Fibre-reinforced metal

Abstract: A fiber-reinforced metal comprising a matrix metal and a glass fiber impregnated with said matrix metal, said glass fiber having a nitrogen content of at least 8 atomic %. The fiber-reinforced metal has a high tensile strength and elasticity.

Description: Field of the Invention The present invention relates to glass-reinforced metal. Background of the Invention In fiber-reinforced metal (hereinafter referred to briefly as FRM), physical characteristics not found in the metal itself have been realized by the combination of the metal with a fiber. Representative species of the hitherto-known FRM include aluminum alloys reinforced with carbon fiber, ceramic fibers [SiC fiber, Si-Ti-C-O fiber (tilano fiber), alumina fiber, boron fiber, etc.] or glass fiber, in which high tensile strength and rigidity and low coefficients of thermal expansion have been imparted to matrix metals. However, in the conventional FRM, where the reinforcing fiber is carbon fiber, for instance, a reaction takes place between molten aluminum and reinforcing fiber to form aluminum carbide Aℓ₄C₃ so that the strength of FRM is not much increased. SiC or Si-Ti-C-O (tilano fiber), which is a ceramic fiber, cannot give a FRM with sufficient strength because of poor wetting by aluminum. Moreover, Aℓ₂O₃ fiber containing SiO₂, which is among alumina fibers, reacts with molten aluminum, while SiO₂-free alumina fiber is not reactive and good in wetting property but is low in strength (141 kg/mm²). Moreover, boron fiber is so large in fiber diameter that it does not lend itself well to complicated product configurations so that it connot function well as a reinforcing fiber for FRM. These ceramic fibers have the additional serious disadvantage of high costs. Kevlar, which is a high-strength organic fiber, is low in heat resistance, and glass fibers in general are reactive with molten alloys and low in elasticity and strength. Thus, the conventional FRM, thus made up of reinforcing fiber and matrix metal, are disadvantageous, for example in that the reinforcing fiber and matrix metal react at their interfaces of the fiber can hardly be wetted by the molten metal. Thus, if the metal matrix reacts with the reinforcing fiber across the interface in the course of manufacture, the strength of the product FRM is adversely affected. On the other hand, if the wettability of the reinforcing fiber by the matrix metal is poor, there is obtained no sufficient bond between the two components so that the resulting FRM cannot enjoy the benefit of combination in strength and elasticity, thus failing to exhibit satisfactory physical characteristics. For this reason, it has been proposed and practiced, in the manufacture of FRM, to plate the surface of the reinforcing fiber with nickel or other metal or treat the surface with an inorganic compound, such as SiC, by the plasma coating technique, before impregnation of matrix metal. However, such processes are costly and involve complicated procedures. In view of the above-mentioned disadvantages, the present invention is based on the possibility of using oxynitride glass fibre, which is a high-elasticity fibre, as the reinforcing fibre for FRM. It has been found that an oxynitride glass containing at least a certain proportion of nitrogen is not reactive with molten metal even in the absence of plating or other pretreatment and is highly wettable, so that substantially the additive effect of the two components can be realised in the resulting FRM. EP-A-0181207 discloses an inorganic fibre-reinforced metallic composite material, wherein the metal matrix consists of Al, Mg and Ti alloys thereof, and the fibre is an amorphous material with a nitrogen content of 10-35% by weight. Summary of the Invention The present invention provides a fibre-reinforced metal, comprising a glass fibre having a nitrogen content of 8 to 23.4 atomic % and a matrix metal impregnated with said glass fibre. The raw material, Si₃N₄, is relatively expensive, and a high nitrogen content of the glass gives less spinnability, so that a nitrogen content of not less than 8 atomic % is used. The nitrogen content is preferably not less than 12 atomic %, since the glass fibre is sufficiently wetted by molten metal that the strength of the resulting FRM is as high as desired. Brief Description of the Drawings Figs. 1, 2 and 3 are microphotographs (X 1000) showing the sectional textures of FRM. Detailed Description of the Invention The glass fiber employed in the FRM of the present invention is preferably an oxynitride glass fiber containing an Si-M₁-M₂-O-N system which satisfies the following expressions in mole %: 65≦ (SiO₂+3Si₃N₄+M₁O)×100/(100+2Si₃N₄) <100 (a) 0.7≦ (SiO₂+3Si₃N₄)/M₁O≦2.3 (b) [weherin M₁ means Ca or Ca + Mg and M₂ means one or more metals selected from the group consisting of Aℓ, Sr, La, Ba, Y, Ti, Zr, Ce, Na, K, Sb, B, Cr, Pb, V and Sn] . Therefore, the oxynitride glass used in the present invention has an Si-Ca-M₂-O-N or Si-Ca-Mg-M₂-O-N system. The metal M₂ may be a single metal species or a combination of two or more metals. Furthermore, this glass preferably contains 0 to 40 % mole of SiO₂, 26 to 70 mole % of CaO, 0 to 20 mole % of MgO and not more than 22 atomic % of M₂. Therefore, the preferred composition for the oxynitride glass to be used as the reinforcing fiber in the present invention satisfies the following expressions in mole %. 65≦ (SiO₂ +3Si₃N₄+CaO+MgO)×100/(100+2Si₃N₄)<100 0.7≦ (SiO₂+3Si₃N₄)/(CaO+MgO)≦2.3 In the above expressions, CaO represents the mole % of CaO or a compound convertible to CaO and MgO represents the mole of MgO or a compound convertible to MgO. The diameter of such glass fiber may range from 3 to 50 µm. The fiber may be a continuous fiber or a short staple measuring 0.5 to 100 mm. As the matrix metal, such metals as aluminum, titanium, magnesium, nickel and copper, and various alloys thereof can be employed. For impregnating the reinforcing fiber with the metal, various techniques can be employed. A preferred process comprises placing the oxynitride glass in a metal mold, pouring a molten matrix into the mold, applying a pressure and cooling the mixture to solidify. To give a specific example, one may place the reinforcing fiber in a metal mold preheated at 500∼600°C, then pour a molten aluminum alloy heated at about 800°C , apply a pressure of about 1 to a few hundred MPa, and cooling the mixtrue to solidify into an FRM. By this process, the manufacture of FRM in the atmospheric air is feasible up to a temperature as high as about 900°C. For the manufacture of the FRM of the invention, various techniques such as techniques of powder metallurgy, composite wire process, plasma spraying, flame spraying, vapor deposition, die casting as the above-described casting process, whereby an FRM having an optional shape can be manufactured. In the present invention, the reinforcing fiber does not react with the matrix metal and the fiber is uniformly wetted by the metal. Accordingly, high tensile strength and elasticity are realized in FRM without resort to any special pretreatment such as the surface treatment of reinforcing fiber. The following examples are further illustrative of the invention. In the examples, % stands for mole. Example 1 (Production of reinforcing fiber) The material powders [SiO₂: 8.6%, Si₃N₄: 19.4%, CaO: 59.8%, MgO: 6.9%, Aℓ₃O₃: 5.2%; nitrogen content 23.4 atomic %, expression (a) = 96.2, expression (b) = 1.00] were mixed and put in a molybdenum crucible, which was then heated with a graphite heater. The resulting glass was withdrawn in filaments from the bottom of the crucible. For spinning, the glass melted at 1,780°C for one hour was held at 1,570°C and allowed to drop from the nozzle disposed at the bottom of the crucible and the resulting filaments were taken up on a winder at a takeup speed of about 1,000 m/minute. The filaments had a tensile modulus of 205 GPa, a tensile strength of 3.62 GPa, a fiber diameter of 12 µm and a density of 2.89 g/cm³. (Manufacture of FRM) A metal mold (5 mm × 5 mm × 20 mm) held at 550°C was charged with 0.72 g of the above-mentioned filaments as pre-oriented, which was maintained at that temperature for 10 minutes. Then, aluminum alloy 6061 (an Aℓ-Mg-Si model material; (wt%) Si:0.4∼0.8, Fe:0.7, Cu:0.15∼0.40, Mn:0.15, Mg:0.8∼1.2, Cr:0.04∼0.35, Zn:0.25, Ti:0.15, Aℓ:resd.) melted at 800°C was poured into the mold and pressurized at 23 MPa. The contents were cooled under the same pressure to solidify. Fig. 1 is a microphotograph showing the sectional texture of the resulting FRM, which indicates clear interfaces between fiber and metal without signs of reaction as well as good wettability as evidenced by a uniform penetration of the metal between the interfiber spaces. Furthermore, the results of EPMA determination showed no migration of elements, with the fiber not having undergone reaction with the matrix but remaining intact. The FRM thus obtained contained 50 volume percent of oxynitride glass fiber and had a bending modulus of 137 GPa and a flexural strength of 1.76 GPa. The matrix aluminum alloy 6061 itself has a tensile modulus of 68.6 GPa (bending modulus: 60.5 GPa) and a tensile strength of 309 MPa (flexural strength 340 MPa). Example 2 Using a charge of 30.5% of SiO₂, 9.5% of Si₃N₄, 49.4% of CaO, 6.0% of MgO and 4.6% of Aℓ₂O₃ (nitrogen content 12.6 atomic %, expression (a) = 96.1, expression (b) = 1.06), a glass fiber was produced in the same manner as Example 1. However, the melting temperature was 1,700°C and the spinning temperature was 1,510°C . The resulting glass fiber had a tensile modulus of 113 GPa, a tensile strength of 3.43 GPa, a fiber diameter of 12 µm and a density of 2.85 g/cm³. Using 0.71 g of the above fiber, an FRM was manufactured in otherwise the same manner as Example 1. Fig. 2 is a microphotograph showing the sectional texture of the resulting FRM. As in Fig. 1, no reaction zone was found at the fiber-Aℓ alloy interface, with good wettability as evidenced by a uniform penetration of the metal into the interfilament spaces. The reinforcing fiber content of the product FRM was 60 volume %. This FRM had a bending modulus of 88.2 GPa and a flexural strength of 1.67 GPa, thus attesting to an additive effect. Comparative Example 1 Using a charge of 39.3% of SiO₂, 4.0% of Si₃N₄, 46.0% of CaO, 5.0% of MgO and 5.0% of Aℓ₂O₃ (nitrogen content 5.6 atomic %, expression (a) = 95.4, expression (b) = 0.99), a glass fiber was produced in the same manner as Example 1. However, the melting temperature was 1,600°C and the spinning temperature was 1,430°C . This glass fiber had a tensile modulus of 100 GPa, a tensile strength of 3.43 GPa, a fiber diameter of 12 µm and a density of 2.82 g/cm³. Using 0.70 g of the above fiber, an FRM was manufactured in the same manner as Example 1. The reinforcing fiber content of this FRM was 50 volume %. This FRM had a bending modulus of 66.6 GPa and a flexural strength of 392 MPa. Thus, substantially no reinforcing effect on aluminum alloy was obtained. Example 3 (Production of reinforcing fiber) The material powders [SiO₂: 35.29%, Si₃N₄: 10.38%, CaO: 36.23%, MgO: 6.04%, Aℓ₃O₃: 12.08%; nitrogen content 8.1 atomic %, expression (a) = 90, expression (b) = 0.83] were mixed and put in a molybdenum crucible, which was then heated with a graphite heater. The resulting glass was withdrawn in filaments from the bottom of the crucible. For spinning, the glass melted at 1,670°C for 2 hours was held at 1,500°C and allowed to drop from the nozzle disposed at the bottom of the crucible and the resulting filaments were taken up on a winder at a takeup speed of about 1,000 m/minute. The filaments had a tensile modulus of 103 GPa, a tensile strength of 3.43 MPa, a fiber diameter of 12 µm. (Manufacture of FRM) The above-mentioned filaments (ca. 5g) pre-oriented were wrapped in a frame (35 mm × 20 mm × 5 mm) of nickel mesh, and were charged together with the frame into a metal mold (5 mm × 5 mm × 20 mm), which was maintained at 500 °C for 10 minutes. Then, 1050 type aluminum alloy (Si: 0.25 wt%, Fe: 0.40, Cu: 0.05, Mn: 0.05, Mg: 0.05, Zn: 0.05, V: 0.05, Aℓ: resd.) melted at 800°C was poured into the mold and pressurized at 6.86 MPa. The contents were cooled under the same pressure to solidify. Fig. 3 is a microphotograph showing the sectional texture of the resulting FRM, which indicates clear interfaces between fiber and metal without signs of reaction as well as good wettability as evidenced by a uniform penetration of the metal between the inter fiber spaces. The FRM thus obtained contained 30 volume percent of oxynitride glass fiber and had a bending modulus of 63.7 GPa and a flexural strength of 833 MPa. The matrix 1000 type aluminum alloy itself has a bending modulus of 49 GPa and a flexural strength of 49 MPa. Example 4 Using magnesium alloy (MC 5; Aℓ:9.3∼10.7, Zn:0.3>, Mn:0.1∼0.5, Si:0.3>, Cu:0.1>, Ni:0.01>, Mg: resd.), an FRM was manufactured in otherwise the same manner as Example 1. However, the filaments and the metal mold were held at a temperature of 500 °C, and the temperature of the melted magnesium alloy was 700 °C . A chlorid flux was used to suppress the reaction of magnesium with air. The resulting FRM has no reaction zone at the fiber-Mg alloy interface, with good wettability as evidenced by a uniform penetration of the metal into the interfilament spaces. The reinforcing fiber content of the product FRM was 50 volume %. This FRM had a bending modulus of 123 GPa and a flexural strength of 1.58 GPa, thus attesting to an additive effect. The matrix magnesium alloy itself has a bending modulus of 54.7 GPa and a flexual strength of 267 MPa.

Claims: A fiber-reinforced metal comprising a matrix metal and a glass fiber impregnated with said matrix metal, said glass fiber having a nitrogen content of 8 to 23.4 atomic %. A fiber-reinforced metal as claimed in claim 1, wherein the glass has a nitrogen content of at least 12 atomic %. A fiber-reinforced metal as claimed in claim 1 or claim 2, wherein the glass is an oxynitride glass having a Si-M₁₋M₂-O-N system and containing SiO₂, Si₃N₄ and M₁O in amounts which, as mole%, satisfy the following equations (a) and (b): 65≦ (SiO₂ +3Si₃N₄+M₁O)×100/(100+2Si₃N₄)<100 0.7≦(SiO₂+3Si₃N₄)/M₁O≦2.3 wherein M₁ is Ca or Ca + Mg; and M₂ is a metal other than Ca and Mg. A fiber-reinforced metal as claimed in claim 3, wherein M₂ is one or more metals selected from Aℓ, Sr, La, Ba, Y, Ti, Zr, Ce, Na, K, Sb, B, Cr, Pb, V and Sn. A fiber-reinforced metal as claimed in any preceding claim, wherein, the matrix metal is selected from aluminium, titanium, magnesium, nickel, copper, and alloys thereof.

Inventors: FUJII HIROYUKI, KADA KATSUHIKO, KANAMARU KUNIAKI, MINAKUCHI HIROYOSHI, OSAFUNE HARUO, SUGANUMA KATSUAKI, FUJII, HIROYUKI, KADA, KATSUHIKO, KANAMARU, KUNIAKI, MINAKUCHI, HIROYOSHI, OSAFUNE, HARUO, SUGANUMA, KATSUAKI
Applicants: SHIMADZU CORP, SHIMADZU CORPORATION
Application year: 1990
Main classification: C22C1
IPC codes: C03C3, C03C13, C22C49, C22C47