Ab initio study of AlCu2M (M = Sc,Ti and Cr) ternary compounds under pressures

The structural, electronic and elastic properties of the AlCu₂M (M = Sc, Ti and Cr) compounds in the pressure range of 0–100 GPa was investigated based on density functional theory. The calculated lattice parameters of the AlCu₂M compounds at zero pressure and zero temperature are in very good agreement with the existing experimental data. The bulk modulus, shear modulus and Young’s modulus increases with the increase of pressure, which indicates that higher materials hardness may be obtained when increasing pressures. The bulk modulus and Young’s modulus of AlCu₂Cr is the greatest under pressure. The shear modulus of AlCu₂Ti is the highest above 30 GPa, while that of the AlCu₂Sc is the strongest below 30 GPa. The calculated B/G values at zero and higher pressure indicated that they are ductile materials. The electronic densities of states and bonding charge densities have been discussed in details, revealing these compounds exhibit half-metallic behavior. In addition, the pressure dependences of Debye temperatures of AlCu₂M compounds have also been calculated. The results indicate that Debye temperatures increase with increasing pressure.     

First-principles investigations on structural,elastic and electronic properties of SnO2 under pressure

We investigate the structural, elastic, and electronic properties of rutile-type SnO₂ by plane-wave pseudopotential density functional theory method. The lattice constants, bulk modulus and its pressure derivative are all calculated. These properties at equilibrium phase are well consistent with the available experimental and theoretical data. Especially, we study the pressure dependence of elastic properties such as the elastic constants, elastic anisotropy, aggregate acoustic velocities and elastic Debye temperature Θ. It is concluded that this structure becomes more ductile with increasing pressure up to 28 GPa. Moreover, our compressional and shear wave velocities V_P = 7.02 km/s and V_S = 3.84 km/s, as well as elastic Debye temperature Θ = 563 K at 0 GPa compare favorably with the experimental values. The pressure dependences of band structures, energy gap and density of states are also investigated.     

High pressure neutron diffraction study of the magnetoresistive 1222-type ruthenocuprate,RuSr2Nd0.9Y0.2Ce0.9Cu2O10

The crystal structure of the 1222-type ruthenocuprate RuSr₂Nd_0.9Y_0.2Ce_0.9Cu₂O₁₀ has been studied by time-of-flight neutron diffraction at temperatures 100–160 K and pressures up to 5 GPa. The structure has tetragonal I4/mmm symmetry throughout (e.g. a = 3.8104(2) Å and c = 28.125(3) Å at 160 K and 5.1 GPa) with no significant distortions observed at the 140 K Ru spin ordering transition. The strongly bonded Cu–O and Ru–O network leads to a bulk modulus of 145 GPa which is high for layered cuprates, with a low anisotropy in the cell compressibility (k_c/k_a = 1.32). The Cu–O–Cu buckling angle and the tilting of the CuO₅ square pyramids decreases with pressure, but the in-plane rotation of the RuO₆ octahedra increases.     

High-rate pulsed reactive magnetron sputtering of oxide nanocomposite coatings

The article reports on the oxide nanocomposite coatings reactively sputtered by a pulsed dual magnetron and is divided into two parts. The first part briefly describes main problems in the reactive sputtering of oxides, i.e. low deposition rate a_D and arcing at the target surface and then focuses on the discharge of the dual magnetron. The ways how a_D can be increased and arcing eliminated are shown. The second part is devoted to transparent oxide coatings. Two types of oxide coatings are described in detail: (1) Si–Zr–O coatings containing ≤5 at.% of Zr and (2) Zr–Al–O coatings with Zr/Al > 1. It is shown that (a) Si–Zr–O coatings exhibit high thermal stability up to 1500 °C, almost 100% optical transparency and can be deposited with very high a_D ≈ 800 nm/min from a molten magnetron target and (b) Zr–Al–O coatings with relatively high hardness H ≈ 18–19 GPa, low effective Young’s modulus E¹ satisfying the ratio H/E¹ > 0.1 are highly elastic (the elastic recovery W_e > 70%) and exhibit an enhanced resistance to cracking. The last finding is of key importance for development of new hard coatings with enhanced toughness.     

Nanocomposite protective coatings based on Ti–N–Cr/Ni–Cr–B–Si–Fe,their structure and properties

The first results of manufacturing and investigations of a new type of nanocomposite protective coatings are presented. They were manufactured using a combination of two technologies: plasma-detonation coating deposition with the help of plasma jets and thin coating vacuum-arc deposition. We investigated structure, morphology, physical and mechanical properties of the coatings of 80–90 μm thickness, as well as defined the hardness, elastic Young modulus and their corrosion resistance in different media. Grain dimensions of the nanocomposite coatings on Ti–N–Cr base varied from 2.8 to 4 nm. The following phases and compounds formed as a result of plasma interaction with the thick coating surface were found in the coatings: Ti–N–Cr (200), (220), γ-Ni₃–Fe, a hexagonal Cr₂–Ti, Fe₃–Ni, (Fe, Ni)N and the following Ti–Ni compounds: Ti₂Ni, Ni₃Ti, Ni₄Ti, etc. We also found that the nanocomposite coating microhardness increased to H = 31.6 ± 1.1 GPa. The Young elastic modulus was determined to be E = 319 ± 27 GPa – it was derived from the loading–unloading curves. The protective coating demonstrated the increased corrosion resistance in acidic and alkaline media in comparison with that of the stainless steel substrate.     

Structural,electronic, elastic and thermodynamic properties of AlSi2RE (RE = La,Ce, Pr and Nd) from first-principle calculations

It is of academic interest to study the ternary intermetallic compounds of the Al–Si–RE system for the development of both structural and functional materials. In this work, the structural, electronic, elastic and thermodynamic properties of the AlSi₂RE (RE = La, Ce, Pr and Nd) compounds was investigated using first-principle calculations based on density functional theory. The calculated structural parameters of AlSi₂RE compounds are consistent with the experimental data. Due to the fact that there is strong Coulomb correlation among the partially filled 4f electron for RE atoms, we present a combination of the GGA and the LSDA + U approaches to investigate the electronic structures of Al₃RE compounds in order to obtain the appropriate results. The elastic constants were determined from a linear fit of the calculated stress–strain function according to Hooke’s law. The bulk modulus B, shear modulus G, Young’s modulus E, and Poisson’s ratio ν of polycrystalline AlSi₂RE compounds were determined using the Voigt–Reuss–Hill (VRH) averaging scheme. The Debye temperature of AlSi₂RE compounds can be obtained from elastic constants. The temperature dependence of the internal energy, free energy, entropy and heat capacity for AlSi₂RE compounds were also calculated by using the quasi-harmonic approximation.     

Effects of Si addition on microstructure and mechanical properties of Mg–8Gd–4Y–Nd–Zr alloy

Effects of Si addition (1.0 wt.%) on microstructure and mechanical properties of Mg–8Gd–4Y–Nd–Zr alloy have been investigated using scanning electron microscopy (SEM) equipped with energy dispersive spectrum (EDS), X-ray diffraction (XRD), hardness measurements and tensile testing. The results indicated that the addition of Si led to the formation of Mg₂Si and (RE + Si)-rich particles, which enhanced the Young’s modulus of the alloy by 7 GPa while decreased the yield strength and ultimate strength by 10 MPa and 31 MPa, respectively. The tensile properties of the Mg–8Gd–4Y–Nd–Zr–Si alloy are as follows: Young’s modulus E = 51 GPa, yield strength σ_0.2 = 347 MPa, ultimate strength σ_b = 392 MPa and elongation δ = 2.7%. The increase in Young’s modulus was attributed to the formation of particles with high Young’s modulus, while the decrease in strength was ascribed to the decrease in volume fraction of metastable β′ precipitates caused by the consumption of rare earth atoms due to the formation of the rare earth containing particles.     

Electroluminescence of Ti- and Ca-doped YAlO3 crystals in the visible region

The electroluminescence (EL) of perovskite-type YAlO₃ single crystal thin slabs doped with Ti and Ca was investigated. The thin slabs were prepared from rod-shaped single crystals grown in a reducing atmosphere by the floating-zone method. Samples of 0.1% Ti-doped YAlO₃, 1% Ti-doped YAlO₃ and 0.1% Ca-doped YAlO₃, on which Au and Al electrodes were deposited, showed green EL when electric fields greater than ± 1 × 10⁶ V/m were applied, with drive frequencies between 0.2 Hz and 1 kHz and a bipolar symmetrical drive waveform. The strongest EL band with narrow widths (FWHM = 3–4 nm) appeared at the same peak wavelength (546 nm) for all three samples. This gives rise to possible uses of Ti- and Ca-doped YAlO₃ crystals in EL devices that emit monochromatic green light.     

In situ synthesized low modulus biomedical Zr-4Cu-xNb alloys

In order to develop new biomaterials for hard tissue replacements, the Zr-4Cu-xNb (x = 0, 0.3, 0.6 and 0.9) biomedical alloys with required properties were designed and prepared using vacuum arc melting method for the first time. Phase analysis and microstructure observation showed that all the as-cast Zr-4Cu-xNb samples consisted of α-Zr and Zr₃Cu. In addition, the lamellar eutectoid is found near the grain boundary. These alloys exhibited moderate compressive strength (1150–1300 MPa), yield stress (750–1000 MPa), favorable plastic strain (19%–27%), high elastic energy (11 MJ/m³–16 MJ/m³) and low Young's modulus (25 GPa–31 GPa). This good combination of mechanical properties indicates them potential biomedical materials for biological hard tissue replacements.     

Investigation of structural,optical and micro-mechanical properties of (NdyTi1 − y)Ox thin films deposited by magnetron sputtering

TiO₂ and (Nd_yTi_1 − y)O_x thin films were deposited by reactive magnetron sputtering process from mosaic Ti–Nd targets and characterised by X-ray diffraction (XRD), Raman optical spectroscopy and nanoindentation technique. XRD measurements revealed that as-prepared titanium dioxide and TiO₂ thin films with 4 and 7 at.% of Nd had nanocrystalline rutile structure, while coatings with larger amount of Nd were amorphous. Raman spectroscopy investigations showed that the increase of the neodymium concentration caused amorphisation of the coatings and hindered their crystal growth. All as-prepared coatings were transparent in the visible wavelength range with a transmittance of approximately 80%. The refractive index and extinction coefficient of the thin films gradually decreased with the increase of the neodymium concentration. Micro-mechanical properties, i.e. hardness and elastic modulus, were determined using traditional load-controlled nanoindentation testing and continuous stiffness measurements. The highest hardness and elastic modulus values were obtained for thin films with 7 at.% of Nd and were approximately 14.8 GPa and 166.3 GPa, respectively.     

Boron-alloyed Fe–Cr–C–B tool steels — Thermodynamic calculations and experimental validation

This study focuses on the development of boron-alloyed tool steels. The influence of Cr additions from 0 to 10 mass% on microstructural changes were investigated for a constant metalloid content (C + B = 2.4 mass%). In the first step, thermodynamic calculations were performed to map the quaternary Fe–Cr–C–B system. In the second step, thermodynamic calculations were validated with laboratory melts that were investigated with respect to the microstructure and phase composition. The results of thermodynamic calculations correspond to real material behavior of Fe–Cr–C–B alloys. Furthermore, the influence of chromium on hard phase formation was investigated by means of phase analysis methods, X-ray diffraction (XRD), and energy dispersive spectrometry (EDS). Nanoindentation was used to determine hard phase properties (hardness, Young's modulus). It was shown that chromium promotes the formation of M₂B-type borides. An increase in the Cr content within the M₂B phase led to a transformation from the tetragonal structure into an orthorhombic structure. This transformation is accompanied by an increase in hardness and in the Young's modulus. In contrast, Cr also promotes the formation of Cr-rich carboborides of type M₂₃(C,B)₆. However, an increased Cr content within the M₂₃(C,B)₆ phase is not associated with an increase in hardness or elastic modulus.     

Stoichiometric and non-stoichiometric films in the Si–O–N system: mechanical,electrical, and dielectric properties

A novel low-temperature (600–850 °C), chemical vapor deposition method, involving a simple reaction between disiloxane (H₃Si–O–SiH₃) and ammonia (NH₃), is described to deposit stoichiometric, Si₂N₂O, and non-stoichiometric, SiO_xN_y, silicon oxynitride films (5–500 nm) on Si substrates. Note, the gaseous reactants are free from carbon and other undesirable contaminants. The deposition of Si₂N₂O on Si (with (1 0 0) orientation and a native oxide layer of 1 nm) was conducted at a pressure of 2 Torr and at extremely high rates of 20–30 nm min⁻¹ with complete hydrogen elimination. The deposition rate of SiO_xN_y on highly-doped Si (with (1 1 1) orientation but without native oxide) at 10⁻⁶ Torr was ∼1.5 nm min⁻¹, and achieved via the reaction of disiloxane with N atoms, generated by an RF source in an MBE chamber. The phase, composition and structure of the oxynitride films were characterized by a variety of analytical techniques. The hardness of Si₂N₂O, and the capacitance–voltage (C–V) as a function of frequency and leakage current density–voltage (J_L–V) characteristics were determined on MOS (Al/Si₂N₂O/SiO/p-Si) structures. The hardness, frequency-dispersionless dielectric permittivity (K), and J_L at 6 V for a 20 nm Si₂N₂O film were determined to be 18 GPa, 6 and 0.05–0.1 nA cm⁻², respectively.     

Nanoscale characterization of natural fibers and their composites using contact-resonance force microscopy

Contact-resonance force microscopy (CR-FM) has been used for the first time to evaluate the mechanical properties of the interphase in natural fiber-reinforced composites and of cell wall layers of natural fibers. With CR-FM, quantitative images of the spatial distribution in nanoscale elastic properties were acquired. The images were calibrated with nanoindentation values. From the modulus images, the average interphase width was found to be (49 ± 5) nm for composite without any treatment, and (139 ± 21) nm for one with a maleic anhydride polypropylene treatment. There was a gradient of modulus across the interphase that ranged between the values of fiber and the polymer. The average values of indentation modulus obtained for different cell wall layers within a fiber were 22.5–28.0 GPa, 17.9–20.2 GPa, and 15.0–15.5 GPa for the S₂ and S₁ layers and the compound middle lamellae, respectively.     

FP-LAPW study of the structural,elastic and thermodynamic properties of spinel oxides ZnX2O4 (X = Al,Ga, In)

We have performed density functional self-consistent calculations based on the full-potential augmented plane wave plus local orbital method with the local density approximation to investigate the structural, elastic and thermal properties of three spinel oxides: ZnAl₂O₄, ZnGa₂O₄ and ZnIn₂O₄. The computed ground state structural parameters, i.e. lattice constant, free internal parameter, bulk modulus and its pressure derivative, are in good agreement with the available theoretical an experimental works. Single and polycrystalline elastic parameters and their pressure dependence are calculated and compared with the previous theoretical results. Thermal and pressure effects on some macroscopic properties of ZnAl₂O₄, ZnGa₂O₄ and ZnIn₂O₄ are predicted using the quasi-harmonic Debye model in which the lattice vibrations are taken into account. We have computed the variations of the lattice constant, bulk modulus, volume expansion coefficient, heat capacities and Debye temperature with pressure and temperature in the ranges of 0–30 GPa and 0–1600 K.     

Mechanical properties of a medical β-type titanium alloy with specific microstructural evolution through high-pressure torsion

The effect of high-pressure torsion (HPT) processing on the microstructure and mechanical biocompatibility includes Young's modulus, tensile strength, ductility, fatigue life, fretting fatigue, wear properties and other functionalities such as super elasticity and shape memory effect, etc. at levels suitable for structural biomaterials used in implants that replace hard tissue in the broad sense (Sumitomo et al., 2008 [4]). In particular, in this study, the mechanical biocompatibility implies a combination of great hardness and high strength with an adequate ductility while keeping low Young's modulus of a novel Ti–29Nb–13Ta–4.6Zr (TNTZ) for biomedical applications at rotation numbers (N) ranging from 1 to 60 under a pressure of 1.25 GPa at room temperature was systematically investigated in order to increase its mechanical strength with maintaining low Young's modulus and an adequate ductility.TNTZ subjected to HPT processing (TNTZ_HPT) at low N exhibits a heterogeneous microstructure in micro-scale and nano-scale consisting of a matrix and a non-etched band, which has nanosized equiaxed and elongated single β grains, along its cross section. The grains exhibit high dislocation densities, consequently non-equilibrium grain boundaries, and non-uniform subgrains distorted by severe deformation. At high N which is N > 20, TNTZ_HPT has a more homogeneous microstructure in nano-scale with increasing equivalent strain, ε_eq. Therefore, TNTZ_HPT at high N exhibits a more homogenous hardness distribution. The tensile strength and 0.2% proof stress of TNTZ_HPT increase significantly with N over the range of 0 ≤ N ≤ 5, and then become saturated at around 1100 MPa and 800 MPa at N ≥ 10. However, the ductility of TNTZ_HPT shows a reverse trend and a low-level elongation, at around 7%. And, Young's modulus of TNTZ_HPT decreases slightly to 60 GPa with increasing N and then becomes saturated at N ≥ 10. These obtained results confirm that the mechanical strength of TNTZ can be improved while maintaining a low Young's modulus in single β grain structures through severe plastic deformation.     

First-principles calculations of the structural and elastic properties of OsSi2 at high pressure

We investigated the pressure dependence of the structural and elastic properties of OsSi₂ in the range 0–60 GPa using first-principles calculations based on density functional theory. Calculations were performed within the local density approximation as well as the generalized gradient approximation to the exchange correlation potential. The calculated lattice constants and atomic fractional coordinates are in good agreement with previous experimental results. The pressure dependence of nine independent elastic constants, c₁₁, c₂₂, c₃₃, c₄₄, c₅₅, c₆₆, c₁₂, c₁₃, and c₂₃, of orthorhombic OsSi₂ has been evaluated. The isotropic bulk modulus, shear modulus, Young’s modulus, Poisson’s ratio, elastic anisotropy, and Debye temperature of polycrystalline OsSi₂ under pressure are also presented.     

The effects of loading conditions and specimen environment on the nanomechanical response of canine cortical bone

Bone is a viscoelastic connective tissue composed primarily of mineral and type I collagen, which interacts with water, affecting its mechanical properties. Therefore, both the level of hydration and the loading rate are expected to influence the measured nanomechanical response of bone. In this study, we investigated the influence of three distinct hydration conditions, peak loads and loading/unloading rates on the elastic modulus and hardness of canine femoral cortical bone via nanoindentation. Sections from three canine femurs from multiple regions of the diaphysis were tested for a total of 670 indentations. All three hydration conditions (dry, moist and fully hydrated tissue) were tested at three different loading profiles (a triangular loading profile with peak loads of 600, 800 and 1000 μN at loading/unloading rate of 60, 80 and 100 μN/s, respectively; each test was 20 s in duration). Significant differences were found for both the elastic modulus and hardness between the dry, moist and fully hydrated conditions (p ≤ 0.02). For dry bone, elastic modulus and hardness values were not found to be significantly different between the different loading profiles (p > 0.05). However, in both the moist and fully hydrated conditions, the elastic modulus and hardness were significantly different under all loading profiles (with the exception of the moist condition at the 600- and 800-μN peak load). Given these findings, it is critical to perform nanoindentation of bone under fully hydrated conditions to ensure physiologically relevant results. Furthermore, this work found that a 20-s triangular loading/unloading profile was sufficient to capture the viscoelastic behavior of bone in the 600- to 1000-μN peak load range. Lastly, specific peak load values and loading rates need to be selected based on the structural region for which the mechanical properties are to be measured.     

Experimental and micro-mechanical analysis of the mechanical and transport properties of mortar containing heat-induced micro-cracks

This paper focuses on the effect of micro-cracks induced by a slow heating/cooling process (also called heat-treatment) in a mortar, upon its poro-elastic properties under drained hydrostatic compression, and upon its intrinsic permeability. Prior to the experiments, mortar samples are subjected to a slow heating-cooling cycle up to one temperature T = 105, 200, 300 and 400 °C. The reference state of mortar is taken after drying at 60 °C until constant mass. Experimental results show that the effective drained bulk modulus K_b of mortar decreases significantly with heat-treatment temperature T. A transition from elastic to plastic behavior with increasing heat-treatment temperature T is also observed. These effects are mainly attributed to heating-induced micro-cracks, and, to a lesser extent, to the increase in connected porosity. We also measure a significant increase in permeability.Based on these experimental evidences, a micro-mechanical analysis is proposed, which describes micro-cracks as independent 3D penny-shaped cracks of varying aspect ratio α. A relationship between the degradation of bulk modulus and heating-induced micro-cracks is established. The distribution of aspect ratio of micro-crack porosity is determined for each heat-treatment temperature. The correlation between heating-induced crack porosity (or with crack aspect ratio) and permeability is also determined. Finally, a phenomenological law is proposed to describe the increase in plastic deformation with T. Good correlation with experimental stress–strain curves is found.     

Effect of plasma CVD operating temperature on nanomechanical properties of TiC nanostructured coating investigated by atomic force microscopy

The structure, composition, and mechanical properties of nanostructured titanium carbide (TiC) coatings deposited on H₁₁ hot-working tool steel by pulsed-DC plasma assisted chemical vapor deposition at three different temperatures are investigated. Nanoindentation and nanoscratch tests are carried out by atomic force microscopy to determine the mechanical properties such as hardness, elastic modulus, surface roughness, and friction coefficient. The nanostructured TiC coatings prepared at 490 °C exhibit lower friction coefficient (0.23) than the ones deposited at 470 and 510 °C. Increasing the deposition temperature reduces the Young's modulus and hardness. The overall superior mechanical properties such as higher hardness and lower friction coefficient render the coatings deposited at 490 °C suitable for wear resistant applications.     

Dependence of pressure on elastic,electronic and optical properties of CeO2 and ThO2: A first principles study

The phase transformation of CeO₂ and ThO₂ from fluorite to cotunnite-type structure under pressure is predicted within the density functional theory implemented with the GGA-PW91 method, the pressure induced structural phase transition occurs at 28.9 GPa for CeO₂ and 29.8 GPa for ThO₂. These values are in excellent agreement with the experimentally measured data. The elastic, electronic and optical properties at normal as well as for high-pressure phase have been calculated, particular attention is devoted to the cotunnite phase. Further, the dependence of the elastic constants, the bulk modulus B, the energy band gaps and the dielectric function on the applied pressure are presented.