Method of making in-situ composites comprising amorphous alloys
View Patent ↗A method of forming in-situ composites of metallic alloys comprising an amorphous phase are provided. The method generally comprising the steps of transforming a molten liquid metal at least partially into a crystalline solid solution by cooling the molten liquid metal down to temperatures below a “remelting” temperature, then allowing the solid crystalline metal to remain at temperatures above the glass transition temperature and below the remelting temperature such that at least a portion of the metal remelts to form a partially amorphous phase in an undercooled liquid, and finally subsequently cooling the composite alloy to temperatures below the glass transition temperature.
1. A method for forming an in-situ composite of a metallic alloy comprising the steps of:
providing an initial alloy composition that forms a crystalline solid solution phase at temperatures below the alloy's liquidus temperature, wherein the initial alloy has a composition represented by the generic formula AxZy, wherein A is the primary element, Z is the solute element, and x and y are percent quantities, and wherein size of the atomic radii of the primary element and the solute element are different by more than about 10%;
heating a quantity of the initial alloy composition to a temperature above the alloy's liquidus temperature to form a molten alloy;
cooling the molten alloy from above the liquidus temperature, down to a temperature range below the liquidus temperature such that at least a portion of the molten alloy transforms to the crystalline solid solution phase to form an at least partially crystallized alloy;
further cooling the at least partially crystallized alloy down to a remelting temperature range below a metastable remelting temperature and above the glass transition temperature of the alloy;
holding the alloy within the remelting temperature range sufficiently long to form a significant volume fraction of an undercooled liquid alloy from the at least partially crystallized alloy; and
quenching the undercooled liquid alloy down to temperatures below the glass transition temperature of the alloy such that the material is frozen as a composite metallic glass alloy having at least a partial crystalline amorphous phase therein.
2. The method of claim 1 , wherein the composite metallic glass alloy comprises a continuous amorphous matrix phase having the crystalline phase embedded therein.
3. The method of claim 2 wherein the individual crystals of the crystalline phase are embedded in the amorphous matrix phase.
4. The method of claim 2 , wherein the volume fraction of the amorphous phase is between 5 vol. % an 95 vol. %.
5. The method of claim 1 , wherein the crystalline solid solution at least partially nucleates and grows to form solid dendrites.
6. The method of claim 5 , wherein the remelting step produces a liquid phase enveloping the dendrites to form a continuous liquid matrix.
7. The method of claim 1 , wherein the molten alloy is transformed fully into the crystalline solid solution and cooled down to ambient temperatures to form a solid alloy, further comprising the steps of: heating the solid alloy to a temperature above the glass transition temperature and below the metastable remelting temperature to form an at least partially undercooled liquid amorphous phase by remelting the crystalline solid solution to form the undercooled liquid alloy; and quenching the undercooled liquid alloy to temperatures below the glass transition to form the composite metallic glass alloy having at least a partial amorphous phase therein.
8. The method of claim 1 , wherein the composition of the crystalline solid solution phase is within 10 atomic % of the molten alloy.
9. The method of claim 1 , wherein the composition of the crystalline solid solution phase is within 20 atomic % of the molten alloy.
10. The method of claim 1 , wherein the size of the atomic radii of the primary element and the solute element are different by more than about 20%.
11. The method of claim 1 , wherein the A represents a moiety for solvent elements, and the Z represents a moiety for solute elements.
12. The method of claim 1 , wherein the temperature at which the free energies of the liquid and crystalline phase of the initial alloy are equal lies between the solidus and liquidus temperatures of the alloy.
13. The method of claim 1 , wherein during the remelting, the alloy is cooled at a rate of between 0.1 and 100 K/s.
14. The method of claim 1 , wherein during the remelting, the alloy is cooled at a rate of between 0.1 and 10 K/s.
15. An in-situ composite of a metallic alloy formed in accordance with the method described in claim 1 .
16. An article formed from an in-situ composite of a metallic alloy formed in accordance with the method described in claim 1 .