FORMING THE STRUCTURE AND PROPERTIES OF SINTERED COPPER MATRIX COMPOSITES DISPERSION-STRENGTHENED

Preliminary results from the studies on preparation of the copper-based composite materials reinforced with the particles of Y2O3 and ZrO2 have been presented. The effect of the chemical composition and fabrication parameters on the structure and properties of the examined materials was investigated. The fabrication process included mechanical alloying of the powders of copper and the oxides of yttrium and zirconium with the composition of 0.5, 1.0 and 1.5 vol. %, respectively, followed by their consolidation by double-action pressing and sintering. An additional double-action pressing under the pressure of 500 MPa was also used, which was followed by annealing recrystallizing as a final operation. The changes in a size of powder particles after milling and quality of the obtained compacts were analysed. Morphology of the starting powders has been characterised and analysis of particle size distribution has been carried out. The X-ray studies showed that high-energy disintegration in a planetary ball mill results in the formation of nanocrystalline structure within powder particles at the size of the crystallites of an order of 49, 135 nm. Measurements of the density and electrical conductivity of the composites have been carried out at particular stages of technological process showing that re-compressing and annealing of the powders had beneficial effect on both these parameters. It was found that both at low and high contents of a hardening phase, an additional pressing followed by annealing resulted in a density increase by 16%, on an average, in case of the compacts with an addition of Y2O3 and by 13% in the compacts with ZrO2 compared to density of the compacts after pressing. As a result of annealing, electrical conductivity of the compacts increased by 8 MS/m, on an average. Based on microstructure examination of the obtained composite materials it was found that the reinforcing particles were nonuniformly distributed within a matrix. Moreover, numerous clusters of the oxide phase particles and few pores of a different size were observed. The compression tests have also been carried out both at the room temperature and at elevated temperatures (450 and 750(circle)C) in order to determine the main strength properties (Rc(0.2)) and ductility (Delta l, a(c)).