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A Co-free as-cast AlCrFe2Ni2 medium entropy alloy (MEA) with multi-phases was remelted by fiber laser in this study. The effect of laser remelting on the microstructure, phase distribution and mechanical properties was investigated by characterizing the as-cast and the remelted AlCrFe2Ni2 alloy. The laser remelting process resulted in a significant decrease of grain size from about 780 μm to 58.89 μm (longitudinal section) and 15.87 μm (transverse section) and an increase of hardness from 4.72 ± 0.293 GPa to 6.40 ± 0.147 GPa (longitudinal section) and 7.55 ± 0.360 GPa (transverse section). It was also found that the long side plate-like microstructure composed of FCC phase, ordered B2 phase and disordered BCC phase in the as-cast alloy was transformed into nano-size weave-like microstructure consisting of alternating ordered B2 and disordered BCC phases. The mechanical properties were evaluated by the derived stress-strain relationship obtained from nano-indentation tests data. The results showed that the yield stress increased from 661.9 MPa to 1347.6 MPa (longitudinal section) and 1647.2 MPa (transverse section) after remelting. The individual contribution of four potential strengthening mechanisms to the yield strength of the remelted alloy was quantitatively evaluated, including grain boundary strengthening, dislocation strengthening, solid solution strengthening and precipitation strengthening. The calculation results indicated that dislocation and precipitation are dominant strengthening mechanisms in the laser remelted MEA.

In this paper, we present an efficient and effective method to predict the pressure dependence and temperature dependence of second-order elastic constants (SOECs) by introducing third-order elastic constants (TOECs) in the monocarbide ultrahigh temperature ceramics. The method is validated by comparing with experiments and previous calculations in four TMCs (TM = Nb, Ti, V, Zr). Using this method, we investigate the derivatives of SOECs against pressure and temperature as well as the anisotropic properties of polycrystalline modulus. In addition, we fit the SOECs with pressure and temperature under the framework of CALPHAD for practice usage.

Here, we report a novel topotactic method to grow 2D free-standing perovskite using KNbO3 (KN) as a model system. Perovskite KN with monoclinic phase, distorted by as large as ∼6 degrees compared with orthorhombic KN, is obtained from 2D KNbO2 after oxygen-assisted annealing at relatively low temperature (530 °C). Piezoresponse force microscopy (PFM) measurements confirm that the 2D KN sheets show strong spontaneous polarization (Ps) along [101]pc direction and a weak in-plane polarization, which is consistent with theoretical predictions. Thickness-dependent stripe domains, with increased surface displacement and PFM phase changes, are observed along the monoclinic tilt direction, indicating the preserved strain in KN induces the variation of nanoscale ferroelectric properties. 2D perovskite KN with low symmetry phase stable at room temperature will provide new opportunities in the exploration of nanoscale information storage devices and better understanding of ferroelectric/ferroelastic phenomena in 2D perovskite oxides.

Dilute magnetic semiconductors (DMSs), such as (In, Mn)As and (Ga, Mn)As prototypes, are limited to III–V semiconductors with Curie temperatures ( T c ) far from room temperature, thereby hindering their wide application. Here, one kind of DMS based on perovskite niobates is reported. BaM x Nb (1− x ) O 3− δ ( M = Fe, Co) powders are prepared by the composite-hydroxide-mediated method. The addition of M elements endows BaM x Nb (1− x ) O 3− δ with local ferromagnetism. The tetragonal BaCo x Nb (1− x ) O 3− δ nanocrystals can be obtained by Co doping, which shows strong saturation magnetization ( M sat ) of 2.22 emu g −1 , a remnant magnetization ( M r ) of 0.084 emu g −1 and a small coercive field ( H c ) of 167.02 Oe at room temperature. The ab initio calculations indicate that Co doping could lead to a 64% local spin polarization at the Fermi level ( E F ) with net spin DOS of 0.89 electrons eV −1 , this result shows the possibility of maintaining strong ferromagnetism at room temperature. In addition, the trade-off effect between the defect band absorption and ferromagnetic properties of BaM x Nb (1− x ) O 3− δ is verified experimentally and theoretically.

Melting temperature has great influence on the high temperature properties and working temperature limits of ultra-high temperature ceramics (UHTCs) In order to bypass the challenge in the measurement of ultra-high melting points, this paper proposed a novel method to predict UHTCs melting temperature via machine learning. A dataset including more than ten thousand melting temperature data has been established, which covers 8 elements and most of the known non-oxide UHTCs. We built up an element to ceramic system framework by back propagation artificial neural network (BPANN) with the accuracy approaching to 90% and the correlation coefficients approaching to 0.95. Our work provides a probability to get the high accuracy melting temperature of UHTCs, and a more convenient way to develop novel materials with higher working temperature. The given case of melting temperature prediction of Hf-C-N ceramics proves the generality of the artificial neural network (ANN). An inter-validation of melting temperature prediction using our network with materials thermodynamics and density functional theory (DFT) has been demonstrated, indicating that our network is of powerful prediction ability.

Quenching and partitioning (QP meanwhile, the number of experiments was reduced significantly. When treated by quenching at 180 °C followed by partitioning at 330 °C for 20 min, the steel reached the best combination between strength and ductility. In detail, the product of ultimate tensile strength and reduction in area was 1.36 times (from 64.9 to 88.8 GPa%) that treated by quenching and tempering. In addition, owing to the grain refinement, the strength and ductility increase simultaneously. Specifically, the reduction in area increased by 27.4% (from 35.8% to 45.6%) coupled with a little improvement in ultimate tensile strength (7.4%).

In this work, numerical modeling and simulation method was firstly used to obtain the hot-pressing sintering parameter of high entropy alloy (HEA). The finite element model was built to describe the consolidation process. Constitutive relation of powder material was applied assuming that metal powder is a kind of elasto-plastic material with an elliptical yield criterion. The change law of relative density for sintered bulk varying with pressure, time and temperature were obtained. Besides, the flow stress as well as relative density distributions were acknowledged with different sintering time. The simulation results indicate that the HEA would achieve a relative density of more than 95 % if the pressure above 45 MPa at 1150 ℃. The relative density from experiment is well agreement with that of simulation results when the sintering parameter are within the predicted range. This work is of great importance to the study of hot-press sintering of HEA.

The influence of alloying elements on phase stability, elastic and thermodynamic properties of random Nb-Ti-V-Zr high entropy alloys was investigated by virtual crystal approximation (VCA) based on first principles calculation. The lattice constant, elastic constant and thermal expansion coefficient of equimolar NbTiVZr agree well with other calculations and experiments, which indicates that VCA scheme is suitable for random Nb-Ti-V-Zr system. The stable crystal structure was judged by energy criterion, which shows that BCC is the most stable structure except NbxTiVZr(x ≦ 0.4) and NbTiVZrx(x ≧ 1.6). Based on BCC structure, the dependence of elastic stiffness on composition was built using CALPHAD model, which fits well with the value calculated by first principles. Furthermore, the polycrystalline elastic modulus and anisotropy were estimated. In addition, the thermodynamic properties, such as thermal expansion coefficient, as a function of component and temperature were calculated using quasi-harmonic Debyeg-Gruneisen model.

The Polar discontinuity at heterointerface and the bare surface reconstructs the electronic phase of perovskite oxides. This gives rise to confined free electrons which intrinsically transit material from band insulator to metal. However, the insulator–metal transition induced by free holes has not been investigated so far due to the challenge in obtaining free hole state in oxides. Here, we propose a simple method whereby free holes can be obtained via polar facet reorientation. In the high polarity case, free holes can be supported by the lift up of O 2p subbands, which split into three independent subbands (one heavy hole subband and two light hole subbands) due to strong quantum confinement. Results show that both of the free electron and hole states are confined in a two dimensional quantum well, subjecting to the confined energy (E − EF) and occupied density of states around the Fermi level, indicating a finite thickness for preserving the metal states.

Here, we report a strong room-temperature magnetism in Ni-doped BaNbO3. The tetragonal BaNixNb(1-x)O3-δ nano-powders are prepared by the composite-hydroxide-mediated method. The as-prepared BaNixNb(1-x)O3-δ has a saturation magnetization (Msat) of 2.54 emu/g, a remnant magnetization (Mr) of 0.228 emu/g, and a small coercive field (Hc) of 99.14 Oe at room temperature, presenting as a short-range magnetic order. The Ni-doping leads to an incommensurate valence state of Nb, and the oxidation state of Ni in the matrix is + 2. It brings not only strong local spin polarization to the matrix, but also balances the oxygen defects and gives rise to a more doping content. The strong magnetism originated from the existence of short-range magnetic order and the strong local net spin polarization at the Fermi level (EF), which are proved by the first-principle calculations.

The effect of fabrication methods on microstructures, mechanical properties, and strengthening mechanisms of high-entropy alloys has been systematically studied. In this work, a non-equiatomic Fe0.25CrNiAl medium-entropy alloy (MEA) was selected and fabricated by arc-melting, spark plasma sintering (SPS), and hot-press sintering (HPS). The results indicate that the fabrication method has little effect on the main phase compositions of Fe0.25CrNiAl MEA while marked impacts on microstructures, mechanical properties, and strengthening mechanisms. All alloys mainly consist of a disordered body-centered cubic (BCC) phase and an ordered body-centered cubic (B2) phase. However, the arc-melted alloy possesses a typical dendritic structure, while a speckle-like microstructure for the SPS-ed and HPS-ed alloys. Particularly the grain is refined dramatically by powder metallurgical methods of SPS and HPS. The yield strength of powder metallurgical alloys is over 400 MPa higher than that of arc-melted alloy, and without sacrificing the ductility (~30%). The strengthening mechanism analysis demonstrates that precipitate strengthening plays a significant role for arc-melted alloy while grain boundary strengthening is the dominant strengthening mechanism for powder metallurgical alloys. The Fe0.25CrNiAl MEAs by powder metallurgy achieve a trade-off between high strength and strain-to-failure, which suggests that the method is available for improving the mechanical properties of high-entropy alloys.

In this letter, we study the higher-order effect on the third-order elastic constants (TOECs) of diamond using longitudinal stress-uniaxial strain (LSUS) approach based on density functional theory. The result shows that the higher-order effect on TOECs is not negligible in the shock wave experiments and similar calculations. By taking the higher-order elastic response (up to fifth order) into consideration, the convergence of TOECs against maximum stain gets improved significantly and resolves the discrepancy of several different theoretical methods and experiments., 9 pages, 3 figures, 2 tables

Based on first principles calculations of density functional theory, the adsorption behaviour of H 2S on the surface of intrinsic and Pd loaded VO 2 was studied. According to the analysis of the ad...

The current design strategies focus on the solidification characteristics to discover new MACs with promising properties in an enormous search space composed of considerable composition combinations in a specific system. In the present study, the associated correlations between alloying elements and solidification interval characteristics are uncovered via machine learning (ML) in the multi-component systems. Given the Fe–Cr–Ni–Al system, testing accuracy value using FNN model in identifying the input and output features is above 89%, and the Cr and Al are the critical elements. With these understanding, FeCrNiAl 0.8 alloy was successfully designed and prepared, and the properties are tested to confirm the reliability of the alloy design strategies. The experimental investigations not only provide strong evidence for the predicted accuracy, but also find superior mechanical properties. The designed FeCrNiAl 0.8 alloy exhibits fracture strength and plastic strain of 2839 MPa and 41%, respectively, accompanied with remarkable work hardening capacity. Beyond that, the extraordinary specific strength make it competitive against virtually known high performance metals and polycrystalline superalloys even in high temperature applications. Our work provides new ideas to search for compositionally complex alloys and is also applicable to assist in developing advanced MACs for engineering applications.

The present study proposes a dynamic model to describe the solidification characteristics of FeCrNiAl multi-component alloy. The as-cast FeCrNiAl multi-component alloy was prepared via vacuum arc melting technique and its crystal structure, microstructure, density and hardness were reported. The alloy has the density of 6.72 g/cm3 and hardness value of 491 kgf/mm, respectively. The FeCrNiAl alloy is a double-phase alloy consisting of the ordered (Ni,Al) phase and disordered [Fe, Cr] phase. The morphology of alloy was dendritic structure with the segregation of Al and Ni elements in dendritic regions as well as the Cr and Fe in interdendritic regions. The experimental data combined with the results of the thermodynamic modeling reveals that the (Ni,Al) phase firstly solidified from the melt as the primary phase. While the [Fe, Cr] phase distributes in the interdendritic region. At the end of solidification, the two bcc phases coexist, which indicates the formation of (Ni,Al)/[Fe, Cr] eutectics. Moreover, the thermodynamic parameters Ω and δr confirms the stability of solid solution phases in FeCrNiAl multi-component alloy. And the simplified dynamic solidification model proposed in this paper would provide theoretical explanation for the formation of its double-phase structures.

A non-equiatomic FeCr 1.2 Ni x Al alloys were introduced and characterized employing various characterization techniques. The great application prospect is expected because of their high mechanical properties and superior specific strength. In this study, the effect of Ni addition on the microstructure, mechanical properties and work-hardening behavior at room and high temperatures have been systematically investigated. Dual phases of ordered (Ni, Al) structure and disordered [Fe, Cr] structures are involved in alloys. The EDS analysis indicates the formation of Fe/Cr-rich regions in interdendrite and Ni/Al-rich regions in grains. The alloys show remarkable advantages in density and microhardness. The experimental results show that the Ni addition significantly increases the compressive strength of the as-cast alloys attributed to the solution strengthening and fine grain strengthening, and more importantly, simultaneous enhancements in specific strength. However, the additive Ni is found to cause a little decrease at high temperature owing to the crystal boundary weakening, accompanied with a decline in specific strength. The alloys possess higher work-hardening ability rather than many other alloys and metallic materials. The value of work-hardening exponent and capacity slightly increase with the additive Ni and the FeCr 1.2 Ni 1.3 Al alloy performs the most desirable. Due to these significant advancements, the proposed alloys are attractive for use in aerospace and automotive technology fields.

This study proposed a multi-component alloy FeCrNiAl 0.5 as a candidate materials for structural applications at high temperatures. The phase structure, microstructure and chemical composition of the alloy were characterized. The results show that the alloy possesses only BCC crystal structure consisting of the ordered (Ni,Al) phase and disordered [Fe, Cr] phase. Microstructural observation combined with XRD results clearly show that the as-cast alloy exhibits a non-homogeneous microstructure with pronounced dendritic and interdendritic regions. Besides, the as-cast alloy possesses great electrical and thermal conductivity compared with other HEAs and nickel-based alloy. Moreover, the oxidation behaviors at high temperature were systematically investigated and shows a surprisingly good oxidation resistance property compared with commercially available steels and alloys. The oxidation active energy is 259.3740 kJ/mol ranging from 1173 to 1273 K. The predominant oxide is Al 2 O 3 , Cr 2 O 3 and FeCr 2 O 4 and the oxidation mechanisms were further discussed. This study suggests that FeCrNiAl 0.5 multi-component alloy exhibites great promise for high temperature structural materials.

A grain refined FeCrNiAlTi0.2 high entropy alloy (HEA) was firstly produced by powder metallurgy, and the alloy combines well with high strength, good ductility and low cost. The sintered HEA exhibits a major body-centered cubic (BCC) matrix and a minor ordered BCC (B2) phase. The alloy possesses an excellent properties, reaching the yield strength of 1877 MPa and plastic strain of 26.6% at room temperature. Compared with the current FeCrNi-based HEAs, the compressive strength is improved distinctly without sacrificing plastic strain. The analysis of strengthening mechanism suggests that the main strengthening contribution is the grain boundary strengthening.

Bridging both the edges and the center of multicomponent space, which have been widely investigated in traditional alloys and high entropy alloys respectively, is significant but difficult in the design of alloys. In this paper, the single-crystal elastic constant model of the quaternary BCC Nb-Ti-V-Zr system across full composition space was established using first principles combined with the CALPHAD model. The accuracy of the model was confirmed by comparing with previous calculations and experiments. Using the fitted model, the alloying effect on stability and polycrystalline elastic properties of the current research system was analyzed. We find that there exists an area where BCC becomes unstable, and all the instability is caused by breaking C11-C12 > 0. And all of the stable Nb-Ti-V-Zr is ductile. In addition, there lies a surface on which the alloys are completely isotropic in elasticity. Furthermore, some alloys promising in some special aspects are predicted, such as gum metal, directional auxetic properties and biomedical application materials.

An as cast high entropy alloy AlCrFeMnNiTi was synthesised to investigate the microstructures and crystal structure. The atomic structure models of this AlCrFeMnNiTi alloy were also built to further investigate the stability and bonding behaviour. It was found that the as cast AlCrFeMnNiTi alloy formed two body centred cubic structures, and typical dendrite and interdendrite microstructures were observed. Two reasonably models based on AlNi and Fe matrix were built to simulate the structures of two phases formed in as cast AlCrFeMnNiTi high entropy alloy. The electron density difference and atomic Mulliken population were also calculated, which revealed the chemical bonding in as cast AlCrFeMnNiTi high entropy alloy. In this study, the probable process of spinodal decomposition in this alloy was also discussed and presented.

According to the experimental dataset on the as cast high entropy alloys with cubic structure, the relationship between the stability and physical parameters of cubic structure has been investigated from the view of the atomic size difference, mixing enthalpy, electronegativity difference and valence electron concentration in the present work to reveal the stability and structure formation in as cast high entropy alloys. The results indicated that the mixing enthalpy is the effective parameter that can predict the stability of solid solutions in as cast high entropy alloys. The atomic size difference, electronegativity difference and valence electron concentration also play important roles in the formation of body centred cubic and face centred cubic crystals. Moreover, the back propagation artificial neural network was established using data collected from the calculated solid solution physical parameters and the structure characteristic of as cast high entropy alloys, and the structure of alloys...

The multi-component AlCrCuFeMnTi high entropy alloy was prepared using a vacuum arc melting process. Serial annealing processes were subsequently performed at 590 °C, 750 °C, 955 °C and 1 100 °C respectively with a holding time of 4 h at each temperature. The effects of annealing on microstructure, mechanical and electrical properties of as-cast alloy were investigated by using differential thermal analysis (DTA), X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The experimental results show that two C14 hexagonal structures remain unchanged after annealing the as-cast AlCrCuFeMnTi alloy specimens being heated to 1 100 °C. Both annealed and as-cast microstructures show typical cast-dendrite morphology and similar elemental segregation. The hardness of alloys declines as the annealing temperature increases while the strength of as-cast alloy improves obviously by the annealing treatment. The electrical conductivities of annealed and as-cast alloys are influenced by the distribution of interdendrite regions which is rich in Cu element.

The effects of the addition of 5 mol.% aluminum, copper, silver or gold on the densification, microstructures, mechanical properties and oxidation resistance in thin air of TaC ceramics were investigated. Full density and relatively high flexural strength (up to 738 MPa) were observed in the case of the Au addition after spark plasma sintering at 1700 °C for 5 min under 30 MPa pressure. Due to wetting of the TaC grains by a thin metallic film, the consolidated materials showed enhanced oxidation resistance against thin air.

The quenching processes of A357 aluminum alloy large complicated thin-wall workpieces were investigated by finite element method (FEM) simulation based on ABAQUS software. Heat transfer coefficients of different quenchants were accurately calculated by a traditional method of inverse heat transfer. The accurate heat transfer coefficients of different quenchants can ensure accuracy FEM results of temperature field of A357 alloy large complicated thin-wall workpieces during quenching. The quenchants of water, machine oil and 5%-UCON quenchant A were used. Quenching residual stress and distortion were investigated by considering the influence of quenchant and quenchant temperature. The maximum residual stress and distortion of quenched workpieces were predicted by using FEM simulation based on ABAQUS software.

The structural, elastic and electronic properties of nonmagnetic TiCr 2 , TiMn 2 and antiferromagnetic TiFe 2 with hexagonal C14 structure were investigated by mean of the first-principles calculations within the frame work of density functional theory (DFT). The calculated lattice constants were in good agreement with the experimental values. The obtained cohesive energy and formation enthalpy showed TiCr 2 , TiMn 2 and TiFe 2 are of the structural stability from the energetic point of view. The five independent elastic constants were calculated, showing that these compounds are mechanically stable. Then the polycrystalline elastic parameters (bulk modulus B , shear modulus G , Young's modulus E , and Poisson's ratio ν ) were obtained by using the Voigt–Reuss–Hill (V–R–H) approximation, and the ductility and plasticity of these compounds were further analyzed. The elastic anisotropy of these compounds was also discussed in details. Finally, the electronic density of states (DOS) and charge density distribution were also calculated, indicating the existence of a combination of metallic, covalent and ionic bonding in these C14 compounds.

The workpieces of A357 alloy were routinely heat treated to the T6 state in order to gain an adequate mechanical property. The mechanical properties of these workpieces depend mainly on solid-solution temperature, solid-solution time, artificial aging temperature and artificial aging time. An artificial neural network (ANN) model with a back-propagation (BP) algorithm was used to predict mechanical properties of A357 alloy, and the effects of heat treatment processes on mechanical behavior of this alloy were studied. The results show that this BP model is able to predict the mechanical properties with a high accuracy. This model was used to reflect the influence of heat treatments on the mechanical properties of A357 alloy. Isograms of ultimate tensile strength and elongation were drawn in the same picture, which are very helpful to understand the relationship among aging parameters, ultimate tensile strength and elongation.

The structural, elastic and electronic properties of ordered face-centered cubic (L1 2 ) γ′-Ni 3 Ti were studied using the projector-augmented-wave (PAW) method within the generalized gradient approximation (GGA). The fact that the elastic constants meet the requirements of mechanical stability for a cubic crystal indicates that γ′-Ni 3 Ti is mechanically stable at 0 K. The bulk modulus, shear modulus, Young's modulus and Poisson's ratio are estimated from the calculated elastic constants of single crystal. The ratio of the bulk modulus to shear modulus ( B / G ) is 2.00 and the material is ductile. Through the quasi-harmonic Debye model, the pressure and temperature dependences of the linear expansion coefficient, bulk modulus, the Debye temperature and heat capacity have been investigated for the first time.

The quenching process of A357 aluminum alloy cylindrical bars with 80 mm diameter and with heights of 40, 80, 120, 160, 200 and 240 mm were investigated by using finite element method (FEM) simulation. Heat transfer coefficient was accurately calculated by using a traditional method of inverse heat transfer. Residual stresses caused by quenching of A357 alloy cylindrical bars are inevitable. Residual stresses reduction through cold stretching process was studied by using FEM simulation. Three numerical examples were used to illustrate the accuracy and efficiency of our method. The results show that this quenching model is able to predict the residual stress with high precision. The influence of some factors (quenching water temperature, aspect ratio of cylindrical bar, pre-stretching ratio and stretching rate) on the residual stress of quenched cylindrical bars after cold stretching was investigated.

Nanoindentation and high resolution electron backscatter diffraction (EBSD) were combined to examine the elastic modulus and hardness of α and β phases, anisotropy in residual elastic stress–strain fields and distributions of geometrically necessary dislocation (GND) density around the indentations within TA15 titanium alloy. The nano-indention tests were conducted on α and β phases, respectively. The residual stress–strain fields surrounding the indentation were calculated through cross-correlation method from recorded patterns. The GND density distribution around the indentation was calculated based on the strain gradient theories to reveal the micro-mechanism of plastic deformation. The results indicate that the elastic modulus and hardness for α phase are 129.05 GPas and 6.44 GPa, while for β phase, their values are 109.80 GPa and 4.29 GPa, respectively. The residual Mises stress distribution around the indentation is relatively heterogeneous and significantly influenced by neighboring soft β phase. The region with low residual stress around the indentation is accompanied with markedly high 〈 a 〉 type and prismatic-GND density.

The structural, elastic and electronic properties of Al 2 La, AlLa 3 and Al 3 La binary intermetallics in the Al–La alloy system were investigated using the first-principles method. The calculated lattice constants were consistent with the experimental values. Formation enthalpy and cohesive energy showed that the studied Al 2 La, AlLa 3 and Al 3 La all have a higher structural stability, and the alloying ability of Al 2 La and Al 3 La is stronger than that of AlLa 3 . The single-crystal elastic constants ( C ij ) as well as polycrystalline elastic parameters (bulk modulus B , shear modulus G , Young's modulus E , Poisson's ratio υ and anisotropy value A ) were calculated by the Voigt–Reuss–Hill (V–R–H) approximations, and the relationship of these elastic parameters between Al 2 La, AlLa 3 and Al 3 La phases were discussed in detail. The results showed that Al 2 La and Al 3 La which are anisotropic materials are absolutely brittle, while the isotropic AlLa 3 is slightly ductile. Finally, the electronic density of states (DOS) was also calculated to reveal the underlying mechanism of structural stability.

The objective of the present work was to establish an accurate thermal-stress mathematical model of the quenching operation for A357 (Al–7Si–0.6Mg) alloy and to investigate the deformation behavior of this alloy. Isothermal compression tests of as-quenched A357 alloy were performed in the temperature range of 350–500 °C and at the strain rate range of 0.001–1 s −1 . Experimental results show that the flow stress of as-quenched A357 alloy decreases with the increase of temperature and the decrease of strain rate. Based on the hyperbolic sine equation, a constitutive equation is a relation between 0.2 pct yield stress and deformation conditions (strain rate and deformation temperature) was established. The corresponding hot deformation activation energy ( Q ) for as-quenched A357 alloy is 252.095 kJ/mol. Under the different small strains (≤0.01), the constitutive equation parameters of as-quenched A357 alloy were calculated. Values of flow stress calculated by constitutive equation were in a very good agreement with experimental results. Therefore, it can be used as an accurate thermal-stress model to solve the problems of quench distortion of parts.

The lattice constants, elastic properties, electronic structure and thermodynamic properties of Al3Nb with DO22 structure have been investigated by the first-principles calculation. The calculated lattice constants were consistent with the experimental values, and the structural stability was also studied from the energetic point of view. The single-crystal elastic constants (Cij) as well as polycrystalline elastic parameters (bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio υ and anisotropy value A) were calculated, and brittleness of Al3Nb was discussed in detail. Besides, the electronic structure of tetragonal Al3Nb was studied, which indicates a mixture of metallic bond and covalent bond in Al3Nb and reveals the underlying mechanism of the stability and elastic properties of Al3Nb. Finally, the thermodynamic properties of Al3Nb were calculated and the physical properties such as heat capacity and Debye temperature were predicted within the quasi-harmonic approximation.

The nanometer coherent structure evolution of spinodal decomposition and ordering coexistence phase transformation in Fe-24Al alloys is investigated by the microscopic phase field kinetic model. The results show that the concentration and long-range order parameters all continuously change towards to their equilibrium values during phase transformation. With the increase of elastic interaction energy, the anisotropy along [01] or [10] elastic soft direction is more obvious and the time reaching equilibrium state is also shortened. According to the results, the formation of nanometer coherent structures during phase transformation is composed of the initial decreasing stage of order degree stage, the incubation stage, the continuous increasing stage of concentration order parameter and long-range order parameter, and the later stable stage. The spinodal decomposition and ordering is interaction; the initial ordering stage is a necessary condition of the coexistence phase transformation. The nanometer coherent structures are not found to grow during the whole phase transformation. The simulation results are in accordance with the results in experiment obtained by the aging treatment in Fe-24Al alloys.

The crystal plasticity finite element method has been adopted to study the plastic deformation behaviour, such as the slip system activation, the number and magnitude of the actived slip system, the rotation character and the macromechanics response of face centred cubic (fcc) single crystal metal during uniaxial tension. Five typical crystalline orientations, including four types of typical fcc texture orientation: Goss orientation, copper orientation, S orientation and brass texture, have been considered, and its effects to plastic deformation have been studied and compared. The results show that the orientation between crystalline and loading direction will influence the slipping character and the macromechanical response: the S crystalline orientation (60, 32 and 65°) has the least number of active slip system (just only 3); the brass texture (35, 45 and 0°) has the smallest magnitude of crystalline lattice rotation; and the brass texture orientation (35, 45 and 0°) has the highest yield stress value.

We studied the three-dimensional (3D) morphology and crystal orientation distribution of coarse primary α, fine second α lamellae, and retained β layers in a near α titanium alloy using a 3D microtomographic electron backscattering diffraction method (3D EBSD). The results demonstrate that primary α lamellae are more like a thick plate in 3D space. The second α lamellae have lower in-grain (mis)orientation gradients than primary α. The retained β is a continuous network structure and contains many cavities for α lamellae embedding.

In order to establish an accurate thermal stress mathematical model of the quenching operation for A357 alloy, isothermal compression tests were performed in the temperature range of 200–500°C and the strain rate range of 0·001–1 s−1 on as quenched A357 (Al–7Si–0·6Mg) alloy. Based on the experimental results, the deformation behaviour of as quenched A357 alloy was investigated in terms of artificial neural network with a back propagation learning algorithm. Using the deformation temperature, strain rate and strain were used as inputs, and flow stress was used as the output in the network. The average absolute relative error between the predicted results that used the back propagation network and the experimental data obtained from compression tests is 2·89%, which indicates that this artificial neural network model is able to predict the flow stress with high precision. Therefore, it can be used as an accurate thermal stress model to solve the problems of quench distortion of parts.

The B2 (FeAl) antisite defects and microstructure evolution during homogenous transformation of Fe–Al alloys are investigated by phase field kinetic model considering long-range elastic interaction energy. The results show that congruent ordering transformation dominates the aging initial stage, and two phase structures of B2 ordered phase and disorder phase are formed. The antisite atom occupation probability which indicates antisite defects decreases during congruent ordering transformation of aging initial stage. With increasing aging time, spinodal decomposition occurs within B2 structure ordered phases, and spinodal decomposition and ordering coexistence microstructures are formed at this stage. At the aging of final stage, the increase of antisite atom occupation probability is attributed to the presence of spinodal decomposition. For Fe–Al alloys with different composition, we find that with increasing Al atom concentration, the AlFe antisite defects increase, and the FeAl antisite defects decrease. In contrast, with the increase of Fe atom contents, the numbers of FeAl antisite defects increase and that of the AlFe antisite defects decrease.

The goal of this study is to establish relationships between the hot compression deformation behaviors and the fractal dimension of primary phase morphology of TA15 titanium alloy using the analytical methods of metallurgical microscope and transmission electron microscope coupled with box-counting dimension method. The hot compression deformation behaviors vary with decreasing fractal dimension owing to the change of microstructure caused by different parameters of the hot compressive deformation. The results indicate that TA15 alloy shows dynamic recrystallization characteristics at deformation temperature lower than 850 °C while fractal dimension exhibits a moderate decreasing trend with the temperature increasing, and shows dynamic recovery characteristics at deformation temperature higher than 850 °C while fractal dimension reduces rapidly with the temperature increasing. The fractal dimension displays non-linear relationship with fraction of primary phase and with aspect ratio of primary phase.

A Mo-Si-C-N multi-layered anti-oxidation coating was in-situ fabricated by introducing nitrogen atmosphere during the fused sintering of Mo-Si slurry pre-layer on carbon/carbon composites. The phase composition and microstructure of the Mo-Si-C-N coating were characterized by X-ray diffractometry, optical microscopy, scanning electron microscopy with energy dispersive spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscopy. The Mo-Si-C-N coating exhibited a three-layered structure. Besides the MoSi2/Si main-layer and the SiC bonding-layer, a surface layer of about 10 µm in thickness was synthesized on the coating surface. The surface layer mainly consisted of SiC nanowires and contained some Si3N4 and Si phases. SiC nanowires of 10 to 200 nm in diameter presented a terrace and distortion structure. Transmission electron microscopy indicated that the SiC nanowires grew along the preferred 〈111〉 direction. During oxidation test, SiC nanowires transmuted into SiO2 glass, which can play an important role in improving the oxidation resistance of C/C composites.

In this paper, aluminum alloy matrix hybrid composite reinforced by Al18B4O33 with the addition of BaPbO3 was fabricated by squeeze casting technique. The fabrication and characterization of the hybrid composite were investigated. The result of microstructural characterization shows that BaPbO3 particles have a reaction with 6061Al alloy to produce an interfacial reaction layer which contains nanosized Pb agglomeration and Ba0.956Mg0.912Al10.088O17 compound during fabrication process. The hybrid composite has better specific strength and specific stiffness compared with conventional anti-radiation materials. Meanwhile, the theoretical calculation of mass attenuation coefficient demonstrates that the introduction of BaPbO3 particles can improve the radiation protection property of the matrix indeed. The hybrid composite has a good combination of mechanical properties and radiation protection property.

Effect of aging temperature on modulated structures of Co-free 00Ni 12 Cr 5 Mo 3 TiAlV maraging steel was studied. With increasing the aging temperature, the modulated structures become more obvious. When the temperature is lower, the occurrence of spinodal decomposition only can be indicated by a little elongation of diffraction spots. However, when the temperature is higher, the in situ intermetallic precipitates of modulated structures are distributed along 0 1 0 direction (the elastic soft direction). The coherent relationship was kept between matrix and precipitates. The extra high strength and good ductility are mainly attributed to the in situ precipitation strengthening and coherent effect of modulated structures.

Diameter and wall thickness of self-assembled peptide nanotube of cyclo[(-d-Ala-l-Ala)4-] were characterised by molecular simulation. In order to verify the existence of peptide nanotube of cyclo[(-d-Ala-l-Ala)4-], cyclo[(-d-Ala-l-Ala)4-] was firstly synthesised through Fmoc solid-phase synthesis method and then self-assembled in trifluoroacetic acid. Based on the results of experiment, the single nanotube structure was further characterised by molecular dynamics (MD) employing the COMPASS force field. The results indicate that cyclo[(-d-Ala-l-Ala)4-] is self-assembled into nanotube bundles of about 0.5 μm in diameter and 10 μm in length; the inner and outer diameter of the single nanotube is 8.5 and 15.9 A, respectively, and the nanotube wall thickness is 3.3 A.

The structural, electronic and elastic properties of orthorhombic and hexagonal Mo2C were investigated using first principles with a pseudopotential plane-wave method. The results for the formation enthalpy of these compounds indicate that Ortho-Mo2C can form more easily than Hexa-Mo2C. The calculated electronic structure indicates that the bonds of Mo2C have both covalent and metallic properties. The stability of multicomponent carbides (Mo,M)2C (M = Cr, Nb) in both orthorhombic and hexagonal form was also investigated.

To improve the oxidation resistance of Mo Si fused slurry coating fabricated in vacuum, Mo Si N multi-layer coatings were synthesized on C/C composites in nitrogen atmosphere by fused slurry using same Mo and Si element powders. The phase compositions and microstructures were characterized by X-ray diffractometry (XRD), optical microscopy (OM), scanning electron microscopy (SEM) with energy-dispersive spectroscopy (EDS). The results indicate that the Mo Si N coating contains SiC inner layer and MoSi2/Si main layer, which was similar with Mo Si coating. Additionally, a thin outer layer with nano-filiform morphology has been found on the coating surface, which consists of SiC, Si3N4, AlN, Al2O3 and sialon phase. Oxidation experiments show that the Mo Si N multi-layer coating exhibits excellent oxidation resistance at 1400 °C and anti-oxidizing potential ability at 1450 °C.

The precipitation microstructure and the associated hardness and electrical conductivity have been systematically studied in a 7150 alloy during the ageing treatment. The evolution of the GP zones during the one step and the two step ageing processes is discussed in details. Experimental results show that the electrical conductivity of the alloy treated in the two step ageing regime is higher than that of the alloy treated in the one step ageing regime. The two step ageing regime increases the stability of GP I zones and restrains the coarsening of precipitates. During the two step ageing treatment, GP I zones are present when the ageing temperature at the second stage is 160 °C (36 h), which could not be detected in the one step ageing for short times at the same temperature. Both the GP I and GP II zones disappeared after ageing for 4 h at 180 °C. The achievement of the high strength of the alloy is ensured by a large volume fraction of fine GP zones and η′ precipitates.

Elevated temperature compressive deformation behaviour of TA15 titanium alloy was investigated at temperatures from 1023 to 1273 K and strain rates from 10−3 to 1 s−1. It was found that the flow stresses of the TA15 alloy dropped with increasing deformation temperature and decreasing strain rate. The microstructure of TA15 alloy was observed and analysed using optical microscope. The volume fraction and the shape of primary alpha phase are influenced by deformation temperature and strain rate.

ZrO2–NiCr functionally graded material (FGM) was developed by powder metallurgical process. After investigating the preforming and sintering process of mixed powders with different compositions, the suitable fabrication procedure of FGM was determined. Microscopic observations demonstrate that the chemical composition and microstructure of ZrO2–NiCr FGM distribute gradually in stepwise way, eliminating the macroscopic ceramic/metal interface such as that in traditional ceramic/metal joint. The mechanical properties of ZrO2–NiCr system strongly depend on constitutional variation, and display various graded distributions as well.

The structure, elastic properties and electronic structure of VC and V 4 C 3 have been studied by the first-principles pseudopotential plane-wave method based on density functional theory. Compared with VC, V 4 C 3 has lower values of 13.3%, 19.2% and 17.7% in bulk modulus, shear modulus and Young modulus, respectively. The total density of states (DOS) of VC and V 4 C 3 were calculated. The higher shear modulus of VC is due to the differences of DOS for VC and V 4 C 3 . The overlap populations of the V–C bonds in VC and V 4 C 3 were analyzed and the hardnesses of VC and V 4 C 3 were calculated. The calculated hardness of V 4 C 3 is 15.8 GPa, which is lower than that of VC. The calculated hardness of VC is 28.5 GPa, which matches fairly the experimental one.

Functional gradient material (FGM) of the ZrO2-Ni system was developed by a powder metallurgical process, and investigated for its microstructure by means of X-ray diffractometry (XRD), electron probe microanalysis (EPMA), transmission electron microscopy (TEM) and optical microscopy. It was shown that the sintered body of ZrO2-Ni FGM is almost fully densified, and its chemical composition and microstructure have the expected gradient distribution. With composition variation, the microstructure changes gradually from zirconia particles dispersed in a nickel matrix to the converse with nickel particles dispersed in a zirconia matrix, with network structures in the intermediate composition range. Therefore, no distinct interfaces appear in the FGM due to the gradient change of components, that is, both zirconia and nickel are present everywhere in the microstructure. In phase composition, the sintered ZrO2-Ni FGM consists of nickel, tetragonal zirconia and a little monoclinic zirconia. No reaction between nickel and zirconia has been detected. The substructure of nickel and monoclinic zirconia are twins, and strain fringes can also be found in zirconia.