Strengthening effects in precipitation and dispersion hardened powder metallurgy copper alloys

Abstract

The hardening of copper and copper alloy matrix using powder metallurgy (PM) techniques and different ways for dispersoids formation, as well as analysis of their single and combined effects on the strength of obtained material at room and elevated temperatures, have been presented and discussed. Gas atomized Cu-3.8 wt.%Ti and Cu-0.6 wt.%Ti-2.5 wt.%TiB2 (Cu-Ti-TiB2) powders and mechanically alloyed powder Cu-4 wt.%TiB2 were used as starting materials. The powders were consolidated by hot isostatic pressing (HIP) and hot pressing (HP). Optical, scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDAX), as well as transmission electron microscope (TEM) were used for microstructure characterization of the compacts. High strengthening of the Cu-Ti compacts was achieved by thermal treatment (aging) as a consequence of the development of modular structure and precipitation of metastable Cu4Ti(m). Hardening in the Cu-Ti-TiB2 compacts is due to simultaneous influence of the following factors: the development of modular structure, precipitation of metastable Cu4Ti(m), and the presence of TiB2 dispersoid nanoparticles. Incase of Cu-TiB2 compacts, high starting values of hardness and hardness on the elevated temperatures result from the presence of finely distributed TiB2 particles in copper matrix obtained by mechanical alloying. Cu-Ti-TiB2 composite yields much higher hardness values compared with the binary Cu-Ti alloys, owing to primary TiB2 dispersions formed during atomization. Separation of metastable Cu4Ti precipitate and the presence of significantly finer TiB2 particles in the copper matrix are the reason for higher hardness values at peak temperatures (400-500 degrees C) in multiple-hardened copper alloy compared to the dispersion-hardened. (C) 2013 Elsevier Ltd. All rights reserved.