AVS 49th International Symposium
    Surface Engineering Tuesday Sessions
       Session SE+NS-TuM

Paper SE+NS-TuM1
The Effect of Columnar Growth in the Hardness of TiN/NbN Superlattices

Tuesday, November 5, 2002, 8:20 am, Room C-111B

Session: Nanocomposite and Nanolayered Coatings
Presenter: J.M. Molina-Aldareguia, Linkoping University, Sweden
Authors: J.M. Molina-Aldareguia, Linkoping University, Sweden
T. Joelsson, Linkoping University, Sweden
M. Oden, Linkoping University, Sweden
W.J. Clegg, Cambridge University, UK
L. Hultman, Linkoping University, Sweden
Correspondent: Click to Email
Nitride superlattices can be much harder than the individual component materials of which they are made, for a comparable defect and residual stress state. However, there appears to be considerable variation in the observed magnitude of this effect. The aim of this work was to investigate the origin of this variation by comparing two series of epitaxial TiN/NbN superlattices grown by reactive magnetron sputtering on MgO(001) single crystals: one that displayed superlattice hardening and another that did not. According to X-Ray Diffraction and X-Ray Reflectivity studies, the composition modulation was strong and the composition change at the interfaces abrupt in both series, indicating that the hardening is strongly influenced by some other microstructural parameter besides the layering. To investigate this, the deformation mechanisms were studied using a focused ion beam workstation to prepare cross-sectional transmission electron microscopy specimens under nanoindentations. These studies show that the superlattices with no hardening possess a columnar structure with voided boundaries, which act as preferential sites for shear to take place. This implies that the incorporation of porosity at the columnar boundaries, which is dependent on the growth conditions, is responsible for the variation observed in the magnitude of the hardening effect in TiN/NbN superlattices.