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The fracture mechanics of frozen rock are important to engineering in cold regions, yet the basic properties and influences remain unclear. The fracture toughness of semi-circular bend (SCB) samples with different initial saturation degrees (ISDs) was tested at − 20 ℃. Acoustic emission (AE) and digital image correlation (DIC) systems were used to capture AE signals and surface deformation under load testing. In addition, the phase composition in rock pores was measured by low-field nuclear magnetic resonance (LF-NMR). It was found that: (1) Fracturing of frozen sandstone generally consists of three stages: pore or microcrack closing, elastic deformation and microcrack propagation which is evidenced by the variation of AE counts and the maximum horizontal strain within the fracture process zone (FPZ) under loading. (2) The ISD has a great influence on fracture toughness and the microcrack propagation process. With increases in ISD, both the fracture toughness and fracture energy of frozen sandstone varies in a mode of slow increase (ISD < 40%), rapid increase (ISD 40–90%) and slight decrease (ISD 90–100%). (3) The phase composition in pores of frozen rock with low ISD (< 40%) is significantly different from that with high ISD (40–100%). At ISDs of < 40%, the ice in rock pores mainly originates from adsorbed water; however, at ISDs of 40–100%, the ice increasingly comes from free and capillary water. Based on the test results, the difference in fracture mechanical properties of frozen sandstone introduced by different ISDs can be attributed to the changes in pore phase composition, which determines the interaction between pore ice/unfrozen water and rock skeleton involving three processes: strengthening due to the filling effect of pore ice, strengthening due to the adhesion force and tensile strength of pore ice, and weakening due to frost damage.HighlightsFreezing strengthens water-bearing sandstone significantly, and the fracture toughness of frozen sandstone increases with its initial saturation degree.Initial saturation degree differs the fracturing process of frozen sandstone in terms of energy release and range of fracture process zone.Pore phase composition primarily determines the fracturing behaviour of frozen sandstone involving ice–pore interactions.The ice–pore cementation and tensile strength of ice are the main contributors to the increase of fracture toughness of frozen rock.

Four kinds of (Ta, Nb, Ti, V, W)C high-entropy ceramics with different combinations of bonding phases, namely Co, CoNi, CoNiCr, and CoNiCrFe, have been successfully prepared by conventional pressureless sintering method, and their microstructures and mechanical properties have been investigated. The results show that the complete high-entropy ceramics can be made using various metal elements as binder phases, which enhances the high-entropy formation ability of (Ta, Nb, Ti, V, W)C series high-entropy ceramics and improves their mechanical properties, and the transverse rupture strength of the CoNi combination reaches 797.42 MPa, the hardness of the CoNiCr combination reaches 1680 HV 30 , and the fracture toughness of the CoNiCrFe combination reaches 8.1 MPa. The present study shows that the multi-element combination mode is favorable to improve the grain formation ability of high-entropy cemented carbide ceramics and is important for reducing the Co element dependence in the field of pressureless sintering of ceramics. Graphical abstract

This study aims to provide insights into the experimental conditions used during the melting/casting process and subsequent thermal treatments of low-alloy steels, particularly regarding recycled scrap metals. As sustainable practices in metallurgy gain importance, optimizing scrap metal recycling is crucial for producing steel grades with desired chemical compositions, microstructures, and physical properties. Understanding these conditions is vital for enhancing the efficiency and quality of steel production from recycled materials. This study emphasizes the critical role of specific experimental conditions in the steelmaking process, especially with recycled scrap metals. It closely examines the atmosphere during melting/casting to identify key parameters that must be rigorously controlled in lab-scale steel production using a vacuum induction furnace. The findings indicate that both the chemical composition and recyclability of low-alloyed steels are significantly influenced by the surrounding atmosphere during melting and casting. Inert environments, such as vacuum or argon, are shown to be ideal for steelmaking with induction technology, particularly when recycling scrap metals. Additionally, this study highlights the importance of precise heat treatments, including homogenization and normalization, by controlling both thermal conditions and the atmosphere to produce high-quality steel from recycled scraps.

Nanostructured materials, due to the production conditions and structural features, are nonequilibrium formations. The structure and its thermal stability, as well as various properties of nanomaterials, depend significantly on the method of external action initiating the passing of many processes. The paper presents the results obtained by studying the thermal stability of the structure and phase composition of a nanocrystalline titanium film formed on a substrate by vacuum plasma (argon plasma) electric arc sputtering of a cathode made of technically pure grade VT1-0 titanium. The film structure was thermally exposed by pulsed electron beam irradiation (10 and 15 J/cm2, 17 keV, 200 μs, 0.3 s–1, 3 pulses) in argon at a pressure of 0.02 Pa. Prior to irradiation, the titanium film was found to be a single phase (α-Ti) material; it has a columnar structure with 1.3–2.7 nm crystallites forming columns. The irradiation of the film with a pulsed electron beam is accompanied by the formation of a surface layer containing titanium oxide nanoparticles (2.6–8.3 nm). It was observed that the relative content of these nanoparticles increased with increasing electron beam energy density.

In this study, the high-temperature oxidation behavior of a series of AlTiNiCuCox high-entropy alloys (HEAs) was explored. The AlTiNiCuCox (x = 0.5, 0.75, 1.0, 1.25, 1.5) series HEAs were prepared using a vacuum induction melting furnace, in which three kinds of AlTiNiCuCox (x = 0.5, 1.0, 1.5) alloys with different Co contents were oxidized at 800 °C for 100 h, and their oxidation kinetic curves were determined. The microstructure, morphology, structure, and phase composition of the oxide film surface and cross-sectional layers of AlTiNiCuCox series HEAs were analyzed using scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS), and X-ray diffraction (XRD). The influence of Co content on the high-temperature oxidation resistance of the HEAs was discussed, and the oxidation mechanism was summarized. The results indicate that, at 800 °C, the AlTiNiCuCox (x = 0.5, 1.0, 1.5) series HEAs had dense oxide films and certain high-temperature oxidation resistance. With increasing Co content, the high-temperature oxidation resistance of the alloys also increased. With increasing time at high temperature, there was a significant increase in the contents of oxide species and Ti on the oxide film surface. In the process of high-temperature oxidation of AlTiNiCuCox series HEAs, the interfacial reaction, in which metal elements and oxygen in the alloy form ions through direct contact reaction, initially dominated, then the diffusion process gradually became the dominant oxidation factor as ions diffused and were transported in the oxide film.

In order to transform the crystalline form of Ca2SiO4 (C2S) in phosphorus-containing slag from monoclinic β-polycrystalline to square γ-polycrystalline, a volume expansion of about 11% was generated, which caused the phosphorus-containing slag to undergo self-powdering. The CaO-SiO2-Al2O3-MgO-MnO-P2O5-FeO slag system was analyzed using FactSage7.1 thermodynamic software, and the effects of different P2O5, FeO and basicity on the mineral phase composition of slag system were analyzed in the range of 1300~1700 °C. It was shown that P2O5, FeO and basicity all have an effect on the composition of the mineral phases. When the mass fraction of P2O5 in the slag was lower than 0.25%, it had less effect on the transformation of C2S crystalline structure. When the P2O5 content was higher than 0.25%, it was favorable to the generation of low-melting-point substances, but the P2O5 in the slag reacted with C2S in the silicate phase, making P5+ solidly soluble in C2S, inhibiting the transformation of β-C2S to γ-C2S and hindering the self-powdering of the slag. The FeO content in the slag system ranged from 20% to 28%, and as the FeO content increased, the C2S content in the silicate phase decreased from 33.3% to 25.9%, while the temperature at which the silicate was completely dissolved into the liquid phase decreased from 1600 °C to 1500 °C and the complete melting temperature of the slag decreased. The low FeO content facilitates the self-powdering of slag. In the high-phosphorus slag, at temperatures below 1450 °C, with the increase of basicity, the proportion of C2S in the silicate phase first increased and then decreased. With basicity at 1.8; the highest content of silicate phase, accounting for 33.7%; and the temperature exceeding 1450 °C, the silicate phase dissolved into the liquid phase, which is conducive to the removal of phosphorus from the slag, achieving the self-powdering of high-phosphorus slag.

This paper investigates the structure and phase composition of Al–TiB2 metal matrix composites prepared from the Al–Ti–B system powder using self-propagating high-temperature synthesis (SHS) in semi-industrial conditions (the amount of the initial powder mixture was 1000 g). The samples produced in semi-industrial conditions do not differ from the laboratory samples, and consist of the aluminum matrix and TiB2 ceramic particles. The temperature rise leads to the growth in the average size of TiB2 particles from 0.4 to 0.6 µm as compared to the laboratory samples. SHS-produced composites are milled to the average particle size of 42.3 µm. The powder particles are fragmented, their structure is inherited from the SHS-produced Al–TiB2 metal matrix composite. The obtained powder can be used as the main raw material and additive in selective laser sintering, vacuum sintering, and hot pressing products. It is worth noting that these products can find their own application in the automotive industry: brake pads, drums, rail discs, etc.

In this work, La2Ce2O7-yttria-stabilized zirconia (LC-YSZ) composites with different weight fractions of YSZ (40–70 wt.%) were prepared by hot pressing at 1400 °C and investigated as a material for thermal barrier-coating (TBC) applications. For this purpose, the effect of YSZ addition on the phase composition, microstructure, mechanical performance and thermal behavior was studied. X-ray diffraction analysis showed that the LC-YSZ composites were mainly composed of a cubic ZrO2 and La2O3-CeO2-ZrO2 solid solution with a pyrochlore structure, indicating that the reaction between LC and YSZ took place during hot pressing. Scanning electron microscopy revealed the high microstructural stability of the prepared composites, as the pore formation was significantly controlled and a high relative density (>97%) was obtained. The microstructure of LC-YSZ bulk samples was relatively fine-grained, with an average grain size below or very close to 1 µm. YSZ doping improved the Vickers hardness of the LC-YSZ composites; the highest hardness, with value of 12 ± 0.62 GPa, was achieved for the composite containing 70 wt.% of YSZ. The fracture toughness of LC-YSZ composites was in the range from 2.13 to 2.5 MPa·m1/2. No statistically significant difference in heat capacity or thermal conductivity was found between the composites with different content of YSZ. The results showed that LC-YSZ composites have relatively low thermal conductivities from room temperature (1.5–1.8 W·m−1·K−1) up to 1000 °C (2.5–3.0 W·m−1·K−1). This indicates that the prepared LC-YSZ composite materials are promising candidates for TBC applications.

This paper describes synthesis in 5Ti + 3Si +  Al( %) activated mixtures and in an 5Ti + 3Si + 10% Al initial mixture. The effect of mechanical activation and aluminum content on burning rate, maximum combustion temperature, morphology, elongation, integrity, and phase composition of combustion products is studied. Mechanical activation expands the limit of Al content to 40% at which samples can burn without preheating. The following intermetallic alloys are synthesized on the basis of Ti–Si–Al: solid solutions based on Ti(Si Al  titanium silicide and those based on Ti(Al Si  aluminide titanium.

The structure, phase composition, and mechanical and corrosion properties of plates made of a structural aluminum Al–Cu–Mg alloy are studied in its various states. The results obtained are compared with the properties of its commercial analog (AK4-1 alloy). The alloy under study is found to surpass its analog in strength properties at room and elevated (up to 175°C) temperatures by 9–12%. The impact toughness KCU of the Al–Cu–Mg alloy is twofold that of the AK4-1 alloy. The increase in the strength and corrosion properties of the alloy after operational heating is shown to be explained by the phase composition and morphology of intermetallic phases, including transition-metal phases, which form in the surface layers of samples in small quantities.