Michael Tkadletza, Alexandra Lechnera, Nina Schalka, Bernhard Sartoryc, Andreas Starkd, Norbert Schelle, Christian Saringer, Christian Mitterer, Christoph Czettl
Recently, it was shown that annealing of nanolamellar CVD fcc-Ti 1-x Al x N at temperatures of 1000-1200 °C results in the formation of complex phase ﬁelds consisting of still intact nanolamellar face centered cubic (fcc) zones, side by side with non-lamellar fully decomposed and transformed fcc and wurtzite (w) zones. It can be assumed that the observed phase ﬁelds and their microstructure strongly correlate with their mechanical properties. Consequently, this work focuses on the investigation of the eﬀects of spinodal decomposition and fcc →w phase transformation of a nanolamellar CVD fcc-Ti 0.2 Al 0.8 N coating on the corresponding global and local mechanical properties. The sequence of spinodal decomposition and fcc →w phase transformation of a compact coating sample was investigated by in situ high temperature synchrotron X-ray diﬀraction up to a maximum temperature of ~1250 °C. Conventional nanoindentation experiments on the surfaces of samples annealed between 900 to 1300 °C in vacuum were performed to illustrate the age hardening and overaging behavior. Finally, the inﬂuence of the observed phase ﬁelds on the local mechanical properties was investigated by correlative SEM/EBSD and nanomechanical mapping experiments on a cross-section of a coating annealed at 1050 °C. Maps of the lateral microstructure, phase composition, Young´s modulus and hardness of the coating were successfully obtained with a resolution of ≤ 100 nm. The lateral phase ﬁelds could be clearly identiﬁed and correlated with the observed mechanical properties. The results indicate that age hardening of nanolamellar CVD fcc-Ti 0.2 Al 0.8 N coatings occurs homogeneously, while overaging is associated to the fcc →w transformation and thus, locally conﬁned.