Effect Of Nanosized Ag, Fe Precipitates On Micro-structure And Properties Of Cu-base Filamenary Composites

In this study, Fe and Ag were selected as representative of bcc and fcc structure alloy elements. Binary Cu-6 wt.% Ag and Cu-2.5 wt.% Fe alloys with initial microstructure consisting of nanosized Ag or Fe precipitates embedded in Cu matrix were parapered by solution and aging treatment. Ternary Cu-6 wt.% Fe-4 wt.% Ag alloy with nanosized Ag-Fe composite precipitates was prepared by mechanical/heat treatment,Cu-6 wt.% Fe alloy was produced in the same way for comparision. The microstrue of at various wire drawing strains was observed by optical microscopy and electron microscopy. The tensile strength of the specimens at virous drawing strains was tested on an electrical universal test machine. The electrical resistivity was testd by the standard four-point method.The morphology of Fe precipitates was almost unchanged during cold wire drawing. There was no orientation relationship between Fe precipitates and Cu matrix. The Ag precipitates deformed to filamentary morphology, and kept cube-on-cube orientation relationship with Cu matrix. All above was established in Ag-Fe composite precipitates, too.The process of the interface between Ag-Fe composite precipitates and Cu matrix acting as dislocation source emitting partial dislocation, forming stacking flauts and twins was observered. The stacking flauts were hard to retain in Cu matrix, while were much easier in Ag phase and formed twins. The formation of stacking flauts and twins may be one of the important ways of the Ag phase deformation in Ag-Fe composite precipitates. A value of internal stress about 1.38 GPa around the Ag-Fe composite precipites was estimated according to the critical stress for activation of Schockley partial dislocation source. Based on this, the critical stress for deformation of the Fe precipitates would be above G/59.Interface cracking of Ag-Fe composite precipitates occurred at Cu/Fe interface near the phase junction. Then it developed along the Ag/Fe interface. This should be the main reason for fracture.A strength model based on interface density was proposed. By defining the coefficient k of interface strengthening term, the relationship between the strengthening from interface and the specific demension of the materials was built, which represented the size effect. The strength of composites with different compositions and initial scales was well fitted.The tendency of electrical resistivity dependent on drawing strain was almost the same between Cu -6 wt.% -4 wt.% Ag and Cu -6 wt.% Fe. The difference of electrical resistivity between Cu -6 wt.% -4 wt.% Ag and Cu -6 wt.% Fe vibrated around the value of electrical resistivity contributed by foreign Ag sloutes in Cu. This result means the influence of nanosized Ag filaments to the mean matrix free path was covered by that of Fe filaments. And it is possible to improve strength and almost not damage electrical conductivity by adding nanosized Ag fibers in Cu-bcc systems.