Nanocrystalline copper based microcomposites

Purpose: The aim of this work was to investigate microstructure, mechanical properties and deformation behavior of copper microcomposites: Cu- Y2O3, Cu- ZrO2 and Cu-WC produced by powder metallurgy techniques. Design/methodology/approach: Tests were made with Cu-Y2O3, Cu-ZrO2 and Cu-WC microcomposites containing up to 2% of a strengthening phase. The materials were fabricated by powder metallurgy techniques, including milling of powders, followed by their compacting and sintering. The main mechanical properties of the materials were determined from the compression test and, additionally, measurements of HV hardness and electrical conductivity were made. Analysis of the initial nanocrystalline structure of these materials was made and its evolution during sintering and cold deformation was investigated. Findings: It was found out that addition of up to 2 wt.% of a strengthening phase significantly improves mechanical properties of the material and increases its softening point. The obtained strengthening effect have been discussed based on the existing theories related to strengthening of nanocrystalline materials. The studies have shown importance of “flows” existing in the consolidated materials and sintered materials in pores or regions of poor powder particle connection which significantly deteriorate the mechanical properties of micro-composites produced by powder metallurgy. Research limitations/implications: The powder metallurgy techniques make it possible to obtain copper-based bulk materials by means of input powder milling in a planetary ball mill, followed by compacting and sintering. Additional operations of hot extrusion are also often used. There is some danger, however, that during high-temperature processing or application of these materials at elevated or high temperatures this nanometric structure may become unstable. Practical implications: A growing trend to use new copper based microcomposites is observed recently world-wide. Within this group of materials particular attention is put to those with nanometric grain size of a copper matrix, which show higher mechanical properties than microcrystalline copper. Originality/value: The paper contributes to the knowledge of mechanical properties and the nanostructure stability of Cu-Y2O3, Cu-ZrO2 and Cu-WC microcomposites. A controlled process of milling, compacting, sintering and cold deformation provides possibility to obtain nanocrystalline copper based materials with improved functional properties.