The activation and the spreading of deformation in a fully lamellar Ti–47 at.% Al–1 at.% Cr–0.2 at.% Si Alloy

The spreading of deformation in a lamellar Ti–47?at.% Al–1?at.% Cr–0.2?at.% Si alloy deformed under compression is studied at 25°C and 600°C. This microstructure is largely dominated by twin-related variants which are separated by either twin interfaces or thin α ₂ slabs. The alloy deforms at both temperatures by ordinary dislocations and twins. Deformation in a particular γ variant and its adjacent twin-related variant involves the same kind of glide system, either ordinary dislocations or twins. This property is found to be true for all twin-related lamellae. The occurrence of this correlated glide is explained by the introduction of the notion of pilot and driven orientations. The lamellar orientation in which the operating glide system is activated on the basis of Schmid factor considerations is termed the pilot orientation. It imposes its deformation system on to the twin-related lamella, called the driven orientation, whose deformation may not involve the slip system most favoured by the applied stress.     

Continuous-cooling α-to-γ transformation behaviour of Ti–45.5 at.% Al–0.05 at.% B alloy

The continuous-cooling transformation behaviour of Ti–45.5?at.%?Al–0.05?at.%?B alloy was quantitatively measured using a real-time resistivity–temperature–time measurement apparatus operating under a high vacuum. The addition of a small amount of B does not significantly alter the α–γ-phase equilibria but significantly raises the α–γ lamellar start temperature of Ti–45.5?at.%?Al alloy at most cooling rates. Furthermore, it markedly increases the critical cooling rate for the ordering reaction. The effect of B addition, which greatly stabilizes the lamellar structure up to a fast cooling rate, is to accelerate the lamellar formation kinetics; the lamellar spacing was nevertheless distinctively larger in a B-doped alloy. This is because lamellae in B-doped alloy nucleate heterogeneously on titanium borides at the grain boundary; the borides are effective nucleation sites particularly since local Ti depletion can occur near the interface of the growing titanium borides during cooling. In the absence of B addition, the lamellar structure starts to form only at temperatures below T ₀, suggesting that a large undercooling is required for the nucleation of lamellae even at the grain boundaries. On the other hand, the B addition greatly retards the kinetics of the α-to-α₂ ordering reaction by markedly increasing its critical cooling rate without a large change in the ordering temperature. This is believed to be due to its tendency to segregate strongly to the antiphase boundaries.     

Initiation of discontinuous precipitation at interphase boundaries in a two-phase Zn–6.3 at.% Ag alloy

Discontinuous precipitation (DP) was found to initiate at both η′–ε interphase and η′–η′ grain boundaries in a two-phase Zn–6.3?at.%?Ag alloy consisting of ε and supersaturated η′ phases. The η′–ε interphase boundaries at which DP has initiated illustrated a sinusoidal interface during ageing, which implies that the morphological instability is a prerequisite for the DP initiation at an η′–ε interphase boundary. The application of the morphological instability model for solid–solid interfaces has indicated that the interface protuberances grow into the supersaturated η′ and the interphase boundary becomes unstable since the observed wavelength of serrated η′–ε interphase boundaries was larger than the critical value predicted by the model. A solute-depleted region is therefore established in front of the η′–ε interphase boundary, which provides an appropriate site leading to a DP reaction. Based on this, a nucleation mechanism of DP at the interphase boundaries is proposed accordingly: the allotriomorphs of DP can be directly developed from ε protuberances of a serrated interphase boundary.     

Defect-dependent nitride surface layer development upon nitriding of Fe–1 at.% Mo alloy

Upon nitriding of binary Fe–1 at.% Mo alloy in a NH₃/H₂ gas mixture under conditions (thermodynamically) allowing γ′-Fe₄N_{1– x} compound layer growth (nitriding potential: 0.7?atm^?1/2 at 753?K (480?°C) – 823?K (550?°C)), a strong dependency of the morphology of the formed compound layer on the defect density of the specimen was observed. Nitriding of cold-rolled Fe–1 at.% Mo specimens leads to the formation of a closed compound layer of approximately constant thickness, comparable to nitriding of pure iron. Within the compound layer, that is, in the near-surface region, Mo nitrides are present. The growth of the compound layer could be described by a modified parabolic growth law leading to an activation energy comparable to literature data for the activation energy of growth of a γ′-Fe₄N_{1? x} layer on pure iron. Upon low temperature nitriding (i.e. ?793?K (520?°C)) of recrystallized Fe–1 at.% Mo specimens, an irregular, ‘needle-like’ morphology of γ′-Fe₄N_{1? x} nucleated at the surface occurs. This γ′ iron nitride has an orientation relationship (OR) with the matrix close to the Nishiyama–Wassermann OR. The different morphologies of the formed compound layer can be interpreted as consequences of the ease or difficulty of precipitation of Mo as nitride as function of the defect density.     

Thermal stability of the microstructure of 12% chromium ferritic–martensitic steels after long-term aging at high temperatures

The structure of EK-181 (RUSFER-EK-181, low-activation) and ChS-139 12% Cr ferritic–martensitic steels is investigated and their mechanical properties are tested after long-term (13500 h) aging at 450 and 620°C. The microstructure of the steels exhibits a high thermal stability, which provides the retention of their initial short-term mechanical properties at test temperatures.     

Magnetostriction trend of non-oriented 6.5% Si–Fe

Non-oriented electrical steel is produced in strip form typically 0.35–1.0 mm thick and containing 0–3 wt% silicon. It is well-known that non-oriented electrical steel is not quite isotropic but has small anisotropy. In the last decade, NKK produced 0.1 mm thick, non-oriented steel 6.5% Si which has applications such as in high-frequency transformer due to its high electrical resistivity, low core losses, near zero magnetostriction, and high permeability. The magnetostriction of 6.5% silicon steel samples with dimensions 280 mm×30 mm×0.1 mm was measured when magnetised sinusoidally between 0.5 and 1.0 T at frequencies between 0.5 and 6 kHz. Test samples were clamped at one end and the peak-to-peak displacement of the free end was measured with the aid of the single-point laser vibrometer. The average peak–peak magnetostriction was 0.2–0.25 με apart from a sharp rise to 1.2 με at 2 kHz magnetising frequency. This agrees well with the predicted value of 2 kHz for l=0.28 m, d=7430 kg/m³ and E=166 GPa. This shows that although the 6.5% silicon steel is often thought of as having near zero magnetostriction, care is needed to avoid lamination lengths corresponding to resonance points which could induce higher noise in laminated cores.     

Nonlinear optical properties of antimony–germanium–sulfur glasses at 1560 nm

Nonlinear (NL) optical properties of antimony–germanium–sulfur (Sb–Ge–S) glasses were investigated using laser pulses of 65 fs at 1560 nm. Samples having concentration ratio [S]/[Ge]=2.69 with different antimony concentrations were studied. Glasses with different oxidation states of Sb were investigated using the thermally managed Z -scan technique. The influence of the Sb oxidation state on the NL properties was evaluated. NL refraction indices of electronic origin, n ₂≈10⁻¹³ cm²/W, two-orders of magnitude larger than for fused silica and NL absorption coefficients smaller than 0.55 cm/GW were measured. Appropriate figures-of-merit for photonic applications were determined.     

Directional solidification of Ti–49 at.%Al alloy

Ti–49Al (at.%) alloy was directionally solidified in Bridgman-type directional solidification furnace. The specimens were directionally solidified under an argon atmosphere with the different growth rate (V=5–30 μm/s) at a constant temperature gradient (G=12.1 K/mm), and with the different temperature gradient (G=2.8–12.1 K/mm) at a constant growth rate (V=10 μm/s). The dendritic spacings (λ ₁) were measured from both transverse and longitudinal sections of the specimens. The dependence of λ ₁ on the growth rate (V) and temperature gradient (G) were determined by using linear regression analysis. According to the experimental results, the value of λ ₁ decreases with the increase of values of V and G. The experimental results were compared with the current theoretical and numerical models, and similar previous experimental results.     

Oxidation parameters determination of Cu–Al–Ni–Fe shape-memory alloy at high temperatures

In this study, isothermal oxidation behavior of a Cu–Al–Ni–Fe shape-memory alloy between 500 and 900 °C was investigated. Alloy samples were exposed to oxygen by TG/DTA for 1 h at a constant temperature, allowing for calculation of the oxidation constant and activation energy values of the oxidation process. The oxidation constant value increased with temperature, reaching saturation at 800 °C. The effect of oxidation on crystal structure, surface morphology and chemical composition of the Cu–Al–Ni–Fe alloy was determined by X-ray diffractometer (XRD) and scanning electron microscope (SEM)–energy-dispersive X-ray (EDX) analyses. With increasing oxidation temperature, number and intensity of the characteristic 18R martensite phase peaks were reduced while Al₂O₃ phase peaks were increased. In parallel to the XRD results, the same variations were also detected by SEM–EDX measurements.     

Rayleigh–Taylor instability at spherical interfaces of incompressible fluids

Rayleigh–Taylor instability(RTI) of three incompressible fluids with two interfaces in spherical geometry is derived analytically. The growth rate on the two interfaces and the perturbation feedthrough coefficients between two spherical interfaces are derived. For low-mode perturbation, the feedthrough effect from outer interface to inner interface is much more severe than the corresponding planar case, while the feedback from inner interface to the outer interface is smaller than that in planar geometry. The low-mode perturbations lead to the pronounced RTI growth on the inner interface of a spherical shell that are larger than the cylindrical and planar results. It is the low-mode perturbation that results in the difference between the RTI growth in spherical and cylindrical geometry. When the mode number of the perturbation is large enough, the results in cylindrical geometry are recovered.     

Comparison of the deformation behaviour of commercially pure titanium and Ti–5Al–2.5Sn(wt.%) at 296 and 728 K

The tension and tensile-creep deformation behaviours of a fully-α phase commercially pure (CP) Ti and a near-α Ti–5Al–2.5Sn(wt.%) alloy deformed in situ inside a scanning electron microscope were compared. Tensile tests were performed at 296 and 728?K, while tensile-creep tests were performed at 728?K. The yield stress of CP Ti decreased dramatically with increasing temperature. In contrast, temperature had much smaller effect on the yield stress of Ti–5Al–2.5Sn(wt.%). Electron backscattered diffraction was performed both before and after the deformation, and slip trace analysis was used to determine the active slip and twinning systems, as well as the associated global stress state Schmid factors. In tension tests of CP Ti, prismatic slip was the most likely slip system to be activated when the Schmid factor exceeded 0.4. Prismatic slip was observed over the largest Schmid factor range, indicating that the local stress tensor varies significantly from the global stress state of uniaxial tension. The basal slip activity in Ti–5Al–2.5Sn(wt.%) was observed in a larger faction of grains than in CP Ti. Pyramidal ?c?+?a? slip was more prevalent in CP Ti. Although twinning was an active deformation mode in tension tests of the CP Ti, it was rare in Ti–5Al–2.5Sn(wt.%). During creep, dislocation slip was the primary apparent deformation mechanism in CP Ti, while evidence for dislocation slip was much less apparent in Ti–5Al–2.5Sn(wt.%), where grain boundary sliding was dominant. A robust statistical analysis was carried out to assess the significance of the comparative activity of the different slip systems under the variety of experimental conditions examined.     

Unusual nucleation and growth of γ′ iron nitride upon nitriding Fe–4.75 at.% Al alloy

The influence of substitutionally dissolved Al in ferritic Fe–4.75 at.% Al alloy on the nucleation and growth of γ′ iron nitride (Fe₄N_{1? x} ) was investigated upon nitriding in NH₃/H₂ gas mixtures. The nitrided specimens were characterised employing optical microscopy, scanning electron microscopy, transmission electron microscopy, electron probe microanalysis and X-ray diffraction. As compared to the nitriding of pure ferrite (α-Fe), where a layer of γ′ develops at the surface, upon nitriding ferritic Fe–4.75 at.% Al an unusual morphology of γ′ plates develops at the surface, which plates deeply penetrate the substrate. In the diffusion zone, nano-sized precipitates of γ′ and of metastable, cubic (NaCl-type) AlN occur, having, with the ferrite matrix, a Nishiyama–Wassermann orientation relationship and a Bain orientation relationship, respectively. The γ′ plates contain a high density of stacking faults and fine ε iron nitride (Fe₂N_{1? z} ) precipitates, although the formation of ε iron nitride is not expected for the employed nitriding parameters. On the basis of dedicated nitriding experiments it is shown that the unusual microstructural development is a consequence of the negligible solubility of Al in γ′ and the obstructed precipitation of the thermodynamically stable, hexagonal (wurtzite-type) AlN in ferrite.     

Quasi-isentropic compressibility of deuterium and helium at pressures of 1500–5000 GPa

The quasi-isentropic compressibilities of deuterium and helium plasmas are measured in the pressure range 1500–5000 GPa at densities up to 8 g/cm³ using spherical experimental devices and an X-ray complex consisting of three betatrons and a multichannel optoelectronic system for taking X-ray images. The experimental results demonstrate the possibilities of high-energy-density experimental physics to reproduce the extreme states of substance typical of the Universe under laboratory conditions using the energy of traditional condensed explosives.     

A Proof of Factorization Theorem of Drell–Yan Process at Operator Level

An alternative proof of factorization theorem for Drell–Yan process that works at operator level is presented in this paper. Contributions of interactions after the hard collision for such inclusive processes are proved to be canceled at operator level according to the unitarity of time evolution operator. After this cancellation, there are no longer leading pinch singular surface in Glauber region in the time evolution of electromagnetic currents. Effects of soft gluons are absorbed into Wilson lines of scalar-polarized gluons. Cancelation of soft gluons is attribute to unitarity of time evolution operator and such Wilson lines.     

Phase diagram of the Al–Er–Mo ternary system at 873 K

The phase relationship in the Al–Er–Mo ternary system at 873 K has been investigated based on the equilibrated method mainly by means of X-ray powder diffraction and scanning electron microscopy. The existence of 10 binary compounds and two ternary compounds has been confirmed. The results present that the isothermal section at 873 K is governed by 15 single-phase regions, 29 two-phase regions and 15 three-phase regions. By using the phase-disappearing method, Al₈Mo₃ has a narrow homogeneity range (from 72 to 73 at% Al), while the homogeneity range of AlMo₃ is from 21% to 28.5% at% Al. Also, the maximum solubility of Al in Mo is about 16 at%.     

Activation cross-sections of titanium isotopes at neutron energies of 13.5–14.8 MeV

The cross-sections for ~(46) Ti(n,2 n)~(45) Ti, ~(46) Ti(n,p)~(46 m+g) Sc+~(47) Ti(n,d*)~(46 m+g) Sc, ~(46)Ti(n,p)~(46 m+g) Sc, ~(47) Ti(n,p)~(47) Sc+~(48) Ti(n,d*)~(47) Sc, ~(47) Ti(n,p)~(47) Sc, ~(48) Ti(n,p)~(48) Sc+~(49) Ti(n,d*)~(48) Sc,~(48) Ti(n,p)~(48) Sc, and ~(50) Ti(n,α)~(47) Ca reactions were investigated around neutron energies of 13.5–14.8 Me V by means of the activation technique. Fast neutrons were produced by the~3 H(d,n)~4 He reaction. Neutron energies from different directions in the measurements were obtained in advance using the method of cross-section ratios for ~(90) Zr(n,2 n)~(89 m+g) Zr and ~(93) Nb(n,2 n)~(92 m) Nb reactions. The results obtained are analyzed and compared with the experimental data provided by the literature and verified nuclear data in the JEFF-3.3,CENDL-3.1, ENDF/B-VIII.0 libraries, as well as results calculated by Talys-1.9 code.     

The transport and magnetic properties of La–Pb–Mg–Mn–O manganites at low temperatures

The structure, transport properties and the magnetoresistance behavior in the temperature interval 77–400 K of the perovskite-like lanthanum manganites La_0.6Pb_0.4−xMg_x+yMnO₃ (x=0, 0.1, 0.2 and y=0, 0.2) were investigated. Polycrystalline bulk samples were prepared by sol–gel self-combustion and subsequent heat treatment at 1000 °C for different times, 40, 80, 160 and 320 min. All manganites exhibit a peak in the resistivity around 200–250 K, below the ferromagnetic ordering temperature (320–330 K). An isotropic and negative magnetoresistance has been observed in all compounds. Magnetoresistance MR exhibits a peak in the temperature range 130–150 K, below SC–metal transition temperature. Magnitude of MR at the peaks was nearly 27% in the magnetic field of 2 T. At room temperature, a magnetoresistance of 9.5% for La_0.6Pb_0.2Mg_0.2MnO₃ composition was obtained. Longer heat treatment time enhanced the magnetorezistive properties.     

Measurement of quasi-isentropic compressibility of helium and deuterium at pressures of 1500–2000 GPa

The quasi-isentropic compressibility of helium and deuterium plasmas at pressures of up to 1500?C2000 GPa has been measured using devices with spherical geometry and an X-ray diagnostic complex comprising three betatrons and a multichannel imaging system with electro-optic gamma detectors. A deuterium density of 4.5 g/cm³ and a helium density of 3.8 g/cm³ have been obtained at pressures of 2210 and 1580 GPa, respectively. The internal energy of a deuterium plasma at the indicated pressure is about 1 MJ/cm³, which is about 100 times greater than the specific energy of condensed chemical explosives. Analysis of the obtained data shows that the degree of helium ionization under the achieved plasma compression parameters is about 0.9.