Analytical TEM study of annealed nanocrystalline cobalt-phosphorous electrodeposits

Investigation of thermal stability of two nanocrystalline Co-P alloys shows that P atoms segregate to the grain boundaries upon annealing until precipitation of Co(2)P and CoP precipitates takes place. The P-rich precipitates formed have been investigated by analytical transmission electron microscopy to obtain statistical results of precipitate size, volume fraction and spatial distribution. Electron spectroscopic imaging maps show that the P-rich precipitates are 33 +/- 9 nm in Co-1.1at.%P and 33 +/- 12 nm in Co-3.2at.%P. The main differences between the alloys are the precipitate size distribution (Co-3.2at.%P having broader distribution) and precipitate volume number density (Co-3.2at.%P has 1.8 times more precipitates than Co-1.1at.%P). The volume fraction of precipitates is 3.0% in Co-1.1at.%P and 4.4% in Co-1.1at.%P. Most of the precipitates are of nearly spherical or slightly elongated shape, and only a few have a platelet-like shape as expected from previous tomographic atom probe measurements. Due to the truncation and projection effects, the composition of the precipitates could not be determined.