Activated Sintering of Cu-Al2O3 powders

Abstract

A technique for production of high-density composite material (Cu-1 wt % Al₂O₃) by single-fold cold compacting and sintering was developed. It is known that presence of gases in ductile metals, e.g., copper, inhibits consolidation of powder metal products. The technique is able to succeed in degassing of the composite material during heating in a hydrogen atmosphere. The technique is based on addition of cobalt and copper oxalates in a mixture of Cu and Al₂O₃. The efficiency of the technique was estimated by the relative density and hardness values of produced Cu-Al₂O₃ composite materials. The mechanism of impact of activated sintering on compaction of composite materials was investigated. It was found that decomposition of cobalt and copper oxalates at heating in hydrogen atmosphere synchronizes activated reduction of copper oxides and degassing of products, supporting permeability of composite materials. Composition of active admixture 0.5 wt % CoC₂O₄ + (2–2.5) wt % CuC₂O₄ is optimized. It was found experimentally that addition of oxalates produces a positive impact on consolidation processes and properties of composite materials on the basis of copper and Al₂O₃ micro- and nanoparticles irrespective of preparation techniques: electrolysis, evaporation-condensation, salt decomposition, precipitation and coprecipitation of hydroxides with further reducing heat treatment and milling. Application of activated sintering of powders obtained by coprecipitation of hydroxides and compacted at 700 MPa enables the formation of Cu-1% Al₂O₃ composite material with improved properties. As a result, composite material with homogeneous structure (grain size of 2–10 μm), increased values of density (8.4 g/cm³), and Brinell hardness up to 780 MPa was produced.