Effect of ordered N vacancies driven by increasing Mo content in multi-principal-element Ti-Al-Zr-Mo-N coatings

Multi-Principal-Element Nitrides (MPENs) are an emergent alternative gaining attention for protective coatings due to the promise of outstanding tribomechanical performance. However, the operational response of MPEN coatings depends on selecting constituent elements and determining proper composition ratios, which will determine their final microstructure and morphology. Herein, we report the deposition of MPEN sputtering coatings of the Ti-Al-Zr-Mo-N system following the microstructure and morphology behavior as a function of the variation of Mo from 0 to 31.5 at.%. The phase evolution evidences significant changes from a predominant B1 (NaCl-type) structure with disordered N vacancies for the lower Mo contents to a predominant β (tetragonal) phase with ordered N vacancies for the higher Mo contents, which leads to remarkable morphological changes in the coatings. In addition, we found the best tribomechanical performance in the coating with a mixture between B1 (disordered N vacancies) and β (ordered N vacancies), due to a synergistic effect based on the resultant texture in each phase. Furthermore, the best protective character against corrosion was found to have a decreasing trend as the Mo content increased. These results demonstrate the need for optimization strategies to determine the balance between opposing effects of phenomena that occur during the deposition of MPENs, mainly those driven by the nature of the metal constituents and their atomic ratio. The present work could contribute to the design, synthesis, and optimization of MPEN coatings based on predetermined properties of interest for specific applications of the protective coating industry.