Bulk Metallic Glass/Graphite Composites

Abstract

A composite material based on a bulk metallic glass is disclosed. In an amorphous alloy phase forming a substantially continuous matrix, a second phase comprising graphite particles is embedded. The alloy is preferably zirconium based. The particles may have a carbide surface layer, which may be formed phase comprising carbide particles may also be present. The composite material has high plasticity, high yield strength, good elasticity and low coefficient of friction, which renders it a good candidate for applications like joints, frictional bearings or Springs.

1 . A composite material comprising:
 a substantially amorphous first phase forming a substantially continuous matrix, said first phase consisting essentially of an alloy; and   a second phase embedded in said matrix, said second phase comprising graphite particles.   
   
   
       2 . The composite material according to  claim 1 , wherein said graphite particles have a size in the range between 1 and 100 micrometers. 
   
   
       3 . The composite material according to  claim 1 , wherein said graphite particles have a size in the range between 25 and 75 micrometers. 
   
   
       4 . The composite material according to  claim 1 , wherein said second phase occupies between 3 volume percent and 20 volume percent of said composite material. 
   
   
       5 . The composite material according to  claim 1 , wherein said second phase is selected such that, under compressive deformation of said composite material up to yield, it induces a distribution of shear bands spaced apart by less than about 5 micrometers around said graphite particles. 
   
   
       6 . The composite material according to  claim 1 , wherein said alloy of the first phase, in the liquid state, is capable of wetting said second phase. 
   
   
       7 . The composite material according to  claim 1 , wherein said alloy comprises at least about 40 atomic percent of a metal having a negative enthalpy of formation for the reaction with graphite to form a metal carbide. 
   
   
       8 . The composite material according to  claim 1 , wherein said alloy comprises at least about 40 atomic percent of zirconium. 
   
   
       9 . The composite material according to  claim 1 , wherein said alloy consists essentially of Zr 52.5 Cu 17.9 Ni 14.6 Al 10 Ti 5 . 
   
   
       10 . The composite material according to  claim 1 , wherein at least a fraction of said graphite particles in said second phase have a core consisting essentially of graphite and a surface layer comprising at least one metal carbide. 
   
   
       11 . The composite material according to  claim 10 , wherein said surface layer has a thickness of at least 100 nanometers. 
   
   
       12 . The composite material according to  claim 10 , wherein said graphite particles have a size of at least about 25 micrometers. 
   
   
       13 . The composite material according to  claim 10 , wherein said surface layer comprises at least one metal carbide formed in situ by a reaction of graphite with said alloy. 
   
   
       14 . The composite material according to  claim 10 , wherein said surface layer consists essentially of zirconium carbide. 
   
   
       15 . The composite material according to  claim 1 , further comprising a third phase embedded in said matrix, wherein said third phase comprises crystalline particles. 
   
   
       16 . The composite material of  claim 15 , wherein said third phase comprises crystalline particles composed of the same elements as said alloy of the first phase. 
   
   
       17 . The composite material of  claim 15 , wherein said third phase comprises carbide particles. 
   
   
       18 . The composite material according to claim  17 , wherein said carbide particles comprise at least one metal carbide formed in situ by a reaction of graphite with said alloy. 
   
   
       19 . The composite material according to  claim 17 , wherein said carbide particles consist essentially of zirconium carbide. 
   
   
       20 . The composite material according to  claim 17 , wherein said carbide particles have a size of less than or equal to about 10 micrometers. 
   
   
       21 . Use of a composite material according to  claim 1  for manufacturing an object for use in a device selected from: a frictional bearing, a joint, and a spring. 
   
   
       22 . A method for manufacturing a composite material, said method comprising:
 heating an alloy above its liquidus temperature to form a liquid alloy;   dispersing graphite powder in the liquid alloy to form a finely dispersed mixture;   cooling the mixture below its glass transition temperature sufficiently rapidly for forming a composite material comprising a substantially amorphous first phase forming a substantially continuous alloy matrix and a second phase embedded in said matrix, said second phase comprising graphite particles.   
   
   
       23 . The method of  claim 22 , wherein said alloy is heated above its liquidus temperature by induction melting on top of said graphite powder. 
   
   
       24 . The method of  claim 22 , wherein said mixture is remelted at least once for a time sufficiently long for a distinct carbide layer to form on the surface of said graphite particles. 
   
   
       25 . The method of  claim 22 , wherein said mixture is remelted at least once for a time sufficiently long for a fraction of said graphite particles reacting with at least one metal component of said alloy to form metal carbide particles.