Search Results (28)

Refractory high-entropy alloys (HEAs) are promising candidates for next-generation nuclear applications, particularly fusion reactors, due to their excellent high-temperature mechanical properties and irradiation resistance. Here, the microstructure and mechanical behavior were investigated for an equimolar WTaTiVZr HEA, designed from a palette of low-activation elements. The as-cast alloy exhibited a dendritic microstructure composed of W-Ta rich dendrites and Zr-Ti-V rich inter-dendritic regions, both possessing a body-centered cubic (BCC) crystal structure. Room temperature bulk compression tests showed ultra-high strength of around 1.6 GPa and plastic strain ~6%, with fracture surfaces showing cleavage facets. The alloy also demonstrated excellent high-temperature strength of ~650 MPa at 500 °C. Scratch-based fracture toughness was ~38 MPa√m for the as-cast WTaTiVZr HEA compared to ~25 MPa√m for commercially used pure tungsten. This higher value of fracture toughness indicates superior damage tolerance relative to commercially used pure tungsten. These results highlight the alloy’s potential as a low-activation structural material for high-temperature plasma-facing components (PFCs) in fusion reactors. Full article

The proteolytic processing of the SARS-CoV-2 spike glycoprotein by host cell membrane-associated proteases is a key step in both the entry of the invading virus into the cell and the release of the newly generated viral particles from the infected cell. Because of the critical importance of this step for the viral infectivity cycle, it has been a target of extensive efforts aimed at identifying highly specific protease inhibitors as potential antiviral agents. An alternative strategy to disrupt the pre-fusioviden processing of the SARS-CoV-2 S glycoprotein aims to protect the substrate rather than directly inhibit the proteases. In this work, we focused on furin, a serine protease located primarily in the Golgi apparatus, but also present on the cell membrane. Its cleavage site within the S glycoprotein is located within the stalk region of the latter and comprises an arginine-rich segment (SPRRARS), which fits the definition of the Cardin–Weintraub glycosaminoglycan recognition motif. Native mass spectrometry (MS) measurements confirmed the binding of a hexadecameric peptide representing the loop region at the S1/S2 interface and incorporating the furin cleavage site (FCS) to heparin fragments of various lengths, as well as unfractionated heparin (UFH), although at the physiological ionic strength, only UFH remains tightly bound to the FCS. The direct LC/MS monitoring of FCS digestion with furin revealed a significant impact of both heparin fragments and UFH on the proteolysis kinetics, although only the latter had IC50 values that could be considered physiologically relevant (0.6 ± 0.1 mg/mL). The results of this work highlight the importance of the long-range and relatively non-specific electrostatic interactions in modulating physiological and pathological processes and emphasize the multi-faceted role played by heparin in managing coronavirus infections. Full article

GH4099 is a nickel-based, high-temperature, precipitation-strengthened alloy with excellent mechanical properties and corrosion resistance, widely used in aerospace components. The performance of parts produced by additive manufacturing depends significantly on alloy powder quality and heat treatment. In this study, GH4099 alloy powder was prepared using the EIGA method, and its morphology, particle size distribution, and flowability were analyzed. The mechanical properties and microstructure of parts before and after solution-aging treatment were compared. Results showed that the powder had good sphericity and flowability, with a median diameter D50 of 28.88 μm. The formed parts underwent solution treatment at 1140 °C for 2 h followed by aging at 850 °C for 8 h. After heat treatment, the transverse tensile strength increased to 1122.11 MPa (+15.1%) and the yield strength to 866.56 MPa (+22.3%), while the longitudinal tensile strength reached 1116.81 MPa (+29.4%) and the yield strength 831.61 MPa (+35.2%). This improvement is attributed to the precipitation of γ′ phase. Fractographic analysis revealed a mixed fracture mode characterized by ductile dimples and cleavage facets, indicating that the alloy exhibits favorable toughness-related features under mechanical loading. These findings demonstrate the excellent microstructure and mechanical performance of GH4099 alloy in AM applications, providing a basis for its further use in high-performance aerospace components. Full article

Resistance spot welding (RSW) is now the primary joining process used in the automobile and aerospace sectors. Mechanical parts, when put into service, often undergo cyclic stress. As a result, avoiding fatigue failure should be the top priority when designing these parts. Given that spot welds are a type of localised joining that results in intrinsic circumferential notches, they increase the likelihood of stress concentrations and subsequent fatigue failures of the structure. Most of the fatigue failures in automotive parts originate around a spot weld. To that end, this study seeks to examine the mechanical properties and fatigue behaviour RSW joints made of titanium (Ti) grade 2 alloy and AISI 304 austenitic stainless steel (ASS) with equal and unequal thicknesses of 0.5 and 1 mm. Based on the mechanical properties and fatigue life results, the maximum tensile shear strength and fatigue life for the RSW titanium joint were 613 MPa and 7.37 × 10⁵ cycles for the 0.5–0.5 mm case, 374.7 MPa and 1.39 × 10⁶ cycles for the 1–1 mm case, and 333.5 MPa and 7.69 × 10⁵ cycles for the 1–0.5 mm case, respectively. The maximum shear strength and fatigue life of ASS welded joints were 526.8 MPa and 4.56 × 10⁶ cycles for the 1–1 mm case, 515.2 MPa and 3.35 × 10⁶ cycles for the 0.5–0.5 mm case, and 369.5 MPa and 7.39 × 10⁵ cycles for the 1–0.5 mm case, respectively. The assessment of the shear strength and fatigue life of the dissimilar joints revealed that the maximum shear strength and fatigue life recorded were 183.9 MPa and 6.47 × 10⁵ cycles for the 1 mm Ti–0.5 mm ASS case, 115 MPa and 3.7 × 10⁵ cycles for the 1 mm Ti–1 mm ASS case, 156 MPa and 4.11 × 10⁵ cycles for the 0.5 mm Ti–0.5 mm ASS case, and 129 MPa and 4.11 × 10⁵ cycles for the 0.5 mm Ti–1 mm ASS case. The fatigue life of titanium and stainless steel welded joints is significantly affected by the thickness, particularly at maximum applied stress (0.9% UTS), meaning that similar thicknesses achieve a greater fatigue life than unequal thicknesses. Conversely, the fatigue life of the dissimilar joint reached the greatest extent when an unequal thickness combination was used. The ductile failure of similar Ti and ASS welded joints was demonstrated by the scanning electron microscopy (SEM) examination of fatigue-fractured surfaces under the high-cycle fatigue (HCF) regime, in contrast to the brittle failure noticed in the low-cycle fatigue (LCF) regime. Brittle failure was confirmed by the SEM fatigue of dissimilar joint fractured surfaces due to interfacial failure. The Ti and ASS fractured surfaces presented river-like cleavage facets. On the Ti side, tiny elongated dimples suggest ductile failure before fracture. The topography results showed that the roughness topography parameters of similar and dissimilar fractured specimens made from Ti grade 2 and AISI 304 for the HCF regime were lower than those of the fractured specimens with LCF. The current study is expected to have practical benefits for the aerospace and automotive industries, particularly the manufacturing of body components with an improved strength-to-weight ratio. Full article

This study investigates the impact of multi-step austenitization heat treatment on the in-service life of modified AISI A8 cold work tool steel knives used in wood cutting. The knives were subjected to two treatment methods: single quenching and double tempering (SQDT) and double quenching and double tempering (DQDT). Both treatments were followed by physical vapor deposition (PVD) coating to enhance surface properties. The DQDT treatment resulted in a finer microstructure and more uniform carbide distribution. Field tests on 24 knives over 124 h demonstrated up to 130% improvement in wear resistance for DQDT knives, along with superior edge stability and better PVD coating preservation. DQDT knives exhibited ductile fractures characterized by dimples, contrasting with the brittle fracture and cleavage facets in SQDT knives. Residual stress measurements showed higher compressive stresses in DQDT knives (−280 MPa) compared to SQDT knives (−30 MPa), which increased further after field testing. The enhanced performance of DQDT knives is attributed to their refined microstructure, improved carbide distribution, and higher compressive residual stresses, offering significant potential for improving wood cutting tool efficiency and durability. Full article

Additive manufacturing of duplex (DSS) and super duplex stainless steel (SDSS) has been successfully demonstrated using laser powder bed fusion (LPBF) in recent years. Owing to the high cooling rates, as-built LPBF-processed DSS and SDSS exhibit close to 100% ferritic microstructures and require heat treatment at 1000–1300 °C to obtain the desired duplex microstructure. In this work, the mechanical properties of DSS and SDSS processed via LPBF were investigated in three building directions (vertical, horizontal, diagonal) and three processing conditions (as-built, stress-relieved, annealed, and quenched) using uniaxial tensile testing. As-built samples exhibited tensile and yield strength greater than 1000 MPa accompanied by less than 20% elongation at break. In comparison, the water-quenched samples and samples annealed at 1100 °C exhibited elongation at break greater than 34% with yield and tensile strength values less than 950 MPa. Stress relief annealing at 300 °C had a negligible impact on the mechanical properties. Austenite formation upon high-temperature annealing restored the reduced ductility of the as-built samples. The as-built and stress-relieved SDSS showed the highest yield and tensile strength values in the horizontal build direction, reaching up to ≈1400 and ≈1500 MPa (for SDSS), respectively, as compared to the vertical and diagonal directions. Fractographic investigation after tensile testing revealed predominantly a quasi-ductile failure mechanism, showing fine size dimple formation and cleavage facets in the as-built state and a fully ductile fracture in the annealed and quenched conditions. The findings in this study demonstrate the mechanical anisotropy of DSS and SDSS along three different build orientations, 0°, 45°, 90°, and three post-processing conditions. Full article

For the application of forged medium-Mn steels on flywheel rotors, the effect of annealing temperatures from 300 °C to 650 °C on the impact toughness of 0.16C-6.5Mn forged steel was investigated to demonstrate the microstructural characteristics and austenite reverse transformation determining the impact toughness. The results obtained through standard Charpy V-notch impact tests at ambient temperature show that the impact absorbed energy holds at lower than 10 J almost constantly at annealing temperatures of 300 °C to 500 °C, and a representative intergranular fracture is presented. At an annealing temperature of 600 °C, the impact absorbed energy increases to 147 J, with the ductile fracture characteristics showing plenty of fine dimples, and the high impact toughness is attributed to the high volume fraction above 30% and the moderate stability of reverted austenite. Subsequently, the annealing temperature rises higher than 600 °C, the impact absorbed energy decreases, and the fracture morphology shows brittleness characterized by more flat facets of intergranular fractures and small quasi-cleavage facets, presumably corresponding to the insufficient transformation and twinning-induced plasticity effect due to weakening the Mn partitioning from quenched martensite to reverted austenite, which results in lower austenitic stability. Furthermore, the ductile-to-brittle transition temperature (DBTT) of the 0.16C-6.5Mn forged steel annealed at 600 °C, which holds the highest impact absorbed energy, and is explored for the possibility of flywheel rotor application in a service environment. The DBTT reaches −21 °C, obtained through the Boltzmann function, and the impact absorbed energy is approximately 72 J. Full article

The relationship between modernization and religion is contested, with the literature differing in how and in what ways religion helps or hinders countries’ social, economic, and political development. This paper draws upon the history of Christianity in South Korea to critically explore the links between religion and modernization. It makes two arguments. First, discussions of the link between religion and modernization frequently employ static definitions of religion, but Christianity is characterized by oscillations between worldly (institutionalizing) and unworldly (countercultural) impulses that theoretically make very different contributions to social, economic, and political development. Second, in the case of South Korea, it is shown that both impulses have made vital contributions to the country’s modernization at different times. This suggests that the dynamic tug-of-war between the institutional and countercultural facets of Korean Christianity, although problematic for individual believers and religious leaders, helped it become an important contributor to the country’s success story. However, this paper concludes on a cautionary note by warning that extreme instances of these impulses have caused cleavages between Christianity and the Korean state and society and could undermine its future contributions. This suggests that diversity and toleration—a hallmark of Korean Christianity—will continue to be the best pathway forward. Full article

Phase-specific damage tolerance was investigated for the AlCoCrFeNi_2.1 high entropy alloy with a lamellar microstructure of L1₂ and B2 phases. A microcantilever bending technique was utilized with notches milled in each of the two phases as well as at the phase boundary. The L1₂ phase exhibited superior bending strength, strain hardening, and plastic deformation, while the B2 phase showed limited damage tolerance during bending due to micro-crack formation. The dimensionalized stiffness (DS) of the L1₂ phase cantilevers were relatively constant, indicating strain hardening followed by increase in stiffness at the later stages and, therefore, indicating plastic failure. In contrast, the B2 phase cantilevers showed a continuous drop in stiffness, indicating crack propagation. Distinct differences in micro-scale deformation mechanisms were reflected in post-compression fractography, with L1₂-phase cantilevers showing typical characteristics of ductile failure, including the activation of multiple slip planes, shear lips at the notch edge, and tearing inside the notch versus quasi-cleavage fracture with cleavage facets and a river pattern on the fracture surface for the B2-phase cantilevers. Full article

ARGONAUTE (AGO) proteins are key components of the RNA-induced silencing complex (RISC) that mediates gene silencing in eukaryotes. Small-RNA (sRNA) cargoes are selectively loaded into different members of the AGO protein family and then target complementary sequences to in-duce transcriptional repression, mRNA cleavage, or translation inhibition. Previous reviews have mainly focused on the traditional roles of AGOs in specific biological processes or on the molecular mechanisms of sRNA sorting. In this review, we summarize the biological significance of canonical sRNA loading, including the balance among distinct sRNA pathways, cross-regulation of different RISC activities during plant development and defense, and, especially, the emerging roles of AGOs in sRNA movement. We also discuss recent advances in novel non-canonical functions of plant AGOs. Perspectives for future functional studies of this evolutionarily conserved eukaryotic protein family will facilitate a more comprehensive understanding of the multi-faceted AGO proteins. Full article

A 9%Cr martensitic steel with Ta and B additions was subjected to thermo-mechanical treatment (TMT) including rolling in the range of metastable austenite at 900–700 °C followed by water quenching and tempering at different temperatures. Applied TMT with tempering at T ≥ 700 °C substantially improved the impact toughness. The application of the TMT with subsequent tempering at 780 °C decreased the ductile–brittle transition temperature from 40 to 15 °C and increased the upper shelf energy from 300 to 380 J/cm² as compared to the normalized and tempered (NT) condition. The microstructural observations with scanning and transmission electron microscopes showed the precipitation of fine Ta-rich MX carbonitride and M₂₃C₆ carbide during TMT and subsequent tempering. The analysis of the cleavage facets and the secondary cracks with electron back-scattered diffraction (EBSD) revealed that the brittle fracture occurred via cleavage cracking along {100} planes across the laths, while the high-angle boundaries of martensite blocks and packets were effective barriers to the crack propagation. The increased impact toughness of the tempered TMT steel sample was attributed to enhanced ductile fracture owing to the uniform dispersion of the precipitates and favorable {332}⟨113⟩ crystallographic texture. Full article

Herein, the chloride-induced stress corrosion cracking (SCC) mechanisms of UNS S32205 duplex stainless steel (DSS) reinforcing bars in alkaline and carbonated solutions are studied. Electrochemical monitoring and mechanical properties were tested using linear polarization resistance and electrochemical impedance spectroscopy, coupled with the slow strain rate tensile test (SSRT) to evaluate the SCC behavior and unravel the pit-to-crack mechanisms. Pit initiation and crack morphology were identified by fractographic analysis, which revealed the transgranular (TG) SCC mechanism. HCO₃⁻ acidification enhanced the anodic dissolution kinetics, thus promoting a premature pit-to-crack transition, seen by the decrease in the maximum phase angle in the Bode plot at low frequencies (≈ 1 Hz) for the carbonated solution. The crack propagation rate for the carbonated solution increased by over 100% compared to the alkaline solution, coinciding with the lower phase angle from the Bode plots, as well as with the lower charge transfer resistance. Pit initiation was found at the TiN nonmetallic inclusion inside the ferrite phase cleavage facet, which developed TG-SCC. Full article

Electron Beam Melting (EBM) is a widespread additive manufacturing technology for metallic-part fabrication; however, final products can contain microstructural defects that reduce fatigue performance. While the effects of gas and keyhole pores are well characterized, other defects, including lack of fusion and smooth facets, warrant additional investigation given their potential to significantly impact fatigue life. Therefore, such defects were intentionally induced into EBM Ti-6Al-4V, a prevalent titanium alloy, to investigate their degradation on stress-controlled fatigue life. The focus offset processing parameter was varied outside of typical manufacturing settings to generate a variety of defect types, and specimens were tested under fatigue loading, followed by surface and microstructure characterization. Fatigue damage primarily initiated at smooth facet sites or sites consisting of un-melted powder due to a lack of fusion, and an increase in both fatigue life and void content with increasing focus offset was noted. This counter-intuitive relationship is attributed to lower focus offsets producing a microstructure more prone to smooth facets, discussed in the literature as being due to lack of fusion or cleavage fracture, and this study indicates that these smooth flaws are most likely a result of lack of fusion. Full article

Additive manufacturing (AM) by electron beam melting (EBM) is a technique used to manufacture parts by melting powder metal layer-by-layer with an electron beam in a high vacuum, thereby generating a 3D topology. This paper studies the low-cycle fatigue of Ti–6Al–4V specimens obtained by EBM. Static tests were carried out according to ASTM E8 for a yield stress of 1023 MPa, a fracture stress of 1102 MPa, and a maximum tensile strength of 1130 MPa with a maximum true normal strain at fracture ε_max = 9.0% and an elastic modulus of 120 GPa. Then, fatigue tests were conducted at a load inversion rate of R = −1. It was observed that the material exhibited plastic strain softening, which was attributed to the Bauschinger effect. These results were plotted on a strain vs. life (ε−N) curve using the Ong version of the Coffin–Manson rule and the Baumel–Seager and Meggiolaro–Castro rules. The results were compared to forged Ti–6Al–4V alloys. The cyclic stress–strain behavior was described with the Ramberg–Osgood model. Finally, the fracture surface was analyzed using scanning electron microscopy (SEM) to observe the formation of primary cracks. The fracture morphology showed a mixed surface, also known as a “quasi-cleavage”, which is characterized by dimples, cleavage facets, extensive primary cracks with broken slipping planes, and a large number of inclusions. This phenomenon caused a possible brittle behavior in the material. Full article

The room temperature tensile deformation of Ti-22Al-25Nb alloy with an equiaxed α₂ phase microstructure and the activated slip system of α₂ particles were investigated by a combination of in situ tensile tests and electron backscatter diffraction experiments. The results demonstrate that only a few wide and long slip bands occur in the B2 matrix in the initial stage of yielding. With the tensile displacement increases, a large number of slip bands, including multiple- and cross-slip bands, appear in the B2 matrix and the distance between two adjacent slip bands decreases significantly. Meanwhile, the movement of the slip bands is hindered by the α₂ particles and the B2 grain boundaries, and the slip bands appear only in a small number of the α₂ particles. From the beginning of the tensile process to the final fracture, there are lots of α₂ particles without slip bands. The slip bands penetrate the needle-like lamellar O phase without changing the slip direction. Compared with the α₂ particles, the hindering effect of needle-like O phases on the motion of the slip bands is quite small. The microcracks nucleated at the α₂/B2 phase boundaries or within the α₂ particles, and microcracks propagated along the α₂/B2 phase boundaries or across the α₂ particles. The fracture surface shows the quasi-cleavage feature, which contains a large number of small and shallow dimples on planar facets. The analysis indicates that the plastic deformation of the alloy is mainly contributed by the B2 phase. For room temperature tensile deformation of α₂ phase, there are three types of slip systems that can be activated, including the prism <a> type slip, the basal <a> type slip and the pyramidal <a+c> type slip. The prism <a> type slip is most likely to be activated, followed by the basal <a> type slip and finally the pyramidal <a+c> type slip. In addition, the critical resolved shear stress (CRSS) for the pyramidal <a+c> type slip is the highest among the three types of slip systems. Therefore, the deformation in the α₂ phase is mainly contributed by the prism <a> type slip and the basal <a> type slip. Full article