Free-volume evolution of glassy Zr_(65)Al_(7.5)Ni_(10)Cu_(17.5) during inhomogeneous deformation

Free-volume evolutions of the as-cast and pre-annealed Zr65Al7.5Ni10Cu17.5 metallic glasses during cold-rolling were investigated using differential scanning calorimetry. As deformation degree increases, free volume in the glasses always increases first and then saturates above a critical strain, while the structure remains completely amorphous. The glass with less initial free volume possesses a higher increase rate of free-volume content during deformation, and as a result the free-volume contents of all the glasses approach each other at higher strains. Coalescence of free volume in shear bands into nanovoids is proposed to be responsible for the saturation of free-volume content at high strains.     

Influence of external constraint and rolling geometry on deformation banding of copper single crystals with {123}<634> orientation

In order to further understand the similarity and difference between deformation mechanisms of single crystals and polycrystalline materials, the influence of external constraint and rolling geometry on the deformation behaviour of copper single crystals with {123}<634> orientation was investigated by embedding them into metal frames of different strengths. The metal frames were made of aluminum and mild steel, respectively. The results show that the deformation banding degree of the crystal increases with the strength of metal frame and shear strain. For the crystals rolled under lower γ_g (γ_g is the ratio of the geometrical redundant shear strain to the normal rolling strain), the deformation is homogeneous. For the crystals rolled under higher γ_g, the deformation is extremely inhomogeneous. The deformation is more homogeneous in the crystals rolled in steel frames than that rolled in aluminum frames. The S-orientation is more stable in the crystals rolled under lower γ_g than that rolled under higher γ_g.     

Microstructural morphology of the semi-solid high carbon steel T12 before and after rheo-rolling

The semi-solid high carbon steel T12 was rolled in a closed box groove under a certain condition by the rheo-rolling equipment, and the microstructural morphology of the semi-solid T12 before and after deformation was investigated by optical microscope to analyze and summarize the microstructure evolution law of T12 deformed in semi-solid state. The experiment results show that the grain shape before deformation of the semi-solid T12 steel displays globule or ellipse by the electromagnetic stirring, the distribution of solid and liquid phases is homogeneous. But the microstructure of semi-solid product after rheo-rolling exhibits macrosegregation that the distribution of liquid and solid phases changes, the liquid phases divorce from the solid phases. In the transverse section, most of the solid phases get together in the center of the specimen, the liquid phases flow to the surface or the edge of the specimen, and the grains occur plastic deformation while reduction increased. In longitudinal section, the middle microstructure of the specimen is more homogeneous than that at the head or tail, the head microstructure is similar to the tail and the size of the grains is not homogeneous.     

Microstructural morphology of semi-solid high carbon steel T12 before and after rheo-rolling

The semi-solid high carbon steel T 12 was rolled in closed box groove under a certain condition by the rheo-rolling equipment developed by our research group, and the microstructural morphology of semi-solid T12 before and after deformation was investigated by optical microscope in order to analysis and summarize the microstructure evolution law of T 12 deformed in semi-solid state. The experiments results show that the grains shape before deformation of semi-solid T12 steel display globule or ellipse by the electromagnetic stirring, the distribution of solid and liquid phase is homogeneous, but the microstructure of semi-solid product after rheo-rolling exhibits macrosegregation that distribution of liquid and solid phases changes, the liquid phases divorce from the solid phases, most of solid phases get together in the center of the specimen and liquid phases flow to the surface or the edge of the specimen, the grains occur plastic deformation while reduction increased in transact. The middle microstructure is more homogeneous than head or tail position in longitudinal direction, the head microstructure is similar to the tail and the size of grain is not homogeneous.     

Hot deformation behavior of a Cr-containing low carbon steel in the ferrite range

A low carbon steel with Cr addition of 0.46wt% combined with trace elements of Mn and Ti was studied. The apparent activation energy of deformation and the hot deformation equation of the steel in the ferritic range were determined by means of single hot compression tests. The hot-rolled strip of 3 mm in thickness rolled in the ferritic range was obtained using a laboratory hot rolling mill. The mechanical properties show that the values of yield strength and ultimate tensile strength are 230 and 330 MPa, respectively, and the elongation is 33%. The average r-value is 1.1. Large polygonal ferrite recrystallization grains with about 40 grn in size and the strong { 111 } recrystallization texture can be obtained in the hot-rolled strip.     

Work toughening effect in Zr_（41）Ti_（14）Cu_（12.5）Ni_（10）Be_（22.5） bulk metallic glass

Work hardening is a well-known phenomenon occurring in crystalline metals during deformation,which has been widely used to increase the strength of metals although their ductility is usually reduced simultaneously. Here we report that the plastic strain of Zr41Ti14Cu12.5Ni10Be22.5 (at.%) bulk metallic glasses has been increased from 0.3% for the as-cast sample to 2.5%-8.0% for samples that have experienced pre-deformation under constrained conditions. The pre-deformed glassy alloys possess more free volume and abundant introduced shear bands,which are believed to promote the activation of shear bands in post-deformation and result in an increase in plasticity. The orientation of the pre-introduced shear bands relative to the loading direction will affect the deformation behavior of pre-deformed samples. The present results show that pre-deformation of this glassy alloy will result in work toughening. This work toughening effect can be removed by isothermal annealing at a sub-Tg (glass transition) temperature,which causes annihilation of free volume and healing of shear bands.     

The first record of Helicoprion Karpinsky （Helicoprionidae） from China

A new species,Helicoprion jingmenense sp. nov.,from the Lower Permian Qixia Formation of Hubei Province,China,is described based on a nearly complete symphyseal tooth spiral preserved as part and counterpart. The specimen is a large elliptical symphyseal tooth spiral with 41/3 volutions,with cutting blade being relatively wide,and its width being greater than the height after 31/2 volution,middle portion being higher than the cutting blade,narrowed base being short. There is a distinct space not covered by enameloid in two adjacent tooth crowns in the outermost two volutions; the height of the compound root is moderate,and the ventral groove is about 1/10 of the same tooth crown. In com-parison with other known Helicoprion species of the world,the new species resembles H. ferrieri and H. bessonowi. However,it can be easily distinguished from H. ferrieri by the wider cutting blade,the shorter narrowed base and lower compound root,and also from H. bessonowi by its more narrowed compound root and less than 39 tooth crowns per volution. Helicoprion jingmenense sp. nov. is obvi-ously different from helicoprionid species previously found in China in general shape,size and his-tology. However,it is very difficult to identify their relationships because of the fragmentary nature of holotypes of the latter. Because the new specimen is the first record of Helicoprion and the most com-plete fossil dentition of helicoprionids from China,the new species is of significance for biostratigra-phy and paleobiogeography.     

Effect of oxygen on the microstructure and mechanical properties of Ti-23Nb-0.7Ta-2Zr alloy

The influence of oxygen content on the microstructure and mechanical properties of Ti-23Nb-0.7Ta-2Zr (at%) alloy in as-cast and cold-rolled states was investigated systematically in this paper. It is found that the alloy containing oxygen element is only composed of a single β phase, while the alloy without oxygen element consisted of β and α″ phases. Although the grain size becomes larger, the elastic deformation ratio, strength, and hardness of the alloy are all increased with an increase of oxygen content. The as-cast alloy has excellent plastic deformation ability, but the cold-rolled alloy containing oxygen element exhibits brittle characteristics. A conclusion can be drawn that oxygen element can stabilize β phase, inhibit the phase transformation from β to α″, and furthermore help to increase the strength and elastic deformation ability of the alloy.     

Influence of reaction stresses induced by dislocation slips on the orientation evolution in bcc metals

A plastic deformation model for bcc metals is proposed in consideration of reaction stresses.The shear strains and the corresponding reaction stresses induced by the activation of dislocations are calculated in the model,which will influence the following dislocation activation.The rolling texture in bcc metals is simulated up tp 80% reduction,whille the ratio of critcal resolved shear stresses between the dislocations slippingon the {110}and{112}planes is chosen as 0.95.The corresponding calculation is also conducted with the activation of second dislocation,if the difference between the orientation factor of the two dislocations with maximal orientation factors is lower than 5%.It is shown that the simulated texture is closer to that of the 80% rolled interstitial free steels than other modeling.It is believed that the new model can give more attention to both of the strain and stress continuities during the plastic deformation of polycrystalline metals,and therefore approaches closer to the real deformation process in bcc metals.     

Effect of cold working and sandblasting on the microhardness,tensile strength and corrosion resistance of AISI 316L stainless steel

The aim of this work is to investigate the effect of cold working and sandblasting on the microhardness, tensile strength and corrosion rate of AISI 316L stainless steel. The specimens were deformed from 17% to 47% and sandblasted for 20 min using SiC particles with a diameter of 500-700 μm and an air flow with 0.6-0.7 MPa pressure. The microhardness distribution and tensile test were conducted and a measurement on the corrosion current density was done to determine the corrosion rate of the specimens. The result shows that the cold working enhances the bulk microhardness, tensile and yield strength of the specimen by the degree of deformation applied in the treatment. The sandblasting treatment increases the microhardness only at the surface of the specimen without or with a low degree of deformation. In addition, the sandblasting enhances the surface roughness. The corrosion resistance is improved by cold working, especially for the highly deformed specimen. However the follow-up sandblasting treatment reduces the corrosion resistance. In conclusion, the cold working is prominent to be used for improving the mechanical properties and corrosion resistance of AISI 316L stainless steel. Meanwhile, the sandblasting subjected to the cold worked steel is only useful for surface texturing instead of improving the mechanical properties and corrosion resistance.     

Rolling-induced microstructure change in Zr_(65)Al_(7.5)Ni_(10)Cu_(12.5)Ag_5 bulk metallic glass

The microstructures and free-volume evolutions of as-cast and pre-annealed Zr65Al7.5Ni10Cu12.5Ag5 bulk metallic glasses during rolling deformation have been investigated. No phase transformation is detected in the as-cast/rolled specimen. However,the structural stability of the glass against plastic deformation is worse after pre-annealing,indicated by nanocrystallization in preannealed/rolled specimens with large deformation degrees. Moreover,with increasing deformation degree,the free-volume content in a ...     

Free-volume evolution of glassy Zr65Al7.5Ni10Cu17.5 during inhomoseneous deformation

Free-volume evolutions of the as-cast and pre-annealed Zr65Al7.5Ni10Cu17.5 metallic glasses during cold-rolling were investigated using differential scanning calorimetry. As deformation degree increases, free volume in the glasses always increases first and then saturates above a critical strain, while the structure remains completely amorphous. The glass with less initial free volume possesses a higher increase rate of free-volume content during deformation, and as a result the free-volume contents of all the glasses approach each other at higher strains. Coalescence of free volume in shear bands into nanovoids is proposed to be responsible for the saturation of free-volume content at high strains.     

Electrochemical properties of LiNi<Subscript>0.5</Subscript>Mn<Subscript>1.3</Subscript>Ti<Subscript>0.2</Subscript>O<Subscript>4</Subscript>/Li<Subscript>4</Subscript>Ti<Subscript>5</Subscript>O<Subscript>12</Subscript> cells

Spinel compounds LiNi_0.5Mn_1.3Ti_0.2O₄ (LNMTO) and Li₄Ti₅O₁₂ (LTO) were synthesized by different methods. The particle sizes of LNMTO and LTO are 0.5–2 and 0.5–0.8 μm, respectively. The LNMTO/LTO cell exhibits better electrochemical properties at both a low current rate of 0.2C and a high current rate of 1C. When the specific capacity was determined based on the mass of the LNMTO cathode, the LNMTO/LTO cell delivered 137 mA·h·g⁻¹ at 0.2C and 118.2 mA·h·g⁻¹ at 1C, and the corresponding capacity retentions after 30 cycles are 88.5% and 92.4%, respectively.     

Polysaccharide separation mechanism in polysulfone-Fe<Subscript>3</Subscript>O<Subscript>4</Subscript> magnetic composite membranes

Polysulfone (PSF)-Fe3O4 composite membranes were prepared by the phase-inversion process and their polysaccharide separation mechanism was explored using chondroitin sulfate (CS) and dextran. The mechanism was analyzed from constraints on the magnetic field and geometric deformation. It was found that variations in dextran rejection from 58% to 46% were mainly influenced by the geometric deformation of the composite membrane, while the magnetic field had a significant influence on variations in CS rejection from 82% to 35%. The results indicate that it is possible to continuously separate different types of polysaccharide with a composite membrane by adjusting the external magnetic field.     

Preparation and radar-absorbing properties of Al<Subscript>2</Subscript>O<Subscript>3</Subscript>/TiO<Subscript>2</Subscript>/Fe<Subscript>2</Subscript>O<Subscript>3</Subscript>/Yb<Subscript>2</Subscript>O<Subscript>3</Subscript> composite powder

Al₂O₃/TiO₂/Fe₂O₃/Yb₂O₃ composite powder was synthesized via the sol-gel method. The structure, morphology, and radar-absorption properties of the composite powder were characterized by transmission electron microscopy, X-ray diffraction analysis and RF impedance analysis. The results show that two types of particles exist in the composite powder. One is irregular flakes (100-200 nm) and the other is spherical Al₂O₃ particles (smaller than 80 nm). Electromagnetic wave attenuation is mostly achieved by dielectric loss. The maximum value of the dissipation factor reaches 0.76 (at 15.68 GHz) in the frequency range of 2-18 GHz. The electromagnetic absorption of waves covers 2-18 GHz with the matching thicknesses of 1.5-4.5 mm. The absorption peak shifts to the lower-frequency area with increasing matching thickness. The effective absorption band covers the frequency range of 2.16-9.76 GHz, and the maximum absorption peak reaches -20.18 dB with a matching thickness of 3.5 mm at a frequency of 3.52 GHz.     

Electro-deoxidation of V<Subscript>2</Subscript>O<Subscript>3</Subscript> in molten CaCl<Subscript>2</Subscript>-NaCl-CaO

The electro-deoxidation of V₂O₃ precursors was studied. Experiments were carried out with a two-terminal electrochemical cell, which was comprised of a molten electrolyte of CaCl₂ and NaCl with additions of CaO, a cathode of compact V₂O₃, and a graphite anode under the potential of 3.0 V at 1173 K. The phase constitution and composition as well as the morphology of the samples were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). 3 g of V₂O₃ could be converted to vanadium metal powder within the processing time of 8 h. The kinetic pathway was investigated by analyzing the product phase in samples prepared at different reduction stages. CaO added in the reduction path of V₂O₃ formed the intermediate product CaV₂O₄.     

Chemical quenching and inhibition of positronium in Cr<Subscript>2</Subscript>O<Subscript>3</Subscript>/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> catalysts

The pore structure of Cr2O3/Al2O3 catalysts and the surface chemical properties of these pores were characterized by positron lifetime and coincidence Doppler broadening (CDB) measurements. Four lifetime components could be resolved from the positron lifetime spectrum, with two long lifetime components and two short lifetime components. The two long lifetimes τ4 and τ3 are attributed to ortho-positronium (o-Ps) annihilation in large pores and microvoids, respectively. With increasing Cr2O3 content, both τ4 and its intensity I4 show sharp decrease, while τ3 and its intensity I3 keep nearly unchanged. The Doppler broadening S parameters also show sharp decrease with increasing Cr2O3 content. Detailed analysis of the CDB spectrum reveals that the parapositronium (p-Ps) intensity also decreases with increasing Cr2O3 content. This indicates that the change of o-Ps lifetime τ4 is due to the chemical quenching by Cr2O3 but not spin-conversion of positronium. The decrease of o-Ps intensity I4 indicates that Cr2O3 also inhibits positronium formation.     

Preparation and upconversion luminescence of YVO<Subscript>4</Subscript>:Er<Subscript>3+</Subscript>, Yb<Subscript>3+</Subscript>

YVO₄:Er³⁺, Yb³⁺ with varying Yb³⁺ concentrations were prepared by a precipitation method. The results of X-ray diffraction (XRD) show that all the samples have a tetragonal zircon structure; the calculated average crystallite sizes are in the range of 14–22 nm. The lattice constants and cell volume of the samples decrease slightly with the increase in Yb³⁺ concentration. The upconversion luminescence spectra of all the samples were studied under 980 nm laser excitation. The strong green emission is observed, which is attributed to the ²H_11/2 → ⁴I_15/2 and ⁴S_3/2→⁴I_15/2 transitions of Er³⁺, and the red emission peaks in 650–675 nm can be ignored. The emission intensity for the sample depends on the Yb³⁺ concentration. These results reveal that the upconversion processes of YVO₄:Er³⁺, Yb³⁺ are related to the structure and the doping Yb³⁺ concentration of the sample.