AVS 53rd International Symposium
    Advanced Surface Engineering Friday Sessions
       Session SE1-FrM

Paper SE1-FrM4
Decomposition Process of Ti@sub 3@SiC@sub 2@(0001) Thin Films

Friday, November 17, 2006, 9:00 am, Room 2007

Session: Coatings with Enhanced Thermal Stability & MAX Phases
Presenter: J. Emmerlich, RWTH Aachen University, Germany
Authors: J. Emmerlich, RWTH Aachen University, Germany
D. Music, RWTH Aachen University, Germany
H. Willman, Linköping University, Sweden
P. Eklund, Linköping University, Sweden
H. Högberg, Linköping University, Sweden
J.M. Schneider, RWTH Aachen University, Germany
L. Hultman, Linköping University, Sweden
Correspondent: Click to Email
MAX phases (M: early transition metal; A: group-A element (13-15), X: C and/or N), such as, Ti@sub 3@SiC@sub 2@ exhibit metallic (e.g. well-conducting and ductile) and ceramic (e.g. oxidation resistance, high Young's modulus of ~340 GPa) properties. The main reason for the interesting set of properties is the nanolaminated crystal structure consisting of twinned Ti@sub 3@C@sub 2@ slabs interleaved with an atomic layer of Si acting as mirror plane weakly bonded to the Ti@sub 3@C@sub 2@ slabs. Epitaxial Ti@sub 3@SiC@sub 2@(0001) thin films were deposited on Al@sub 2@O@sub 3@(0001) substrates using DC magnetron sputtering. In our earlier investigations, these samples were vacuum-annealed from 800-1400°C with in-situ x-ray diffraction analysis. Between ~1000 and 1100°C the onset of decomposition was observed followed by the complete decomposition of the film after 25h annealing at 1200°C. Here, we present a 4-stage decomposition model based on the findings of transmission electron microscopy and supported by ab-initio calculations. The Si out-diffusion and evaporation initiated at the surface at 1100°C is followed by the O-uptake and SiO evaporation resulting in Ti@sub 3@C@sub 2@ relaxation, detwinning, and TiC@sub 0.67@ formation by C-redistribution with void formation. Initial differential scanning calorimetry measurements on as-deposited Ti@sub 3@SiC@sub 2@(0001) films show that the MAX phase is stable up to at least 1400°C for cases, where Si out-diffusion and O-uptake are prevented by means of Ti@sub 3@SiC@sub 2@(0001) films mechanically put face-to-face and heated in an Al@sub 2@O@sub 3@ crucible in Ar atmosphere. This further supports the validity of the presented model.