The research aims to analyze the impact that severe plastic deformation arising during Rotary Swaging has on mechanical properties and corrosion resistance of a near-α-titanium alloy Ti-2.5Al-2.6Zr ...(Russian industrial name PT7M). The nature of corrosion decay in fine-grained alloys caused by hot salt corrosion is known to vary from pit corrosion to intercrystalline corrosion at the onset of recrystallization processes. Resistance to hot salt corrosion in a fine-grained titanium alloy Ti-2.5Al-2.6Zr is shown to depend on the structural-phase state of grain boundaries that varies during their migration as a result of “covering” corrosive doping elements (aluminum, zirconium) distributed in the crystal lattice of a titanium alloy.
•Fine-grained (FG) structure in near-α-alloy Ti-2.5Al-2.6Zr was formed with Rotary Swaging.•Hot salt corrosion mechanisms in coarse-grained (CG) and FG alloys are studied.•Corrosion defects of type I in a CG alloy are stitched as a result of β-phase particles precipitation.•Corrosion defects of type II in a CG alloy look similar to intercrystalline corrosion (ICC).•Corrosion decay in a FG alloy changes from pit corrosion to ICC when the migration of grain boundaries starts.
We present the first extensive radio to γ-ray observations of a fast-rising blue optical transient, AT 2018cow, over its first ∼100 days. AT 2018cow rose over a few days to a peak luminosity Lpk ∼ 4 ...× 1044 erg s−1, exceeding that of superluminous supernovae (SNe), before declining as L ∝ t−2. Initial spectra at δt 15 days were mostly featureless and indicated large expansion velocities v ∼ 0.1c and temperatures reaching T ∼ 3 × 104 K. Later spectra revealed a persistent optically thick photosphere and the emergence of H and He emission features with v ∼ 4000 km s−1 with no evidence for ejecta cooling. Our broadband monitoring revealed a hard X-ray spectral component at E ≥ 10 keV, in addition to luminous and highly variable soft X-rays, with properties unprecedented among astronomical transients. An abrupt change in the X-ray decay rate and variability appears to accompany the change in optical spectral properties. AT 2018cow showed bright radio emission consistent with the interaction of a blast wave with vsh ∼ 0.1c with a dense environment ( for vw = 1000 km s−1). While these properties exclude 56Ni-powered transients, our multiwavelength analysis instead indicates that AT 2018cow harbored a "central engine," either a compact object (magnetar or black hole) or an embedded internal shock produced by interaction with a compact, dense circumstellar medium. The engine released ∼1050-1051.5 erg over ∼103-105 s and resides within low-mass fast-moving material with equatorial-polar density asymmetry (Mej,fast 0.3 M☉). Successful SNe from low-mass H-rich stars (like electron-capture SNe) or failed explosions from blue supergiants satisfy these constraints. Intermediate-mass black holes are disfavored by the large environmental density probed by the radio observations.
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It is shown that the working volume of the RED-100 two-phase emission detector, which operates in a ground-based laboratory with liquid xenon used as a working substance, is a source of ...single-electron noise signals with a characteristic frequency of ~200 kHz. Possible mechanisms of generation of these noises and methods for their suppression are discussed.
Abstract
The paper investigates the service satellite control system when approaching a non-cooperative spacecraft in the state of uncontrollable motion. The service satellite control system is ...considered as a two-level multichannel control system, and multicriteria optimization methods with cross-links are developed. The mathematical model of the control system for a free-flying space manipulation robot at the guidance and stabilization phase is proposed. The efficiency criteria are presented.
We report on the bright burst detected by four Interplanetary network (IPN) spacecraft on 2015 April 12. The IPN localization of the source is consistent with the position of the recently discovered ...soft gamma-repeater SGR 1935+2154. From the Konus-Wind (KW) observation, we derive temporal and spectral parameters of the emission, and the burst energetics. The rather long duration of the burst (~1.7 s) and the large measured energy fluence (~2.5 x 10 super( -5) erg cm super( -2)) put it in the class of rare 'intermediate' soft gamma-repeater (SGR) flares, and this is the first one observed from SGR 1935+2154. A search for quasi-periodic oscillations in the KW light curve yields no statistically significant signal. Of four spectral models tested, optically thin thermal bremsstrahlung and a single blackbody (BB) function can be rejected on statistical grounds; two more complex models, a cutoff power law (CPL) and a sum of two BB functions (2BB), fit the burst spectra well and neither of them may be ruled out by the KW observation. The CPL and 2BB model parameters we report for this bright flare are typical of SGRs; they are also consistent with those obtained from observations of much weaker and shorter SGR 1935+2154 bursts with other instruments. From the distribution of 2BB spectral fit parameters we estimate the SGR 1935+2154 distance to be <10.0 kpc, in agreement with that of the Galactic supernova remnant G57.2+0.8 at 9.1 kpc.
•Al-(1, 2, 3)%Zn alloys were fabricated by induction casting and ECAP.•Increasing of Zn concentration results in reduction of recrystallization activation energy.•The increasing of Zn concentration ...results in increasing of maximum elongation to failure in creep regime (at Т = 200 °С).•In superplasticity regime, dynamic recrystallization of the Al-Zn alloys was observed.•The elongation to failure of the Al-Zn alloys in the superplasticity regime doesn't depend on the Zn concentration.
Mechanical properties of fine-grained Al-(1, 2, 3)%Zn alloys obtained by Equal Channel Angle Pressing were studied. The recrystallization activation energy was found to decrease with increasing Zn content. The Hall-Petch coefficient for the Al-Zn alloys was found to change nonmonotonously during annealing. An increased Zn concentration at the grain boundaries was shown to result in altering the creep and superplasticity mechanisms of the Al-Zn alloys. The corrosion rate of the Al-Zn alloys was found to depend on the annealing temperature nonmonotonously. The corrosion rate in the Al-(2,3)%Zn alloy was shown to decreasing down to 8–9 mm/year with increasing the annealing temperature up to 200 оC. The increasing of the annealing temperature up to 300 оC leads to the increasing of the corrosion rate up to 11.4–11.9 mm/year. The obtained results were analyzed on the base of a concept of solid phase wetting of the grain boundaries in the Al by Zn. The effect of solid state wetting of the grains boundaries was shown to allow explaining majority of anomalia observed in the Al-Zn alloys: (i) the effect of the reduction of the recrystallization activation energy; (ii) the effect of a non-monotonous variation of the Hall-Petch coefficient during annealing; (iii) an increasing of plasticity of the Al-Zn alloys in the creep regime, etc. In order to describe the anomalia in the corrosion resistance of the Al-Zn alloys, one should also take into account a nonuniform Zn distribution in the specimens.
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