Claims:
1. A method for joining at least two metals to obtain a metal matrix composite, said method comprising the steps of:
a) preparing a feed material containing a metallic powder composition and a thermite mixture mixed in a predefined weight proportion;
b) cold compacting the feed material of step a) followed by shaping into a ring having a central hole therein;
c) positioning the feed material of step b) between a fixed rod and a rotary rod thereby partially covering the fixed rod and the rotary rod through a containing envelope;
d) rotating the rotary rod at a predefined speed thereby facilitating a stub of said rotary rod to be positioned within the central hole thereby generating a high friction at the stub;
e) sliding the rotary rod towards the fixed rod at a predefined axial force for generating a predefined temperature essential for igniting the thermite mixture to melt the ring; and
f) gradually cooling the fixed rod and the metal rod thereby forming the metal matrix composite.

2. The method as claimed in claim 1, wherein the predefined weight proportion of the metallic powder composition and the thermite mixture is 0.01: 99.99 to 99.99:0.01.

3. The method as claimed in claim 1, wherein the fixed rod has a diameter in a range of 0.1 mm to 100 m.

4. The method as claimed in claim 1, wherein the rotary rod has diameter in a range of 0.1 mm to 100 m.

5. The method as claimed in claim 1, wherein the diameter of the containing envelope is in a range of is in a range of 0.1mm to 100 m.

6. The method as claimed in claim 1, wherein the predefined speed of the rotary rod is in a range of 1 rpm to 100 million rpm

7. The method as claimed in claim 1, wherein the predefined axial force is in a range of 1 N to 100 million N.

8. The method as claimed in claim 1, wherein the predefined temperature is in a range of 2000 0C to 5000 0C.
, Description:Field of the invention
The present invention relates to methods for preparation of metal matrix composites and more particularly to a method for preparation of metal matrix composite involving ignition of feed material and thermite mixtures.
Background of the Invention
Metal matrix composite (MMC, hereinafter) normally constitutes two components, namely a metal acting as a supporting matrix anda material typically called as reinforcement. In some of the structural applications, the supporting matrix is usually selected from Aluminum, Magnesium, or Titanium. The supporting matrix provides a compliant support for the reinforcement. However, the reinforcement material is selected from a ceramic or an organic compound. The reinforcement can be continuous or discontinuous in most of the MMCs known in the art.
However, the reinforcement affects the physical properties such as wear resistance, friction coefficient, or thermal conductivity of the material. The metal matrix composites with discontinuous reinforcements have isotropic properties. These can be mechanically worked and machined to shapes. The most common discontinuous reinforcing materials are Alumina and Silicon Carbide. The continuous reinforcements have anisotropic properties. The continuous reinforcement uses monofilament wires or fibers such as Carbon Fiber or Silicon Carbide.
A thermite reaction is a process wherein the metal powders are combined in predefined proportions and ignited in presence of metal oxides. It is well known fact that the ignition reactions require extremely high temperatures which undergo an exothermic reduction-oxidation (Redox) reaction when ignited. Most of the varieties of thermite mixtures are non-explosive but they show brief bursts of high temperature.
The thermite mixtures aregenerally pyrotechnic composition of pure metal powder and metal oxide that have diverse compositions. For example, the metal powder of the thermite mixture includes Aluminum, Magnesium, Titanium, Zinc, Silicon, and Boron and the like. However, Aluminum is the most commonly preferred metal used because of its high boiling point and low cost. The metal powder should have high heat of combustion and produce oxides with low melting point and high boiling point. The metal oxide powders are commonly called as oxidizers. The metal oxide powders generally include Bismuth Oxide, Boron Oxide, Silicon Oxide, Chromium Oxide, Manganese Oxide, Iron Oxide, Copper Oxide, Lead Oxide and the like.
The methods commonly used for carrying out these reactions are powder blending and consolidation, stir casting, squeeze casting, reactive processing and the like.The powder blending and consolidation method includes mixing of powdered metal and discontinuous reinforcement and their bonding through a process of compaction, degassing, and thermo-mechanical treatment. In stir casting method, discontinuous reinforcement is stirred into molten metal and allowed to solidify. In squeeze casting method, the molten metal is injected into a form with fibers pre-placed inside it. The reactive processing reactions are chemical reactions wherein the reactants form matrix and reinforcement.
However, these methods have a plurality of limitations. These methods can prepare only few thermite mixtures as most of the other mixtures are too sensitive to heat and may ignite before sufficient intermixing can occur. Also, these methods have further limitation such as long mixing time which is substantially unsuitable for reactive reinforcements. Moreover, the capital requirement for the dedicated metal matrix composite unit in foundries is very high.
Accordingly, there is need of a faster and economic method for preparation of metal matrix components that overcomes all the drawbacks of the prior art.

Summary of the invention
The present invention discloses a method for joining at least two metals to obtain a metal matrix composite. The method comprises an initial step of preparing a feed material containing a metallic powder composition and a thermite mixture mixed in a predefined weight proportion. In next step, the feed material is cold compacted followed by shaping into a ring having a central hole therein. In next step, the feed material is positioned between a fixed rod and a rotary rod thereby partially covering the fixed rod and the rotary rod through a containing envelope. In next step, the rotary rod is rotated at a predefined speed thereby facilitating a stub of said rotary rod to be positioned within the central hole thereby generating a high friction at the stub. In further step, the rotary rod is moved towards the fixed rod at a predefined axial force for generating a predefined temperature essential for igniting the thermite mixture to melt the ring. In last step, the fixed rod and the metal rod are gradually cooled thereby forming the metal matrix composite.

Brief description of the drawings
Fig. 1 is a perspective view of an arrangement for a method for preparation of metal matrix composite; and
Fig. 2 is a top view of an arrangement for a method for preparation of metal matrix composite.
Detailed description of the invention
The invention described herein is explained using specific exemplary details for better understanding. However, the invention disclosed can be worked on by a person skilled in the art without the use of these specific details.
References in the specification to "one embodiment" or "an embodiment" means that a particular feature, structure, characteristic, or function described in connection with the embodiment is included in at least one embodiment of the invention. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.
References in the specification to “preferred embodiment” means that a particular feature, structure, characteristic, or function described in detail thereby omitting known constructions and functions for clear description of the present invention.
In accordance with the present invention, a method for joining at least two metals to obtain a metal matrix composite, said method comprising the steps of:
a) preparing a feed material containing a metallic powder composition and a thermite mixture mixed in a predefined weight proportion;
b) cold compacting the feed material of step a) followed by shaping into a ring having a central hole therein;
c) positioning the feed material of step b) between a fixed rod and a rotary rod thereby partially covering the fixed rod and the rotary rod through a containing envelope;
d) rotating the rotary rod at a predefined speed thereby facilitating a stub of said rotary rod to be positioned within the central hole thereby generating a high friction at the stub;
e) sliding the rotary rod towards the fixed rod at a predefined axial force for generating a predefined temperature essential for igniting the thermite mixture to melt the ring; and
f) gradually cooling the fixed rod and the metal rod thereby forming the metal matrix composite.
Referring to FIGS. 1 and 2, an arrangement 100 joining at least two metals thereby utilizing a metal matrix composite is shown. The arrangement 100 comprises a fixed rod 102 and a rotary rod 104 such that a feed material 106 is positioned there between. The feed material 106 is adapted to be ignited by a thermite reaction. In the context of the present invention, the feed material 106 includes a metallic powder composition along with a thermite mixture added and mixed in a predefined proportion. The predefined weight proportion of the metallic powder composition and the thermite mixture is 0.01:99.99 to 99.99:0.01. The fixed rod 102 and the rotary rod 104 are partially covered by a containing envelope 108. The fixed rod 102 and the rotary rod 104 are preferably made of a metallic material in accordance with the present invention. The fixed rod 102 and rotary rod 104 respectively have a diameter in a range of about 0.1 mm to 100 m. The containing envelope 108 is preferably made of ceramic material in this one embodiment. However, the containing envelope 108 may be made of metallic material in other alternative embodiments of the arrangement 100. The containing envelope 108 respectively has an inner or outer diameter in a range of about 0.1 mm to 100 m depending upon the diameters of rods 102, 104. The Fixed rod 102 preferably has a flat cross section. The rotary rod 104 preferably has a circular cross section. The rotary rod 104 includes a stub 109 that is configured to protrude through the feed material 106 thereby contacting the fixed rod 102.
The method for joining at least two metals thereby utilizing a metal matrix composite is described in detail hereinafter:
In an initial step, the feed material 106 is placed within the fixed rod 102 and the rotary rod 104 of the arrangement 100. It is understood here that the feed material 106 is cold compacted and preferably placed within the containing envelope 108. In next step, the feed material 106 is shaped in a ring form thereby forming a central hole 110 therein.
In next step, the rotary rod 104 is rotated by a motor to attain a predefined speed such that the stub 109 of the rotary rod 104 contacts the fixed rod 102 and subsequently moves inside the central hole 110 with a predefined axial force. It is understood here that the axial force is in a range of about 1 N to 100 million N. In this step, the rotary rod 104 generates a high friction at the stub 109 thereby attaining a predefined temperature thatignites the feed material 106. It is understood here that the predefined speed of the rotary rod 104 varies from about 1 rpm to about 100 million rpm. In this step, the motor is disengaged after attaining the predefined speed. In this step, sliding of the rotary rod 104 facilitates sliding of the metallic powder composition and the thermite mixture against each other at high speed. This generates the predefined temperature to weld the metallic powder composition and the thermite mixture together. In the context of the present invention, the predefined temperature is from about 20000C to about 50000C. It is understood here that the predefined temperature essential to ignite the thermite mixture is substantially dependent the of the metallic powder composition. Selection of the metallic powder is dependent on the type of the metals to be connected through the method of the present invention.
In next step, the melted mixture of the metallic powder composition and the thermite mixture slowly cool to form a solid composite matrix in accordance with the present invention. However, the feed material 106 remains in semi solid stage while cooling that facilitates substantially fine structure with good mechanical properties to the solid composite matrix.
In operation, themethod for preparation ofalloys and metal matrix composite produces composite materials containing metal matrix and various kinds of reinforcement materials. In operation, the axial force is application of lateral force that upsets and fuses the materials together. It is a solid state process that combines welding and forging.
The embodiments were chosen and described in order to best explain the principles of the present invention and its practical application, to thereby enable others, skilled in the art to best utilize the present invention and various embodiments with various modifications as are suited to the particular use contemplated.
It is understood that various omission and substitutions of equivalents are contemplated as circumstance may suggest or render expedient, but such are intended to cover the application or implementation without departing from the spirit or scope of the present invention.