Methods for treating metal nanocrystals and for forming bulk nanostructured metal alloys
Methods of treating metal nanocrystals are provided. In embodiments, such a method comprises exposing metal nanocrystals comprising a metal and characterized by at least one twinning boundary therein, to a plating solution comprising a reducing agent and coating metal cations comprising a different metal, under conditions to form a coating of the different metal on surfaces of the metal nanocrystals via electroless deposition by chemical reduction of the coating metal cations, thereby providing coated metal nanocrystals. Methods of forming bulk nanostructured metal alloys from the coated metal nanocrystals are also provided.
1 . A method of forming a bulk nanostructured metal alloy, the method comprising applying pressure to a collection of coated metal nanocrystals while heating, wherein the coated metal nanocrystals comprise metal nanocrystals comprising a metal and characterized by at least one twinning boundary therein, and a coating of a different metal on surfaces of the metal nanocrystals, and wherein the bulk nanostructured metal alloy comprises the metal of the metal nanocrystals and the different metal of the coating, the bulk nanostructured metal alloy characterized by the at least one twinning boundary therein, wherein the metal of the metal nanocrystals is selected from silver, copper, iron, and combinations thereof; and the different metal of the coating is selected from copper, nickel, silver, cobalt, and combinations thereof.
2 . The method of claim 1 , wherein the bulk nanostructured metal alloy further comprises one or more metal nanocrystals embedded therein, the one or more metal nanocrystals derived from the coated metal nanocrystals.
3 . The method of claim 1 , wherein the metal of the metal nanocrystals is silver and the different metal of the coating is copper or the metal of the metal nanocrystals is copper and the different metal of the coating is silver.
4 . The method of claim 1 , wherein the metal nanocrystals consist of silver nanowires and the coating consists of copper.
5 . The method of claim 4 , wherein the copper is present at an amount in a range of from 0.2 weight % to 15 weight % as compared to a total weight of the copper and the silver nanowires.
6 . A method of forming a bulk nanostructured metal alloy, the method comprising applying pressure to a collection of coated metal nanocrystals while heating, wherein the coated metal nanocrystals comprise metal nanocrystals comprising a metal and characterized by at least one twinning boundary therein, and a coating of a different metal on surfaces of the metal nanocrystals, and wherein the bulk nanostructured metal alloy comprises the metal of the metal nanocrystals and the different metal of the coating, the bulk nanostructured metal alloy characterized by the at least one twinning boundary therein, wherein the pressure is from 40 MPa to 1000 MPa and the heating uses a temperature from greater than room temperature to no more than 50% of the different metal's melting temperature.
7 . The method of claim 3 , wherein the bulk nanostructured metal alloy has a microhardness of at least 1200 MPa.
8 . The method of claim 1 , wherein the nanocrystals of the metal nanocrystals are nanowires, nanoplatelets, or combinations thereof.
9 . The method of claim 1 , wherein the nanocrystals of the metal nanocrystals are nanowires.
10 . The method of claim 1 , wherein the metal of the metal nanocrystals is silver and the different metal of the coating is copper; the metal of the metal nanocrystals is silver and the different metal of the coating is nickel; the metal of the metal nanocrystals is copper and the different metal of the coating is silver; the metal of the metal nanocrystals is copper and the different metal of the coating is cobalt; or the metal of the metal nanocrystals is iron and the different metal of the coating is copper.