Direct Observation of Precipitation in a Cu-2.3%Fe Alloy

Abstract

Precipitation in a Cu-2.3 wt%Fe alloy was observed by transmission electron microscopy. In the specimens quenched into ice water after solution treatment, dislocations and dislocation loops were observed, but precipitation was not found. The characteristic contrast images were observed in the specimens aged for 18 min, 28 min, 160 min and 45 hr at 650°C, and each contrast image seems to be due to the elastic strain in the matrix around a spherical coherent precipitate particle. The diameter of the precipitate particles in the above-mentioned specimens were about 50 Å, 110 Å, 200 Å and 430 Å, respectively. In the specimens aged for 120 hr at 700°C, the precipitate particles were about 1000 Å in diameter, around which interfacial dislocations, moiré patterns, and usual glide dislocations generated from the particles were observed. The particles in these specimens would be quasi-coherent or non-coherent. A number of tangled dislocations were observed at the periphery of the non-coherent particles in the specimens aged for 340 hr or 1000 hr at 700°C. The spherical particles indicated a fcc structure. The spherical particle-free regions or elongated discontinuous precipitates were found in a limited area along grain boundaries in some aged specimens. The discontinuous precipitates were seldom observed within the grain and had a fcc structure. Homogenious precipitation occurred in the specimens which were cold-rolled to 6% or 28% reduction after the solution treatment and then aged 160 min at 650°C. In the specimens, cooled from 1050°C to 900°C or to 800°C in the furnace and then quenched, precipitates in peculiar shape were observed. They appeared to grow three-dimensionally in some of ⟨100⟩ and ⟨110⟩ directions and had a fcc structure.