Fabrication and characterization of nanostructured immiscible Cu-Ta alloys processed by high-pressure torsion.

Abstract

Nanostructured Cu–Ta alloys show great potential as high strength nanocrystalline materials due to their excellent mechanical properties and limited grain growth at high temperatures. This report describes the fabrication of nanostructured immiscible Cu-Ta alloys in bulk by high-pressure torsion (HPT) using a stack of Cu/Ta/Cu discs at room temperature. A microstructural study after HPT processing showed that the internal Ta layer breaks into small individual flakes which distribute uniformly over the Cu matrix through increases in the numbers of HPT turns. There is solid-state diffusion between the Cu and Ta when the HPT processing increases to 100 turns due to microstructural refinement and increasing crystalline defects. After processing through 150 turns, a composite microstructure of two phases is formed including supersaturated Cu-Ta solid solutions (Cu81Ta19 and Ta78Cu22 alloys) with a crystallite size of ~35-45 nm. This fine microstructure produces exceptional mechanical properties including a high hardness of over 350 Hv corresponding to ~3.43 GPa, a tensile strength of ~1300 MPa and a tensile elongation of about 40%.