High resolution microstructure analysis of the decomposition of Cu90Co10 alloys

Homogeneous Cu-Co alloys with a Co concentration up to 10 at.% Co are prepared by rapid quenching. This allows for the first time the investigation of the decomposition process of the Cu90Co10 supersaturated solid solution on a nanometer scale using a combination of atom probe/field ion microscopy (AP/FIM) analyses and transmission electron microscopy. Annealing of a Cu(90)Co(10) alloy at 440 degrees C for various times leads to a compositional modulated microstructure. The composition profiles determined by AP/FIM analyses clearly exclude a classical nucleation and growth behavior and instead suggest a spinodal type decomposition whereby the compositions of the precipitates continuously increase. In contrast, at the grain boundaries of the Cu90Co(10) alloy heterogeneous nucleation of pure Co particles is observed.