In this work, the interatomic potentials for modeling diffusion in the C15 Cr2Ta Laves phase were constructed within the N-body approach. The potential for Ta–Ta interactions reproduces the lattice ...parameter, cohesive energy, elastic constants, equation of state, thermal expansion, point defect energies, and phonon dispersion of body-centered cubic Ta in qualitative agreement with density functional theory (DFT) data and almost quantitative agreement with available experimental data in the temperature range of stability of C15 Cr2Ta Laves phase. The potential for Cr–Ta interactions reproduces the elastic constants, point defect properties, equilibrium volumes, and formation enthalpies of Cr–Ta structures in qualitative agreement with DFT data. Also, it reproduces the lattice stability and high-temperature formation enthalpy of C15 Cr2Ta Laves phase in very close agreement with the available experimental data. The calculations of diffusion coefficients with constructed potentials showed that diffusion in C15 Cr2Ta lattice is governed by Cr atoms which cannot move without creation of vacancies. The constructed potentials can be used in further investigations of diffusion processes in Cr–Ta phases at temperatures up to 2000 K, while the obtained results on diffusion coefficients in C15 Cr2Ta Laves phase would be useful in the rational design of Cr–Ta based alloys.
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We use ab initio calculations to analyze the influence of 4d and 5d transition metal alloying elements on cohesive properties of the bulk and a representative grain boundary in Cr within the ...framework of the Rice–Thomson–Wang approach. The results obtained for Cr are combined with the analogous results for Ni to select Ta and Nb as promising alloying additions to dual-phase (α/γ) Cr-Ni-base high-temperature alloys. Ta and Nb are added to the alloying system of an existing alloy I (Cr-Ni-W-V-Ti) in an attempt to design a chemical composition of a new alloy II (Cr-Ni-W-V-Ti) + (Ta-Nb). Investigation of the microstructure of the Ta-bearing Cr-Ni-alloy reveals a Ta enrichment of large γ-areas near GBs in α-matrix that we consider as potency to increase the cohesive strength of GBs and the cohesive energy of the bulk in γ-phase. Mechanical testing of alloys I and II demonstrates that the alloy II has improved tensile strength and creep resistance at high temperatures.
The structure and electron beam induced crystallization kinetics of amorphous ZrO
2
films obtained via ion-plasma and laser sputtering were compared. The studies were performed by electron ...diffraction and transmission electron microscopy with recording video films in situ. The effect of an electron beam on an amorphous film in a vacuum was accompanied by the formation of zirconia microcrystals with an FCC lattice. For laser evaporation, the density of crystallization nuclei was β ~ 10
9
cm
–2
, and the characteristic length unit was
D
0
~ 0.48 μm. For ion-plasma evaporation, β ~ 10
10
cm
–2
, and
D
0
~ 0.06 μm. The kinetic curves of the crystallization of amorphous films were analyzed using the β-variant of the Kolmogorov model as a basis.
We used the results of ab initio calculations to improve the high temperature mechanical properties of a Cr-Ni-base alloy (Cr-33Ni-2W-0,3Ti-0,3V, wt.%) (alloy I) with two-phase α - γ microstructure. ...It was established that γ – phase in Cr-Ni-base alloy (I) plays a key role in the processes of plastic deformation. By analogy with Ni-base superalloys the bulk and grain boundaries cohesion in γ – phase of the Cr-Ni-base alloy (I) were strengthened by adding a package of the “low alloying” elements (Zr, Hf, Nb, Ta) (alloy II) chosen in accordance with our theoretical predictions. We further investigated an influence of a sum (Ta, Nb, Hf, Zr) like the low alloying additions on the mechanical properties of Cr-Ni-base alloy (I). The results of mechanical testing revealed a significant strengthening of the alloy (II) in comparison with (I) at the temperature 1080 oC in accordance with our predictions. We also investigated the microstructure’s peculiarities of the alloys (I) and (II).
We discuss development and integration of a coherent fiber array system composed of densely packed fiber collimators with built-in capabilities for adaptive wavefront phase piston and tilt control at ...each fiber collimator. In this system, multi-channel fiber-integrated phase shifters are used for phase locking of seven fiber collimators and the precompensation of laboratory-generated turbulence-induced phase aberrations. Controllable x and y displacements of the fiber tips in the fiber collimator array provide additional adaptive compensation of the tip and tilt phase aberration components. An additional control system is utilized for equalization of the intensity of each of the fiber collimator beams. All three control systems are based on the stochastic parallel gradient descent optimization technique. The paper presents the first experimental results of adaptive dynamic phase distortion compensation with an adaptive phase-locked fiber collimator array system.
Experiments were carried out to develop methods of diffusion welding of joints between single-crystal molybdenum and polycrystalline molybdenum through a titanium interlayer in the hot isostatic ...pressing (HIP) conditions. The structure and the mechanical and physical properties of the diffusion welded joints Mo
single
+ Ti + Mo
poly
were investigated. Composite molybdenum single-crystal mirrors with areas of 5000 and 8000 mm
2
were produced and subjected to successful tests.
We consider the effect of protective PVD coatings of various chemical compositions on the wear rate of cutting tools equipped with polycrystalline superhard materials (PSHM) based on cubic boron ...nitride (PcBN). A coating of the nanolayered structure was applied to cutting inserts made of superhard composites of the BH group by a vacuum-arc method using a Bulat-6 setup. Previous tests, carried out under conditions typical for finishing hardened steel, demonstrated high efficiency of coatings containing Ti, Zr, and Cr nitrides. The (TiAlSiY)N/CrN coating is the most effective. The study of the kinetics of tool wear shows that under test conditions, the wear rate of tools along the flank surface of the wear chamfer
h
z
of tools equipped with modified cutting inserts is significantly reduced by an average of 2.3 times. At the same time, no significant differences in the roughness of surfaces processed by tools with uncoated and coated composites were found under test conditions. The results also indicate that the coating does not decrease the wear rate of the tool equipped with PSHM of group BN when processing materials containing a significant amount of the carbide phase in their structure.
This paper presents a detailed study of the formation of chromium-based alloys, Cr–Ta–W + plasticizing additives (Nb and Zr) and Cr–Ta–Si, during milling of powder mixtures in a Fritsch (P-7) ...planetary mill under an Ar atmosphere. It is shown that, after milling for 18 h, all the components of the starting mixtures convert into a Cr-based BCC solid solution. The powders of chromium alloys obtained in this study are readily compacted by hot isostatic pressing (HIP) under conditions typical of the processing of powders of high-temperature nickel alloys. Heating of the powders and compacts leads to the decomposition of the supersaturated solid solution and the formation of two forms of the Cr
2
M Laves phase with cubic crystal lattices. The formation of a mixed-phase fine microstructure in the chromium alloys after HIP suggests that the materials studied here are potentially attractive as a base of next-generation chromium-based high-temperature alloys.
Multicomponent nanostructured (Ti-Zr-Hf-V-Nb)N coatings produced by the cathodic-arc-vapor-deposition method have been studied using several complementary methods of elemental and structural ...analysis, such as those based on the use of slow positron beam (SPB); proton microbeam (μ-PIXE); electron micro- and nanobeam (EDS and SEM analysis); and X-ray diffraction phase analysis (XRD), including the
a
-sin
2
ϕ method of measuring the stress-strain state (X-ray tensometry). The elemental composition, microstructure, residual stresses in nanograins, and in-depth and surface distributions of defects and atoms, as well as the phase composition, stress-strain state, and texture of the coatings have been studied in a 3D representation. It has been found that creating a state of elastic stress-strain compression in the coating can significantly enhance its resistance to oxidation upon annealing. A redistribution of elements and defects (their aligning and segregation) due to diffusion and termination of spinodal segregation has been revealed near interfaces, around grains and subgrains, which occurred without a significant change in the average size of nanograins.
We report on CrN/MoN multilayer coatings, their structure, elemental and phase composition, residual stresses, mechanical properties and their dependence on deposition conditions. The hardness and ...toughness were considered as main parameters for improvement of the protective properties of coatings. Multilayers with varying bilayer periods, ranging from 40 nm to 2.2 μm, were obtained by using cathodic arc physical vapour deposition (Arc-PVD) on stainless steel substrate. The elemental analysis was performed using wavelength-dispersive X-ray spectroscopy (WDS). The surface morphology and cross-sections were analysed with scanning electron microscopy (SEM). The X-ray diffraction (XRD) measurements, including grazing incidence X-ray diffraction (GIXRD), in-plane diffraction analysis and electron backscatter diffraction (EBSD), were used for microstructure characterisation. Mechanical properties of deposited films were studied by measuring hardness (H) and Young's modulus (E) with micro-indentation, H/E and H3/E2 ratios were calculated. The dependences of internal structure and, hence, mechanical properties, on layer thickness of films have been found. Significant enhancement of hardness and toughness was observed with decreasing individual layer thickness to 20 nm: H = 38–42 GPa, H/E = 0.11.
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•Multilayer CrN/MoN films were obtained by using cathodic arc vapour deposition.•Structure, elemental and phase composition, mechanical properties were studied.•Presence of cubic CrN, γ-Mo2N and metastable MoNx phase was detected.•Crystallite/grain size decreases at lower values of individual layer thickness.•Enhancement of hardness and toughness was observed; wear resistance was improved.
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