Effect of powder processing and alloying additions (Al/ZrB2) on the microstructure, mechanical and electrical properties of Cu

Abstract

The present work elucidates the effect of powder processing conditions (milling/mixing) and conductive alloying element (Al: aluminium) and ceramic (ZrB2: zirconium diboride) reinforcement addition on the densification, microstructure and electrical conductivity of copper (Cu) processed via hot pressing route. Disregard of alloying element/reinforcement/content or powders preparation method, the density of Cu materials varied between 92.16 and 99.76% ρth (theoretical density) after hot pressing at a low temperature of 500 °C. In case of Cu-Al alloys, the powder processing method significantly influenced its microstructure and conductivity. Particularly the Cu-Al alloys processed using mixed powders consisted of various phases Cu, α-Cu, γ1 (Cu9Al4), δ (Cu3Al2), ζ1 (Cu4Al3), η2 (CuAl) and θ (CuAl2) and the Cu alloys prepared using milled powders composed of either only α-Cu or α-Cu and γ1 (Cu9Al4) phases (depending on the Al content). Whereas, only Cu and ZrB2 phases were observed with the Cu-ZrB2 composites processed using either milled or mixed powers. In case of Cu-Al alloys, the hardness (0.88–3.41 GPa) and strength (540.30–1120.18 MPa) of Cu increased with the addition of Al. Interestingly, the hardness (0.88–2.55 GPa) and strength (508.50–970.60 MPa) of Cu increased upto 5 wt% ZrB2 and then they lowered with further addition of ZrB2. In particular, the hardness and strength of Cu-ZrB2 composites are lower than Cu-Al alloys reflecting the effectiveness of solid solution strengthening in the Cu alloys as compared to dispersion strengthening mechanism in Cu composite. The pure Cu prepared using milled powders exhibited low conductivity (75.70% IACS) than Cu processed using as-received/un-milled powders (97.00% IACS). Also, the Cu-ZrB2 composites measured with better electrical conductivity than Cu-Al alloys. Depending on the milling conditions and alloying/reinforcement amount, the conductivity of Cu-ZrB2 composites varied between 44.10 and 88.70% IACS.