Behaviour of Di-Transition-Metal Nitride Ti 1-x

By means of density-functional theory with the generalized gradient approximation and using the virtual-crystal approximation, we report first-principles calculation results on the structural and elastic properties of $Ti_{1-x}Zr_{x}N$ alloy. In order to gain some further information on the mechanical properties of $Ti_{0.5}Zr_{0.5}N$ compound, we also calculated the Young modulus, Poisson ratio, and anisotropy factor. The variation of calculated unit cell parameter for $Ti_{1-x}Zr_{x}N$ structure increases with Zr content x. A linear dependence of the elastic constants and the bulk modulus over a range of composition x is found. All the $C_{ij}$ of $Ti_{0.5}Zr_{0.5}N$ increase linearly with increasing pressure. The same behaviour is observed for the other compounds with Zr compositions x

Behaviour of Di-Transition-Metal Nitride Ti1−xZrxNTi_{1-x}Zr_{x}N Alloy at High Pressure

By means of density-functional theory with the generalized gradient approximation and using the virtual-crystal approximation, we report first-principles calculation results on the structural and elastic properties of $Ti_{1-x}Zr_{x}N$ alloy. In order to gain some further information on the mechanical properties of $Ti_{0.5}Zr_{0.5}N$ compound, we also calculated the Young modulus, Poisson ratio, and anisotropy factor. The variation of calculated unit cell parameter for $Ti_{1-x}Zr_{x}N$ structure increases with Zr content x. A linear dependence of the elastic constants and the bulk modulus over a range of composition x is found. All the $C_{ij}$ of $Ti_{0.5}Zr_{0.5}N$ increase linearly with increasing pressure. The same behaviour is observed for the other compounds with Zr compositions x

Density functional prediction of the structural, elastic, electronic, and thermodynamic properties of the cubic and hexagonal (c, h)-Fe2Hf

Using density functional theory (DFT), the structural, elastic, electronic, and thermodynamic properties of Fe2Hf in the cubic and hexagonal solid phases with Fd-3m and P63/mmc are reported with generalized gradient approximations (GGA). To achieve energy convergence, we report the k-point mesh density and plane-wave energy cut-offs. The calculated equilibrium parameters are in good agreement with the available theoretical data. A complete elastic tensor and crystal anisotropies of the ultra-incompressible Fe2Hf are determined in the wide pressure range. Finally, by using the quasi-harmonic Debye Model, the isothermal and adiabatic bulk modulus and heat capacity of Fe2Hf are also successfully obtained in the present work. By the elastic stability criteria, it is predicted that Fd-3m and P63/mmc structures of Fe2Hf are stable in the pressure range studied, respectively

Structural, elastic, thermoelastic and electronic properties of M2O3 (M = Cr, Fe, Al) compounds: Experimental and theoretical study

We derived the chemical compositions and the micro hardness of the two studied steels Fe20Mn5Cr and Fe9S28Mn. The contamination of these two compounds by oxygen gives the series M2O3 (M = Fe, Cr, Al). Rhombohedral crystal structure of these compounds was determined by means of the X-rays diffraction. First principles calculations were performed to investigate structural, elastic and mechanical properties of M2O3 (M = Fe, Cr, Al) compounds at equilibrium pressure. Fe2O3 and Cr2O3 are classified as ductile materials, while Al2O3 is brittle. The Debye temperature, the elastic wave velocities and the integration of elastic wave velocities in various directions of the single crystal were obtained. All these compounds are elastically and chemically stable. The calculated elastic constants are in good agreement with the experiment values in the approximation of the gradient generalized for the correlation and exchange potential. We calculated the partial and total densities of states PDOD and TDOS for M2O3 (M = Fe, Cr, Al) compounds. As a result, electronic bands, DOS at the Fermi level, were obtained for the first time especially for Fe2O3 and Cr2O3. Keywords: Band structure, Bulk moduli, Electronic propertie

Structural stability and electronic properties of M

Using a Plane-Wave Pseudo-Potential (PWPP) method, total energy and band structure calculations for M2TaN3, ε-TaN and MTa2N3 (M = a transition metal, TM) compounds have been performed in order to understand their structural stability and electronic properties. To do that, we first focus on ε-TaN compounds. The exchange correlation is treated using the Generalized Gradient Approximation (GGA). The Virtual Crystal Approximation (VCA) is then used to examine the structural stability when substituting Ti, Zr or Hf to a Ta atom either in a cell corner [c(M)(Ta2N3)] or inside the cell [in(M2)(TaN3)]. Actually, substitution of Ta by a Ti, Zr or Hf atom at a corner site does slightly change the corresponding lattice constant. Also we calculate ground-state quantities such as elastic constants, shear moduli, Young’s modulus and bulk modulus as well as Poisson’s ratio. The corresponding results for band structures and densities of states are shown as well. As far as we know our work is a pioneer attempt to determine elastic, mechanic and electronic properties for M2TaN3 and MTa2N3 (M = TM) compounds

Heat treatment and kinetics of precipitation of β-Mg17Al12 phase in AZ91 alloy

This study investigated the effect of aging on the precipitation and kinetics of second phase Mg17Al12 in AZ91 magnesium alloy (Mg-9 wt% Al-1 wt% Zn), using X-ray diffraction, microhardness measurements and differential scanning calorimetric analysis (DSC). With the last instrument, the all samples were heated from room temperature to 400 °C, at heating rates of 10–30 °C/min. The results were supplemented by measuring the average of activation energies, using isothermal treatments by Johnson–Mehl–Avrami (JMA) methods and by non-isothermal treatments using Ozawa, Boswell, Kissinger, Mahadevan, Augis and Bennett methods, were around 67.18 and 62.02 kJ/mol. The frequency factor k0 calculated by the isothermal treatment is equal to 1.24 109 s−1. In non-isothermal treatment, the numerical factor m and the Avrami parameter n is estimated to be approximately equal to 3 and 2.79 respectively. This value corresponding that the bulk nucleation with a constant number of nuclei was dominant in three-dimensional (polyhedron) controlled by interface reaction. Keywords: AZ91, DSC, Mg17Al12, Precipitation, Activation energ

Prediction study of structural, elastic and electronic properties of FeMP (M = Ti, Zr, Hf) compounds

First principles calculations are applied in the study of FeMP (M = Ti, Zr, Hf) compounds. We investigate the structural, elastic, mechanical and electronic properties by combining first-principles calculations with the CASTEP approach. For ideal polycrystalline FeMP (M = Ti, Zr, Hf) the shear modulus, Young’s modulus, Poisson’s ratio, elastic anisotropy indexes, Pugh’s criterion, elastic wave velocities and Debye temperature are also calculated from the single crystal elastic constants. The shear anisotropic factors and anisotropy are obtained from the single crystal elastic constants. The Debye temperature is calculated from the average elastic wave velocity obtained from shear and bulk modulus as well as the integration of elastic wave velocities in different directions of the single crystal. Keywords: FeTP, FeHfP, Electronic band structure, Bulk modul