Effect of strain rate on the tensile behavior of a single crystal nickel-base superalloy

The effect of various strain rates on the tensile behavior of a single crystal nickel-base superalloy was studied. Single crystals with 0 0 1 crystal orientation were tested at 800 and 1000 °C under three kinds of strain rate of 10⁻³, 10⁻⁴ and 6 × 10⁻⁵ s⁻¹. The yield strength increased with the increase of strain rate, while the configuration of the stress–strain curves was independent of strain rate. Additionally, fracture surface was related to strain rate at two temperatures. At 800 °C the amount of cleavage surface was different at three strain rates, which resulted from the difference of activated slip systems. The elongation increased with the decrease of strain rate, which was influenced by the heterogeneous ductile deformation. At 1000 °C the difference of fracture surface was attributed to the microvoid at higher strain rate, while the γ/γ′ interfaces also played an important role at lower strain rate; elongation rate was independent of strain rate.     

Experiments and simulations of directionally annealed ODS MA 754

Both directional and isothermal annealing experiments have been performed on the hot-rolled ODS nickel-based superalloy MA 754. Directional annealing of MA 754 produced an elongated, coarse grain structure with a {1 1 0}1 0 0 texture for all hot-zone velocities examined, with the grain aspect ratio and twin boundary density decreasing with increasing hot-zone velocity. Isothermal annealing also produced elongated structures, but with larger grain aspect ratios and a stronger {1 1 0}1 0 0 texture. In order to elucidate the results of the experimental studies, a front-tracking computer-based model [H.J. Frost, C.V. Thompson, C.L. Howe, J.H. Whang, Scripta Metall. 22 (1988) 65–70] was modified to simulate the directional/isothermal annealing processes for materials with particles. Simulations of directional annealing with particles aligned in the direction of hot-zone movement could produce (at the appropriate hot-zone velocities) columnar grain structures with some finer grains clustered around the particles. Contrary to experimental observations, simulations of isothermal annealing in similar particle-containing material did not produce columnar grain structures, but equi-axed grains whose size was defined by the spacing between the lines of particles. Thus, the simulation results suggest that it is the texture, and not the particles, of the hot-rolled MA 754 that leads to a columnar grain structure.     

Effect of texture and testing conditions on strain localization during cyclic deformation of copper polycrystals

Fatigue tests were performed on pure copper polycrystals with a crystallographic texture different from that produced by ‘standard’ thermomechanical treatments, which emphasize multi-slip 111–100 textures. The texture along the loading axis deviated by 10–15° from these two poles for the samples used here. The experiments were initiated by ramp loading as a mechanical pretreatment and the cyclic stress–strain curve (CSSC) was established by step tests using enough cycles at each step to insure saturation. Under these conditions, a plateau was observed in the CSSC at an appropriate stress level and in a reproducible fashion.     

Electrical characterization of CMOS transistors subject to externally applied mechanical stress

Hole and electron mobilities in CMOS structures are significantly influenced by a mechanical strain state. In the present work a new experimental device has been designed, able to apply a uniaxial in-plane strain along different crystallographic orientations. A hole mobility enhancement of +10% and an electron mobility decrease of −5% have been demonstrated with the application of a 0.05% compressive 1 1 0 strain; a hole mobility enhancement of +2% and an electron mobility decrease of −3% have been induced into the material with the application of a 0.05% compressive 1 0 0 strain.     

Grain-boundary structure of oxygen-free high-conductivity (OFHC) copper subjected to severe plastic deformation and annealing

The influence of grain-boundary structure on grain growth in copper subjected to severe plastic deformation has been studied using orientation imaging microscopy. The investigation was carried out on oxygen-free high-conductivity (OFHC) copper which was wire drawn to a true strain of about 4 and processed by equal-channel angular extrusion (ECAE) to 4 and 8 passes via “route B_c” (where the billet is rotated by 90° in the same direction between consecutive passes). The grain-boundary character distribution (GBCD) of the as-drawn wire was similar to that of ECAE-processed specimens, and both materials possessed a higher fraction of high-angle grain boundaries (HAGBs) than special coincidence-site lattice (CSL) boundaries. While the high fraction of HAGBs was retained in the annealed wires, they were transformed to CSL boundaries in the annealed ECAE-processed materials. In spite of an initially smaller grain size, when annealed at 750 °C for 1 h, the grain size of the 4-pass ECAE-processed material was larger than that of the wire drawn to a similar strain. This difference was attributed to a high density of high-mobility 35–50° 0 0 1 boundaries in the 4-pass ECAE materials. On the other hand, the presence of 50–60° 1 1 1  pinning boundaries in the annealed 8-pass material accounted for the smaller grain size after recrystallization.     

Dependencies of grain refinement on processing route and die angle in equal channel angular extrusion of bcc materials

The efficiency of grain refinement in equal channel angular extrusion of body-centered cubic (bcc) materials is investigated based on slip activities from crystal plasticity simulations, which account for both the macroscopic and crystallographic features of deformation. It is shown that the characteristics of slip activities, especially the relative contributions of slip systems newly activated or reversed at the transitions between successive passes, vary significantly with the processing routes (A, B and C) and die angles ( = 90° and 120°). The simulations assuming {1 1 0}111 slip suggest that routes B and A lead to the most significant contributions of newly activated slip systems and hence are most efficient for grain refinement with  = 90° and 120°, respectively. Further incorporation of {1 1 2}111 slip systems leads to the highest efficiency by route B for both die angles. These predictions are in partial agreement with experimental observations in the literature. Comparison of these results with those of face-centered cubic materials reveals the relevance of crystal structure and deformation mechanism during grain refinement.     

Effect of the extrusion conditions on microstructure evolution of the extruded Al–Mg–Si–Cu alloy rods

Hot extrusion experiment was conducted using an Al–Mg–Si–Cu alloy and the effect of the extrusion conditions on microstructure and texture changes through the radial direction was investigated by using SEM/EBSP analysis method. In the surface layer where severe frictional shear deformation is predominant, the recrystallized 1 1 0//ED grains surrounded by high angle grain boundaries are formed in spite of the existence of some peripheral overcoarse grains. Strong 1 0 0//ED and 1 1 1//ED fiber textures evolve in the center where axisymmetric deformation along the extrusion direction is intensive. As the extrusion ratio increases, number of 1 1 1//ED grains remarkably decreases while the number of 1 0 0//ED grains apparently increases. It is also found that the 1 0 0//ED grains surrounded by low angle grain boundaries form orientation colonies in the center of the extruded rods.     

Length scale effects on recrystallization and texture evolution in Cu layers of a roll-bonded Cu–Nb composite

Recrystallization textures were investigated in thin layers of both pure Cu and alloyed Cu combined with Nb in roll-bonded composites. Texture analysis using X-ray revealed that Cube orientation was the dominant texture component after recrystallization in rolled monolithic pure Cu whereas {2 1 5} 2 1 1 and B/S were the dominant components for the recrystallized alloyed Cu. In the composites, however, the rolling texture is retained during annealing in both the pure Cu and the alloyed Cu layers when the layer thickness enters the sub-micron regime. This is attributed to the nucleation and growth of recrystallizing grains being impeded via a reduction in recrystallization driving pressure and the grain boundary movement and growth being limited due to the layer thickness effect. A new term—“confined recrystallization” was also introduced to describe more accurately the morphological evolution observed within the sub-micron thick layers after annealing and highlights the contrast to either simple recovery or continuous recrystallization.     

Preparation and characterization of ultrafine alumina via sol–gel polymeric route

Ultrafine alumina powder was prepared through resin formation between urea and formaldehyde. Aluminium stearate soap was introduced during resin preparation. Ethylene glycol was used to terminate the thermosetting reaction. Calcination of the product was carried out at 700, 1000, 1100, 1300 and 1400 °C to obtain aluminium oxide.IR and Raman spectroscopic analysis indicated the occupation of Al³⁺ at different sites in the polymer network (CO, NH₂, CO, NH, and CH₂OH).X-ray diffraction of powder calcined at 1000 °C revealed the presence of a mixture of α- and θ-alumina together, while a mixture of α- and β-alumina phases were obtained on calcination at 1400 °C. Transmission electron microscope (TEM) examination of the powder fired at 700 °C showed uniform grains in the form of clusters with average size between 22.02 and 30.5 nm. Clusters are multi-particles as evident from the electron diffraction pattern. Crystallite size of alumina powder calcined at 1000 °C was found to be ≈25.67 nm, while that of powder calcined at1400 °C was ≈30.52 nm. The calculated specific surface area of alumina powder calcined at 1000 °C was 59.17 m² g⁻¹, while that calcined at 1400 °C was 49.77 m² g⁻¹.     

Grain boundary plane distributions and single-step versus multiple-step grain boundary engineering

The ‘five-parameter’ (i.e. both misorientation and grain boundary plane) distribution in type 304 austenitic stainless steel has been measured and evaluated for an ‘as-received’ (AR) specimen and specimens undergoing both single-step grain boundary engineering processing (SSGBE) and multiple-step grain boundary engineering processing (MSGBE) comprising three iterations. The results showed that the fundamental requirement for twinning-related GBE is to maximise concomitantly the proportion of both Σ3 and Σ9 boundaries, which in turn supports the development of special planes in the grain boundary network. 1 1 0 and 1 1 1 tilt and twist boundaries play a key role in the formation of ‘special’ grain boundary planes. MSGBE added increased proportions of Σ3 boundaries and resulted in development of different characteristics in the planes distribution compared to SSGBE. These modifications are likely to result in improved grain boundary properties after MSGBE compared to SSGBE.     

Biosensor enhanced by glucose oxidase biomimetic membrane containing the platinum and silica nanoparticles

In this paper, glucose biosensor is fabricated with immobilization of glucose oxidase (GOx) in platinum and silica sol. The glucose biosensor combined with Pt and SiO₂ nanoparticles could make full use of the properties of nanoparticles. A set of experimental results indicates that the current response for the enzyme electrode containing platinum and silica nanoparticles increases from 0.32 µA cm^− 2 to 33 µA cm^− 2 in the solution of 10 mM β-D-glucose. The linear range is 3 × 10^− 5 to 3.8 × 10^− 3 M with a detection limit of 2 × 10^− 5 M at 3σ. The effects of the various volume ratios of Pt and SiO₂ sols with respect to the current response and the stability of the enzyme electrodes are studied.     

Mechanism of nucleation and growth of cubic boron nitride thin films

The mechanism and the crystallography of the nucleation and growth of cubic boron nitride (c-BN) films deposited on 100-oriented silicon substrate by RF bias sputtering have been studied by means of cross-sectional high-resolution transmission electron microscopy and X-ray photoelectron spectroscopy. Both methods provide experimental information showing no sp²-bonded BN layer formation in the subsurface region of c-BN phase. This is clear evidence for layer-by-layer homoepitaxial growth of cubic boron nitride without graphitic monolayers in the near-surface region of the film. The turbostratic boron nitride (t-BN) consists of thin sub-layers, 0.5–2 nm thick, growing in such a way that a sub-layer normal is almost parallel to the growth direction. t-BN also comprises a large volume fraction of the grain boundaries with high interface energies. The present result and the finding by Shtansky et al. [Acta Mater. 48, 3745 (2000)], who showed that an individual sub-layer consists of parallel lamellae in both the hexagonal (h-BN) and rhombohedral (r-BN) configurations, demonstrate that high intrinsic stress in the films is due to the complex structure of sp²-bonded BN. The crystallography of c-BN films indicates heteroepitaxial nucleation of cubic phase on the graphitic BN structural precursor. The present results are consistent with stress-induced c-BN formation.     

Electrical and optical properties of 12CaO·7Al2O3 electride doped indium tin oxide thin film deposited by RF magnetron co-sputtering

12CaO·7Al₂O₃ electride (C12A7:e⁻) doped indium tin oxide (ITO) (ITO:C12A7:e⁻) thin films were fabricated on a glass substrate by an RF magnetron co-sputtering system with increasing number of C12A7:e⁻ chips (from 1 to 7) and at various oxygen partial pressure ratios. The optical transmittance of the ITO:C12A7:e⁻ thin film was higher than 70% in the visible wavelength region. In the electrical properties of the thin film, a decrease of the carrier concentration from 2.6 × 10²⁰ cm^− 3 to 2.1 × 10¹⁸ cm^− 3 and increase of the resistivity from 1.4 × 10^− 3 Ω cm to 4.1 × 10^− 1 Ω cm were observed with increasing number of C12A7:e⁻ chips and oxygen partial pressure ratios. It was also observed that the Hall mobility was decreased from 17.27 cm²·V^− 1·s^− 1 to 5.13 cm²·V^− 1·s^− 1. The work function of the ITO thin film was reduced by doping it with C12A7:e⁻.     

Chemical deposition of Al2O3 thin films on Si substrates

Uniform Al₂O₃ films were deposited on silicon substrates by the sol–gel process from stable coating solutions. The technological procedure includes spin coating deposition and investigating the influence of the annealing temperature on the dielectric properties. The layers were studied by Fourier transform infrared spectroscopy and Scanning Electron Spectroscopy. The electrical measurements have been carried out on metal–insulator–semiconductor (MIS) structures. The C–V curves show a negative fixed charge at the interface and density of the interface state, Dit, 3.7 × 10¹¹ eV^− 1cm^− 2 for annealing temperature at 750 °C.     

Molecular dynamics simulations on nanoindentation mechanisms of multilayered films

Molecular dynamics (MD) simulations were carried out to study the effects of indention deformation, contact, and adhesion on Al, Ni, and Al/Ni multilayered films. The results show that when the indention depth of the sample increased, the maximum load, plastic energy, and adhesion increased. Jump-contact behavior was observed at the beginning of the loading process. Force relaxation and adhesion took place at the holding depth and during the unloading process, respectively. The glide bands of the interface were on the {1 1 1} 1 1 0 slip systems and the maximum width of the glide bands was about 1 nm. The mechanical responses of the indented films are also discussed.     

Structural, electrochemical and optical comparisons of tungsten oxide coatings derived from tungsten powder-based sols

Tungsten trioxide (WO₃) electrochromic coatings have been formed on indium tin oxide-coated glass substrates by aqueous routes. Coating sols are obtained by dissolving tungsten powder in acetylated (APTA) or plain peroxotungstic acid (PTA) solutions. The structural evolution and electrochromic performance of the coatings as a function of calcination temperature (250 °C and 400 °C) have been reported. Differential scanning calorimetry and X-ray diffraction have shown that amorphous WO₃ films are formed after calcination at 250 °C for both processing routes; however, the coatings that calcined at 400 °C were crystalline in both cases. The calcination temperature-dependent crystallinity of the coatings results in differences in optical properties of the coatings. Higher coloration efficiencies can be achieved with amorphous coatings than could be seen in the crystalline coatings. The transmittance values (at 800 nm) in the colored state are 35% and 56% for 250 °C and 400 °C-calcined coatings, respectively. The electrochemical properties are more significantly influenced by the method of sol preparation. The ion storage capacities designating the electrochemical properties are found in the range of 1.62–2.74 × 10^− 3 (mC cm^− 2) for APTA coatings; and 0.35–1.62 × 10^− 3 (mC cm^− 2) for PTA coatings. As a result, a correlation between the microstructure and the electrochromic performance has been established.     

Effect of orientational order of tris(8-hydroxyquinolinato)aluminum(III) on electroabsorption

The electroabsorption (EA) spectrum was analyzed in terms of the orientational order of tris(8-hydroxyquinolinato)aluminum(III) (Alq₃) molecules, where the orientational order parameter P_n(cosθ) (θ: the tilt angle of molecule; P_n: nth Legendre polynomial; : thermodynamic average) was used to quantify the anisotropic orientational order of Alq₃. It was shown that the EA intensity is a function of S₁ and S₂ at the modulation frequency ω, whilst it is a function of S₂ at the second-harmonic frequency 2ω. The EA spectrum for the vacuum deposited Alq₃ was obtained from the optical transmittance measurement. The results suggested that the spontaneous polarization of Alq₃ is generated in the evaporated films.     

Analyses of nano-crystalline LiCoVO4 prepared by solvothermal reaction

LiOH·H₂O, Co(NO₃)₂·6H₂O and NH₄VO₃ were used to prepare nano-crystalline LiCoVO₄ by 150 °C solvothermal reaction in isopropanol for 10–360 h and subsequent calcination at 300–500 °C for 6 h. XRD, TEM and selected area electron diffraction (SAED) revealed the presence of nano-crystalline LiCoVO₄ with inverse spinel structure. The V–O stretching vibration modes of VO₄ tetrahedrons were detected by FTIR over the range 617–835 cm^− 1 and by Raman spectrometer at 805.7 and 783.1 cm^− 1. Co, V and O were detected by EDX. TGA of solvothermal products shows weight loss due to the evaporation and decomposition processes at 40–648 °C.     

Structural investigations of sol–gel derived silicate gels using Eu ion-probe luminescence

Undoped and Eu³⁺-doped CaF₂–SiO₂ gels were prepared by the sol–gel method and their optical properties have been studied. The UV–VIS–NIR absorption and photoluminescence spectra have shown the bands typical for the Eu³⁺ ions transitions. When the Eu-doped gel is annealed at temperatures up to 800 °C (i.e. above the CaF₂ crystallisation peak at 460 °C) the photoluminescence spectra intensity increase, the 590 nm (⁵D₀→⁷F₁) and 620 nm (⁵D₀→⁷F₂) luminescence bands become comparable and a structuring of the 620 nm band is observed. The phonon sidebands peaks associated with the ⁵F₀→⁷D₂ transition of the Eu³⁺ ion were observed at around 1000 and 620 cm⁻¹ and have been assigned to the Si–O and Ca–O bonds, respectively. A phonon sideband signal in the range of 300–400 cm⁻¹ was attributed to Ca–F bonds in the precipitated CaF₂ phase. From the optical absorption, photoluminescence and phonon sidebands spectra we have concluded that in the gels annealed at 800 °C, the Eu³⁺ ions are incorporated into the silica network and in the precipitated CaF₂ phase.     

Investigation of hot ductility in Al-killed boron steels

The influence of boron to nitrogen ratio, strain rate and cooling rate on hot ductility of aluminium-killed, low carbon, boron microalloyed steel was investigated. Hot tensile testing was performed on steel samples reheated in argon to 1300 °C, cooled at rates of 0.3, 1.2 and 3.0 °C s⁻¹ to temperatures in the range 750–1050 °C, and then strained to failure at initial strain rates of 1 × 10⁻⁴ or 1 × 10⁻³ s⁻¹. It was found that the steel with a B:N ratio of 0.19 showed deep hot ductility troughs for all tested conditions; the steel with a B:N ratio of 0.47 showed a deep ductility trough for a high cooling rate of 3.0 °C s⁻¹ and the steel with a near-stoichiometric B:N ratio of 0.75 showed no ductility troughs for the tested conditions. The ductility troughs extended from 900 °C (near the Ae₃ temperature) to 1000 or 1050 °C in the single-phase austenite region. The proposed mechanism of hot ductility improvement with increase in B:N ratio in these steels is that the B removes N from solution, thus reducing the strain-induced precipitation of AlN. Additionally, BN co-precipitates with sulphides, preventing precipitation of fine MnS, CuS and FeS, and forming large, complex precipitates that have no effect on hot ductility.