Rate-dependent serrated flow and plastic deformation in Ti45Zr16Be20Cu10Ni9 bulk amorphous alloy during nanoindentation

The plastic deformation of Ti₄₅Zr₁₆Be₂₀Cu₁₀Ni₉ bulk metallic glass has been investigated by nanoindentation performed with loads ranging from 10 to 200 mN in a wide range of loading rates. The plastic flow in the alloy exhibited conspicuous serrations at low loading rates. The serrations, however, became less prominent as the rate of indentation increased. Atomic force microscopy showed a significant pile-up of materials around the indents, indicating that a highly localized plastic deformation occurred under nanoindentation. The possible mechanism governing the plastic deformation in bulk metallic glass specimens is tentatively discussed in terms of strain-induced free volume.     

Rate-dependent serrated flow and plastic deformation in Ti45Zr16Be20Cu10Ni9 bulk amorphous alloy during nanoindentation

Abstract

The plastic deformation of Ti₄₅Zr₁₆Be₂₀Cu₁₀Ni₉ bulk metallic glass has been investigated by nanoindentation performed with loads ranging from 10 to 200 mN in a wide range of loading rates. The plastic flow in the alloy exhibited conspicuous serrations at low loading rates. The serrations, however, became less prominent as the rate of indentation increased. Atomic force microscopy showed a significant pile-up of materials around the indents, indicating that a highly localized plastic deformation occurred under nanoindentation. The possible mechanism governing the plastic deformation in bulk metallic glass specimens is tentatively discussed in terms of strain-induced free volume.     

Effect of randomization on ductility of brittle Fe-Si-B glass

Using the Vickers indentation method, a critical plastic deformation energy, E _c, of collapse was proposed to be a convenient measurement to determine the ductility. It was found that the randomization increases the E _c value of a brittle Fe-Si-B alloy glass which is cooled slowly. Namely, the randomization enhances the ductility of the metallic glass.     

Failure of brittle polymers by slow crack growth

The mechanical properties of a silica particle-filled epoxy resin composite system have been investigated in air as a function of volume fraction of particles for volume fractions ranging from 0 to 0.52. The Young's modulus and the compressive yield stress both increase as the volume fraction of silica particles is increased and various models of particle strengthening have been used to explain this behaviour. Slow crack growth in the various particulate composites has been studied using a fracture mechanics approach. The variation of crack velocity (V) with stress intensity factor (K _I) has been measured for each of the compositions investigated. In each case, a unique relationship between V and K _I has been found with K _I increasing with volume fraction of particles at a given value of V. The failure mechanisms and the variation of other fracture mechanics parameters, for example, crack opening displacement and plastic zone size with increasing particle volume fraction have been discussed.     

Structural and electrochemical behaviour of sputtered vanadium oxide films: oxygen non-stoichiometry and lithium ion sequestration

Structural and electrochemical aspects of vanadium oxide films recently reported from ICMCB/ ENSCPB have been examined using appropriate structural models. It is shown that amorphous films are nonstoichiometric as a result of pre-deposition decomposition of V₂O₅. It is proposed that the structure of amorphous films corresponds to a nanotextured mosaic of V₂O₅ and V₂O₄ regions. Lithium intercalation into these regions is considered to occur sequentially and determined by differences in group electronegativities. Open circuit voltages (OCV) have been calculated for various stoichiometric levels of lithiation using available thermodynamic data with approximate corrections. Sequestration of lithium observed in experiments is shown to be an interfacial phenomenon. X-ray photoelectron spectroscopic observation of the formation of V³⁺ even when V⁵⁺ has not been completely reduced to V⁴⁺ is shown to be entirely consistent with the proposed structural model and a consequence of initial oxygen nonstoichiometry. Based on the structural data available on V₂O₅ and its lithiated products, it is argued that the geometry of VO_n polyhedron changes from square pyramid to trigonal bipyramid to octahedron with increase of lithiation. A molecular orbital based energy band diagram is presented which suggests that lithiated vanadium oxides, Li_xV₂O₅, become metallic for high values ofx.     

Plastic flow and fracture of Pd40Ni40P20 metallic glass under an indentor

The geometry of plastic flow under spherical and Vickers indentors in Pd₄₀Ni₄₀P₂₀ metallic glass has been investigated by sectioning and etching. The surface pile-ups and slip lines around the indentations are found to be only a small part of the total deformation. Beneath the surface extensive plastic zones are formed in which material is moved radially away from the indentor, but this movement is produced by slip on surfaces of high shear stress rather than by direct radial flow or compaction. Networks of cracks or incipient cracks also form around an indentation but are not normally visible until the material is etched.     

Impedance spectroscopy studies of orthorhombic FeNbO4

Electrical characterization of the FeNbO₄ compound, with orthorhombic structure, has been carried out. Compact bodies were prepared by sol-gel and ceramic routes. Pellets for electrical measurement were sintered in air, and samples for electrical tests were electroded with platinum, gold and silver paste. Equivalent circuit models were established that fit the impedance spectroscopy data with good agreement. Comparison of impedance responses showed that samples prepared by different routes have similar electrical behaviour. These measurements, in conjunction with I–V characteristic curves, indicate the existence of a small bulk resistance, which does not change at the higher experimental temperatures considered. Interfacial impedances due to the metallic contact regions contribute the greatest part of the overall impedance. The response of the sample with different electrode materials (platinum, gold, silver) was studied. I–V characteristic curves indicate a space charge-limited current phenomenon at the platinum contact, followed by a charge avalanche process at higher voltages.     

Structure and properties of impact diamonds from the Popigai Deposit and polycrystals based on them

Properties of impact diamonds from the Popigai Deposit have been studied in a free state and in a composition of a compact. Raman spectra have been taken of the initial micron powders and polycrystals HP-HT sintered both in the presence of sintering aids and without them. Hardness, H _V , of sintered polycrystals have been found, structural variations in diamond crystal lattice depending on the sintering conditions have been studied.     

The fracture toughness of bast fibre reinforced polyester composites Part 1 Evaluation and analysis

Hemp and jute fibre reinforced polyester composites were fabricated to various fibre volume fractions (V _f) up to 0.45. Laminates reinforced with a chopped strand mat (CSM) glass fibre were also manufactured. The tensile properties of these materials were evaluated. Fracture toughness was assessed, using linear elastic fracture mechanics (LEFM) principles, under quasi-static loading conditions. At equivalent V _f (0.2) it was found that the fracture toughness (K _Ic) of the CSM glass fibre reinforced material was approximately 3 times greater than that of the natural fibre reinforced laminates and an order of magnitude greater than the unreinforced polymer alone. Critical strain energy release rates (G _c) and plastic zone radii were computed. The G _c of the natural fibre reinforced laminates was approximately an order of magnitude lower than that of the CSM reinforced material at the same V _f. It was hypothesised that the size of the crack-tip plastic zone influences the energy absorbing capacity of the material. By comparing the relative volumes of the plastic zones, implications regarding the toughening mechanisms operative in natural fibre reinforced composites have been made. The applicability of LEFM to characterise toughness in these materials is discussed.     

Mg-based hydrogen storage materials: Surface segregation in Mg2Cu and related catalytic effects

Fresh surfaces of Mg₂Cu polycrystals cleaved in UHV have been investigated by AES, XPS and X-ray induced AES at room temperature. They show chemical decomposition of the surface leading to pronounced increase of surface Mg content. In contrast to the Mg the Cu remains essentially metallic, even on air exposed samples. It is suggested that this segregation prevents the formation of a compact oxide or hydroxide layer, thereby enabling dissociation of molecular hydrogen at the metallic Cu precipitations and/or the metallic Mg₂Cu subsurface. The results support comparable conclusions drawn earlier for LaNi₅, FeTi and Mg₂Ni.     

Mechanical and corrosion behaviour of in situ intermetallic phases reinforced Mg-based glass composite

A (Mg₆₅Cu₁₀Ni₁₀Y₁₀Zn₅)₉₁Zr₉ bulk metallic glass matrix composite, reinforced by in situ formed intermetallic phase, has been fabricated. In contrast to the monolithic Mg-based bulk metallic glasses (BMGs), the composite showed much higher fracture strength of 1039?MPa and a significant plastic strain of more than 5%. Moreover, the effect of in situ formed intermetallic phase on the corrosion behaviour of the composite was also studied. The results indicated that the corrosion resistance of the composite was only slightly lower than that of the monolithic Mg-based BMGs, but still much higher than that of the AZ31 magnesium alloy. This finding gives us a new clue to enhance the mechanical properties and corrosion resistance of Mg-based alloy by designing appropriate metallic glass composites.     

Impacts of energy efficiency standard on motor energy savings and emission reductions

Electrical motors use about 30–80% of total industrial energy for some selected countries around the world. Experiences from other countries show that government intervention in the form of regulations such as mandatory and voluntary approaches can save huge amount of energy along with the reduction of emissions associated with energy savings. In this paper, use of high efficient motors to replace standard motors to save energy have been quantified and presented. Emission reductions associated with the energy savings have been estimated and presented as well. Based on estimation, it has been found that 15,111, 6507 and 4295 MWh of energy can be saved for 50, 75 and 100% motor loadings, respectively, for using high efficient motors. These savings will correspond to US967,074, US 967,074, US 416,461 and US$ 274,892 savings for 50, 75 and 100 motor loadings, respectively, by replacing standard motors with high efficiency motors. It was also found that 7,562,070 kg of CO₂, 45,266 kg of SO₂, 21,326 kg of NO _x and 4,599 kg of CO could be avoided by using energy efficient motors for 50% load. It was also found that payback period for implementing high efficient motors are in the range from 1.22 to 6.05, which is economically very viable for motor loadings of 50%.     

Thermal expansion and electrical conductivity of M4 ± x V6O16 ± x (M = K,Rb, Cs) polyvanadates

The thermal expansion coefficient of the M_{4 ± x} V₆O_{16 ± x} (M = K, Rb, Cs) polyvanadates is a nonmonotonic function of temperature, with sharp minima at 663, 558, and 713 K, respectively, which are accompanied by no changes in cell symmetry (tetragonal) or a/c axial ratio. The polyvanadates are shown to be ionic-electronic conductors. The activation energy for electronic conduction in the three polyvanadates is 0.43 ± 0.02 eV. In the range 675–740 K, the conductivity of K_4.2V₆O_16.2 shows metallic behavior. Rubidium polyvanadate has a narrower temperature range of unactivated conduction, and Cs_3.8V₆O_15.8 has no such range. The conclusion is made that these phases undergo cation disordering due to deviations from the M₄V₆O₁₆ stoichiometry. Original Russian Text ? V.L. Volkov, N.V. Podval’naya, 2008, published in Neorganicheskie Materialy, 2008, Vol. 44, No. 2, pp. 221–225.     

Enhancement of photoluminescence due to erbium-doped in CdS thin films

Cadmium sulfide (CdS) thin films were synthesized by chemical bath deposition on glass substrates at 80 °C. The CdS thin films were doped with erbium (Er³⁺) during the growth process by adding aqueous solutions of Er(NO₃)₃·3H₂O to the CdS chemical bath. The relative volume (V _r) of the doping-solution was varied to obtain ten different doping levels. X-ray diffraction patterns displayed the zincblende crystalline structure for all the CdS:Er samples, with a remarked preferred orientation along the (111) direction. The (111) interplanar distance (ID) first decreased, reaching a minimum value at V _r = 3%, after which point it increased up to saturation for largest values of V _r. The dependence of the band-gap energy (E _g) on V _r followed an opposite behavior to that described by the ID. The photoluminescence (PL) spectra showed essentially two main bands: the green emission (GE) band of CdS and a red emission (RE) band. The increasing of the PL signal, for V _r ≤ 4% has been associated with the presence of Er³⁺ into the CdS lattice. For V _r > 4%, Er degrades the lattice. In addition, the crystalline quality (CQ) and PL of the material improved for low V _r values, which was in agreement with measurements of the mobility.     

Optimization of mixed silanes agent solution and curing process for composite γ-glycidoxypropyl trimethoxysilane (γ-GPS)/bis-1.2-(triethoxysilyl)ethane (BTSE) silane film on Q235 steel surface

In this investigation, the mixed γ-GPS/BTSE silane solution for preparing well adhered composite γ-GPS/BTSE silane film on Q235 carbon steel surface has been successfully optimized by orthogonal test, and the curing process parameters of temperature and time have also been optimized. The results indicate that the optimized hydrolysis parameters for mixed silanes agent solution are as follows: V_ethanol/V_water 3 : 1, V_γ-GPS/V_BTSE 2 : 3, V_silanes 6 vol.%, pH 4.0 and hydrolysis time 72 h. In addition, the optimized curing condition for composite γ-GPS/BTSE silane film is 120 °C and 30 min. After immersion in the optimized mixed γ-GPS/BTSE silanes agent solution and curing under the optimized condition, the prepared composite γ-GPS/BTSE silane film on Q235 steel surface can have an adhesion strength of 24.52 MPa to underlying steel substrate.     

An integration procedure based on multi‐surface plasticity for plane stress plasticity: Theoretical formulation and application

An integration procedure designed to satisfy plane stress conditions for any constitutive law initially described in 3D and based on classical plasticity theory is presented herein. This method relies on multi‐surface plasticity, which allows associating in series various mechanisms. Three mechanisms have ultimately been used and added to the first one to satisfy the plane stress conditions. They are chosen to generate a plastic flow in the 3 out‐of‐plane directions, whose stresses must be canceled (σ₃₃,σ₁₃, and σ₂₃). The advantage of this method lies in its ease of use for every plastic constitutive law (in the general case of the non‐associated flow rule and with both nonlinear kinematic and isotropic hardening). Method implementation using a cutting plane algorithm is presented in its general framework and then illustrated by the example of a J2‐plasticity material model considering linear kinematic and isotropic hardening. The approach is compared with the same J2‐plasticity model that has been directly derived from a projection of its equations onto the plane stress subspace. The performance of the multi‐surface plasticity method is shown through the comparison of iso‐error and iso‐step contours in both formulations, and lastly with a case study considering a hollow plate subjected to tension. Copyright © 2014 John Wiley & Sons, Ltd.     

The temperature dependence of microhardness of the transition-metal carbides

Microhardness as a function of temperature has been measured for single crystals of TiC_0.96, ZrC_0.94, and NbC_0.87 from room temperature through their ductile-brittle transitions and for single crystals of V₆C₅ through the order-disorder transition. The present data confirm the result observed for polycrystalline specimens that forT<0.5T _m , the decrease in hardness with increasing temperature for the carbides is substantially more rapid than for metals and semiconductors. Above the ductile-brittle transitions, the ratios of hardness to yield stress are factors of 1.5 to 3 larger than calculated from theory. We suggest that the larger values result from the higher strainrates and larger strains involved in the hardness tests. Arrhenius plots of the hardness data forT>0.25T _m are linear and exhibit changes in slope near 0.33 and 0.44T _m. The former temperature is near the ductile-brittle transition temperature for the disordered carbides, and the latter is at the temperature for which a similar change in Arrhenius slope occurs in published yield-stress data. In addition, a change in slope is found for VC at 0.48T _m (1275 °C) which is the order-disorder transition temperature for V₆C₅→VC_0.84. These changes in slope are suggestive of corresponding changes in the thermally-activated processes governing plastic flow.     

High-pressure/high-temperature synthesis, crystal structure, and electrical properties of CaCu3 ? xFexV4O12

A perovskite-like compound of composition CaCu_{3 − x} Fe _x V₄O₁₂ (x = 0.7−1.0) has been synthesized at high pressures (p = 5.0−8.0 GPa) and temperatures (t = 1000−1300°C). Its crystal structure has been determined by X-ray diffraction (sp. gr. Im[`3]Im\bar 3, Z = 2, a = 7.3051(5) angles have been evaluated. The electrical conductivity of the high-pressure phase CaCu₂FeV₄O₁₂ exhibits metallic behavior.     

Enhancement in electrical conductivity of Li<Subscript>2</Subscript>O: B<Subscript>2</Subscript>O<Subscript>3</Subscript>: V<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

The study of electrical conductivity of 30Li₂O: (70 − x) B₂O₃: xV₂O₅ glass samples has been carried out. The results have been explained by dividing the temperature range into two regions. In region I, conductivity shows Arrhenius behaviour for all the samples. The conductivity increases with addition of V₂O₅. The results have been explained in the light of Anderson and Stuart Model. In region II, an anomalous enhancement in the conductivity is observed for all the samples up to certain temperature beyond which the conductivity decreases. The enhancement in the conductivity in the annealed glass sample has been attributed to nanocrystallization.     

A new approach for estimation of Poisson’s ratio of porous powder compacts

A new correlation between Poisson’s ratio (ν) and ultrasonic longitudinal wave velocity (V _L) has been established and the resulting correlation has been shown to agree well with experimental data on ν versus V _L for a variety of porous powder compacts. Further, it has been demonstrated that ultrasonic longitudinal wave velocity can be used to estimate the elastic properties of sintered powder compacts.