ABSTRACTJanus transition metal dichalcogenides (TMDCs) type two-dimensional materials have been widely studied because of their unique asymmetrical structures and properties. In the preparation of Janus TMDCs, replacing the top layer S atoms of MoS2 with H atoms could yield unique Janus MoSH, which has been scarcely reported. In this work, the electronic, mechanical and piezoelectric properties of Janus MoSH are systematically studied using first principles calculations for the first time. The band structure of Janus MoSH is of metallic nature with two bands crossing the Fermi level. This material has a stable structure, and the Poison ratio ν > 1/3 indicates the good ductility. The relatively higher piezoelectric coefficients, e11 of −4.27 × 10−10 C/m and d11 of −5.09 pm/V for Janus MoSH, compared with the typical piezoelectric semiconductor materials MoS2 (3.64 × 10−10 C/m and 3.73 pm/V, respectively) may reflect suitable piezoelectric effect in the former. The above calculations may show that Janus MoSH would be potentially adopted as efficient sensors and piezoelectric components.

ABSTRACTA methodical study of the thermal properties of a hydrogen molecular ion strongly confined in a flat semiconductor quantum ring under external probes: intense laser-field radiation and static electric fields were carried out. The corresponding Schrödinger equation for these two coupled donors system was numerically solved by using the finite element method within the effective mass approximation. The effects of the donor angular and radial positions on the entropy, heat capacity and internal energy were analysed. Results show that the entropy of the system is maintained low as long as the molecule preserves its integrity but if the molecule is fragmented, the randomness of the system is substantially increased. Nevertheless, applying an intense laser or an external electric field can reduce this property in real time.

ABSTRACTWe present the numerical results obtained by the two-dimensional diagonalisation method concerning the anisotropy and internuclear distance dependence of the electronic structure, total energy and diamagnetic susceptibility of an artificial hydrogen molecule ion confined in the quantum dot (QD). We have demonstrated the existence of the tunability of the diamagnetic susceptibility and energy levels of the D2+ complex by adjusting the QD size, distance between the impurity atoms and the anisotropy of the QD. Consequently, results reveal that a precise tuning of the electronic states and diamagnetic susceptibility of the system can be achieved by proper control of the anisotropy.

ABSTRACTThe present work is aimed at examining the effect of solid solution on the development of recrystallization microstructure and texture in FCC materials where SFE remains unchanged on alloying addition. To elucidate the mechanisms of texture formation during recrystallization, pure Ni and Ni-Fe (20 and 40 wt.% Fe) alloys were investigated. After recrystallization, pure Ni showed a cube and a non-uniform α-fibre texture, whereas the Ni-Fe alloys showed a texture characterised by the rotated cube component, brass recrystallization (BR) orientation, and a non-uniform α-fibre. Addition of Fe to pure Ni has led to some fine differences in the recrystallization texture that have been attributed to the role of highly heterogeneous deformed microstructure in the Ni-Fe system because of alloying. However, in all the cases Cu-oriented grains are prone to early recrystallization due to relatively more heterogeneously deformed regions, whereas deformed grains having orientation || ND have shown slow recrystallization. In all cases, the entire stage of recrystallization is dominated by the formation of annealing twin (Σ3) boundary. The mobility of these twin boundaries plays an important role in the evolution of the recrystallization texture, which in turn, depends on its coherency, i.e. grain boundary plane (K1) of twin boundaries. The mechanism of evolution of recrystallization texture and the role of different deformation features during recrystallization is investigated. The cellular automata simulation technique was used to simulate the recrystallization behaviour of the alloys. The simulation results were used to discuss experimental observations.

ABSTRACTThe effect of In-doping on the quantum information entropy of the hydrogenic impurity states in the InxGa1-xN quantum dot has been studied for the first time. By exploring the Shannon entropy in the position space (Sr), in the momentum-space (Sp) and the Shannon entropy sum St, we find some novel and interesting phenomenon. First, although Sr increases and Sp decreases monotonically with the radius of InxGa1-xN quantum dot, the Shannon entropy sum St exhibits a series of peaks and valleys with the confinement radius. The physical origin of the minimum and maximum values in the Shannon entropy sum St is analysed in great detail. Second, the BBM entropy uncertainty principle (St≥3[1+ln⁡(π)]) holds for the hydrogenic impurity state in the semiconductor quantum dot, which can be used to replace the Heisenberg uncertainty principle in the quantum mechanics. Third, the content of the doping In element in the InxGa1-xN quantum dot has a great influence on the Shannon entropy of the hydrogenic impurity state. Since the Shannon entropy sum St is usually used to measure the position-momentum correlation, therefore, we can explore the uncertainty of position and momentum of the hydrogenic impurity states by changing the content of the doping element in the semiconductor quantum dots. This study has some practical applications in semiconductor material and quantum information measurement, and may guide future experimental researches for the localisation and delocalisation characteristics of hydrogenic impurities states in the semiconductor quantum dots.

ABSTRACTMolecular dynamics simulations are performed to explore nanoindentation characteristics of tungsten, and the influences of grain size, indenter velocity, indenter size, and temperature are discussed. The results illustrate that the hardness reduces as the grain size (5.00 ∼ 24.62 nm) decreases. There is no phase change observed during the whole deformation process. For monocrystalline W, the dislocation nucleation and propagation dominate the deformation mechanisms. Differently, the primary deformation mode of nanocrystalline W is the grain split and motion of GBs. Dislocations primarily nucleate below the contact surface of the indenter and substrate and then glide in the grain core. The monocrystalline W has better pattern-forming ability than nanocrystalline. Besides, the pattern-forming ability of nanocrystalline W is negatively correlated with the average grain size (5.00 ∼ 24.62 nm). The von Mises stress is mainly concentrated in the interface between the indenter and substrate, the dislocation area for monocrystalline, and grain boundaries for nanocrystalline. The indentation force and hardness are positively correlated with indenter radius size (30 ∼ 80 Å), negatively correlated with temperature (10 ∼ 1500 K), and insensitive to the indenter velocity when velocity is lower than 3.0 Å /ps (300 m/s).

ABSTRACTAlthough TiAl3 is widely used in various high-temperature fields, the adjustment of the balance between the strength and ductility of the tetragonal TiAl3 remains a challenge. To solve the key problem, here, we apply the first-principles method to study the influence of four transition metals (TM = V, Cr and Mo) on the mechanical properties of the tetragonal TiAl3. The structural stability of the TM-alloyed TiAl3 is examined by the impurity formation energy and phonon dispersion. The calculated results show that the TM-doped TiAl3 is stable at the ground state. In particular, the Mo-alloyed TiAl3 has better thermodynamic stability than the other TM-alloyed TiAl3. Importantly, the alloyed elements enhance the bulk modulus of TiAl3 because the alloyed elements improve the electronic hybridisation between the Ti atom and the Al atom. Here, the Mo-alloyed TiAl3 has the highest bulk modulus among the four TM-alloyed TiAl3. Furthermore, it is found that the alloyed elements improve the ductility of TiAl3.

ABSTRACTHalf-Heusler compounds have excellent power generation performance at high temperatures. The scattering mechanism is an essential factor affecting the electrical transport properties of thermoelectric materials. In computational simulations, only the role of acoustic phonon scattering on the thermoelectric properties of materials is considered, whereas other scattering mechanisms are neglected. In this work, we investigate the thermoelectric properties of NbCoGe compounds with different combinations of acoustic deformation potential, polar optical phonon, and ionised impurity scattering mechanisms. The calculated results show that the ZT values of n-type and p-type NbCoGe compounds reach 8 and 2.8, respectively, when only acoustic deformation potential scattering is considered, indicating that this sole scattering is insufficient. The calculated ZT values of p-type NbCoGe compounds reach 1.8 at 1200 K and more than 1 at 800 K for p- and n-type NbCoGe compounds under the combined effect of the three scattering mechanisms due to their high–power factor. This provides solid theoretical guidance for the search for potentially high–temperature half-Heusler thermoelectric materials.

ABSTRACTCu-W70-90 (wt.%) alloys were prepared by infiltration method, and the laser ablation experiments were conducted. The laser ablation resistance mechanism of Cu-W alloy was revealed with the guidance of the mathematic model coupling heat and fluid flow. By comprehensively analysing the calculation and the experimental results, the laser spot generated giant heat which will vaporise and melt the alloy respectively close to and away from the centre of the laser spot. The vaporisation of the alloy and the temperature gradient opposite to the laser propagation direction will significantly affect the flow field and make the molten alloy splash around. It was also quantitively proven that the W-rich phases with a high melting point can significantly increase the ablation resistance of Cu-W alloy by decreasing the ablation depth. The calculation results present a relatively high accuracy, this work will thus contribute to the application of the mathematic models in the laser processing field.

ABSTRACTThe twin-roll strip casting (TRSC) process was introduced because of its sub-rapid solidification characteristics, and the element segregation and ageing precipitation of the Cu-6Ni-1.4Si-0.1Cr alloy were studied. The results are as follows: TRSC can effectively refine grain size and inhibit the segregation of the Cu-6Ni-1.4Si-0.1Cr alloy. Two types of precipitates are formed mainly during the ageing process: disk-shaped δ-Ni2Si and rod-shaped β-Ni3Si. The comprehensive properties of the alloy are improved, and the precipitation strengthening mechanism is either from the dislocation shearing mechanism or the Orowan mechanism in different stages of ageing. The Cu-6Ni-1.4Si-0.1Cr alloy achieves optimum performance after ageing at 350°C for 4 h, where the tensile strength and conductivity are 1112 MPa and 27.35% IACS, respectively. The Avrami equations were established for the alloy to describe the kinetics of phase transformation and electrical conductivity during ageing, and the calculated results are consistent with the experimental data.

ABSTRACTUndeformed tungsten suffers from a brittleness that makes it unsuitable for applications at low temperatures. Cold-worked tungsten materials such as drawn wires or rolled plates can however show considerable ductility even at low temperatures. The reason for this behaviour is so far not understood. We investigated a series of potassium-doped tungsten wires that were subsequently drawn from one sintered ingot, making them chemically identical. Hence, the properties of the wires could be studied without the influence of different impurity levels. Using transient mechanical tests, namely repeated stress relaxation experiments and strain-rate jump tests, the effective activation volumes Veff and strain-rate sensitivities m of the wires were determined at room-temperature. Based on the obtained results, it is deduced that the motion of (a0/2)⟨111⟩ screw dislocations by formation and dissociation of kink-pairs is controlling the rate of plastic deformation in all wires that show plasticity at room temperature. It is hence concluded that the ductility of drawn tungsten wires at low temperatures is not due to a change in the rate-controlling deformation mechanisms, but should be a consequence of the microstructural and textural changes during wire drawing.

ABSTRACTTheoretical calculations were used to evaluate the response of a tridimensional (spatial) external electric field on the binding energy (Eb), polarisability (α) of a hydrogenic donor impurity and diamagnetic susceptibility versus the dot width (Ld) and the tridimensional electric field intensity F, and the impurity location (x0) in a GaAs/Ga1−xAlxAs double symmetrical quantum dot. The numerical computations were accomplished by utilising the effective mass approximation and the variation method. Our calculations showed that the polarisability diminishes as the applied tridimensional electric field F rises, especially when the dot width is large. Nevertheless, this polarisability is independent of the tridimensional field strength F when the confinement is strong. It has been observed that the degeneracy of the binding energy is broken under the effect of a tridimensional field F. Furthermore, in the absence of a tridimensional field, the diamagnetic susceptibility χdia is symmetric in relation to the centre of the barrier material, having two peaks. However, this symmetry is broken when a spatial electric field is applied.

ABSTRACTGlassy matter like crystals resists change in shape. Therefore a theory for their continuous melting should show how the shear elastic constant μ goes to zero. Since viscosity is the long wave-length low frequency limit of shear correlations, the same theory should give phenomena like the Volger-Fulcher dependence of the viscosity on temperature near the transition. A continuum model interrupted randomly by asymmetric rigid defects with orientational degrees of freedom is considered. Such defects are orthogonal to the continuum excitations, and are required to be imprisoned by rotational motion of the nearby atoms of the continuum. The defects interact with an angle dependent μ/r3μ/r3μ/r3 potential. A renormalisation group for the elastic constants, and the fugacity of the defects in 3D is constructed. The principal results are that there is a scale-invariant reduction of μ as a function of length at any temperature TT<T0, above which it is 0 macrosopically but has a finite correlation length ξ(T)ξ(T)ξ(T) which diverges as T→T0. Viscosity is shown to be proportional to ξ2(T) and has the Vogel-Fulcher form. The specific heat is ∝ξ−3(T). As T→T0, the Kauzman temperature from above, the configuration entropy of the liquid is exhausted. The theory also gives the ‘fragility’ of glasses in terms of their T0/μ.

ABSTRACTIn this paper, we theoretically studied a 3D structure of GaAs/Al0.3Ga0.7As triple concentric quantum rings submitted to the combined action of a non-resonant intense laser and a static electric field. The 3D model was built using the cross-sectional profile of the structure that corresponds to a realistic experimental case of triple rings with different heights and widths. The electric field and the laser field have opposite influence on the energy levels, decreasing or increasing all studied levels, respectively. Linear or quadratic Stark effect can be seen in specific ranges of electric field values, depending on the anisotropy induced by the intense laser field, for given fields orientations. The observed anti-crossings are explained by wave-functions delocalisation from one ring to another or by symmetry exchange between the wave-functions of the inner ring. For the most deformed potential created by perpendicular orientation of electric field and intense laser polarisation, very large absorption peaks, blue-shifts, red-shifts or an oscillatory behaviour in peaks energy and amplitude are obtained in a controllable way by proper manipulation of the fields. This can be helpful for the tunability and optical features improvement of THz detectors or solar cells.

ABSTRACTBragg–Williams (BW) modelling is a mean-field approach to order–disorder phase transformations (ODPT´s) in substitutional alloys. While the BW theory itself is for thermal equilibrium, the relaxation of the alloy to the equilibrium state in terms of the BW approach was studied by Dienes who introduced the chemical balance equation for temporal evolution of the long-range order parameter S. Here, results of solving numerically the Dienes equation are presented, with taking additionally into account that ordering in the alloy occurs through vacancies in atomic lattice. In such a description there are three important parameters that affect the ordering kinetics, namely (1) the interdiffusion coefficient in a disordered alloy, (2) the ratio of initial to equilibrium (thermal) concentration of vacancies, r, and (3) the characteristic timescale τ∝L2 for vacancy relaxation, where L is the effective distance between sinks/sources of vacancies in the alloy. With example of Fe-rich Fe aluminides FexAl1-x (x = 0.6), it is found that, at sufficiently large r, an additional step arises in temporal evolution of S for a time which can be much shorter (scaled as ∝r−1) than the characteristic timescale for ordering at r = 1. The height of this step increases up to unity at sufficient r. The lowest values of r and L are determined, at which non-equilibrium vacancies injected into the alloy can still play the role. This study would be of potential interest for developing the technology of functional alloys (lowering of ordering temperatures) and for obtaining a kind of information about vacancy behaviour in crystals.

ABSTRACTZnNi alloy coatings with low Ni content (1–4 wt.% Ni) were electrodeposited over mild steel. Ni addition changed the coating morphology from faceted to hillock, decreased the crystallite size, and shifted the basal plane texture to higher energy (011¯1) texture. Zn-1.5 wt.% Ni coating exhibited significantly improved corrosion resistance, even better than the pristine Zn coating. The corrosion resistance properties, however, degraded considerably as the Ni content increased (2.7 and 3.7 wt% Ni). The high corrosion resistance of the Zn-1.5 wt.% Ni coatings was due to the presence of nearly basal texture, low coating strain and evolution of stable γ-phase in the Zn matrix. The corrosion rate for higher Ni addition increased due to high energy surface texture and higher coating strain.

ABSTRACTA combined nickel–cobalt-based eutectic high entropy alloy (Ni-Co-based HEA) has been designed based on the valence electron concentration (VEC) value. The microstructure of the developed alloy consists of a face-centered cubic (FCC) and ordered cubic (B2) structure, which was validated using CALPHAD. The microstructure is hierarchical with length scales in micrometers (lamellar eutectic morphology) and nanometers (B2 length scale). B2 phase precipitation was observed in the supersaturated FCC primary phase. The orientation relationship (OR) between the phases exhibited a strong Kurdjimov-Sachs (KS) type OR, typical of FCC/BCC interface structures. This EHEA displayed good yield strength at room temperature and strain rate insensitivity in the 10−3–10−1 strain rate range.

ABSTRACTInfluence of configurational design of single crystal Al-Al90Sm10 metallic glass nanolaminates on torsion deformation behaviour of Al/Al90Sm10 nanolaminate (Configuration 1) and Al90Sm10/Al nanolaminate (Configuration 2) from a structural evolution aspect have been analysed by employing Molecular Dynamics for a torsion speed of 1/600 revolution/ps. Adaptive common neighbour (a-CNA) analysis, Dislocation extraction algorithm (DXA), atomic shear strain analysis, and Voronoi Polyhedral (VP) analysis have been carried out to reveal the structural evolution in the nanolaminates specimen subjected to torque. As a consequence of dislocation density localisation under torsional loading in Al/Al90Sm10 nanolaminate high atomic strain gradient is developed in the nanolaminate specimen causing torsional buckling of the Al/Al90Sm10 nanolaminate. The localisation of dislocation density rings induces the formation of dislocation substructure in Al/Al90Sm10 nanolaminate. The crystalline/amorphous interface serves as a free surface and encourages the formation of such dislocation substructure. The collective nucleation, coalescence, and growth of shear transformation zones (STZs) leading to the formation of thick shear bands on either end of Al90Sm10/Al nanolaminate inducing an almost homogenous atomic strain gradient across the surface of the nanolaminate specimen thereby averting torsional buckling. The C/A interface serves as a nucleation site for the generation STZs in Al90Sm10/Al nanolaminate. VPs such as , , have the load bearing capacity and are resistant to fragmentation under the subjugation of torsion loading.

ABSTRACTAnti-twin has been experimentally observed in body-centered cubic nanopillars, which naturally raises the reconsideration of twinning pathways at the crack tips. Using molecular dynamics simulations, we find that shuffling anti-twinning and twinning pathways appear simultaneously at the (011¯)[011](011¯)[011](011¯)[011] crack tip; while only twinning pathway appears at the (010)[101](010)[101](010)[101] crack tip. By analysing the shear stress distribution of the two crack models, we reveal that the specific twinning pathway is determined by the direction relationship between the anti-twinning/twinning slip system and the butterfly-like shear stress fields. This study deepens our understanding of anti-twin and extends the knowledge about the twin formation mechanisms at the crack tips of body-centered cubic metals.

ABSTRACTThe fractal dimension of a micrograph is a quantitative parameter of its geometric patterns' complexity, morphological irregularities and characteristics in their spatial arrangements and configurations. Material defects growing during fatigue process are described in terms of fractals. The experimental assessment of fractal dimensions of the novel flaky electron fractographs comprising the 3D planar topography of branched secondary cracks with distinctively oriented striations' islands and tearing ridges' networks on the ‘fatigue crack propagation area’ in three different Zr–Nb alloys have been carried out and correlated with their corresponding low cycle fatigue responses at different temperatures. Image texture analysis has also been implemented to understand the relative ‘energy generation’ of the hierarchical fatigue crack propagation during fatigue−fracture process of these materials as a function of test temperature. The detail invasive fractal character and chaos of these crack/striations' islands and tearing ridge network morphologies after fatigue−fracture have been convincingly revealed.