Influence of γ-Fe precipitates on physical and mechanical properties of Cu–Fe alloys

Abstract

The object in this work was to investigate the influence of aging temperature and time and chemical composition on the mechanical and electrical properties of Cu–Fe alloys. Polycrystalline specimens of Cu–0·5–3Fe alloys after solution treatment at 950°C for 1h were aged at temperatures of 400°, 500°, 600°, and 700°C for times of 0·5, 1, 3, and 10h. The methods used for the investigations were: optical and electron microscopy, Mössbauer spectroscopy, electrical resistance measurements, and mechanical tests. The aging of supersaturated solid solutions of iron in copper has a great influence on the structure and properties of Cu–Fe alloys. However, a change in alloy composition does not cause a change in electrical resistance, but influences only the mechanical properties and precipitation kinetics. In the initial stage of aging there are iron clusters present, which grow with aging time into dispersive, coherent γ-Fe particles. The size of the γ-particles increases with temperature and time of aging and these particles are responsible for the mechanical and electrical properties of Cu–Fe alloys. Thin-foil observations show that there are large cubic γ-Fe precipitates also, which are already present in solution-treated specimens. These are iron particles either undissolved during melting or precipitated during quenching from the solution-treatment temperature. These two kinds of precipitation cause two stages on isothermal curves of electrical resistance. On the isochronous curves there are minima between 500° and 600°C. In the same range of temperatures the mechanical properties reach a peak.