Composition driven phase evolution and mechanical properties of Mo–Cr–N hard coatings

Abstract

Although many research activities concentrate on transition metal nitrides, due to their excellent properties, only little is known about Mo–N based materials. We investigate in detail the influence of Cr on the structural evolution and mechanical properties of Mo–N coatings prepared at different nitrogen partial pressures. The chemical composition as well as the structural development of coatings prepared with N2-to-total pressure ratios (pN2/pT) of 0.32 and 0.44 can best be described by the quasi-binary Mo2N–CrN tie line. Mo2N and CrN are face centered cubic (fcc), only that for Mo2N half of the N-sublattice is vacant. Consequently, with increasing Cr content, also the N-sublattice becomes less vacant and the chemical composition of fcc single-phase ternaries can be described as Mo1−xCrxN0.5(1+x). These coatings exhibit an excellent agreement between experimentally and ab initio obtained lattice parameters of fcc Mo1−xCrxN0.5(1+x). When increasing the N2-to-total pressure ratio to pN2/pT = 0.69, the N-sublattice is already fully occupied for Cr-additions of x ≥ 0.4, as suggested by elastic recoil detection analysis and lattice parameter variations. The latter follows the ab initio obtained lattice parameters along the quasi-binary MoN–CrN tie line for x ≥ 0.5. The single-phase fcc coating with Cr/(Mo+Cr) of x ∼0.2, prepared with pN2/pT = 0.32, exhibits the highest hardness of ∼34 GPa among all coatings studied.

Atomistic Modeling‐Based Design of Novel Materials

“…[104] An acceptable agreement was obtained for the Young's modulus in the h100i The data for the cubic phase are taken from ref. [110] These data were compared also with earlier published observations for the same coating system, but with a preferred orientation along the h111i direction. [110] These data were compared also with earlier published observations for the same coating system, but with a preferred orientation along the h111i direction.…”

“…[103] direction, which was the preferred grain orientation as revealed by X-ray diffraction (XRD). [110] These data were compared also with earlier published observations for the same coating system, but with a preferred orientation along the h111i direction. In this case, the indentation moduli were lower and exhibited a perfect resemblance with the calculated Young's modulus in the h111i direction.…”

Unprecedented thermal stability of inherently metastable titanium aluminum nitride by point defect engineering

“…To this end we compare the reported [72] and calculated stoichiometry of (Cr,Mo)N x in the Supplementary Material. Good agreement between predicted and reported transition from understoichiometric to (over)stoichiometric nitrogen content with increasing chromium content can be observed, corroborating the general applicability for other reactively deposited material systems.…”

The impact of nitrogen content and vacancies on structure and mechanical properties of Mo–N thin films

“…The elemental composition was obtained by energy dispersive X-ray spectroscopy (EDX), quantified with Mo-N thin film standards that have been characterized by elastic recoil detection analyses. 9,36 Nanoindentation tests were conducted using an ultra-micro indentation system (UMIS) equipped with a Berkovich diamond tip and applying loads in the range of 3 to 30 mN. The evaluation of the film-only indentation hardness, H, and modulus, E, from the load-displacement curves was carried out after Oliver and Pharr 37 as described in detail in Refs.…”

“…3,5 Another excellent example is Mo 2 N (with T c ¼ 5-7 K (Refs. 3, 5, and 6)), because its high-temperature modification, cubic-structured c-Mo 2 N (Fm-3m), exhibits excellent mechanical and tribological properties 7,8 and-as shown in our recent studies [9][10][11] -has enormous potentials for being used as wear-resistant coating. Interestingly, like most cubic-structured transition metal nitrides, c-Mo 2 N crystallizes with the NaCl-type structure, yet with 50% randomly distributed vacancies at the N-sublattice.…”