Microstructural characteristics of tungsten-base nanocomposites produced from micropowders by high-pressure torsion

Micropowder mixtures of W–50% Al, W–50% Ti and W–50% Ni were subjected to severe plastic deformation at 573 K using high-pressure torsion (HPT). The powder mixtures were consolidated and nanocomposites of W/Ti, W/Ti and W/Ni, with average grain sizes as small as ～9, ～15 and ～12 nm, respectively, were formed by imposing large shear strains. The nanocomposites exhibited Vickers microhardness as high as ～900 Hv, a level that has rarely been reported for metal–matrix composites. X-ray diffraction analyses together with high-resolution transmission electron microscopy showed that in addition to grain refinement, an increase in the fraction of grain boundaries up to 20%, the dissolution of elements in each other up to ～15 mol.%, an increase in the lattice strain up to 0.6%, and an increase in density of edge dislocations up to 10¹⁶ m^?2 occurred by HPT. The current study introduces the HPT process as an effective route for the production of ultrahigh-strength W-base nanocomposites, fabrication of which is not generally easy when processing at high temperatures because of interfacial reaction and formation of brittle intermetallics.     

Atom probe tomography of nanoscale microstructures within precipitate free zones in Al–Zn–Mg(–Ag) alloys

Solute distributions in the vicinity of grain boundaries in Al–Zn–Mg(–Ag) alloys were studied using a three-dimensional atom probe, in order to elucidate the mechanism of formation of precipitate free zones (PFZs) and the fundamental role of Ag in controlling PFZ width. It is shown that nanoscale clusters are formed within the PFZ in Al–Zn–Mg, despite the solute concentration remaining at the levels in the as-quenched state. Such observations have not previously been possible, and show unambiguously that vacancy depletion is the dominant mechanism of formation of PFZs in this alloy. In the Ag-containing alloy, a narrower PFZ is observed, with a reduced solute level, showing that here the dominant mechanism of PFZ formation is solute depletion. The role of Ag in this change of mechanism appears to be due to its favorable interactions not only with Mg and Zn atoms but also with vacancies.     

用可变长度热源模拟奥氏体不锈钢多层焊对接接头的焊接残余应力

采用可变长度热源模型对奥氏体不锈钢平板多层焊对接接头的残余应力进行了数值模拟,同时也用实验方法测量了平板对接接头上下表面的残余应力,通过比较由热弹塑性有限元计算得到的残余应力与由电阻应变片法测量得到的实验结果得知,采用该模型对多层焊对接接头残余应力的数值模拟,不仅可以大大缩短计算时间,也可以得到较高的计算精度。     

High-pressure torsion of TiFe intermetallics for activation of hydrogen storage at room temperature with heterogeneous nanostructure

TiFe is a potential candidate for the stationary hydrogen storage systems, but it requires initial activation to absorb hydrogen. This study shows that TiFe processed by high-pressure torsion (HPT) absorbs and desorbs 1.7 wt.% hydrogen at room temperature without activation. The absorption pressure decreases from 2 MPa in the first hydrogenation cycle to 0.7 MPa in the latter cycles. The HPT-processed TiFe exhibits heterogeneous microstructures composed of nanograins, coarse-grains, amorphous-like phases and disordered phases with a high hardness of ∼1050 Hv.     

Dietary Protein Derived from Dried Bonito Fish Improves Type‐2 Diabetes Mellitus‐Induced Bone Frailty in Goto‐Kakizaki Rats

Type‐2 diabetes mellitus (T2DM) induces bone frailty. Protein and polyunsaturated fatty acids (PUFA) contained in fish can be effective in enhancing bone quality, but the bone developing effect of fish protein containing less PUFA has not been evaluated in young animals with T2DM. We prepared a bonito fish (BF) and defatted BF (DBF) and hypothesized that protein contained in BF and DBF would be effective for mitigating the effects of T2DM‐induced bone frailty. We mainly evaluated the effect of dietary BF and DBF on bone and apparent calcium absorption in young Goto‐Kakizaki (GK) rats with T2DM. GK rats were divided into 3 groups based on diets (casein, BF, and DBF) and fed with each diet for 6 wk. Wistar rats were fed with the casein diet as a non‐T2DM control. Bone mass, bone strength, apparent calcium absorption, and serum biochemical parameters were determined. The dry weight and strength of the femurs were lower in the GK rats than in the Wistar rats fed with the casein diet. Dietary intake of the BF and DBF diets enhanced the maximum load and dry weight of the femurs and suppressed the serum alkaline phosphatase activity although the apparent calcium absorption was lower in the GK rats fed with the BF and DBF diets than in those fed with the casein diet. These parameters were not different between the rats fed with the BF and DBF diets. Our data suggest that protein contained in the BF and DBF diets improved T2DM‐induced bone frailty.     

Remarkable effect of ordered mesoporous carbon support in tantalum oxide-catalyzed selective epoxidation of cyclooctene

The olefin epoxidation is one of the most important reactions in chemical industry. Metal oxide supports often cause drawbacks in catalytic activity and selectivity, which has been overcome by introducing hydrophobic organic groups onto the oxide supports. The present study utilizes ordered mesoporous carbon (CMK-3 and CMK-1) as structurally defined hydrophobic catalyst support. Well-dispersed tantalum oxides supported on the ordered mesoporous carbon were prepared. Their application in catalytic epoxidation of cyclooctene demonstrates that the tantalum oxide catalysts on the ordered mesoporous carbon supports show higher performances than those of the catalysts supported on activated carbon and ordered mesoporous silica SBA-15.     

Rheological properties and stability of oil-in-water emulsions containing tapioca maltodextrin in the aqueous phase

The present research focuses on the effect of the concentration and dextrose equivalent (DE) values of tapioca maltodextrin in the aqueous phase on rheological behavior and stability of oil-in-water emulsions prepared with Tween80. The critical flocculation concentrations (CFCs) of oil-in-water emulsions containing tapioca maltodextrin with DE of 16 (DE16), 12 (DE12) and 9 (DE9) were 11%, 9% and 7% (w/w) respectively, as revealed by transmittance measurement. Coalescence was observed as maltodextrin concentration increased above the CFC. The rheological parameters of flow behavior index (n) and consistency index (k) have been well-described by the Herschel–Bulkley model. The relative consistency index (k_relative) increased markedly when the concentration of maltodextrin exceeded the CFC because of depleting flocculation. The consistency index (k_emulsion) and yield stress (τ₀) of emulsions containing tapioca maltodextrin increased with increasing maltodextrin concentration or decreasing DE. The emulsions containing maltodextrin showed Newtonian flow behavior when the maltodextrin concentration was below the CFC. At maltodextrin concentrations above the CFC, emulsions containing maltodextrin exhibited shear thinning behavior. An increase in the maltodextrin concentration resulted in a decrease in the n_emulsion until maltodextrin concentration reached 20% (w/w) for DE9, DE12 and 25% (w/w) for DE16. Further increase in the maltodextrin concentration resulted in an increased the n_emulsion because of predominant influence of the continuous phase.     

Turbulent burning velocity of hydrogen–air premixed propagating flames at elevated pressures

Lewis number represents the thermo-diffusive effects on laminar flames. That of hydrogen–air mixture varies extensively with the equivalence ratio due to the high molecular diffusivity of hydrogen. In this study, the influences of pressure and thermo-diffusive effects on spherically propagating premixed hydrogen–air turbulent flames were studied using a constant volume fan-stirred combustion vessel. It was noted that the ratio of the turbulent to unstretched laminar burning velocity increased with decreasing equivalence ratio and increasing mixture pressure. Turbulent burning velocity was dominated by three factors: (1) purely hydrodynamic factor, turbulence Reynolds number, (2) relative turbulence intensity to reaction speed, the ratio of turbulence intensity to unstretched laminar burning velocity, and (3) sensitivity of the flame to the stretch due to the thermo-diffusive effects, Lewis and Markstein numbers. A turbulent burning velocity correlation in terms of Reynolds and Lewis numbers is presented.