102,318 research outputs found
Austempering vs. Q&P: Comparative effects on microstructure and mechanical properties of complex-alloyed TRIP-assisted steel
No full textThis study compares the effect of austempering (AT) and two-step quenching and partitioning (Q&P) treatments on the microstructure and mechanical properties of a 0.2 wt% C Mn-Si-Cr-Mo-V-Nb TRIP-assisted steel. Both treatments included austenitization (770 °C or 900 °C) followed by quenching and isothermal holding (20 min). AT used a 350 °C isothermal hold, while Q&P involved quenching to 200 °C or 230 °C, followed by partitioning at 350 °C. Microstructural analysis (OM, SEM, XRD, EPMA, EBSD) revealed ferrite and (Nb,V)C in both treatments, with bainite (AT) or tempered martensite/bainite (Q&P) and varying retained austenite (RA) content depending on the austenitization temperature. Austenitization at 770 °C resulted in Cr- and Mo-promoted cementite precipitation, reducing the RA volume fraction and ductility. In contrast, 900 °C austenitization resulted in a cementite-free structure with 7–9 vol% RA exhibiting a clear TRIP effect. The ultimate tensile strength (UTS) increased with austenitization temperature (820–880 MPa to 1040–1090 MPa) due to a decreased proeutectoid ferrite, grain refinement, and enhanced TRIP effect, though at some expense of ductility/toughness. Under the same austenitization parameters, Q&P yielded slightly higher UTS (∼ 50 MPa higher), and much greater impact toughness (by 2 times at 770 °C and 1.4 times at 900 °C). Due to a superior strength-ductility-toughness balance, Q&P is identified as a more promising heat treatment for this TRIP-assisted steel
On selection of rational intercritical annealing temperature of a low-alloyed trip-assisted steel
No full textEfremenko B. On selection of rational intercritical annealing temperature of a low-alloyed trip-assisted steel / B. Efremenko, Y. Chabak, V. Greshta, I. Petryshynets, A. Efremenko, W. Kaiming, M. Brykov // Неметалеві вкраплення і гази у ливарних сплавах. Збірник тез ХVІІ Міжнародної науково-технічної конференції (Запоріжжя, 26-27 листопада 2024 року). – Запоріжжя: НУ «Запорізька політехніка», 2025. – С. 35
Alternative Approach for the Intercritical Annealing of (Cr, Mo, V)-Alloyed TRIP-Assisted Steel before Austempering
No full textTRIP-assisted C-Si-Mn steels are usually subjected to austempering with a preliminary intercritical annealing that is targeted at the multi-phase structure with 40-60 vol.% of proeutectoid ferrite. The kinetics and the mechanism of phase-structural transformations can be impacted due to the additional alloying of TRIP-assisted steel by the strong carbide forming elements, thus necessitating an alternative approach for the selection of intercritical annealing parameters. This issue is analyzed in the present work, which investigates the effect of the temperature of intercritical annealing on the "Structure/Properties" correlations in 0.2 wt.% C-Si-Mn-Nb steel additionally alloyed by 0.55 wt.% Cr, 0.20% Mo, and 0.11 wt.% V. The annealing temperature ranged from 770 degrees C to 950 degrees C, and austempering was performed at 350 degrees C for 20 min. It was observed that the addition of the (Cr, Mo, and V) complex significantly improved the steel hardenability. However, the annealing of steel at 770 degrees C (to gain 50 vol.% of proeutectoid ferrite) resulted in the precipitation of coarse cementite lamellas during bainite transformation, thus lowering the amount of retained austenite (RA) and decreasing the strength and ductility of the steel. At higher annealing temperatures, carbide-free bainite was formed, which presented a 2.5-3.5 times increase in the RA volume fraction and a 1.5 times increase in the RA carbon content. The optimal combination of the mechanical properties (UTS of 1040 MPa, TEL of 23%, V-notch impact toughness of 95 J/cm(2), PSE of 23.9 GPa center dot%) referred to annealing at a temperature close to the Ac-3 point, resulting in a structure with 5 vol.% ferrite and 9 vol.% RA (the residue was carbide-free bainite). This structure presented an extended manifestation of the TRIP effect with an enhanced strain hardening rate due to strain-induced martensite transformation. The impact of the alloying elements on the carbon activity in austenite served as the basis for the analysis of structure formation
Chemical composition of Laves phase in 718 inconel-type LPBF alloy modified by surface laser melting
No full textEfremenko B. Chemical composition of Laves phase in 718 inconel-type LPBF alloy modified by surface laser melting / B. Efremenko, A. Lekatou, V. Efremenko, Y. Chabak, K. Wu, S. Arshad, E. Balalaeva // Неметалеві вкраплення і гази у ливарних сплавах. Збірник тез ХVІІ Міжнародної науково-технічної конференції (Запоріжжя, 26-27 листопада 2024 року). – Запоріжжя: НУ «Запорізька політехніка», 2025. – С. 90-91
Going Beyond Counting First Authors in Author Co-citation Analysis
No full textThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
Internatsionalistskii separatism i istoricheskaia politika v nepriznannyh respublikah Pridnestroviia i Donbassa
No full textVariations on the Author
No full text“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
Comparative study on the effect of (Cr, Mo, V)-alloying on transformation and mechanical behavior of 0.2 wt.% C TRIP-assisted steel
No full textThe structure and mechanical properties of two 0.2 wt.% C TRIP-assisted steels (Transformation Induced Plasticity) were compared to evaluate the effect of additional (Cr, Mo, V)-alloying on transformation kinetic and tensile/impact behavior after isothermal bainite transformation (bainitizing) and Q&P (Quenching-and-Partitioning) treatment. The work was performed using SEM, XRD, tensile/impact testing, and computer simulation. It was found that adding 0.55 wt.% Cr, 0.2 wt.% Mo, and 0.11 wt.% V into Mn-Si-Nb steel increased the incubation time in pearlite and bainite temperature ranges by 5.6 and 4.4 times, respectively. More heavily alloyed steel performed an improved combination ???Strength/Ductility/Impact Toughness???: its maximum PSE (Product of Strength and Elongation) value of 24 GPa ?? % referred to bainitizing treatment, whereas the highest KCV20???C values (220???225 J cm???2) corresponded to Q&P treatment. Improved mechanical properties of (Cr, Mo, V)-alloyed steel were attributed to a higher amount of retained austenite and a slower rate of TRIP-effect
A native insect on a non-native plant
No full textThe trans-Palearctic moth Phyllonorycter populifoliella (Lepidoptera: Gracillariidae) is a major pest of the North American Populus balsamifera and its hybrids widely planted as ornamentals in North Asia (i.e., the Asian part of Russia). We DNA barcoded Ph. populifoliella from distant geographical populations in Russia and analyzed them together with the data from eight European countries and India to estimate intraspecific variability and the haplotype richness in the Palearctic, and specifically in North Asia. Furthermore, using next-generation sequencing (NGS, Sequel platform, PacBio), we investigated larval and pupal remnants found in an old herbarium from the Nearctic, where P. balsamifera occurs naturally, to verify if any events of the moth introduction to this biogeographic zone happened in the past. Relatively high intraspecific variability in the COI gene of mtDNA, reaching 3.73%, was recorded in Ph. populifoliella. Overall, 30 COI haplotypes were defined in 83 specimens from the Palearctic, with a noticeable richness in North Asia (21 haplotypes). Using NGS, the remnants of 14 Phyllonorycter specimens dissected from up to 174-year-old herbaria from the Palearctic and Nearctic were sequenced, and four moth species were identified. Among them, there were three Palearctic species, Ph. populifoliella, Ph. pastorella (Zeller), and Ph. apparella (Herrich-Schäffer), and one Nearctic, Ph. nipigon (Freeman). No evidence of Ph. populifoliella introduction to North America was documented based on the examination of the herbarium dated 1850–1974. Three specimens of Ph. populifoliella identified from herbaria from Austria and Poland (dated 1879–1931) represented one haplotype (H7) known from the recent time. Overall, our study clarifies the modern range, provides insights into phylogeography, and defines the haplotype richness of the native leafminer outbreaking on the alien host. Furthermore, it underlines the use of old herbaria to explore the historical distribution of endophagous insect species
Mean flow generation by Görtler Vortices in a rotating annulus with librating side walls
No full textLongitudinal libration of the cylinder side walls of a rotating annulus in the supercritical regime induces a centrifugally unstable Stokes boundary layer which generates Görtler vortices only in a portion of a libration cycle. We show for the first time that these vortices propagate into the fluid bulk and generate an azimuthal mean flow which is retrograde (prograde) over the outer (inner) cylinder side wall. Direct numerical simulations (DNS) are carried out and Reynolds-averaged equations and kinetic energy budget of mean and fluctuating flow are used as diagnostic equations to discuss the generation mechanism and scaling behavior of the azimuthal mean flow in the fluid bulk
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