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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.

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.

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

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.

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.

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 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 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 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.

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 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.

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.

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.

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.

A Mo/Si slurry was coated onto the surface of Al/Si-coated carbon fiber reinforced carbon (C/C) composites and vacuum-sintered to form a fused double-layered coating. The effect of the Al content (6 and 10 mass%) in the Al/Si layer on the oxidation resistance of the composites was investigated. Results indicate that the presence of Al effectively prevents liquid Si infiltration into the composites. The composite with the 10 mass% Al has a much lower oxidation resistance than that with the 6 mass% Al. It is revealed that when the Al content is 10 mass% an Al phase dispersed around MoSi2 grains is found in the Mo/Si layer, which decreases the oxidation resistance of the composite at 1370 ° C. This can be ascribed to voids generated within the Mo/Si layer due to the outward diffusion of Al and pores in Al2O3 formed during oxidation, which provide paths for oxygen diffusion. [New Carbon Materials 2013, 28(3): 222–227]

The plasma sprayed ZrO 2 /NiCoCrAlY graded coating exhibits excellent gradually compositional distribution. The relative density of the graded coating is 90% or so, and contains a few pores inevitably. ZrO 2 component contains some c, t and t’ phases, as well as a little m phase, and the NiCoCrAlY component is mainly consists of γ(Ni) and γ' (Ni 3 Al), as well as a little α-Cr phase and e-Co phase. During spraying process, NiCoCrAlY reacts with oxygen in air, and some NiO, Cr 2 O 3 , Alssss 2 O 3 film formed on the particles surface.

The hot flow stress of as-quenched Al - Cu - Mn alloy was modeled using the constitutive equations. The as-quenched Al - Cu - Mn alloy were treated with isothermal hot compression tests in the temperature range of 350–500°C, the strain rate range of 0.001–1 s-1. The hyperbolic sine equation was found to be appropriate for flow stress modeling and prediction. 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 Al - Cu - Mn alloy was determined to be 251.314 kJ/mol. Parameters of constitutive equation of as-quenched Al - Cu - Mn alloy were calculated at different small strains (≤ 0.01). The calculated flow stresses from the constitutive equation are in good agreement with the experimental results. Therefore, this constitutive equation can be used as an accurate temperature-stress model to solve the problems of quench distortion of Al - Cu - Mn alloy parts.