Production of amorphous metallic foam by powder consolidation

Abstract

The formation of amorphous porous bodies and in particular to a method of manufacturing such bodies from amorphous particulate materials. The method allows for the control of the volume fraction as well as the spatial and size distribution of gas-formed pores by control of the size distribution of the powder particulates. The method allows for the production of precursors of unlimited size, and because the softened state of the amorphous metals used in the method possesses visco-plastic properties, higher plastic deformations can be attained during consolidation as well as during expansion.

What is claimed is: 
     
       1. A method of forming an amorphous metal foam formed of an amorphous metal powder comprising:
 mixing at least one amorphous metal powder and at least one gas-splitting propellant powder into a propellant filled amorphous metal powder mixture, such that upon decomposition of the gas-splitting propellant powder, gas-containing pores are created within the amorphous metal powder mixture; 
 compacting the mixture such that the amorphous metal powder particles are bonded to one another to form a gas-tight seal around the gas-splitting propellant powder particles, the mixture being compacted at a compacting temperature and pressure sufficient to allow for bonding of the mixture, wherein the temperature is below any crystalline transition temperature of the amorphous metal powder, and for a duration not exceeding a time for any crystalline transformation of said amorphous metal powder at the compacting temperature and pressure; 
 cooling the compacted mixture at a cooling rate sufficient that the amorphous metal powder mixture remains amorphous; 
 expanding the compacted amorphous metal powder mixture to form a foam material, said expansion being conducted at an expansion temperature below any crystalline transition temperature of the amorphous metal powder, but sufficiently high to allow bubble expansion, at a surrounding pressure sufficient to promote expansion arising from a difference between a pressure in the gas-containing pores and the surrounding pressure, and for a duration not exceeding the time for any crystalline transformation to take place; and 
 cooling the expanded foam material in order to allow the foam material to remain amorphous. 
 
     
     
       2. The method according to  claim 1  wherein the gas-splitting propellant powder decomposes during expansion. 
     
     
       3. The method according to  claim 1  wherein the gas-splitting propellant powder decomposes during compaction. 
     
     
       4. The method according to  claim 1  wherein heat and pressure are simultaneously suspended after the compacting and cooling of the compacted mixture takes place without the influence of pressure. 
     
     
       5. The method according to  claim 1  wherein the powder mixture further comprises strength reinforcing components. 
     
     
       6. The method according to  claim 5  wherein the compacting is followed by aligning the strength reinforcing components. 
     
     
       7. The method according to  claim 1  wherein the compacting is performed by a method selected from the group consisting of: hot pressing, hot extrusion, hot forging, hot rolling and dyna-packing. 
     
     
       8. The method according to  claim 1  wherein the amorphous metal powder is selected from the group consisting of Zr based alloys, Ti based alloys, Al based alloys, Fe based alloys, La based alloys, Cu based alloys, Mg based alloys, Pt based alloys and Pd based alloys. 
     
     
       9. The method according to  claim 1  wherein at least two different gas-splitting propellant powders with different decomposition temperatures are used. 
     
     
       10. The method according to  claim 1  wherein the compacting takes place in a mold such that the powder mixture is completely or partially surrounded by a propellant-free metal or amorphous metal powder. 
     
     
       11. The method according to  claim 1  wherein the compacting is accomplished by extrusion molding, with the powder mixture being piled against a propellant-free metal piece. 
     
     
       12. The method according to  claim 1  wherein a porous metal body is made by expanding the compacted mixture, said expansion being conducted at an expansion temperature below any crystalline transition temperature of the amorphous metal but above a glass transition temperature of the amorphous metal powder, followed by cooling of the porous metal body to thereby form a foam. 
     
     
       13. The method according to  claim 1  wherein a porous metal body is made by expanding the compacted mixture, said expansion being conducted at an expansion temperature below any crystalline transition temperature of the amorphous metal powder, whereby during expansion of the compacted mixture, different temperature and time values are used as a function of a density of the porous metal body to be produced, followed by cooling of the porous metal body to thereby form a foam. 
     
     
       14. The method according to  claim 1  wherein a porous metal body is made by expanding the compacted mixture, said expansion being conducted at an expansion temperature below any crystalline transition temperature of the amorphous metal powder, with a heating rate being between 1° and 5° C./sec, followed by cooling of the porous metal body at a rate sufficient to interrupt further foaming of the porous metal body. 
     
     
       15. The method according to  claim 1  wherein the gas-splitting propellant powder is selected from the group consisting of: water vapor-releasing agents, hydrogen-releasing agents, carbon monoxide-releasing agents, carbon dioxide-releasing agents, and nitrogen-releasing agents. 
     
     
       16. The method of  claim 1 , further comprising forming the amorphous metal particles prior to the mixing step, wherein the forming the amorphous metal particles comprises heating a crystalline metal or alloy above a melting temperature of the crystalline metal or alloy such that the crystalline metal or alloy melts, and then rapidly cooling the melted crystalline metal or alloy to prevent recrystallization. 
     
     
       17. A method of forming an amorphous metal foam formed of an amorphous metal powder comprising:
 placing an amorphous metal powder in a gas-tight chamber, and pressurizing the chamber with a pressurizing gas at a pressure sufficient to compact and bond the powder around gas-containing pores; 
 heat treating the compacted powder to increase a pressure of the gas within the gas-containing pores at a temperature and pressure sufficient to allow for a visco-plastic deformation of the powder, wherein the temperature is below any crystalline transition temperature of the amorphous metal, and for a duration not exceeding a time for any crystalline transformation of said amorphous metal powder; 
 cooling the compacted powder at a cooling rate sufficient to retain the amorphous state of the powder; 
 expanding the compacted powder to form a foam material, said expansion being conducted at an expansion temperature below any crystalline transition temperature of the metal powder, but sufficiently high to allow visco-plastic deformation during bubble expansion, at a surrounding pressure sufficient to promote expansion arising from a difference between a pressure in the gas-containing pores and the surrounding pressure, and for a duration not exceeding the time for any crystalline transformation to take place; and 
 cooling the expanded foam material such that the material remains amorphous. 
 
     
     
       18. The method of  claim 17  wherein the pressure of the chamber is from vacuum to over 100 atm. 
     
     
       19. The method of  claim 17  wherein the pressure within the gas-containing pores is from about vacuum to over 2000 atm. 
     
     
       20. The method of  claim 17  wherein the gas is selected from the group consisting of: helium, argon, air, nitrogen, and hydrogen. 
     
     
       21. The method according to  claim 17  wherein compacting is performed by a method selected from the group consisting of: hot pressing, hot extrusion, hot forging, hot rolling and dyna-packing. 
     
     
       22. The method according to  claim 17  wherein the amorphous metal powder is selected from the group consisting of Zr based alloys, Ti based alloys, Al based alloys, Fe based alloys, La based alloys, Cu based alloys, Mg based alloys, Pt based alloys and Pd based alloys. 
     
     
       23. A method comprising:
 heating a mixture comprising a propellant and an amorphous-metal powder to a compacting temperature that is below a crystalline transition temperature of the amorphous metal, thereby forming a heated mixture;   applying a pressure to the heated mixture for a duration not exceeding a time for crystalline transformation of the amorphous-metal powder, thereby compacting and bonding the amorphous metal into a structure enclosing at least some of the propellant in gas-tight pores;   forming, within the gas-tight pores, a gas from the propellant; and   expanding the structure at an expansion temperature that is below the crystalline transition temperature of the amorphous metal and at a surrounding pressure sufficient to permit expansion of the structure due to a pressure difference between the gas-tight pores and the surrounding pressure, the expanding occurring for a duration not exceeding the time for crystalline transformation of the amorphous metal.   
     
     
       24. The method according to claim 23 wherein the operation of forming the gas from the propellant comprises decomposing the propellant at least partly during expansion of the structure. 
     
     
       25. The method according to claim 23 wherein the operation of forming the gas from the propellant comprises decomposing the propellant at least partly during compaction of the heated mixture. 
     
     
       26. The method according to claim 23 wherein the mixture further comprises strength reinforcing components. 
     
     
       27. The method according to claim 23 wherein the amorphous metal is selected from the group consisting of Zr based alloys, Ti based alloys, Al based alloys, Fe based alloys, La based alloys, Cu based alloys, Mg based alloys, Pt based alloys, and Pd based alloys. 
     
     
       28. A method comprising:
 applying, to a powder comprising an amorphous metal, a pressure sufficient to compact and bond the powder around gas-containing pores, thereby forming a body;   heat treating the body to increase a pressure of the gas within the gas-containing pores, the heat treating occurring:
 at a temperature below a crystalline transition temperature of the amorphous metal; 
 at a surrounding pressure sufficient to allow for a visco-plastic deformation of the body; and 
 for a duration not exceeding a time for crystalline transformation of the amorphous metal; and 
   expanding the gas-containing pores of the body to form an expanded body, comprising:
 heating the body to an expansion temperature that is below a crystalline transition temperature of the amorphous metal but sufficiently high to cause visco-plastic deformation of the amorphous metal during expansion; and 
 for a duration not exceeding the time for crystalline transformation of the amorphous metal, inducing a pressure difference between the gas-containing pores and a surrounding environment sufficient to cause expansion of the gas-containing pores, thereby creating an expanded body; and 
   forming an article from the expanded body.   
     
     
       29. The method according to claim 28, wherein the body is a unitary structure. 
     
     
       30. The method according to claim 28, wherein the powder comprises a bulk-solidifying amorphous metal alloy. 
     
     
       31. The method according to claim 28, wherein the operation of expanding the gas-containing pores comprises decomposing a propellant to fill the gas-containing pores with a decomposition product of the propellant. 
     
     
       32. The method according to claim 28, further comprising decomposing a propellant during the operation of heat treating the body. 
     
     
       33. The method according to claim 28, wherein the article further comprises strength reinforcing components. 
     
     
       34. The method according to claim 28, wherein the amorphous metal is selected from the group consisting of Zr based alloys, Ti based alloys, Al based alloys, Fe based alloys, La based alloys, Cu based alloys, Mg based alloys, Pt based alloys, and Pd based alloys. 
     
     
       35. The method according to claim 28, wherein the gas containing-pores are elongate. 
     
     
       36. The method according to claim 28, wherein the article has a higher density toward an edge of the article than an interior of the article. 
     
     
       37. The method according to claim 28, wherein the article has a solid cover layer of a higher density than an interior of the article. 
     
     
       38. The method according to claim 28, wherein forming the article comprises forming a foamed sheet from the expanded body. 
     
     
       39. A method comprising:
 compacting a powder comprising an amorphous metal to form a bonded structure defining a plurality of gas-tight pores, the compacting performed:
 at a compacting temperature below a crystalline transition temperature of the amorphous metal; 
 at a compacting pressure sufficient to allow for bonding of the powder; and 
 for a duration not exceeding a time for crystalline transformation of the amorphous metal at the compacting temperature and pressure; 
   inducing a pressure difference between the gas-tight pores and an environment surrounding the structure; and   expanding the structure to produce a foam at an expansion temperature allowing visco-plastic deformation of the amorphous metal during expansion and for a duration not exceeding the time for crystalline transformation of the amorphous metal.   
     
     
       40. The method of claim 39, wherein inducing the pressure difference comprises decomposing a propellant captive within the gas-tight pores. 
     
     
       41. The method of claim 39, wherein inducing the pressure difference comprises reducing a pressure of the environment surrounding the structure. 
     
     
       42. The method of claim 41, wherein inducing the pressure difference further comprises decomposing a propellant captive within the gas-tight pores. 
     
     
       43. The method of claim 41, wherein inducing the pressure difference further comprises drawing a vacuum around the structure. 
     
     
       44. The method of claim 39, wherein the operation of compacting comprises visco-plastically deforming the amorphous metal.