Dresden 2006 – wissenschaftliches Programm
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MM: Metall- und Materialphysik
MM 37: Nanostructured Materials I
MM 37.4: Vortrag
Donnerstag, 30. März 2006, 15:30–15:45, IFW D
Thermal Stability of a Nanocrystalline Cobalt-Phosphorous Alloy — •Catharina Wille1, Taláat Al-Kassab1, Reiner Kirchheim1, Melina da Silva2, and Uta Klement2 — 1Georg-August-Universität Göttingen, Institut für Materialphysik, Friedrich-Hund-Platz 1, D-37077 Göttingen — 2Chalmers University of Technology, Department of Materials and Manufacturing Technology, SE-41296 Göteborg, Sweden
Nano-crystalline Co-2.3at%P layers with a thickness of 200 µm and an average grain size of 12 nm were prepared by means of the pulsed current electro-deposition. These specimens were investigated both in the as prepared state and after different heat treatments by utilizing different analysis techniques such as Field Ion Microscopy (FIM), Tomographic Atom Probe (TAP), Transmission Electron Microscopy (TEM), Differential Scanning Calorimetry (DSC), X-Ray Diffraction (XRD).
The results reveal a high P-segregation at the grain boundaries already in the as prepared state. Between 723 and 753K, the allotropic phase transformation (hcp-Co to fcc-Co) sets in and abnormal grain growth is observed. The onset of abnormal grain growth at 673K is accompanied by the precipitation of the CoP-phase, whereas the formation of the equilibrium Co2P-phase is not detected. For most of the neighboring grain boundaries, the level of P was depleted insofar as no significant excess segregation was detected.
Between 723 and 743K normal grain growth occurs. Thus the thermal stability of this alloy can be mainly attributed to the reduction of grain-boundary energy by P-segregation.