Effects of heat treatments on the ductility of cobalt electrodeposits

The effects of annealing treatments on the structure and mechanical properties of cobalt electrodeposits have been studied. Annealing temperatures range from 250-800 degrees C, i.e. below, as well as above, the allotropic alpha-h c p reversible arrow beta-f c c transformation temperature (417 degrees C). The structural characterization included hydrogen content measurement, relative volume fraction of a and p phases determination by X-ray diffraction, and microstructural investigations by optical and electron microscopy. The results showed that an annealing is a very effective means to optimize the ductility of cobalt electrodeposits. The increase of ductility observed after annealing is essentially due to a decrease of the stacking fault density in the deposits. Annealing treatment above the allotropic transformation temperature also produces, in some deposits, an increase of the ductile beta-f c c phase content, but this fact does not lead to supplementary improvements of ductility. This is due to the detrimental influence of hydrogen that always exists in these deposits. (C) 1998 Kluwer Academic Publishers.