Mechanical synthesis of copper–carbon nanocomposites: Structural changes, strengthening and thermal stabilization

Abstract

► The study characterized Cu–nanodiamond (Cu–nD) and Cu–graphite (Cu–G) composites. ► Preservation of nD crystalline structure during high-energy milling was demonstrated. ► Higher refinement of matrix in Cu–nD comparing to Cu–G is due to a milling mechanism. ► Remarkable thermal stability and microhardness have been achieved in Cu–nD and Cu–G. ► Strengthening resulted mainly from grain refinement and second-phase reinforcement. Processing of copper–carbon nanocomposites by mechanical synthesis poses specific challenges as carbon phases are prone to amorphization and exhibit an intrinsically difficult bonding with copper. The present work investigates Cu–nanodiamond (Cu–nD) and Cu–graphite (Cu–G) composites produced by mechanical synthesis and subsequent heat treatments. Transmission electron microscopy observations showed homogeneous particle distributions and intimate bonding between the metallic matrix and the carbon phases. Ring diffraction patterns of chemically extracted carbon phases demonstrated that milled nanodiamond preserved crystallinity, while an essentially amorphous nature could be inferred for milled graphite. Raman spectra confirmed that nanodiamond particles remained essentially unaffected by the mechanical synthesis, whereas the bands of milled graphite were significantly changed into the typical amorphous carbon fingerprint. Particle-induced X-ray emission spectroscopy showed that the total contamination originating from the milling media remained below 0.7 wt.%. The Cu–nanodiamond composite exhibited remarkable microhardness and microstructural thermal stability when compared with pure nanostructured copper.