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The effect of processing and annealing temperatures on the grain boundary characters in the ultrafine-grained structure of a 304-type austenitic stainless steel was studied. An S304H steel was subjected to multidirectional forging (MDF) at 500-800°C to total strains of~4, followed by annealing at 800-1,000°C for 30 min. The MDF resulted in the formation of ultrafine-grained microstructures with mean grain sizes of 0.28-0.85 μm depending on the processing temperature. The annealing behaviour of the ultrafine-grained steel was characterized by the development of continuous post-dynamic recrystallization including a rapid recovery followed by a gradual grain growth. The post-dynamically recrystallized grain size depended on both the deformation temperature and the annealing temperature. The recrystallization kinetics was reduced with an increase in the temperature of the preceding deformation. The grain growth during post-dynamic recrystallization was accompanied by an increase in the fraction of Σ3 n CSL boundaries, which was defined by a relative change in the grain size, i.e. a ratio of the annealed grain size to that evolved by preceding warm working (D/D 0 ). The fraction of Σ3 n CSL boundaries sharply rose to approximately 0.5 in the range of D/D 0 from 1 to 5, which can be considered as early stage of continuous post-dynamic recrystallization. Then, the rate of increase in the fraction of Σ3 n CSL boundaries slowed down significantly in the range of D/D 0 > 5. A fivefold increase in the grain size by annealing is a necessary condition to obtain approximately 50% Σ3 n CSL boundaries in the recrystallized microstructure.

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Future decades will experience tons of silicon waste from various sources, with no reliable recycling route. The transformation of bulk silicon into SiO2 nanoparticles is environmentally 2 significant because it provides a way to recycle residual silicon waste. To address the needs of silicon recycling, we develop a top-down approach that achieves 100% conversion of bulk silicon to silica nanoparticles with outcome sizes of 8-50 nm. In addition to upcycling the potential of silica, our method also possesses several advantages, such as simplicity, scalability and controllable particle size distribution. Many fields of science and manufacturing, such as optics, photonics, medical, and mechanical applications, require size-controllable fabrication of silica nanoparticles. We demonstrate that control over temperature and hydrolysis time has a significant impact on the average particle size and distribution shape. Additionally, we unravel the process of nanoparticle formation using a theoretical nucleation model and quantum density functional theory calculations. Our results provide a theoretical and experimental basis for silica nanoparticle fabrication and pave the way for further silicon conservation research.

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The 3D printing process is a recent technique, which allows one to produce parts of complex geometry. The influence of printing parameters on the mechanical and structural properties of many materials has been extensively studied. However, despite the considerable amount of research, the task of comparing the results of different scientific groups is complicated. Each research group performs the investigation with different printing conditions. A lot of works contain not full information about the printing process parameters which were applied. This paper presents the results on the mechanical and structural properties of 316L stainless steel according to variable printing parameters, such as laser density energy, scan strategy, and build direction at other fixed conditions. The results reveal a parabolic dependency between the mechanical properties and the laser density energy. The laser density energy of 161 J/mm 3 leads to the best mechanical characteristics (yield strength of 530 MPa, ultimate strength of 580 MPa, and ductility of 63.2%). Scan strategy does not influence the mechanical properties of the samples printed in the vertical direction. At the same time, the strong scan strategy effect is observed for the samples printed in horizontal direction. The difference in the ultimate strength between the vertically and horizontally printed samples reaches up to 70 MPa.

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Direct energy deposition (DED) is an additive manufacturing method that allows repairing the broken parts and building the meter-scale samples. However, the printing of large parts is associated with huge residual stresses and martensite phase formation, which can change the geometry of final samples or initiate the crack. The last factor is especially important for titanium alloys. In this work, we investigated the effect of DED thermal history on the obtained structural and mechanical properties of Ti-6Al-4V using a thermocouple. It was demonstrated that printing with long pauses leads to a¢ phase formation, which embrittles the material. Continuous printing with small pauses between tracks leads to the formation of the dual a+b structure. The effect of the texture on the material properties is also discussed. As a result of the study, the specific DED process parameters allow the same mechanical characteristics for as-built titanium alloy and the alloy after heat treatment.