Enhancing mechanical properties of nanostructured materials with interfacial films
View Patent ↗Nanostructured materials that contain amorphous intergranular films (AIFs) are described herein. Amorphous intergranular films are structurally disordered (lacking the ordered pattern of a crystal) films that are up to a few nanometers thick. Nanostructured materials containing these films exhibit increased ductility, strength, and thermal stability simultaneously. A nanocrystalline material system that has two or more elements can be designed to contain AIFs at the grain boundaries, provided that the dopants segregate to the interface and certain materials science design rules are followed. An example of AIFs in a nanostructured Cu—Zr alloy is provided to illustrate the benefits of integrating AIFs into nanostructured materials.
1. A method for increasing thermal stability and ductility of a nanostructured material ( 214 ), said nanostructured material comprising a base material ( 206 ) in a form of a plurality of crystallites each having a boundary (“crystallite boundary”) ( 204 ) defining a crystalline interior ( 202 ), wherein the method comprises:
(a) selecting a dopant element ( 208 ) compatible with the base material ( 206 ) such that:
i. the dopant element ( 208 ) and the base material ( 206 ) are immiscible;
ii. the dopant element ( 208 ) has a negative heat of mixing;
iii. an atomic size difference between the dopant element ( 208 ) and the base material ( 206 ) is sufficiently large to cause disorder at the crystallite boundaries of the nanostructured material ( 214 ); and
iv. metallic bonding is retained at the crystallite boundary;
(b) mixing ( 102 ) the dopant element ( 208 ) and the base material ( 206 ) to produce a supersaturated solid material alloy ( 216 ), wherein the dopant element ( 208 ) is dispersed throughout the crystallite boundaries ( 204 ) and crystalline interiors ( 202 );
(c) applying a first heat treatment ( 106 ) to the supersaturated solid material alloy ( 216 ) to provide thermal energy sufficient to induce diffusion of the dopant element ( 208 ) to the crystallite boundaries ( 204 ), wherein the crystalline interiors ( 202 ) are substantially depleted of the dopant element ( 208 ) after application of the first heat treatment ( 106 );
(d) applying a second heat treatment ( 108 ) to create an amorphous structure at the crystallite boundaries ( 204 ), wherein the amorphous structure comprises the dopant element ( 208 ) and the base material ( 206 ), wherein the crystalline interiors ( 202 ) remains solid during the second heat treatment ( 108 ); and
(e) quenching ( 110 ) the supersaturated solid material alloy ( 216 ) to freeze the amorphous structure, thus forming amorphous intergranular films (AIFs) ( 210 ) at the crystallite boundaries ( 204 );
wherein segregation of the dopant element ( 208 ) via the diffusion of the dopant element ( 208 ) to the crystallite boundaries ( 204 ) lowers a crystal boundary energy, thereby making the nanostructured material stable at temperatures below the melting temperature of the nanostructured material,
wherein the formation of the AIFs at the crystallite boundaries ( 204 ) of the nanostructured material ( 214 ) increases both strength and ductility of the nanostructured material ( 214 ) as compared to materials lacking AIFs.
2. The method of claim 1 , wherein the mixing ( 102 ) comprises agitating and co-deforming powders of the base material ( 206 ) and the dopant element ( 208 ) to mechanically mix the base material ( 206 ) and the dopant element ( 208 ).
3. The method of claim 2 , wherein the agitating and co-deforming is performed using a ball-milling instrument.
4. The method of claim 1 , wherein applying the first heat treatment ( 104 ) comprises annealing the supersaturated solid material alloy ( 216 ) at a first temperature for a first threshold time and wherein applying the second heat treatment ( 108 ) comprises annealing the supersaturated solid material alloy ( 216 ) at a second temperature for a second threshold time.
5. The method of claim 4 , wherein the second temperature is greater than or equal to the first temperature.
6. The method of claim 4 , further comprising selecting the first temperature, the second temperature, the first threshold time, and the second threshold time based on one or more of the base material ( 206 ), the dopant element ( 208 ), and a phase diagram of the supersaturated solid material alloy ( 216 ).
7. The method of claim 1 , wherein the supersaturated solid material alloy ( 216 ) comprises two or more dopant elements.
8. The method of claim 1 , wherein the supersaturated solid material alloy ( 216 ) comprises two or more base materials.
9. The method of claim 1 , wherein the dopant element ( 208 ) comprises Zr, Fe, Co, Ni, Rh, Pd, Pt, other transition metals, or non-transition metals.
10. The method of claim 1 , wherein the base material ( 206 ) comprises Cu, Fe, steel, Ni, Ti, other transition metals, Al, Mg, or other non-transition metals.
11. A method of forming an amorphous intergranular film (“AIF”) ( 210 ) surrounding crystallite structures of a base material ( 206 ) of a nanostructured material ( 214 ), wherein the crystallite structure comprises a crystalline interior ( 202 ) having a grain boundary ( 204 ), the method comprising:
a. mixing ( 102 ) a dopant element ( 208 ) with the base material ( 206 ) to form a solid material alloy ( 216 ), the dopant element ( 208 ) selected based on:
i. an ability of the dopant element to segregate to the grain boundary ( 204 ) of the base material ( 206 ),
ii. the dopant element ( 208 ) and the base material ( 206 ) being immiscible; and
iii. an atomic size difference between the dopant element ( 208 ) and the base material ( 206 ) being sufficiently large to cause disorder at the crystallite boundaries of the nanostructured material ( 214 );
b. applying a heat treatment ( 104 ) to the solid material alloy ( 216 ) to preferentially segregate the dopant element ( 208 ) to the grain boundary ( 204 ) and to selectively melt an interfacial mixture ( 218 ) at the grain boundary ( 204 ) to form a structure at the grain boundary ( 204 ); and
c. quenching ( 110 ) the solid material alloy ( 216 ) to freeze the structure of the interfacial mixture ( 218 ) at the grain boundary ( 204 ), while maintaining the crystalline interior ( 202 ) solid,
wherein the AIF ( 210 ) formed at the grain boundary ( 204 ) of the base material ( 206 ) increases strength, ductility, and thermal stability of the nanostructured material ( 216 ).
12. The method of claim 11 , wherein applying the heat treatment ( 104 ) includes annealing ( 106 ) the solid material alloy at a threshold temperature for a threshold time to diffuse the dopant element ( 208 ) to the grain boundary ( 204 ) of the base material ( 206 ) and melt the dopant element ( 208 ) and the base material ( 206 ) in the interfacial mixture ( 218 ) to form the AIF ( 210 ) at the grain boundary ( 204 ).
13. The method of claim 12 , wherein the threshold temperature adjusted based on a melting temperature of each of the base material ( 206 ) and the dopant element ( 208 ).
14. The method of claim 11 , wherein the base material ( 206 ) comprises copper (“Cu”), and the dopant element ( 208 ) comprises zirconium (“Zr”) and wherein the solid material alloy ( 216 ) is a Cu-3 atomic percent Zr alloy.