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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.

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.

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 phase formation of high entropy alloys (HEAs) is diversity due to the breadth of the composition space. Most of the studies about phase formation are based on features of solid solution. However, the establishment of the link between compositions and phase formation plays an important role in accelerating novel HEAs development. To achieve this aim, we employed the support vector machine (SVM) to build phase selection models with both the composition dataset and the thermodynamic parameters dataset. The accuracies of both models are above 85%. A dataset with more than a thousand data has been established, which covers 18 elements and most of the HEAs families. The feature dataset was transferred by calculation of thermodynamic parameters. The similar accuracies of the models with compositions dataset and with thermodynamic parameters proved that the prediction of phase formation in HEAs can be carried out directly from compositions. Our models provide a universal approach of phase formation prediction in HEAs.

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.

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

The third-order elastic constants (TOECs) are fundamental to describe crystal’s nonlinear response to stress, and can be applied to explore anharmonic properties of crystals such as Gruneisen parameters, thermal expansion coefficient, and the effect of pressure on second-order elastic constants (SOECs). Here, we report an open-source python package, Elastic3rd, which is able to calculate the SOECs and TOECs using the strain–energy method for crystals with any symmetry from first-principles calculations. An algorithm to generate necessary strain modes and the corresponding coefficients for a given symmetry is proposed. These strain modes are then applied to the fully relaxed structure to generate the deformed structures. The total energies of the strained structures are calculated by a chosen first-principles code, and the SOECs and TOECs are determined by fitting the resulted strain–energy data. The present code has been validated by several case studies of C, Si and Mg, and the case of MnP4 shows the ability for low-symmetry crystals. Program summary Program title: Elastic3rd CPC Library link to program files: https://doi.org/10.17632/n54vr2kwx8.1 Developer’s repository link: https://github.com/hitliaomq/ELASTIC3rd Licensing provisions: GNU General Public License 3 Programming language: Python 2.7.X and Python 3.X. External routines/libraries: Numpy [1], Scipy [2], and Matplotlib [3]. Nature of problem: To automatically calculate the third-order elastic constants for crystals with any symmetry from first-principles calculations. Solution method: Firstly, the deformed patterns and the corresponding coefficients for the second- and third-order elastic constants are automatically generated according to the symmetry. Secondly, the deformed patterns are applied to the initial lattice and the corresponding input files for first-principles calculations are generated. Thirdly, the energies of the deformed structures are calculated by first-principles software such as CASTEP [4] and VASP [5]. Then, the parameters of strain–energy functions are obtained by fitting the strain and energy relationships. Finally, the third-order elastic constants are determined by solving the linear-independent equations, and the second-order elastic constants are calculated by solving the overdetermined equation using the least squares method. Addition comments including restrictions and unusual features: This code is well modularized. Thus, the energy can be calculated using energy-generated first-principles or other packages only by writing few functions. [1] S. Van Der Walt, S.C. Colbert, G. Varoquaux, Comput. Sci. Eng. 13(2011):22–30 [2] P. Virtanen, R. Gommers, T.E. Oliphant, et al., ArXiv:1907.10121 (2019). [3] J.D. Hunter, Comput. Sci. Eng. 9(2007):99–104. [4] S.J. Clark, M. D. Segall, C.J. Pickard, et al. Z. Kristallogr. 220(2005):567-570. [5] G. Kresse, J. Furthmuller, Phys. Rev. B 54 (1996) 11169.

In present study, the relations between hardness and elemental descriptors in the multi-component alloys (MACs) are particularly uncovered via machine learning (ML) and first-principles calculations. The RBF neural network is utilized to efficiently train a large database which allows an acceptable accuracy for identifying the overall role of elemental features for target properties. Detailed information from ML predictions indicates the critical element of Al and its significant advantages for the hardness in a model Al–Cr–Fe–Ni system. Investigations on elastic properties using first-principles calculations provide relations between physical quantities and match well with ML model. Furthermore, the Al 1.2 CrFeNi alloy was selected as an example, experimentally synthesized and properties-identified, to provide a strong validation in this case. Combined with some other reported alloys in this system, the prediction of the developed model can achieve above 90%. Further experimental analysis found that a dual phase microstructure presents in the Al 1.2 CrFeNi alloy, leading to a superior work hardening ability compared with the reported high performance alloys. This study offers reliable composition-properties features and encourages more researches using this integrated approach to guide for tuning novel MACs.

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.

The structural, elastic properties, electronic structure and hydrogen storage behavior of TiCrMn with a hexagonal C14 structure were investigated by the first-principles calculations within the frame work of DFT. The calculated lattice constants were consistent with the experimental values, and obtained cohesive energy and formation enthalpy showed TiCrMn is of the structural stability. These results also indicated that Mn atoms would optionally substitute on the Cr sites of TiCr2 phase to form the ternary intermetallic TiCrMn. The five independent elastic constants as well as polycrystalline elastic parameters (bulk modulus B, shear modulus G, Young's modulus E, Poisson's ratio ν and anisotropy value A) were calculated, and then the ductility and elastic anisotropy of TiCrMn were discussed in details. Furthermore, the electronic DOS and charge density distribution of TiCrMn were also calculated, which revealed the underlying mechanism of structural stability and chemical bonding. Finally, the binding energy of hydrogen in hydride TiCrMn(H3) was investigated, confirming the better hydrogen storage behavior of C14 Laves phase TiCrMn.

The structural, elastic properties and electronic structure of FeTi and its hydrides, and hydrogen diffusion behavior in FeTi alloy were investigated by the first-principles calculations within the frame work of density functional theory (DFT). The calculated lattice constants for FeTi were in good agreement with the experimental values, and the lattice distortion of hydrides increases with the rise of hydrogen content. The calculation results of formation enthalpy, fusion heat of hydrogen and octahedron interstice size showed that hydrogen atom is more likely to exist in the central site of octahedron with the frame of four Ti atoms and two Fe atoms. The independent elastic constants as well as polycrystalline elastic parameters (bulk modulus B, shear modulus G, Young’s modulus E, Poisson’s ratio ν and anisotropy value A) were calculated, and then the ductility and elastic anisotropy of FeTi and its hydrides were discussed in details. In addition, the density of states, electron density difference and population analysis for FeTi and its hydrides were also calculated, which reveals the underlying mechanism of structural stability and chemical bonding. Finally, the activation energy of next nearest neighbor diffusion for H between octahedron interstices in FeTi alloy was calculated to be 2.92 eV, clarifying the atomic mechanism of hydrogen diffusion.

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.

Based on the computational fluid dynamics (CFD) method, a quenching tank with two agitator systems and two flow-equilibrating devices was selected to simulate flow distribution using Fluent software. A numerical example was used to testify the validity of the quenching tank model. In order to take tank parameters (agitation speed, position of directional flow baffle and coordinate position in quench zone) into account, an approach that combines the artificial neural network (ANN) with CFD method was developed to study the flow distribution in the quenching tank. The flow rate of the quenching medium shows a very good agreement between the ANN predicted results and the Fluent simulated data. Methods for the optimal design of the quenching tank can be used as technical support for industrial production.

First-principles calculations were performed to investigate the structural, elastic, electronic and thermal properties of Ni3Nb. The calculated results are agreed well with the available experimental data. The chemical bonding was interpreted by calculating the density of states, electron density distribution and Mulliken analysis. Ni3Nb has a combination of metallic, ionic and covalent bonding properties. Elastic constants were calculated, and the bulk modulus, shear modulus, Young’s modulus and Poisson’s ratio of polycrystalline aggregates were derived. The value of B/G is bigger than 1.75 and the material is ductile. Electronic density of states (DOSs) and charge density distribution were also calculated to reveal the underlying mechanism of structural stability and mechanical properties. Moreover, the pressure and temperature dependences of thermal expansion coefficient, bulk modulus, Debye temperature and heat capacity in a wide pressure (0–40 GPa) and temperature (0–1600 K) ranges are presented in this study.

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.

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.

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.