Synthesis of bulk, fully dense nanostructured metals and metal matrix composites

Abstract

Bulk nanostructured alloys, such as aluminum 5083 alloys reinforced with 10 wt. % particulate B 4 C, was synthesized by cryomilling and spark plasma sintering. Material for the alloy are selected and the selected raw materials are cryomilled, mechanical milling at cryogenic temperatures, to fabricate nanostructured alloys at low temperatures. The cryomilled powders are then degassed, and consolidated using spark plasma sintering into dense bulk materials. The material thus obtained achieved near full density bulk materials, while retaining the nanocrystalline nature. The densities of the compacts were measured using Archimedes method. XRD, SEM, TEM, and hardness testing were used to characterize the cryomilled powders and consolidated compacts.

1 . A method for producing nanostructured materials, the method comprising: 
 (a) providing a metal powder and optionally a reinforcement;    (b) mechanically milling (a) at a cryogenic temperature (cryomilling) to provide a nanostructured powder;    (c) removing gaseous components from the cryomilled powder; and    (d) consolidating the cryomilled powder by spark plasma sintering, wherein the nanostructured material thus produced has a relative density of about 99.0% or higher and an average grain size of less than 100 nm.    
     
     
         2 . The method of  claim 1 , wherein the reinforcement is selected from the group consisting of oxides, carbides, nitrides, borides, metals, intermetallics, and alloys.  
     
     
         3 . The method of  claim 1 , wherein the metal powder is selected from the group consisting of Al, Be, Ca, Sr, Ba, Ra, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, and W, and combinations thereof.  
     
     
         4 . The method of  claim 1 , wherein the metal powder is an aluminum alloy.  
     
     
         5 . The method of  claim 1 , wherein the reinforcement is boron carbide.  
     
     
         6 . The method of  claim 1 , wherein the reinforcement is silicon carbide.  
     
     
         7 . The method of  claim 1 , wherein the reinforcement is aluminum nitride.  
     
     
         8 . The method of  claim 1 , wherein the reinforcement is aluminum oxide.  
     
     
         9 . The method of  claim 1 , wherein the reinforcement is in the form of a particulate.  
     
     
         10 . The method of  claim 1 , wherein the reinforcement is in the form of a platelet.  
     
     
         11 . The method of  claim 1 , wherein the reinforcement is in the form of a whisker.  
     
     
         12 . The method of  claim 1 , wherein cryomilling is continued until an equilibrium grain size of the metal is reached.  
     
     
         13 . The method of  claim 12 , wherein cryomilling is continued between 6 and 10 hours.  
     
     
         14 . The method of  claim 1 , wherein the removal of gaseous component occurs at a temperature between about 200° C. and 600° C.  
     
     
         15 . The method of  claim 14 , wherein the removal of gaseous components occurs at a temperature between about 300° C. and 500° C.  
     
     
         16 . The method of  claim 1 , wherein the spark plasma sintering is carried out at a temperature between 40% and 100% of the absolute melting temperature of the metal phase.  
     
     
         17 . The method of  claim 1 , wherein spark plasma sintering is carried out with different ramping rates and various holding time.  
     
     
         18 . The method of  claim 1 , wherein removal of gaseous components and consolidation of the cryomilled-powder occur simultaneously, to form a fully dense material without a separate degassing step.  
     
     
         19 . The method of  claim 1 , wherein the cryogenic temperature is provided by liquid nitrogen or liquid argon.  
     
     
         20 . The method of  claim 1 , wherein the mechanical milling is conducted in a shaker type mill, an attritor mill, a planetary mill, a ball mill, or a rotary mill.  
     
     
         21 . A method for producing nanostructured aluminum alloy, the method comprising: 
 (a) providing aluminum alloy and a reinforcement    (b) mechanically milling (a) at a temperature of about −150° C. to about −300° C.;    (c) removing gaseous components from (b); and    (d) consolidating (c) by spark plasma sintering, wherein the nanostructured aluminum alloy thus produced has a density of 2.63 g/cm 3  or higher and an average grain size of less than 100 nm.    
     
     
         22 . The method of  claim 21 , wherein the reinforcement is selected from the group consisting of oxides, carbides, nitrides, borides, metals, intermetallics, and alloys.  
     
     
         23 . The method of  claim 21 , wherein the aluminum alloy is aluminum and another metal powder selected from the group consisting of Be, Ca, Sr, Ba, Ra, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Y, Nb, Mo, Tc, Ru, Rh, Pd, Ag, Cd, and W, and combinations thereof.  
     
     
         24 . The method of  claim 21 , wherein the reinforcement is boron carbide.  
     
     
         25 . The method of  claim 21 , wherein the reinforcement is silicon carbide.  
     
     
         26 . The method of  claim 21 , wherein the reinforcement is aluminum nitride.  
     
     
         27 . The method of  claim 21 , wherein the reinforcement is aluminum oxide.  
     
     
         28 . The method of  claim 21 , wherein cryomilling is continued until equilibrium grain size of the metal is reached.  
     
     
         29 . The method of  claim 28 , wherein cryomilling is continued between 6 and 10 hours.  
     
     
         30 . The method of  claim 21 , wherein the removal of gaseous component occurs at a temperature between about 200° C. and 600° C.  
     
     
         31 . The method of  claim 30 , wherein the removal of gaseous components occurs at a temperature between about 300° C. and 500° C.  
     
     
         32 . The method of  claim 21 , wherein removal of gaseous components and consolidation of the cryomilled powder occur simultaneously, to form a fully dense material without a separate degassing step.  
     
     
         33 . The method of  claim 21 , wherein the temperature is provided by liquid nitrogen or liquid argon.  
     
     
         34 . The method of  claim 21 , wherein the spark plasma consolidation is carried out at about 350° C.