Phase chemistry, thermodynamic and kinetic characterization of interfacial reaction between aluminum nitride and titanium

Interfacial reaction between AlN and Ti was characterized in terms of phase chemistry, thermodynamics and diffusional layer growth kinetics. First, the phase equilibria and thermochemistry of the Ti-Al-N system were evaluated by a combination of experimentation and thermodynamic calculation. Various powder mixtures and reaction couples were annealed in an inert atmosphere followed by phase and composition analyses using x-ray powder diffractometry and analytical electron microscopy. The previous Ti-Al-N phase diagram was revised and extended over a much wider range, 900 K to 1873 K. The most significant revisions were made in the aluminum rich region. A new ternary nitride, ;The thermodynamics of Ti-N and ;The growth kinetics of the reaction layers of AlN-Ti reaction couples were characterized both experimentally and theoretically. Growth of all reaction layers followed a parabolic rate dependence. By combining the growth kinetics and thermodynamics, chemical diffusion coefficients and component activity profiles across the reaction zone were estimated. Diffusion mechanisms of both aluminum and nitrogen in TiN were proposed. Phase stability diagrams were constructed to help understand the reaction sequence and phase evolution.;An attempt to clear up the uncertainty of the existence of ;Finally, the interfacial reaction zone between AlN and Ti was characterized by high resolution scanning electron microscopy (HRSEM) and transmission electron microscopy (TEM). Convergent-beam electron diffraction (CBED) and selected-area electron diffraction (SAD) patterns were used for phase identification. The chemistry of the TiN layer was analyzed by electron energy loss spectroscopy (EELS). It was shown that small amounts of aluminum dissolved in TiN but it was not clear as to whether aluminum segregated preferentially to the grain boundaries. Overall morphology of the reaction zone were examined in detail by HRSEM. An interesting feature was that the TiN layer was found to be porous for certain reaction conditions.