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Irradiation induced dislocation loops in Fe-based alloys can cause material hardening by impeding the mobility of dislocation. Using molecular dynamics (MD), the interaction between 1 / 2 < 1 1 1 > { 1 1 ¯ 0 } edge dislocation (ED) and 1/2<1 1 1> interstitial dislocation loops with Burgers vector (BV) along different directions in BCC (body centered cubic)-Fe were investigated, and the influence of interaction geometry (means the relative position between dislocation glide plane (GP) and loop equator plane) on the CRSS (critical resolved shear stress) for dislocation to move again induced by loops was analyzed. It was found that the pinning strength of 1/2<1 1 1> loop was estimated to be 0.2–0.8, varying with the BVs direction of loops and the interaction geometries. The present study clearly showed that when parameterizing the dislocation dynamics, more interaction geometries should be considered in order to get a more quantitative pinning strength. [ABSTRACT FROM AUTHOR]

The segregation of certain impurities to grain boundaries (GBs) which induced by neutron irradiation in Reactor Pressure Vessel (RPV) steels may have adverse effects upon their mechanical properties. In this work, ten symmetrical <110> and <001> tilt GBs in BCC Fe were created based on Coincident Site Lattice method, the GBs segregation embrittling potency was simulated by adding phosphorus, copper, nickel, and manganese to the boundaries and free surface (FS) using molecular static method. We have addressed both high- and low-angle tilt grain boundaries. Systematic Molecular Statics simulations were performed employing recent Embedded Atom Method (EAM) potentials. We show that P will strongly bind to GBs and FS; P and Cu have a detrimental effect on the GB cohesion, and segregation of these two elements will lead to GB embrittlement. [ABSTRACT FROM AUTHOR]

A modified model based on kinetic rate theory is presented to simulate the dose dependence of defects nucleation and growth in reduced-activation ferritic/martensitic (RAFM) steel under helium ion irradiation by considering the motion of dislocation loops. The modeling results are compared with the transmission electron microscopy (TEM) experiments. The TEM analysis shows that the mean size of dislocation loops increases with the increasing atomic displacement damage dose, while the density of the observed loops exhibits minor change. To investigate the evolution of dislocation loops, we compare two cases incorporating mobile and immobile interstitial clusters in our modified model, respectively. The calculated results reveal a good agreement with experiments in the case of considering mobile interstitial clusters. It is included the motion of interstitial clusters plays an important role in the evolution of dislocation loops in RAFM steel. [ABSTRACT FROM AUTHOR]

Abstract: In present work, the irradiation damage in nickel-base alloy C-276 irradiated with Ar-ions was studied. Specimens of C-276 alloy were subjected to an irradiation of Ar-ions (with 120keV) to dose levels of 6 and 10dpa at 300 and 550°C, respectively. The size distributions and densities of dislocation loops caused by irradiation were investigated with transmission electron microscopy. Irradiation hardening due to the formation of the loops was calculated using the dispersed barrier-hardening model, showing that irradiation hardening was greatest at 300°C/6dpa. The microstructure evolution induced by Ar-ion irradiation (0–10dpa) in nickel-base alloy C-276 has been studied using a multi-scale modeling code Radieff constructed based on rate theory, and the size of dislocation loops simulated by Radieff was in good agreement with the experiment. [Copyright &y& Elsevier]

Abstract: In this paper, a new process to integrate methane aromatization over Mo/HZSM-5 catalyst with coal pyrolysis was put forward for improving tar yield. Shenmu coal was used to confirm the validity of the process. The effects of pyrolysis temperature, CH4 flow rate, Mo loading on the tar, water and char yields were investigated in an atmospheric fixed-bed reactor containing upper catalyst layer and lower coal layer. The results show that the tar yield can be improved by integrating the coal pyrolysis with methane aromatization. The tar yield is 21.5wt.% (daf) under the optimum conditions of 700°C pyrolysis temperature, 25ml/min CH4 flow rate, 4wt.% Mo loading and 30min holding time, obviously higher than 14.6% in N2 atmosphere and 15.3% in H2 atmosphere. Further studies confirm the synergistic effect between the coal pyrolysis and methane aromatization. [Copyright &y& Elsevier]

Abstract: Activated carbons (ACs) are of good potential to be the catalysts for methane decomposition to produce hydrogen without CO and CO2. Coal liquefaction residue (CLR) seems to be a promising precursor for ACs. In this work, several types of ACs were prepared by KOH activation from Shenhua CLR with addition of SiO2 or SBA-15. The catalytic activity and stability for methane decomposition were investigated and compared with commercial coal-based AC and carbon black (BP2000). The results show that the prepared ACs have larger surface area, narrower pore distribution, and higher catalytic activity than those directly prepared by KOH activation, and are superior to the commercial carbons. The increased microporosity resulting from the soluble salts formed by the reaction between the additive and KOH is responsible for the high catalytic activity. [Copyright &y& Elsevier]

Abstract: A novel plasma-treated Ni/MgO catalyst was prepared by treating coprecipitated NiCO3–MgCO3 with dielectric-barrier discharge plasma. The results by XRD, TEM and N2 adsorption analyses showed that the plasma-prepared Ni/MgO catalyst possessed smaller particle size, enhanced nickel dispersion, and higher specific surface area than a conventionally reduced Ni/MgO catalyst. The plasma-prepared Ni/MgO catalyst also exhibited better catalytic activity for carbon dioxide reforming of methane. More than 20% higher conversions of methane and carbon dioxide were obtained than those over the conventional Ni/MgO catalyst at 700°C and a space velocity of 96,000mL/(h∙gcat). [Copyright &y& Elsevier]

This research revealed the irradiation hardening mechanism in two novel NbZrTiV and VNbMoTaWTi refractory high entropy alloys (RHEAs). The RHEA sample irradiated by a dual-beam of 0.5 MeV protons and 2 MeV He ions at 300 K. Irradiation-induced defects were characterized by transmission electron microscope (TEM). It was discovered that the defect clusters were mostly consisted of nano-sized dislocation loops and bubbles. The density of defects was higher in the peak region than in the plateau region for both irradiated samples. The effects of irradiation-induced defects on hardening were evaluated by the nanoindentation test and dispersed barrier hardening (DBH) model. The results show that the peak region contributes more to the hardening than the plateau region in both irradiated alloys. The DBH hardness increments agree well with those measured by nanoindentation. Dual-beam irradiation led to ∼14% hardening for NbZrTiV and ∼ 18% for VNbMoTaWTi. The effects of the chemical disorder and lattice distortion induced by compositional complexity on defect formation and hardening were discussed. The excellent irradiation resistance makes RHEAs to be potential candidate materials used as core component in advanced nuclear reactors. • The irradiation effects of two novel BCC RHEAs were studied. • The relationship between irradiation hardening and irradiation-induced defects was established. • The mechanism of compositional complexity on irradiation tolerance of BCC RHEAs was discussed. [ABSTRACT FROM AUTHOR]

The vacuum electron beam welding (EBW) properties of Mo-14Re alloys were studied in this work. The weld morphology and microstructure were observed by optical microscope (OM) and scanning electron microscope (SEM). By using 3D Measuring Laser Microscope, energy dispersive spectroscopy (EDS), electronic probe micro analysis (EPMA) and transmission electron microscope (TEM), the weld pore was further characterized. In addition, its formation mechanism was analyzed. The results showed that the grains in fusion zone (FZ) of the powder metallurgy (PM) alloy weld obviously grew up to about 226.6 ± 75.7 μm and there were a large number of 12∼80 μm spherical pores. The element oxygen was enriched in the pores and a layer of MoO 2 was formed on the surface. The formation of pores may be closely related to the micropores and high oxygen content in the materials. Under the strong stirring of the molten pool, the generated carbon monoxide (CO) and molybdenum monoxide (MoO) bubbles couldn't escape and remained in the weld to form pores. However, no pores were found in the melted alloy weld. It was difficult to generate bubbles by homogeneous nucleation for the melted alloy. Due to the grain coarsening, the microhardness value of the weld significantly decreased. • Some pores with a size of 12∼80 μm were found in the powder metallurgy alloy weld. • A layer of MoO 2 was formed on the weld pore surface. • It is deduced that the CO and MoO bubbles were generated in the weld pool. • The grains in the weld were coarsened and the microhardness was obviously reduced. [ABSTRACT FROM AUTHOR]

[Display omitted] The point defect properties of body-centered cubic medium-entropy alloy NbZrTi were studied by first-principles calculations. Due to severe lattice distortion, a significant portion of conventional vacancy and interstitial structures are unstable and require large structural relaxation, indicating an irregular energy landscape with large site-to-site variations. The average vacancy and interstitial formation energy are 0.95 eV ± 0.34 eV and 1.92 eV ± 0.39 eV, respectively, much lower than that of Nb (2.77 eV and 4.38 eV). The vacancy migration energy exhibits a wide distribution extending to 0 eV, resulting in preferential vacancy migration through low barrier sites. The interstitial diffusion is slower than that of pure Nb due to the reduction of long <111> diffusion induced by the site-to-site variations in stable interstitial orientations. Ti atoms diffuse much faster than Nb and Zr atoms due to the preferential interstitial binding with Ti. The effect of atomic composition and short-range order on elemental and total interstitial diffusion was also investigated. The obtained first-principles results are important for the development of interatomic potentials for radiation damage studies. When irradiated with 3-MeV Fe ions at 675 ∘ C to a peak dose of ∼ 100 dpa, NbZrTi reduced the void formation at high temperature compared to Nb owing to its higher equilibrium vacancy concentration and closer mobility between vacancies and interstitial atoms. [ABSTRACT FROM AUTHOR]

• Interatomic potential for V-Ti-Ta ternary system based on F-S formalism has been developed. • The Ti potential well reproduce the point-defect properties of vacancy and self-interstitial atoms and the pressure-volume relation. • The typical defect energies of solute atoms Ti and Ta in the V matrix and Ti and V in the Ta matrix predicted by the present potential were in good agreement with DFT results. Vanadium (V)-based alloys are potential candidates for structural materials of fusion reactors because of their excellent properties; recently, the V–Ti–Ta alloy has received considerable attention. The irradiation-resistant performance is significant for the development and application of fusion reactor materials. In this study, combining with our previously developed potentials of V and Ta, we developed the V-Ti-Ta interatomic potential based on the Finnis–Sinclair (FS) formalism, which is an important step towards an atomic-scale investigation of V-based alloys. The potential parameters were determined by fitting to a large database of experimental data and density functional theory (DFT) calculations. The formation energies of vacancy and self-interstitial atoms, as well as the pressure-volume relation obtained from the present Ti potential, were well reproduced. The typical defect energies of solute atoms Ti and Ta in the V matrix and Ti and V in the Ta matrix, such as the formation energies of substitutional solute atoms, binding energies between solute atoms and point defects, agree well with DFT results. Thus, the developed potentials are expected to be suitable for atomistic simulations of point defects evolution in the V-Ti-Ta ternary system. [ABSTRACT FROM AUTHOR]

• Ti-V-Cr-Al light-weight medium entropy alloys are developed with outstanding tensile properties at the as-cast state. • The tensile ductility is much improved when Cr and Al are added equiatomically in the Ti 44 V 44 Cr x Al (12−x) alloys. • As-cast (TiV) 91 Cr 4.5 Al 4.5 alloy has a specific tensile yield stress of 160 MPa/(g/cm3) and a fracture elongation of 32%. [Display omitted] Light-weight (LW) high/medium entropy alloys have gained much attention due to the high specific strength, but they usually suffer from poor ductility, especially in the tensile tests at the as-cast state. In this study, the mechanical properties of a series of Ti-V-Cr-Al medium entropy alloys, with Ti and V maintaining equiatomic ratio, are investigated. An outstanding strength-ductility relationship is achieved in a (TiV) 91 Cr 4.5 Al 4.5 alloy, with a relatively low density of 5.1 g/cm3, a high specific yield strength of 160 MPa/(g/cm3), and a high tensile fracture elongation over 30%, even at its as-cast state. The tensile deformation is dominantly through the typical nucleation, planar migration, and entanglement of dislocations. Secondary phase formation and chemical inhomogeneity in this alloy are both insignificant. The frustration of dislocation motions are mainly attributed to the solid solution strengthening, which also enhances the work-hardening, delays the occurrence of necking, and benefits the overall ductility. The outstanding specific strength-ductility combination of this LW-alloy at the as-cast state makes it promising for potential engineering applications. [ABSTRACT FROM AUTHOR]