One common way of increasing the intrinsical relative low strength of copper while retaining its high electrical conductivity is the alloying of copper with different insoluble elements to achieve a particle strengthening. Potential alloying elements can be found in the family of bcc elements (e.g. Cr, W, Ta, Nb, Mo, V). Among them the Cu-Nb alloys show the best mechanical properties. The mutual solubility of niobium and copper is negligibly low whereas they have strongly different melting points. Hence, conventional cast metallurgy cannot be applied on a large scale.
Nevertheless, manufacturing of alloys from immiscible metal system can be carried out by using the following two techniques: rapid solidification (RS) and mechanical alloying (MA). By RS a fine distribution of two phases can be produced, but the formation of solid solution with a high content of the alloyed element is not possible. In contrast, by mechanical alloying alloys with better homogeneity and a higher content of the alloyed element in solid solution can be manufactured. Due the high energy impact during milling, the region of solid state solution extends and alloys with very high homogeneity in the microstructure can be achieved by the use of under the appropriate conditions.
This limit can be extended to strongly supersaturated Cu solid solution of up to 10 at.% Nb provided the appropriate mechanical alloying method is applied. This extention has been observed by X-ray and TEM analysis.
|SEM study of microstructure of Cu-10%Nb powder with mechanical alloying after 4h (left) and 25h (right) milling time|