| AVS 59th Annual International Symposium and Exhibition | |
| Thin Film | Thursday Sessions |
| Session TF+NS+EM-ThM |
| Session: | Thin Films: Growth and Characterization-II |
| Presenter: | L. Rogström, Linköping University, Sweden |
| Authors: | L. Rogström, Linköping University, Sweden M.P. Johansson, SECO Tools AB, Sweden M. Ahlgren, Sandvik Tooling AB, Sweden N. Ghafoor, Linköping University, Sweden J. Almer, Advanced Photon Source, Argonne National Lab L. Hultman, Linköping University, Sweden M. Odén, Linköping University, Sweden |
| Correspondent: | Click to Email |
Transition metal nitrides are widely used as wear protective coatings due to their high hardness also at elevated temperatures. Hence, TiAlN is one of the most common materials for coating of cutting tools. Its attractive mechanical properties are connected with the phase separation of the cubic TiAlN phase when the coating is exposed to high temperatures. The related ZrAlN system is less studied while its large miscibility gap with possibility for phase separation at elevated temperatures makes this material interesting for high temperature applications. Here, we present a comprehensive study of the phase formation in arc-evaporated ZrAlN thin films and their mechanical properties and thermal stability. Zr1-xAlxN thin films with a wide range of compositions (0.12<x<0.73) were grown by cathodic arc-evaporation. The structure of as-deposited and annealed films was characterized by x-ray diffraction and transmission electron microscopy and the mechanical properties were determined by nanoindentation.
The structure of the as-deposited ZrAlN thin films was found to depend on the Al-content. A low Al-content (x<0.38) results in cubic (c) structure films while for high Al-content (x>0.70) a hexagonal (h) ZrAlN phase is obtained [1]. In the compositional range between x=0.38 and x=0.70, the films exhibit a nanocomposite structure with a mixture of cubic, hexagonal, and amorphous phases [1, 2]. In all films, separation of ZrN and AlN takes place during annealing. In films with a nanocomposite structure, the phase transformation is initiated by nucleation and growth of c-ZrN in the ZrN-rich domains while the AlN-rich domains remain largely amorphous at 1100 °C [3]. Nucleation and growth of h-AlN is hindered by a high nitrogen content in the film and takes place at annealing above 1300 °C, simultaneously to loss of the excess nitrogen. The depletion of amorphous phase during annealing results in an improved hardness of the film. In the h-ZrAlN films, ZrN- and AlN-rich domains form within the hexagonal lattice during annealing above 900 °C. The formation of domains with different composition results in an increased hardness, from 24 GPa of the as-deposited film to 31 GPa of the annealed film. The c-ZrAlN phase is found to be stable to annealing temperatures of 1000 °C, while at higher temperatures, h-AlN nucleates and grows. This is different from the c-TiAlN system where spinodal decomposition occurs resulting in age hardening of the films.
[1] L. Rogström et al., J. Vac. Sci. Technol. A 30 (2012) 031504.
[2] L. Rogström et al., Scr. Mater. 62 (2010) 739.
[3] L. Rogström et al., J. Mater. Res., In press (2012)