Synthesis, microstructure and mechanical properties of ZrB2 nano and microparticle reinforced copper matrix composite by in situ processings

• Cu–Zr–ZrB2 prepared by mechanical alloying and hot pressing i.e. laser melting.
• Hot pressing: in situ formation of ZrB2 after hot pressing at 650–690 °C.
• Maximum hardening obtained after 40% cold working and aging at 500 °C.
• Laser melting: in situ formation of ZrB2 in the liquid state; CuZr metastable phase.
• Much higher hardening of Cu matrix with laser melting due to large supersaturation.

Copper matrix composite reinforced with ZrB2 particles was prepared by in situ reaction in two different ways: by mechanical alloying and subsequent hot pressing, i.e. mechanical alloying and followed by laser melting process. Microstructural changes during mechanical alloying, hot pressing and laser melting of Cu, Zr and B powder mixtures were studied using scanning electron microscopy and X-ray diffraction. In particular, changes in the Cu particle size, structural parameters of the powder mixtures and formation of new ZrB2 and CuZr phases during hot pressing, i.e. laser melting were investigated. The mechanisms of in situ formation of reinforcement particles and hardening effects in the copper composite were also studied. Large supersaturation which is possible with laser melting process results in homogeneous nucleation of CuZr precipitates and the presence of finer CuZr precipitates and ZrB2 reinforcements in the Cu matrix. This affected on significantly higher degree of Cu matrix hardening compared to composites obtained by mechanical alloying and hot pressing.