Preparation and characterisation of tantalum carbide as an optional crucible material for bulk aluminium nitride crystal growth via physical vapour transport

This paper reports experimental measured and calculated phase distributions of carburised Ta sheets. Electron back scatter diffraction (EBSD) maps of carburised Ta samples have shown the progress of carburisation in respect of the annealing procedure. The initial stage is characterised by grain boundary and surface carburisation at lower temperatures (T = 2000 degrees C). At elevated annealing temperatures (T = 2200 degrees C) grain boundaries play a negligible role in the transformation of Ta to TaC. Sharply bounded phase layers of TaC1-x and Ta2C are observed in this case. Fast grain coarsening below the carburisation temperature was found. A diffusion controlled phase formation model was introduced. The calculated concentrations of C are in good agreement with the measured phase widths. (c) 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.