Investigation of new aspects in the initial stages of decomposition of Cu2at.%Co with the tomographic atom probe and the field ion microscope

Abstract

The initial stages of nucleation and precipitation of the Co-rich phase in a supersaturated Cu2at.%Co alloy were studied with the field ion microscope (FIM) and the tomographic atom probe (TAP). The specimens of nominal composition Cu2at.%Co were homogenised at 1173 K and aged for different times at different temperatures from 703 to 853 K to follow the decomposition path at these reaction temperatures. In this paper, results on the time evolution of the decomposition are presented. New aspects in the decomposition of CuCo were found, which are discussed. At the initial stages of the nucleation, fluctuations were observed, which could be quantitatively characterised.Decomposition was found to take different paths at different annealing temperatures. At 853 K individual precipitates grew, whereas during coarsening the elastic soft [100] directions were preferred.At 763 K, cigar-shaped precipitates formed along the [100] directions as a metastable state, which degraded into individual spherical precipitates for longer aging times. The initial stages of decomposition were also characterised for 703 K by using the cluster search algorithm.

The influence of elastic strain on the early stages of decomposition in Cu–1.7at% Fe

“…lattice were observed by Heinrich et al [5] in Cu-2 at% Co. They investigated the early stages of decomposition at low annealing temperatures between 703 and 853 K.…”

Analysis of Precipitation Kinetics on the Basis of Particle-Size Distributions

“…Assessment of the effects of strain-field interaction is complex; such interaction may either (locally) promote or inhibit nucleation and growth of particles. The effect of strain-field interaction was suggested to lead to chain-like arrays of Co-rich precipitate particles along elastically soft directions of the Cu-rich matrix as observed for Cu-Co, albeit for alloys of considerably higher solute content featuring much high particle-number densities (10 23 to 10 25 m À3 ) [22,49] . In view of the decline of elastic strain proportional to ðr=ðr þ dÞÞ 3 with distance d from the particle-matrix interface, [50] the effect of strain-field interaction may in first approximation be neglected for the relatively small volume fractions of precipitates and low particle-number densities observed in the present case.…”

Investigation of the Amorphization of iron and austenitic stainless steel films by supersaturation with Boron, Carbon, Nitrogen and Oxygen

“…6.34, the formation of about 10 nm ringlike atom strings can be observed. According to the literature [116], these characteristics are typical for an initiating crystallization and can be observed for complex intermetallic compounds. Thus, it is reasonable to assume that some of the observed inhomogeneities are nano-crystallites.…”