Tuning heterogeneous geometric microstructure of Cu-based materials via powder metallurgy for improving high synergistic strengthening and electrical conductivity

Abstract

Designing heterogeneous structures (HS) is recognized as a promising method to achieve high performance for Cu-based materials. However, how to tune and control stably still remains challenging. In this work, a reproducible method based on powder metallurgy and heat treatment is proposed for designing controllable HS. Herein, spatial distribution of coarse and fine grains can be controlled via addition of different volume fraction of Cu powder. The microstructure evolution of the resultant HSed material was characterized in detail by utilizing electron backscattered diffraction (EBSD) combined with a transmission electron microscope (TEM). An optimal heterogeneous geometric microstructure consisting of individual isolated micron-sized grain completely surrounded and constrained by the hard ultrafine-grained Cu-Cr0.67 matrix is discovered, which produced an excellent combination of high yield strength (531.4 ± 10.3 MPa), uniform elongation (～22.1%)，and conductivity (～90.4% IACS) (International Annealed Copper Standard). The well-dispersed and high-density soft/hard zone interfaces in the resultant HS cause geometrically necessary dislocations (GNDs) piling ups, which produce extra strain hardening to enhance the strength and ductility. This reproducible method provides a feasible strategy to optimize the mechanical properties of metals via tailoring HS.