The thermodynamic stability and mechanical properties of Mo–B and W–B binary compounds are investigated by first principles calculations and compared with other theoretical and experimental results. In order to determine the stability, compressive behavior and mechanical properties of Mo2B5 and W2B5 phases, hydrostatic pressure up to 10 GPa is applied to the crystal. The formation enthalpy, phonon spectrum, electronic structure and mechanical modulus at different pressure are obtained and variety of chemical bonding behavior has close relationship with the change of elastic properties. Temperature-dependent thermodynamics parameters of Mo2B5 and W2B5 are analyzed under different pressure. Moreover, the whole profile of temperature dependent lattice thermal conductivity of Mo2B5 and W2B5 from Debye temperature up to high temperature limit at different pressure is predicted by combining the Slack׳s, Clarke׳s and Cahill׳s model. The difference between the variation of lattice thermal conductivity of Mo2B5 along [001] and [100] directions is attributed to the anisotropic chemical bonding behavior of B–B bonds and M–B bonds under pressure effect.

The interaction of point defects (interstitial atoms and vacancy) in both BCC Fe and FCC Fe lattices were investigated by first-principles calculations. The goals were to find the equilibrium separation of two interstitial atoms in the iron lattice and to establish the maximum trapping capacity of a mono-vacancy in the iron lattice. Based on our study, the equilibrium separation values of C–C, B–B and C–B were about 5.31 Å in the BCC Fe lattice. In the FCC Fe lattice, the equilibrium separation of C–C, B–B and C–B was about 6.42 Å. A mono-vacancy is shown to be capable of steady trapping as many as 3 atoms to form VXn (X = C/B, n = 0, 1, 2, and 3) and VCB, VC2B and VCB2 complexes in the BCC Fe lattice. For the FCC Fe lattice, it is energetically favorable for a mono-vacancy to accommodate 2 C atoms, 3 B atoms, 2 C atoms and 1 B atoms, 1 C atoms and 2 B atoms, and 1 C atoms and 3 B atoms to form VC2, VB3, VC2B, VCB2 and VCB3 clusters, respectively. However, when four interstitial atoms are in the same plane and occupy the nearest interstitial sites around the vacancy, they can also form VC4, VB4, VC2B2 and VCB3 in the BCC Fe lattice and VB4 and VC2B2 in the FCC Fe lattice. Moreover, we also found that the trapping ability of a vacancy is stronger in BCC Fe than in FCC Fe. These results are in good agreement with the available calculations and experiments results.

The purpose of this work was to investigate the elevated temperature sliding wear of a promising high-boron medium-carbon alloy (HBMCA), and to determine whether the material had equal or better tribological behavior relative to alloys that were more expensive to produce. Based on its physical metallurgy, the HBMCA was quenched at either 950 or 1050 °C and then tempered at 500 °C. Data from three-pin-on-disk sliding wear tests were compared with that for a typical high speed steel (HSS) and a high chromium cast iron (Cr25). Results showed that the wear resistance of the HBMCA quenched at 950 °C was more than twice that of HSS, and better than that of Cr25. However, it was lower than that of HSS when quenched at higher temperature owing to the decrease of the borocarbide volume fraction, and more elemental B being dissolved in the matrix at high temperature. The wear mechanism of HBMCA at high temperature included oxidation, abrasive, and adhesive wear. When the quenching temperature was increased, adhesive wear also tended to increase, presumably due to greater precipitation of the carbide M23(B, C)6.

In order to improve the toughness and wear resistance of high-boron medium-carbon alloy (HBMCA), a novel wear-resistant HBMCA comprising granular borocarbide was obtained by titanium, magnesium, and rare earth modifications. These modifications gave rise to greatly refined as-cast eutectic borocarbide structures and a less interconnected continuous borocarbide network. Heat treatment mostly produced broken and spheriodized borocarbides that tended to exist as isolated particles in modified HBMCA. The heat treated modified HBMCA exhibited enhanced hardness than pristine and impact toughness was improved significantly to 12.5 J/cm2. In addition, it displayed 2.39 and 1.7 times greater wear resistance than high-speed steel (HSS) and high nickel-chromium alloy steel (Cr25) at high temperature (500 °C), respectively. Here, the modification mechanisms involving Re2O3, TiN, and MgO/MgS heterogeneous nuclei were discussed.

The equilibrium crystal structures, stability, elastic properties, hardness and electronic structures of Fe–P binary compounds (Fe3P, Fe2P, o-FeP-1, o-FeP-2, FeP2, m-FeP4-1, o-FeP4, m-FeP4-2) are investigated systematically by first principles calculations. The calculated formation enthalpy is used to estimate the stability of the Fe–P binary compounds. Fe3P has the largest formation enthalpy at −44.950 kJ mol−1 and o-FeP-2 has the smallest at −78.590 kJ mol−1. The elastic constants are calculated by the stress–strain method and the Voigt–Reuss–Hill approximation is used to estimate the elastic moduli. The mechanical anisotropy of FexPy compounds are studied using the anisotropic indexes and by plotting the 3D surface contour of Young’s modulus. The electronic structures and chemical bonding characteristics of the Fe–P binary compounds are interpreted by the band structures and density of states. Finally, the sound velocity and Debye temperatures of the Fe–P binary compounds are discussed.

Transition metal carbides have unique physical and chemical properties and been widely used in engineering parts that need to work under high temperatures and pressures. o-Mo2C, h-Mo2C and t-Mo2C are three critical molybdenum carbides polymorphs while remaining are largely unknown in their mechanical anisotropy, hardness and thermal properties. In this work, we investigated systematically the mechanical and thermodynamic properties of these three candidate carbides using first principles calculations based on density functional theory. Our results showed that the bonds in these compounds were mainly of metallic and covalent type. The Gibbs free energy analysis showed thermodynamically stable structures for all the three carbides. Their shear moduli were estimated to range from 149.1 to 153.4 GPa and hardnesses were expected to be less than 20 GPa. Young׳s moduli were analyzed to have more anisotropic features than bulk modulus for all the three compounds. In addition, heat capacities were calculated to predominate by phonon excitations at high temperature but electron excitations at low temperatures near 0 K.

•The anisotropy of shear and Young’s modulus of Fe6W6C are illustrated firstly.•The mechanical properties of Fe6W6C are calculated within different functional.•New method is applied to obtain 3D representation of the anisotropic thermal conductivity.•We find Fe6W6C is a kind of low thermal conductivity ceramic.The optimized structure, chemical bonding characteristics, elastic and thermal properties of Fe6W6C are investigated by the first principle calculations with and without dispersion-corrected methods combined with the quasi-harmonic approximation. The bonding behaviors of Fe6W6C are discussed by the density of states and Mulliken population analysis. Anisotropy of shear and Young’s moduli are characterized by three-dimensional surface contours and the planar projections on different planes. Anisotropy of the minimum thermal conductivity of Fe6W6C is discussed based on Cahill’s model and Clarke’s model and the values are 1.38 and 1.26 W m−1 K−1 predicted by these two models. Moreover, the 3D representation of the anisotropic thermal conductivity of Fe6W6C is obtained based on the Clarke’s model and anisotropic Young’s modulus.

•The stability, electronic properties and elastic constants of M2N (M=Cr, V, Nb, and Ta) compounds have been researched carefully.•The electronic structure indicates M2N compounds have the characteristic of covalent and metallic bonds.•The anisotropy in Young's modulus of M2N compounds have been investigated.Starting from theoretical calculations based on the generalized gradient approximation (GGA), we compute the lattice parameters, cohesive energy and formation enthalpy of trigonal-type M2N (M=Cr, V, Nb and Ta) compounds by first principles. The cohesive energy and formation enthalpy of these compounds show that these compounds are thermodynamically stable. The electronic structure indicates that the bonds of M2N (M=Cr, V, Nb and Ta) have the characteristic of covalent and metallic bonds, and then Ta2N is the most stable in the projected metal nitrides in our work. The values of bulk modulus, shear modulus, Young's modulus and Poisson's ratio indicate M2N compounds are brittle and metallic character. The figures of anisotropy in Young's modulus of M2N (M=Cr, V, Nb and Ta) compounds investigate that these nitrides have the strong anisotropy character in Young's modulus at the (100) plane.

Microstructure of the matrix directly influences the performance and the application of metal matrix composites. By using vacuum casting-infiltration method to manufacture casting tungsten carbide particle reinforced composite, the addition of Ni can alter the microstructure of the matrix of composite. High carbon chromium steel was chosen as the substrate. The casting process was achieved at 1580 °C with vacuum degree of 0.072–0.078 MPa. Padding of the molten steel in each part of the preform was different, and the solidification of each part of the composite was different, too. Microstructure of the matrix was various in different parts of the composite. The Ni addition had enlarged the austenite zone in matrix, which would improve the corrosion resistance of the composite. The phase identification of the composite was performed by X-ray diffraction technique. The result showed that Fe3W3C was the primary precipitated carbide and its composition had a direct link with the decomposition of the casting tungsten carbide particles. The hardness of the matrix mainly depended on the reinforced carbide, i.e. Fe3W3C.

Using the first-principles calculations, the elastic properties, anisotropy properties, electronic structures, Debye temperature and stability of Fe-Al (Fe3Al, FeAl, FeAl2, Fe2Al5 and FeAl3) binary compounds were calculated. The formation enthalpy and cohesive energy of these Fe-Al compounds are negative, and show they are thermodynamically stable structures. Fe2Al5 has the lowest formation enthalpy, which shows the Fe2Al5 is the most stable of Fe-Al binary compounds. These Fe-Al compounds display disparate anisotropy due to the calculated different shape of the 3D curved surface of the Young’s modulus and anisotropic index. Fe3Al has the biggest bulk modulus with the value 233.2 GPa. FeAl has the biggest Yong’s modulus and shear modulus with the value 296.2 GPa and 119.8 GPa, respectively. The partial density of states, total density of states and electron density distribution maps of the binary Fe-Al binary compounds are analyzed. The bonding characteristics of these Fe-Al binary compounds are mainly combination by covalent bond and metallic bonds. Meanwhile, also exist anti-bond effect. Moreover, the Debye temperatures and sound velocity of these Fe-Al compounds are explored.