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.
Department of Materials and Manufacturing Technology, Chalmers University of Technology, Hörsalsvägen 7, SE-412 96 Göteborg, Sweden.
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