AVS 57th International Symposium & Exhibition
    Advanced Surface Engineering Tuesday Sessions
       Session SE-TuM

Paper SE-TuM5
Structure, Mechanical Properties and Thermal Stability of Zr-Al-N Thin Films

Tuesday, October 19, 2010, 9:20 am, Room Cimmaron

Session: Hard and Nanostructured Coatings
Presenter: P.H. Mayrhofer, University of Leoben, Austria
Authors: P.H. Mayrhofer, University of Leoben, Austria
L. Chen, University of Leoben, Austria
D. Holec, University of Leoben, Austria
D. Luef, University of Leoben, Austria
R. Rachbauer, University of Leoben, Austria
Y. Du, Central South University
Correspondent: Click to Email
Zr1-xAlxN thin films were synthesized by magnetron sputtering with AlN mole fractions x ranging from 0 to 0.9. We reveal, via X-ray diffraction (XRD) and transmission electron microscopy (TEM) that the films crystallize in the cubic NaCl (c) structure with x ≤ 0.32 and the wurtzite ZnS (w) structure with x ≥ 0.75. For AlN mole fractions between 0.32 and 0.75 the films crystallize with multiple phases and contain a fully percolated disordered phase. This is in agreement with ab initio calculations suggesting that within a broad x range of 0.38–0.75 the cubic, wurtzite and hexagonal (BN structure) are equally preferred with respect to their energy of formation. Lower AlN mole fractions prefer the cubic structure whereas higher AlN fractions favor the wurtzite structure. The maximum hardness of H ~36 GPa with an indentation modulus of E ~303 GPa is observed for the single-phase cubic Zr0.68Al0.32N coating. For higher Al contents the hardness rapidly decreases to ~22 GPa with x ~0.45 and then slightly decreases further to ~21 GPa for even higher Al contents. This is in perfect agreement with the structural investigations. During thermal annealing to 1500 °C in inert atmosphere the supersaturated phases of the films decompose towards their stable constituents c-ZrN and w-AlN. This is connected with a change in their mechanical properties where two major differences can be observed. The hardness of as deposited single-phase cubic Zr1-xAlxN slightly increases with annealing to Ta ~1000 °C due to the formation of cubic Zr- and Al-rich domains. Contrary to this observation the hardness of as deposited multi-phase Zr1-xAlxN coatings with x values between 0.38 and 0.5 increases by ~10 GPa during annealing to ~900 °C. Here, the observed hardness increase is mainly based on the structural rearrangement during annealing which results in the formation of crystalline areas with compact interface boundaries. As soon as w-AlN is formed, at around 1100 °C, the hardness decreases for as deposited single-phase cubic and multi-phase Zr1-xAlxN coatings.