Computational and experimental studies on structure and mechanical properties of Mo–Al–N. (1st April 2016)

• Record Type: Journal Article
• Authors: Klimashin, F.F.; Euchner, H.; Mayrhofer, P.H.
• Is Part Of: Acta materialia. Volume 107(2016)
• Page Start: 273
• Page End: 278
• Publication Date: 2016-04-01
• Subjects: Mo–Al–N -- Hard coatings -- ab initio -- Nitrogen vacancies -- Mechanical properties; Materials -- Periodicals; Materials science -- Periodicals; Materials -- Mechanical properties -- Periodicals; Metallurgy -- Periodicals; Chemistry, Inorganic -- Periodicals; 620.112
• DOI: 10.1016/j.actamat.2016.01.063
• Languages: English
• ISSNs: 1359-6454

Abstract

Abstract: Ab initio calculations show that with increasing N-vacancy content of Mo1- x Al x N y solid solutions, the cubic structure is increasingly preferred over the wurtzite-type hexagonal structure. While Mo1- x Al x N solid solutions, without N-vacancies, energetically favor the wurtzite-type structure over the whole composition range, Mo1- x Al x N0.5(1+ x ) and Mo1- x Al x N0.5 solid solutions energetically prefer the cubic structure up to ∼45 and 65 at.% Al at the metal sublattice. Detailed ab initio calculations in combination with detailed elemental and phase composition analyses and nanoindentation experiments of reactively sputtered Mo1- x Al x N y coatings prove the formation of face-centered cubic structures for Al-contents x ≤ 0.57. These Mo1- x Al x N y coatings exhibit an Al-dependent population of the nitrogen sublattice, following the MoN0.5 –AlN quasi-binary tie line. For Al-contents x ≥ 0.79 the coatings crystallize in the wurtzite-type hexagonal phase, while in the intermediate composition range both phases, cubic and wurtzite-type hexagonal, coexist. As long as the cubic structure is maintained, the hardness increases from ∼33.0 to 38.4 GPa with increasing Al-content, but drops to ∼22 GPa for x ≥ 0.67, when the films contain hexagonal wurtzite-type phases. Graphical abstract: