Electrodeposited nanocrystalline Co-P alloys: Microstructural characterization and thermal stability

Abstract

Nanocrystalline Co-P has a significantly increased thermal stability compared to other nanocrystalline Ni- and Co-based electrodeposits. By combining observations from transmission electron microscopy in situ annealing with differential scanning calorimetry and tomographic atom probe measurements, the microstructural development of nanocrystalline Co-1.1 at.% P and Co-3.2 at.% P is described. In the as-prepared state, both alloys consist of 10 nm sized hcp-Co grains, and the P-distribution is already inhomogeneous. Upon annealing, P-atoms segregate to the grain boundaries. and grain growth takes place. Initial grain growth is abnormal in both electrodeposits, but occurs slower and more homogeneously in Co-3.2 at.% P. When P-saturation of the grain boundaries is reached, P-rich precipitates form accompanied by rapid (normal) grain growth. Due to the higher initial P-concentration in Co-3.2 at.% P, saturation of P and precipitation occurs earlier leading to a slightly lower thermal stability. Apart from the different P-contents, the effect of impurities, allotropic phase transformation of Co and texture is discussed. (c) 2006 Elsevier B.V. All rights reserved.