Structural and mechanical properties of nitrogen-deficient cubic Cr–Mo–N and Cr–W–N systems

Abstract

The tendency for nitrogen deficiency in cubic Cr-Mo-N and Cr-W-N solid solutions is predicted by a comprehensive evaluation of the lattice spacing, mixing thermodynamics, and elastic properties using first-principles calculations and experimentally confirmed by means of X-ray diffraction. A major conclusion is that these systems exhibit significant amount of N vacancies whose amount scales linearly with the TM content, hence making the Cr 1-x TM x N 1-0.5x chemical formula more precise and informative to describe the chemical composition of cubic Cr-Mo-N and Cr-W-N solid solutions as compared with the conventionally used Cr 1-x TM x N. The cubic Cr 1-x Mo x N 1-0.5x and Cr 1-x W x N 1-0.5x solid solutions exhibit large positive mixing enthalpies towards isostructural phase decomposition into cubic B1-CrN and -Mo 2 N or -W 2 N, respectively. Their ductility increases with increasing Mo or W content and both systems exhibit significantly direction-dependent Young's moduli over the entire composition range, even when using the approach to study their polycrystalline behavior. The excellent agreement between experimentally obtained lattice parameters, Mo-and W-dependent nitrogen content, elastic properties and their calculated values for our model descriptions, Cr 1-x Mo x N 1-0.5x and Cr 1-x W x N 1-0.5x , allows to understand these complex material systems. Based on our results, we can conclude that their content of nitrogen vacancies scales with half of the alloying content Mo or W.2

Atomistic Modeling‐Based Design of Novel Materials

“…[6,108] Directionally dependent Young's modulus can be considered as a first approximation beyond the isotropic elasticity to the elastic response during nanoindentation loading, although the real mechanical response involves complicated plastic and elastic deformations, [109] with stress fields being far from a simple uni-axial loading mode. [104] An acceptable agreement was obtained for the Young's modulus in the h100i The data for the cubic phase are taken from ref. [104] An acceptable agreement was obtained for the Young's modulus in the h100i The data for the cubic phase are taken from ref.…”

“…[97][98][99] It is also worth mentioning that, if all parameters are carefully chosen, both stress-strain and energy-strain approaches yield the same results (as they should, since both are based on the Hooke's law and linear elasticity). [34,37,[99][100][101][102][103][104] For practical reasons, the resulting elastic data are often processed to yield quantities more relevant for experiments dealing with polycrystalline materials. [34,37,[99][100][101][102][103][104] For practical reasons, the resulting elastic data are often processed to yield quantities more relevant for experiments dealing with polycrystalline materials.…”

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

“…Small cubes of Cr (99.99% purity, 3 Â 3 Â 3 mm 3 ) were uniformly arranged (4,8,12,16,20, and 36 pieces) on the race track of a molybdenum target (99.99% purity, Ø75 mm) to vary the Cr/(MoþCr) ratio within the films prepared. The substrates are centered parallel above the target at a distance of 55 mm.…”

“…19 Zhou et al 20 highlighted that single-phase cubic structured Mo-Cr-N phases exhibit a high driving force towards an isostructural decomposition, providing a high potential for spinodal decomposition similar to single-phase cubic structured Ti-Al-N. 21 With increasing Mo content, the metallic bonding character within single-phase cubic Mo-Cr-N increases, leading to an improved ductility. 22 Besides the computational studies, 20,23 there are further experimental investigations within the Mo-Cr-N system, 5,[24][25][26][27][28][29] but these often yield contradictory results. For example, the addition of Mo reduces 5,29 or increases 25,27 the mechanical properties of Cr-N.…”

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

“…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.…”