrator from high temperature and can eliminate drawbacks of conventional ultrasonic wave vibration apparatus in which cracks tend to form in the horn during prolonged use, disturbing the transmittance of vibration to the horn end portion immersed in the molten metal bath. For a better understanding of the present invention, embodiments will be explained in more detail with reference to the accompanying drawings, in which: Fig. 1 is a diagrammatic view of a flow sheet illustrating one embodiment of the present invention; and Fig. 2 is a diagrammatic view illustrating the vibrator portion of an embodiment of the ultrasonic wave vibration apparatus in accordance with the present invention. Referring to Fig. 1, a silicon carbide fiber bundle 2 is unfastened and drawn by means of a fiber bundle tensioning apparatus 1 such that the element fibers constituting the fiber bundle 2 are uniformly arranged in a parallel relation along their length direction, and then the fiber bundle 2 is sprayed with a molten metal, such as molten aluminium or the like, by means of a metal-spraying apparatus 3, such as plasma jet, metalikon or the like, to maintain the relationship of the element fibers of the silicon carbide fiber bundle 2. In the present invention, not only the metal-spraying apparatus 3, but also any means, such as vacuum deposition and the like, which can adhere a metal to the silicon carbide fiber bundle 2 to fix the element fibers in a parallel relationship can be used. In the present invention, the step for spraying or vapor depositing a metal to the silicon carbide fiber bundle can be omitted as long as the parallel arrangement of the fibers is maintained. The silicon carbide fiber bundle 2 adhered with the metal is passed through guide rollers 4a and 4b, and introduced into a vessel 6 filled with a molten metal 5, such as molten aluminium or the like, and impregnated with the molten metal 5 in the vessel 6. During the course of the impregnation of the silicon carbide fiber bundle 2 with the molten metal 5, an electromagnetic vibration may be given to the silicon carbide fiber bundle 2 between the guide rollers 4a and 4b. The metals to be used for the impregnation include aluminium, magnesium, titanium, lead, silicon and the like, and their alloys. The molten metal 5 is vibrated by means of an ultrasonic wave vibration apparatus 7. This ultrasonic wave vibration apparatus 7 comprises an oscillator 8 and a vibrator 9. The lower portion of the horn 10 of the vibrator 9 is immersed in a molten metal 5 filled in a vessel 6. The horn 10 of the vibrator 9 vibrates the molten metal 5 corresponding to the signal transmitted from the oscillator 8. As illustrated in Fig. 2, it is necessary that the horn 10 has at its upper portion a hole 11 for cooling water, or a water-cooling jacket 11, in order not to transmit the heat of the molten metal 5 to the vibrator 9. The hole 11 for cooling water or the water-cooling jacket 11 must be formed or arranged respectively at a position corresponding to a node of the half-wavelength of the ultrasonic wave. When a hole 11 for cooling water is formed or a water-cooling jacket 11 is arranged at this position, cracks do not occur from the horn portion even when an ultrasonic wave treatment is effected for a long period of time, and the drawbacks in a conventional ultrasonic wave vibration apparatus can be eliminated. The relation between the length L of the horn 10 and the frequency is represented by the following formula (1) Ct = L x f (1); in the formula (1), Ct = sonic velocity in the horn at the molten metal temperature; L = horn length; and f = frequency. In the present embodiment, it is necessary that the metal adhered to the surface of the silicon carbide fiber bundle 2 is melted at a position just beneath the horn 10 arranged in the molten metal vessel 6. When the adhered metal is melted before the metal reaches the horn 10 in the vessel 6, the effect of previously fixing the element fibers of the silicon fiber bundle 2 in a parallel relationship is extinguished. On the other hand, when the adhered metal does not melt even when the metal is beneath the horn 10, the impregnating metal cannot fully penetrate the interior of the silicon carbide fiber bundle 2 even in the case where the fiber bundle is subjected to an ultrasonic wave treatment. When these phenomena are taken into consideration, the molten metal bath temperature in the vessel 6 is preferably 20-100°C higher than the melting temperature of the metal. For example, when aluminum is used as a metal, the bath temperature is preferably about 680-760°C. The immersing time of the silicon carbide fiber bundle 2 in a molten metal bath must be not longer than 50 seconds, and is preferably not longer than 2 seconds, particularly preferably not longer than 1 second. The vibration by the ultrasonic wave vibration apparatus 7 is controlled by selecting properly the resonance frequency. In general, a frequency of 19-20 KHz is used. In the ultrasonic wave vibration apparatus 7 of the present invention, it is necessary that the raw material for the horn 10 is properly selected. That is, the horn 10 is consumed in a molten metal 5, and therefore there are used metals having a high resistance against consumption, for example, stainless steel, nickel alloy, molybdenum, tungsten, titanium, ceramics and the like. In general, the use of two horns 10 connected in parallel exhibits the highest vibration efficiency. However, when 3 or more horns are connected in parallel, the vibration efficiency decreases somewhat. The cross-sectional shape of the horn 10 is optional, and circular, rectangular, horseshoe-shaped cross-sectional shapes and the like are used. In the silicon carbide fiber bundle 2, which has been impregnated with a molten metal, such as molten aluminum or the like, and concurrently subjected to an ultrasonic wave treatment under such an unfastened and drawn state that the element fibers are uniformly arranged in a parallel relation along their length direction, the metal, such as aluminum or the like, is fully penetrated between the element fibers, and there are few vacancies between the fibers. The above treated silicon carbide fiber bundle 2 is continuously passed through guide rolls 4c and 4d, and a slit 12 or dies to be formed into a desired shape, and excess metal is squeezed to form a preform wire containing a given amount by volume of fiber, and the preform wire is taken up, for example, on a take-up roll 13. In the present invention, an explanation has been made with respect to the preform wire. However, the term "preform wire" used in the present invention means not only preform wire but also preform sheet or tape as described above. The following example is given for the purpose of illustration of this invention, and is not intended as a limitation thereof. Example According to the steps shown in Fig. 1, a silicon carbide fiber bundle consisting of 500 element fibers was unfastened and drawn such that the element fibers constituting the fiber bundle were arranged in a parallel relation along their length direction, and then the fiber bundle was sprayed with aluminum by means of a plasma jet to adhere the aluminum to the surface of the silicon carbide fiber bundle. Thereafter, the silicon carbide fiber bundle containing aluminum adhered thereto was continuously passed in an aluminum bath kept at 720°C through guide rolls, and was concurrently subjected to an ultrasonic wave treatment, wherein the resonance frequency of the ultrasonic wave vibration apparatus was kept to about 20 KHz and the impregnation time of the silicon carbide fiber bundle with aluminum in the bath was kept to about one second. The aluminum impregnated silicon carbide fiber bundle was passed through a slit and guide rolls to be formed into a desired shape, excess aluminum was squeezed and then the above treated fiber bundle was taken up on a take-up roll to obtain an aluminum preform wire for FRM. In the resulting aluminum preform wire for FRM, the fibers occupied 30% by volume based on the total volume of the preform wire, and the metal was fully penetrated between the element fibers, and there were no vacant spaces between the fibers. The observed value of the tensile strength of the preform wire was 65 kg/mm² (theoretical value: 80 kg/mm²). Further, it was ascertained that the arrangement of the element fibers was not disordered. In order to examine the strength of the silicon carbide fiber bundle in this aluminum preform wire for FRM, aluminum contained in the preform wire was chemically dissolved and removed, and the remaining silicon carbide fiber bundle was taken out. When the tensile strength of the silicon carbide fiber bundle was measured, there was no difference in the strength before and after the treatment. That is, it was ascertained that the deterioration of the fibers due to their reaction with metal did not occur.

Claims: A method of producing a preform wire, sheet or tape for FRM, comprising unfastening and drawing a silicon carbide fiber bundle (2) so that the element fibers constituting the fiber bundle (2) are loosened and uniformly arranged in a parallel relationship along their length, and impregnating the fiber bundle (2), while maintaining the element fibers in their loosened and parallel arrangement, for a period of time of not longer than 50 seconds with a molten metal, which is kept vibrated by means of an ultrasonic wave vibration apparatus (7) having a cooling means (11). A method according to claim 1, wherein a metal is previously sprayed or vapor-deposited on the silicon carbide fiber bundle before the impregnation, so as to maintain the parallel arrangement. A method according to claim 1 or 2, wherein the silicon carbide fiber bundle is electromagnetically vibrated during the impregnation. A method according to any preceding claim, wherein the impregnating metal is aluminium, magnesium, silicon, titanium, lead, copper or an alloy of any of these. A method according to any preceding claim, wherein the impregnation time is not longer than 2 seconds. An ultrasonic wave vibration apparatus comprising a vibrator (9) with a horn (10) and an ultrasonic wave oscillator (8), the vibrator (9) being adapted to vibrate a molten metal bath (5) to be used for impregnating a starting silicon carbide bundle (2) in the production of a preform wire for FRM at a predetermined frequency f, characterised by the further provision of means (1) for unfastening and drawing the bundle (2) prior to impregnation so that the element fibers constituting the fiber bundle (2) are loosened and uniformly arranged in a parallel relationship along their length, and means (3) for maintaining the fibers of the bundle (2) parallel during impregnation, the horn (10) having a cooling water passage or jacket (11) at its upper portion at a position corresponding to a node of the half-wavelength of the ultrasonic wave. An apparatus according to claim 6, wherein the material of the horn is stainless steel, nickel alloy, molybdenum, tungsten, titanium or ceramics. An apparatus according to claim 6 or 7, wherein the horn is a combination of at least two horns connected in parallel. An apparatus according to claim 6, 7 or 8, wherein the horn has a length L represented by the following formula Ct = L x f, where Ct = sonic velocity in the horn at the molten metal temperature, and L = horn length. An apparatus according to any preceding claim, wherein the frequency of the ultrasonic waves is from 19-20 kHz.

Inventors: IMAI, YOSHIKAZU, ISHIKAWA, TOSHIKATSU, NAGATA, YOICHI, TERANISHI, HARUO
Applicants: AGENCY OF INDUSTRIAL SCIENCE AND TECHNOLOGY
Application year: 1985
Main classification: C22C1
IPC codes: C22C47, B01J19, C23C2, B22D19