Specialized metallurgical processes – compositions for use therei – Compositions – Loose particulate mixture containing metal particles
Reexamination Certificate
1999-11-08
2001-09-04
Jenkins, Daniel (Department: 1742)
Specialized metallurgical processes, compositions for use therei
Compositions
Loose particulate mixture containing metal particles
C075S254000
Reexamination Certificate
active
06284014
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates generally to metal matrix compositions. Such compositions or composites comprise one or more base material metals such as, for example, aluminum, titanium, or magnesium, to which is added a selected percentage of ceramic material to alter the properties of the base material metal(s) in a positive manner. Strength, hardness, and drawability are increased. Drawability facilitates fabrication of various articles of manufacture from such composite materials. More specifically, the present invention pertains to an improved metal matrix composite which, in a preferred embodiment, uses boron carbide as the added ceramic material. The composites result from a novel method of manufacture producing a composite which is lighter, stronger, stiffer, and which has a higher fatigue strength than other available alloys of the base material metal, and which is also lighter, stronger, stiffer, and which has a higher fatigue strength than prior art metal matrices, composites, and particularly those metal matrix composites which are of comparable cost.
2. Prior Art
In recent years metal matrix compositions or composites have become popular materials for a variety of applications. This new family of materials has become popular because of improvements in stiffness, strength, and wear properties. Basic metal matrix composites are made typically with aluminum, titanium, or magnesium as the base material metal. Then certain percentages of ceramics are added. Typical ceramics include boron carbide, silicon carbide, titanium diboride, titanium carbide, aluminum oxide, and silicon nitride. Most known metal matrix composites are made by introducing the ceramics into the molten metal. In large production runs of metal matrix composites, the ceramic reinforcement must be wetted by the liquid metal to facilitate incorporation of the reinforcement into the melt. In those metal matrix composites using silicon carbide and aluminum, the silicon carbide is thermodynamically unstable in molten aluminum which leads to the formation of aluminum carbide at the interface and increased concentration of silicon in the material matrix during the solidification process. This interface reaction is believed to have detrimental effects on the mechanical properties of the resulting composite by reducing the interface strength and changing the composition.
Recently, powder metallurgy consolidation has emerged as a competing method of fabricating metal matrix composites by consolidating the powders by means of hot pressing and conventional powder metallurgy operations with vacuum sintering used to achieve a high density green body. By following certain isopressing and sintering techniques, a 99% theoretical density billet can be achieved.
In the present invention, it has been found that the most desirable ceramic candidate for metal matrix composites is boron carbide or silicon carbide. Boron carbide is the third hardest material known and the hardest material produced in tonnage. Boron carbide powders can be formed by a variety of reactions including the carbon reduction of any of several boron-oxygen compounds including boric oxide, borax, boracite, as well as by the direct combination of the elements. Usually, most commercial boron carbide is produced in arc furnaces. Boric acid is added together with carbon in the form of coke and heated to very high temperatures. An electric arc is maintained between graphite electrodes inside a furnace. The synthesis reaction is accompanied by the release of large volumes of carbon monoxide. Venting and disposal of the carbon monoxide gas constitutes a major design consideration. Boron carbide is also the lightest of the ceramics typically used in metal matrix composite technology, but it is very hard and expensive. Its hardness limits its extrudability. Thus it would be highly advantageous if it were possible to produce an improved metal matrix composite which utilizes an advanced ceramic such as boron carbide but which, unlike the prior art, results in an extrudable composite material that allows easy fabrication of various articles of manufacture so that such resulting articles have the specific strength and stiffness improvements as compared to equivalent articles of manufacture using only the base material metals.
SUMMARY OF THE INVENTION
The present invention comprises an improved metal matrix composite which, in a preferred embodiment disclosed herein, utilizes boron carbide as the ceramic additive to a base material metal. The fabrication process is unlike that of a number of other metal matrix composites because it is not made through molten processes. More specifically, instead of melting the boron carbide or silicon carbide with the aluminum, nickel, zinc, magnesium, titanium, or other base material metal, the metal matrix composite of the present invention begins with the blending of powders of all the various elements such as by means of a jet mill which is basically an air blaster used to uniformly mix powdered substances and avoid stratification and settling. After the particles have been sufficiently mixed, they are directed into a die and then into a cylindrical container where the particulates are subjected to extremely high pressures transforming the elements into a solid ingot. It is from these ingots that the extrusion tubes or other articles of manufacture may then be made. The resulting advanced metal matrix composites of the boron carbide embodiment of the invention are 60% lighter, 30% stronger, 40-45% stiffer, and 50% higher in fatigue strength than any of the top of the line 7000 series aluminum alloy materials. In addition, the inventive material is 7-8% lighter, 26% stronger, 5% stiffer, and has 35-40% greater fatigue strength than most popular metal matrix composites available in the prior art. In one embodiment disclosed herein, the base material metal is preferably aluminum, magnesium, or titanium, or an alloy thereof, provided in powder form and preferably being approximately 97% pure with the balance of the material comprising various trace metals such as chromium, copper, iron, magnesium, silicon, titanium, and zinc. The boron carbide powder is 99.5% pure boron carbide having a particulate size in the range of 2-19 microns with a mean or average size of approximately 8.4 microns.
In one typical embodiment of the invention, the metal base material was selected from an aluminum alloy 6061T-6 to which was added approximately 12% by weight the aforementioned boron carbide powder which included silicon in an amount of 0.1-0.4%, iron in the amount of 0.05-0.4%, and aluminum in the amount of 0.05-0.4%. The underlying boron carbide material was approximately 77% boron content and 22% carbon content.
A metal matrix composite made from the aforementioned materials in accordance with the fabrication process of the present invention to be described hereinafter, typically may result in a composite material which exhibits a tensile strength of about 62-108 kpsi, a yield strength of about 58-97 kpsi, and a modulus of elasticity of about 10.0-14.50 Mpsi, Although higher or lower strengths are possible. Furthermore, the resulting material is approximately as hard as chromoly steel but has a density which is even lower than aluminum alloy.
Importantly, the material of the present invention is readily extrudable. Ingots of the metal matrix composites of the present invention are extruded through a titanium diboride die bearing material which exhibits a significant increase in die insert life. The die bearing material alternatively may be tungsten carbide, tungsten carbide composite, boron carbide, carbon nitride, a plasma vapor deposited ceramic such as titanium carbide or a chemically deposited ceramic such as titanium nitride. Furthermore, the present invention is readily weldable. In fact, the coated boron carbide particulates of the material disclosed herein tend to flux and move into the weld pool which creates a very strong weld joint. Thus the present invention is not only highly s
Alyn Corporation
Cooper & Dunham LLP
Jenkins Daniel
LandOfFree
Metal matrix composite does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Metal matrix composite, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Metal matrix composite will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2469375