Machineable metal-matrix composite and method for making the same

Abstract

A method for producing a metal matrix composite having improved properties includes the step of forming a sintered ceramic preform including a network of uniformly distributed ceramic particles having a particle size of 1 micron or less and being bonded together at their points of contact by sintering. After sintering to form a preform, the preform is placed in a mold and infiltrated with molten metal. The molten metal is then solidified to form a shaped body. This shaped body is then subjected to sufficient strain to eliminate at least 50% and preferably 80% of the bonds in the network. The shaped body is then subjected to a metal forming step such as wrought or semisolid forming.

What is claimed is:  
     
         1 . A metal-matrix composite comprising a uniform distribution of calcined ceramic particles having an average particle size no greater than about one micron and a metal or alloy substantially uniformly distributed with said ceramic particles comprising at least 15 volume percent of the metal matrix and wherein at least 50 percent of said particles are free of bonds to another particle.  
     
     
         2 . A metal-matrix composite comprising a uniform distribution of calcined ceramic particles having an average particle size no greater than about one micron and a metal or alloy substantially uniformly distributed with said ceramic particles in which said ceramic particles comprise at least about 15 volume percent of the metal matrix, wherein at least 80 percent of said ceramic particles are uniformly distributed on a scale of three times the particle size and wherein at least 80 percent of said particles are free of bonds to another particle.  
     
     
         3 . The metal-matrix composite according to  claim 2  wherein at least 90 percent of said ceramic particles are uniformly distributed on a scale of twice the particle size.  
     
     
         4 . The metal-matrix composite according to  claim 3  wherein at least 50 percent of said particles are free of bonds to another particle.  
     
     
         5 . The metal-matrix composite according to  claim 4  in which said metal-matrix composite is machineable with a high-speed steel bit for greater than about one minute without excessive wear to said bit.  
     
     
         6 . The metal-matrix composite of  claim 5  wherein said ceramic particles have an aspect ratio of no greater than about 3:1.  
     
     
         7 . The metal matrix composite of  claim 6  wherein said ceramic particles have an aspect ratio of no greater than about 2:1.  
     
     
         8 . The metal-matrix composite according to  claim 7  in which said ceramic particles are of the material selected from the group consisting of oxides, borides, nitrides, carbides, carbon or a combination thereof; and in which said metal or alloy is selected from the group consisting of Al, Li, Be, Pb, Ag, Sn, Mg, Ti, Cu, Zn or mixtures thereof.  
     
     
         9 . The metal-matrix composite of  claim 7  wherein a three-inch diameter billet of said composite is capable of a 50 percent deformation along its longitudinal axis without cracking.  
     
     
         10 . The metal-matrix composite of  claim 9  wherein a three-inch diameter billet is capable of an 80 percent deformation along its longitudinal axis without cracking.  
     
     
         11 . The metal-matrix composite of  claim 7  in which the metal-matrix composite has been deformed by at least about 80 percent without cracking.  
     
     
         12 . A method for forming a metal-matrix composite comprising the steps of: 
 forming a sintered ceramic preform including a network of uniformly distributed ceramic particles having a particle size of one micron or less and being bonded together at their points of contact by sintering;    placing the ceramic preform in a mold;    infiltrating the preform with molten metal;    solidifying the molten metal to thereby form a shaped body;    subjecting the shaped body to sufficient strain to eliminate at least 50 percent of the sintered bonds in the network; and    subjecting the strained shaped body to a metal forming step.    
     
     
         13 . The method for forming a metal-matrix composite according to  claim 12  in which the strained shaped body is subjected to wrought forming.  
     
     
         14 . The method for forming a metal-matrix composite according to  claim 12  in which the metal forming step is semisolid forming.  
     
     
         15 . The method for forming a metal-matrix composite according to  claim 12  in which at least 80 percent of the bonds in the network are broken.  
     
     
         16 . A method for forming metal-matrix composites comprising the steps of: 
 providing a slurry of ceramic particles in a liquid wherein substantially all of the particles have a particle size of one micron or less;    separating the ceramic particles from the liquid to provide a ceramic preform having a substantially uniform distribution of ceramic particles and sintering the ceramic particles to form a network of particles bonded together at their points of contact;    placing the sintered ceramic preform in a mold;    contacting the ceramic preform with a molten metal;    causing the molten metal to penetrate the preform; and    solidifying the molten metal to thereby form a shaped body; and,    subjecting the shaped body to sufficient strain to break at least 50 percent of the bonds in the network to thereby form a metal-matrix composite.    
     
     
         17 . The method for forming metal-matrix composites according to  claim 16  in which the slurry is subjected to a milling step.  
     
     
         18 . The method for forming metal-matrix composites according to  claim 17  in which the step of causing the molten metal to penetrate into the preform is accomplished by pressure infiltration.  
     
     
         19 . The method for forming metal-matrix composites according to  claim 18  in which the steps of subjecting the shaped body to strain comprises compressing the shaped body from about 0.1 to about 10 percent along a first axis.  
     
     
         20 . The method for forming metal-matrix composites according to  claim 19  which includes a further step of wrought forming the metal-matrix composite into a different shape.  
     
     
         21 . The method for forming metal-matrix composites according to  claim 19  which includes a further step of semi-solid forming the metal-matrix composite into a different shape.  
     
     
         22 . The method for forming metal-matrix composites according to  claim 20  in which the step of subjecting the shaped body to strain is applied at a rate of between about 4.44×10 −3 /sec. and about 6.0×10 −2 /sec.  
     
     
         23 . A method for forming a metal-matrix composite comprising the steps of: 
 forming a sintered ceramic preform including a network of uniformly distributed particles having a particle size of between about 0.01 and 0.5μ and being bonded together at their points of contact by sintering;    placing the ceramic preforms in a mold;    infiltrating the preform with a molten metal;    solidifying the molten metal to thereby form a shaped body;    heating the shaped body to a temperature of less than its melting point at about 300° C. below its melting point; and    subjecting the heated shaped body to sufficient strain to eliminate at least 50% of the sintered bonds in a network.    
     
     
         24 . A method for forming a metal-matrix composite according to  claim 23 , in which the ceramic preform is infiltrated with molten aluminum and the shaped body is heated to a temperature of between about 450° C. to about 600° C.  
     
     
         25 . A method for forming a metal-matrix composite comprising the steps of: 
 a) forming a sintered ceramic preform including a network of uniformly distributed particles having a particle size of between about 0.01 and 0.5 μ and being bonded together at their points of contact by sintering;    b) placing the ceramic preform in a mold;    c) infiltrating the preform with a molten aluminum;    d) solidifying the molten aluminum to form a shaped body;    e) heating the shaped body to a temperature of between about 450° C. to about 600° C.; and    f) compressing the shaped body along a first axis by about two to about ten percent to form a first product.    
     
     
         26 . A method for forming a metal-matrix composite according to  claim 25 , which includes the added step of semisolid forming the preselected shape or first product from the compressed shaped body.  
     
     
         27 . A method for forming a metal-matrix composite according to  claim 25 , which includes the added step of wrought forming the preselected shape or first product from the compressed shaped body.  
     
     
         28 . A method for forming a metal-matrix composite according to  claim 26 , which includes the step of cooling the first product from step f) before semisolid forming a preselected shape.  
     
     
         29 . A metal-matrix composite comprising a uniform distribution of calcine ceramic particles having an average particle size of no greater than about 0.5 μ and an aluminum metal substantially uniformly distributed with said ceramic particles comprising at least 15 volume percent of the metal matrix and wherein at least 50% of said particles are free of bonds to another particle and wherein the net shape includes displacement of a portion thereof by at least 25% without cracking.  
     
     
         30 . A metal-matrix composite comprising a uniform distribution of calcine ceramic particles having an average particle size of no greater than about 0.5μ and an aluminum metal substantially uniformly distributed with said ceramic particles comprising at least 15 volume percent of the metal matrix and wherein at least 50% of said particles are free of bonds to another particle and wherein the net shape includes wherein portions have been displaced by at least 50%.  
     
     
         31 . A method for forming metal-matrix composites according to  claim 15  in which the bonds in the network are broken throughout the body before the metal forming step.