Nanostructured metal powder and method of fabricating the same

Abstract

The present invention relates to a nanostructured metal powder and a method of fabricating the same. A twin-wire electric arc process is performed to melt the wire tips, and metal melt is formed. Simultaneously, the metal melt is broken up into melt droplets by an atomizing device. The operating temperature of the electric arc process is controlled between melting point and boiling point of the wire, to avoid vaporization of the melt droplets. Then, a fast cooling is performed to quench the melt droplets. Thus, melt droplets are solidified to μm-scaled, spherical and dense powders comprising nano-grains (d<100 nm).

What is claimed is:  
     
         1 . A nanostructured metal powder, comprising: 
 a plurality of nano-grains; and    grain boundaries formed among the nano-grains;    wherein the nanostructured metal powder is spherical, and an average diameter of the nanostructured metal powder is μm-scaled.    
     
     
         2 . The nanostructured metal powder according to  claim 1 , wherein the nanostructured metal powder is a dense powder.  
     
     
         3 . The nanostructured metal powder according to  claim 1 , wherein the nanostructured metal powder is polycrystalline structure.  
     
     
         4 . The nanostructured metal powder according to  claim 1 , wherein the average diameter of the nanostructured metal powder is 1˜500 μm.  
     
     
         5 . The nanostructured metal powder according to  claim 1 , wherein a method of fabricating the nanostructured metal powder comprises: 
 using metal wires as feedstock;    using two wires as electrodes;    performing a twin-wire electric arc process to melt the wire tips to form a metal melt, and simultaneously, breaking the metal melt into melt droplets by an atomizing device, wherein an operating temperature of the electric arc process is controlled between melting point and boiling point of the wire, to avoid vaporization of the melt droplets; and    performing a quenching process to cool the melt droplets by means of a cooling medium.    
     
     
         6 . The nanostructured metal powder according to  claim 5 , wherein the atomizing device atomizes the metal melt through a pressurized inert gas.  
     
     
         7 . The nanostructured metal powder according to  claim 6 , wherein the inert gas is He (helium) or Ar (argon).  
     
     
         8 . The nanostructured metal powder according to  claim 6 , wherein the pressure of the inert gas is 15˜75 psi.  
     
     
         9 . The nanostructured metal powder according to  claim 5 , wherein the cooling medium is a cool inert gas.  
     
     
         10 . The nanostructured metal powder according to  claim 5 , wherein the cooling medium is liquid nitrogen.  
     
     
         11 . The nanostructured metal powder according to  claim 5 , wherein the cooling medium is cool water.  
     
     
         12 . A method of fabricating the nanostructured metal powder, comprising the steps of: 
 using metal wire as feedstock;    using two wires as electrodes;    performing a twin-wire electric arc process to melt the wire tips to form a metal melt, and simultaneously, breaking the metal melt into melt droplets by an atomizing device, wherein an operating temperature of the electric arc process is controlled between melting point and boiling point of the wire, to avoid vaporization of the melt droplets; and    performing a quenching process to cool the melt droplets by means of a cooling medium.    
     
     
         13 . The method according to  claim 12 , wherein the atomizing device atomizes the metal melt through a pressurized inert gas.  
     
     
         14 . The method according to  claim 13 , wherein the inert gas is He (helium) or Ar (argon).  
     
     
         15 . The method according to  claim 13 , wherein the pressure of the inert gas is 15˜75 psi.  
     
     
         16 . The method according to  claim 12 , wherein the cooling medium is a cool inert gas.  
     
     
         17 . The method according to  claim 12 , wherein the cooling medium is liquid nitrogen.  
     
     
         18 . The method according to  claim 12 , wherein the cooling medium is cool water.  
     
     
         19 . The method according to  claim 12 , wherein each melt droplet is solidified to form a spherical powder comprising a plurality of nano-grains.  
     
     
         20 . A method of fabricating the nanostructured metal powder, suitable for fabricating Pd (palladium) powders, comprising the steps of: 
 using two Pd wires as feedstock and electrodes;    performing a twin-Pd wire electric arc process to melt the Pd wire tips to form a Pd metal melt, and simultaneously, breaking the Pd metal melt into Pd melt droplets by an atomizing device; and    performing a quenching process to cool the melt droplets by means of a cooling medium;    wherein a diameter of each Pd wire is about 1.5 mm;    wherein operating conditions of the electric arc process are 30 DC Voltage and 120 Ampere;    wherein the atomizing device atomizes the metal melt through an inert gas under pressure of about 20 psi.