This study explores the internal oxidation of laminated Hf-Ta coatings with a cyclically gradient chemical concentration distribution along the growth direction. The oxidation behavior was examined by annealing the coatings at 400-600 degrees C in a 15 ppm O-2-N-2 atmosphere for 30 min. The variations in crystalline structure, nanohardness, chemical states, and chemical composition profiles in depth after various annealing conditions were investigated. The results indicate that all the Hf-Ta coatings maintain a laminated structure after annealing at 400-600 degrees C. Internal oxidation conducts during 500 and 600 degrees C annealing, but part of the outmost layers exhibits complex oxides after annealing at 600 degrees C. The nanohardness of annealed Hf-Ta coatings related to the formation of HfO2, Hf6Ta2O17, and amorphous Ta-oxide were studied. (C) 2015 Elsevier B.V. All rights reserved.