Creep of Polycrystalline Nickel

Minimum creep rates of nickel samples were measured in the stress region of 2.5×10⁷ to 2.8×10⁹ dyne per sq cm and the temperature region of 400° to 1100°C. The creep rate seems to be proportional to (stress)^4.6 at stresses below 7×10⁸ dyne per sq cm. The activation energy of creep is approximately 65,000 cal per mol.     

Structural changes associated with strain-induced grain boundary migration in Si-Fe

Strain-induced grain boundary migration was observed in several bicrystal sheet specimens of Si-Fe (3¼ pct Si) which were cold rolled 2 to 12 pct and then annealed at temperatures up to 1200°C. A chrome-acetic acid electroetching method was used to reveal the dislocation sites before and after grain boundary migration. Recovery effects were noted in the microstructure prior to boundary motion. Consequently, the residual strain energy in neighboring grains may determine if boundary migration with resulting increase of area occurs, and its direction of movement. Microstructural data indicate that the region initially traversed by the moving grain boundary has many structural defects in the form of low-angle boundaries and random dislocations of relatively high density. With increased distance of grain boundary migration, the density of these imperfections was found to decrease. Continued annealing at 1200°C, after boundary migration, lowered the density of random dislocations in the swept region to a limiting value of about 2×10⁶ lines per sq cm.     

The Microstructure Evolution of Dual-Phase Pipeline Steel with Plastic Deformation at Different Strain Rates

Tensile properties of the high-deformability dual-phase ferrite-bainite X70 pipeline steel have been investigated at room temperature under the strain rates of 2.5 × 10^?5, 1.25 × 10^?4, 2.5 × 10^?3, and 1.25 × 10^?2 s^?1. The microstructures at different amount of plastic deformation were examined by using scanning and transmission electron microscopy. Generally, the ductility of typical body-centered cubic steels is reduced when its stain rate increases. However, we observed a different ductility dependence on strain rates in the dual-phase X70 pipeline steel. The uniform elongation (UEL%) and elongation to fracture (EL%) at the strain rate of 2.5 × 10^?3 s^?1 increase about 54 and 74%, respectively, compared to those at 2.5 × 10^?5 s^?1. The UEL% and EL% reach to their maximum at the strain rate of 2.5 × 10^?3 s^?1. This phenomenon was explained by the observed grain structures and dislocation configurations. Whether or not the ductility can be enhanced with increasing strain rates depends on the competition between the homogenization of plastic deformation among the microconstituents (ultra-fine ferrite grains, relatively coarse ferrite grains as well as bainite) and the progress of cracks formed as a consequence of localized inconsistent plastic deformation.     

Temperature-Dependent Flow Behavior and Microstructural Evolution During Compression of As-Cast Mg-7.7Al-0.4Zn

The microstructure and mechanical properties improve substantially by hot working. This aspect in as-cast Mg-7.7Al-0.4Zn (AZ80) alloy is investigated by compression tests over temperature range of 30-439°C and at strain rates of 5 × 10^?2, 10^?2, 5 × 10^?4 and 10^?4 s^?1. The stress exponent (n) and activation energy (Q) were evaluated and analyzed for high-temperature deformation along with the microstructures. Upon deformation to a true strain of 0.80, which corresponds to the pseudo-steady-state condition, n and Q were found to be 5 and 151 kJ/mol, respectively. This suggests the dislocation climb-controlled mechanism for deformation. Prior to attaining the pseudo-steady-state condition, the stress-strain curves of AZ80 Mg alloy exhibit flow hardening followed by flow softening depending on the test temperature and strain rate. The microstructures obtained upon deformation revealed dissolution of Mg₁₇Al₁₂ particles with concurrent grain growth of α-matrix. The parameters like strain rate sensitivity and activation energy were analyzed for describing the microstructure evolution also as a function of strain rate and temperature. This exhibited similar trend as seen for deformation per se. Thus, the mechanisms for deformation and microstructure evolution are suggested to be interdependent.     

Organic conductor: Influence of preparation temperature

The conducting polypyrrole–polyethylene glycol (PPy–PEG) composite films were produced at various polymerization temperature ranging from 5 °C to 60 °C using 1 × 10^?3 M PEG, 0.20 M pyrrole and 0.10 M p-toluene sulfonate at 1.20 V (vs. SCE). The polymerization temperature of 5 °C appeared as the optimum preparation temperature showing the highest electrical conductivity of 70 S/cm and the thermal diffusivity of 8.76 × 10^?7 m² s^?1. The electrical conductivity and thermal diffusivity exhibited a decreasing trend with the increase in polymerization temperature in the pyrrole solution used to prepare the composite films. The XRD results reveal that low temperature (5 °C) typically results in more crystalline films, which are denser, stronger and have higher conductivity. The optical microscopy of PPy–PEG shows the globular surface morphology. The surface of the of the solution side of PPy–PEG film prepared at low temperatures showed a globular morphology.     

Simultaneous determination of trace Cu2+, Cd2+, Ni2+ and Co2+ in zinc electrolytes by oscillopolarographic second derivative waves

Simultaneous determination of impurity metal ions in high concentration zinc solution is very important for zinc hydrometallurgy, and the purpose is to establish a method for determining the trace Cu²⁺, Cd²⁺, Ni²⁺ and Co²⁺ in zinc electrolytes at the same time using the second derivative waves of single sweep oscillopolarography. Factors affecting the derivative waves of the ions were researched in a medium of dimethylglyoxime (DMG)-sodium citrate-sodium tetraborate. The results indicated that the interferences of a high concentration of Zn²⁺ and most other coexisting ions on the determination can be eliminated; when the Cu²⁺, Cd²⁺, Ni²⁺ and Co²⁺ are in the ranges of 1×10^?7-3×10^?4, 6×10^?7-2×10^?4, 2×10^?8-1×10^?5 and 1×10^?8-3×10^?5 mol/L, respectively, the relationships between the peak currents of the second derivative waves and the concentrations are linear; the detection limits to determine the Cu²⁺, Cd²⁺, Ni²⁺ and Co²⁺ are 8×10^?8, 2×10^?7, 6×10^?9 and 4×10^?9 mol/L, respectively. Without any sample pretreatment, the method was used to directly determine the trace Cu²⁺, Cd²⁺, Ni²⁺ and Co²⁺ in actual zinc electrolytes with satisfactory results. The method is simple, sensitive and rapid.     

Transgranular Stress-Corrosion Cracking

Abstract

The rates of dissolution of atoms from steps of different widths on a metal surface are calculated. It is shown that there is a critical spacing, below which the rate of dissolution possible from a step falls rapidly. This critical spacing is related to the solution viscosity and hence the solution composition and temperature by the relationship:

l _crit = 8 παb³η10¹³ √2V₂(ε_s ? ε_∞)/ε_s²KT³ For a stainless steel immersed in 42% MgCl₂ solution at 150°, the calculated critical value of the slip line spacing is 6 × 10^?5cm. This agrees well With the experimental observations, as a steel which has a spacing of 4 × 10^?5 cm. takes fifty times longer to fail in a stress-corrosion test under these conditions than does a steel with a spacing of 7 × 10^?5 cm. The reactivities of steps of different widths on copper alloys are also calculated and it is shown that slip line spacings found in cold worked copper-zinc alloys containing between 10–30% Zn lie in the critical range where the reactivity of the step changes rapidly with step width.     

7A85铝合金时效处理过程中位错密度演变的定量研究

采用X射线衍射（XRD）和透射电镜（TEM）研究了时效温度和时效时间对位错密度的影响,揭示了7A85铝合金时效过程中位错的演变规律。结果表明,当时效温度从80 ℃升高到160 ℃时,位错密度从3.59×10¹⁴ m^-2迅速降低到0.62×10¹⁴ m^-2,降低82.7%。同样,随着时效时间的延长,位错密度降低了41%,时效12 h后,位错密度趋于稳定。TEM结果表明,位错倾向于形成低能位错胞,并逐渐向亚晶转变。最后,根据XRD和TEM的结果,分别对位错纠缠态、位错胞和亚晶粒的位错密度进行了量化。     

Impurity-controlled Mo films as diffusion barriers for Cu metallization

Effects of vacuum conditions on the oxygen content and microstructure of Mo layers used with Cu gate lines as thin-film transistor-liquid crystal display diffusion barriers were investigated. Mo was deposited using ion-beam sputtering at 1.0 × 10^?5 and 7.0 × 10^?7 Torr. The Mo layer oxygen content and the microstructure and changes in chemical composition of the Cu/Mo/SiO₂/Si layer during annealing were examined. The Mo layer microstructure was influenced by oxygen; increasing concentration increased the energy required for secondary grain growth. Growth was suppressed at high oxygen levels. Therefore, diffusion barrier performance is enhanced by finer Mo layer grain sizes.     

Influence of oxygen partial pressure on properties of N-doped ZnO films deposited by magnetron sputtering

N-doped ZnO films were radio frequency(RF)sputtered on glass substrates and studied as a function of oxygen partial pressure(OPP)ranging from 3.0×10-4 to 9.5×10-3 Pa.X-ray diffraction patters confirmed the polycrystalline nature of the deposited films.The crystalline structure is influenced by the variation of OPP.Atomic force microscopy analysis confirmed the agglomeration of the neighboring spherical grains with a sharp increase of root mean square(RMS)roughness when the OPP is increased above 1.4×10-3 Pa.X-ray photoelectron spectroscopy analysis revealed that the incorporation of N content into the film is decreased with the increase of OPP,noticeably N 1s XPS peaks are hardly identified at 9.5×10-3 Pa.The average visible transmittance(380-700 nm) is increased with the increase of OPP(from～17%to 70%),and the optical absorption edge shifts towards the shorter wavelength.The films deposited with low OPP(≤3.0×10-4 Pa)show n-type conductivity and those deposited with high OPP(≥9.0×10-4 Pa)are highly resistive(105Ω·cm)     

A study on cobalt electrodeposition onto a carbon steel electrode

Abstract

The electrodeposition of cobalt on to a carbon steel working electrode was studied through the comparison between theoretical and experimental polarisation curves. The former was obtained using the Butler–Volmer equation with electrochemical parameters, such as Tafel slope values, exchange current densities, cathodic limit current densities and equilibrium potential values. The following results were obtained: the anodic region refers to the iron oxidation with a Tafel slope of about 0·055 V decade^?1, which is near the theoretical value (0·059 V decade^?1); the experimental cathodic region represents the cobalt and hydrogen ion reduction; the limiting current density (?1 × 10^?3 to ?1 × 10^?2 A cm^?2) obtained was near the calculated value, ?3·7 × 10^?3 A cm^?2.     

Accelerated Oxidation of V2O5-Deposited Copper

The accelerated-oxidation kinetics of V₂O₅-deposited copper were studied in the temperature range 560?C800 °C in air. The accelerated oxidation followed the parabolic-rate law, indicating that the process was diffusion-controlled. Oxygen diffusion along liquid channels in the oxide scale was inferred to be the rate-limiting step in the overall mechanism. The parabolic-rate constant increased from 3.4 × 10^?6 to 1.6 × 10^?5 kg² m^?4 s^?1 with increasing the deposit mass from 0.075 to 0.225 kg m^?2 at 700 °C.     

Electronic conduction mechanism in chitin–polyaniline blend

The electrical conductivity of chitin–polyaniline blend doped with HCl has been studied in the temperature range 323–373 K for various blend compositions. Conductivity of blends increases from less than ≈10^?7 S/cm to 2.15 × 10^?5 S/cm, depending on the percentage of polyaniline in the blend due to self-doping of LiCl. When these blends are doped with HCl conductivity raises to ≈9.68 × 10^?2 S/cm. Current–voltage data is analyzed using various models available. The results suggest Schottky–Richardson and one-dimensional variable range hopping mechanisms for undoped blend and one-dimensional variable range hopping mechanism in the case of doped blend.     

Electrical and Mechanical Properties of 3D-Printed Graphene-Reinforced Epoxy

Recent developments in additive manufacturing have demonstrated the potential for thermoset polymer feedstock materials to achieve high strength, stiffness, and functionality through incorporation of structural and functional filler materials. In this work, graphene was investigated as a potential filler material to provide rheological properties necessary for direct-write three-dimensional (3D) printing and electrostatic discharge properties to the printed component. The rheological properties of epoxy/graphene mixtures were characterized, and printable epoxy/graphene inks formulated. Sheet resistance values for printed epoxy/graphene composites ranged from 0.67 × 10² Ω/sq to 8.2 × 10³ Ω/sq. The flexural strength of printed epoxy/graphene composites was comparable to that of cast neat epoxy (~ 80 MPa), suggesting great potential for these new materials in multifunctional 3D-printed devices.     

Morphological evolution and growth kinetics of Kirkendall voids in binary alloy system during deformation process—Phase field crystal simulation study

The formation and growth of Kirkendall voids in a binary alloy system during deformation process were investigated by phase field crystal model. The simulation results show that Kirkendall voids nucleate preferentially at the interface, and the average size of the voids increases with both the time and strain rate. There is an obvious coalescence of the voids at a large strain rate when the deformation is applied along the interface under both constant and cyclic strain rate conditions. For the cyclic strain rate applied along the interface, the growth exponent of Kirkendall voids increases with increasing the strain rate when the strain rate is larger than 1.0×10^?6, while it increases initially and then decreases when the strain rate is smaller than 9.0×10^?7. The growth exponent of Kirkendall voids increases initially and then decreases gradually with increasing the length of cyclic period under a square-wave form constant strain rate.     

Effect of Strain Rate on Tensile Properties of Carbon Fiber Epoxy-Impregnated Bundle Composite

The tensile tests for high tensile strength polyacrylonitrile (PAN)-based (T1000GB) carbon fiber epoxy-impregnated bundle composite at various strain rates ranging from 3.33 × 10^?5 to 6.0 × 10² s^?1 (various crosshead speeds ranging from 8.33 × 10^?7 to 1.5 × 10¹ m/s) were investigated. The statistical distributions of the tensile strength were also evaluated. The results clearly demonstrated that the tensile strength of bundle composite slightly increased with an increase in the strain rate (crosshead speed) and the Weibull modulus of tensile strength for the bundle composite decreased with an increase in the strain rate (crosshead speed), there is a linear relation between the Weibull modulus and the average tensile strength on log-log scale.     

Preliminary Examination of the Quenching of Titanium Alloys

From the limited experimental data in the literature, preliminary values were derived for the thermal diffusivity of titanium alloys and for the quenching severity of various mediums used in heat treating them. The thermal diffusivity, under quenching conditions, was found to be approximately 0.006 sq in. per sec. The quenching severity H for brine is approximately 8, for water 4, for oil 0.9, for air 0.08, and for argon 0.02 in.^?1 The quenching severity of the Jominy-Boegehold end quench water jet against titanium alloys appeared effectively infinite. Using these results, graphs were prepared showing ideal round sizes and Jominy positions having cooled conditions equivalent to those at the center and surface of titanium alloy rounds, plates, and sheets quenched in various media.     

AZ41镁合金超塑性成形特性

研究AZ41镁合金在热轧(无后续热变形)条件下的显微组织变化,以确定其在超塑性成形工艺中的适用性,并确定最佳成形参数.采用高温拉伸试验和热气体胀形试验对材料在不同应变速率(1×10?1～1×10?3 s?1)和温度(350～450℃)下的成形性进行评估.利用GOM Aramis相机进行圆形网格分析,了解峰值应变和材料减...     

Corrosion Behavior of 9Cr-1Mo Steel in Sulfur Dioxide Environment

Corrosion behavior of annealed 9Cr-1Mo steel was studied in SO₂ environment at 1173 K, at flow rates from 8.33 × 10^?7 to 33.33 × 10^?7 m³/s, and parabolic rate law was followed. The rate constants were found to be independent of flow rate, within the range of flow rate investigated. Corrosion at temperatures from 973 to 1173 K, at a constant flow rate of 16.66 × 10^?7 m³/s, at 1 atmospheric pressure, for 6 h also exhibited parabolic law, however, the rate constants were observed to increase significantly with rise in temperature. The outer layer of the scale formed at 973 K was essentially of iron oxide, with small amount of chromium oxide whereas the inner layer was predominantly of chromium sulphide and chromium oxide. The scale formed at 1173 K was multilayered, in contrast to double layered formed at 973 K and 1073 K. The outer thick layer of the scale formed at 1173 K, consisted of iron oxide followed by thin substrate of chromium sulphide, iron sulphide/iron oxide, and chromium sulphide/chromium oxide toward the substrate. A model is proposed for the process of corrosion of 9Cr-1Mo steel in SO₂ environment, based on the present investigation.     

Direct measurements of shear band propagation in metallic glasses – An overview

A series of experimental efforts have recently made in an attempt to gain understanding of shear band propagation in metallic glasses. It was found that plastic flow serration observed in compression was actually caused by successive (intermittent) shear along a single shear plane, not random shear band emission. Several experimental techniques, including conventional Instron, attaching linear voltage differential transducer, strain gage, and high-speed camera, were employed to investigate shear band propagation during flow serration. The test results showed that the shear band propagation consisted of the acceleration, deceleration, and the final arrest. The maximum velocity of a propagating shear band was about 4 mm s^?1, which corresponds to a high strain rate of about 10⁵ s^?1. The viscosity of a propagating shear band was evaluated to be only about 1 × 10⁴–5 × 10⁵ Pa s, indicating the shear band was very fluidic. Video images capture from a high-speed camera also revealed that the shear was simultaneous, rather than in a progressive fashion.