Ageing Characteristics of Copper-Iron Alloys

The ageing characteristics of Cu-0.9, 1.4 and 2.3 % Fe alloys were studied by transmission electron microscopy, and measurements of various mechanical properties, the electrical resistivity and the saturation magnetization. Changes in 0.1% proof stress, tensile strength and hardness during ageing were confirmed to show simple single peak curves against ageing time. The main precipitate is initially a spherical coherent particle, and the precipitate grown larger than about 700Å, generates some interfacial dislocations and becomes quai-coherent. Further, grown non-coherent particles with a higher density of dislocations punch out many dislocations into the matrix and preserve a fcc structure. Coalescence of the spherically coherent particles follows the coasening equation of the form 3−03=α(t−t0) fairly well. The precipitate particles are paramagnetic during the ageing and almost all the particles larger than about 100Å in diameter were transformed to ferromagnetic by 93% cold rolling. The transformation of the particles proceeds with increase in tensile strain, and for the larger particle size, the volume fraction transformed by a small strain becomes larger. A very small amount of discontinuous precipitates with a fcc structure is observed at some of grain boundaries in the aged specimens.