Melt overheating method for improved toughness and glass-forming ability of metallic glasses

Abstract

A method of forming a bulk metallic glass is provided. The method includes overheating the alloy melt to a temperature above a threshold temperature, T tough , associated with the metallic glass demonstrating substantial improvement in toughness compared to the toughness demonstrated in the absence of overheating the melt above T liquidus , and another threshold temperature, T GFA , associated with the metallic glass demonstrating substantial improvement in glass-forming ability compared to the glass-forming ability demonstrated in the absence of overheating the melt above T liquidus . After overheating the alloy melt to above T tough and T GFA , the melt may be cooled and equilibrated to an intermediate temperature below both T tough and T GFA but above T liquidus , and subsequently quenched at a high enough rate to form a bulk metallic glass.

1 . A method of forming a bulk metallic glass, comprising:
 melting an alloy by heating the alloy to a temperature above the liquidus temperature, T liquidus ;   overheating the alloy melt to an overheating temperature above a threshold temperature, T tough , associated with the metallic glass demonstrating increased toughness compared to the toughness demonstrated by heating the melt just above T liquidus  and quenching the melt to form a bulk metallic glass.   
     
     
         2 . The method of  claim 1 , wherein the temperature of the overheated alloy melt is also above a threshold temperature, T GFA , associated with the metallic glass demonstrating increased critical rod diameter compared to the critical rod diameter demonstrated by heating the melt just above T liquidus . 
     
     
         3 . The method of  claim 2 , wherein T tough  is greater than T GFA . 
     
     
         4 . The method of  claim 1 , wherein the toughness of the metallic glass is at least 25% greater than the toughness of the metallic glass formed in the absence of overheating above T liquidus . 
     
     
         5 . The method of  claim 1 , wherein the toughness of the metallic glass is at least 50% greater than the toughness of the metallic glass formed in the absence of overheating above T liquidus . 
     
     
         6 . The method of  claim 2 , wherein the critical rod diameter is at least 25% greater than the critical rod diameter attained in the absence of overheating above T liquidus . 
     
     
         7 . The method of  claim 2 , wherein the critical rod diameter is at least 50% greater than the critical rod diameter attained in the absence of overheating above T liquidus . 
     
     
         8 . The method of  claim 1 , further comprising
 cooling the alloy melt to an intermediate temperature below T tough  and T GFA  but above T liquidus ,   equilibrating the alloy melt at the intermediate temperature, and   quenching the alloy melt to form the metallic glass.   
     
     
         9 . The method of  claim 1 , wherein the alloy is selected from a Zr-based alloy, Ti-based alloy, Al-based alloy, Mg-based alloy, Ce-based alloy, La-based alloy, Y-based alloy, Fe-based alloy, Ni-based alloy, Co-based alloy, Cu-based alloy, Au-based alloy, Pd-based alloy, and Pt-based alloy. 
     
     
         10 . The method of  claim 1 , wherein the alloy is represented by the formula X 100-a-b Y a Z b    where:   X is Ni, Fe, Co, Pd, Pt, Au, Cu or combinations thereof;   Y is Cr, Mo, Mn, Nb, Ta, Ni, Cu, Co, Fe, Pd, Pt, Ag or combinations thereof;   Z is P, B, Si, Ge, C or combinations thereof;   a is between 2 and 45 at %; and   b is between 15 and 25 at %.   
     
     
         11 . The method of  claim 1 , wherein the alloy is represented by the formula X 100-a-b Y a Z b , wherein:
 X is Ni, Fe, Co or combinations thereof,   Y is Cr, Mo, Mn, Nb, Ta or combinations thereof,   Z is P, B, Si, Ge or combinations thereof,   a is between 5 and 15 at %, and   b is between 15 and 25 at %.   
     
     
         12 . The method of  claim 1 , wherein the alloy melt is heated by a process selected from inductive heating, resistively heating (in a furnace), a plasma arc heating, and joule heating. 
     
     
         13 . The method of  claim 1 , wherein the melt is held in a crucible comprising a material selected from fused or crystalline silica, a ceramic, alumina, zirconia, graphite, and a water-cooled hearth made of copper or silver. 
     
     
         14 . A method of forming a shaped metallic glass article, comprising:
 melting a metallic glass forming alloy by heating the alloy to a temperature above the liquidus temperature of the alloy, T liquidus .   overheating the alloy melt to an overheating temperature above both a threshold temperature, T tough , associated with the metallic glass demonstrating increased toughness compared to the toughness demonstrated by heating the melt just above T liquidus , and a threshold temperature, T GFA , associated with the alloy demonstrating an increase in critical rod diameter compared to the critical rod diameter demonstrated by heating the melt just above T liquidus ; and   quenching the alloy melt to form the alloy melt into a shaped metallic glass article.   
     
     
         15 . The method of  claim 14 , further comprising cooling and equilibrating the alloy melt to an intermediate temperature below T tough  and T GFA  but above T liquidus ; and quenching the alloy melt to form a shaped metallic glass article. 
     
     
         16 . The method of  claim 14 , wherein the toughness of the metallic glass is at least 25% greater than the toughness of the metallic glass formed in the absence of overheating above T liquidus . 
     
     
         17 . The method of  claim 14 , wherein the toughness of the metallic glass is at least 50% greater than the toughness of the metallic glass formed in the absence of overheating above T liquidus . 
     
     
         18 . The method of  claim 14 , wherein the critical rod diameter is at least 25% greater than the critical rod diameter attained in the absence of overheating above T liquidus . 
     
     
         19 . The method of  claim 14 , wherein the critical rod diameter is at least 50% greater than the critical rod diameter attained in the absence of overheating above T liquidus . 
     
     
         20 . The method of  claim 14 , wherein the alloy comprises a material selected from a group consisting of a Zr-based alloy, Ti-based alloy, Al-based alloy, Mg-based alloy, Ce-based alloy, La-based alloy, Y-based alloy, Fe-based alloy, Ni-based alloy, Co-based alloy, Cu-based alloy, Au-based alloy, Pd-based alloy, and Pt-based alloy.