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Interstitial oxygen embrittles titanium, particularly at cryogenic temperatures, which necessitates a stringent control of oxygen content in fabricating titanium and its alloys. Here, we propose a structural strategy, via grain refinement, to alleviate this problem. Compared to a coarse-grained counterpart that is extremely brittle at 77 K, the uniform elongation of an ultrafine-grained (UFG) microstructure (grain size ~ 2.0 µm) in Ti-0.3wt.%O is successfully increased by an order of magnitude, maintaining an ultrahigh yield strength inherent to the UFG microstructure. This unique strength-ductility synergy in UFG Ti-0.3wt.%O is achieved via the combined effects of diluted grain boundary segregation of oxygen that helps to improve the grain boundary cohesive energy and enhanced dislocation activities that contribute to the excellent strain hardening ability. The present strategy will not only boost the potential applications of high strength Ti-O alloys at low temperatures, but can also be applied to other alloy systems, where interstitial solution hardening results into an undesirable loss of ductility. Oxygen has long been considered as a detrimental impurity in pure titanium since it can severely deteriorate the ductility. Here, the authors propose a simple, yet effective strategy via grain refinement to solve this long-standing issue, while preserving its potential hardening effect.

This work presents a formalism to calculate the configurational entropy of mixing based on the identification of non-interacting atomic complexes in the mixture and the calculation of their respective probabilities, instead of computing the number of atomic configurations in a lattice. The methodology is applied in order to develop a general analytical expression for the configurational entropy of mixing of interstitial solutions. The expression is valid for any interstitial concentration, is suitable for the treatment of interstitial short-range order (SRO) and can be applied to tetrahedral or octahedral interstitial solutions in any crystal lattice. The effect of the SRO of H on the structural properties of the Nb-H and bcc Zr-H solid solutions is studied using an accurate description of the configurational entropy. The methodology can also be applied to systems with no translational symmetry, such as liquids and amorphous materials. An expression for the configurational entropy of a granular system composed by equal sized hard spheres is deduced.

Synergistic effects of the synthetic calcium silicate hydrates (C-S-H)/polycarboxylate (PCE) and Na 2 SO 4 on hydration properties and microstructure of cement-lithium slag (LS) composite binder were analyzed. Results showed that C-S-Hs-PCE and Na 2 SO 4 exhibited a synergistic effect on hydration acceleration of LS-cement binder. Na 2 SO 4 increased alkalinity of interstitial solution and promoted dissolution of LS. Dissolved Al and Si from LS powder reacted with dissolved SO 4 2− from Na 2 SO 4 to produce extra hydrates, and C-S-Hs-PCE accelerated pozzolanic reaction as well as hydration reaction via nucleation effect collaborated with dispersing effect. C-S-Hs-PCE accelerated reaction process of Na 2 SO 4 via nucleation effect, and activation effect of Na 2 SO 4 provided more newly-formed hydrates to act as nucleation seeds or crystal skeleton for the hydration of new phases. Newly formed hydrates promoted exceedingly the appearance of network, leading to a refinement of microstructure.

The morphology of single-particle manganese sulfide (MnS) in sulfur bearing steel without oxygen is polyhedral, while it is spherical in the steel containing 70 ppm oxygen. Oxygen can dissolve in MnS to form oxysulfide (Mn(S,O)), the dissolution form of oxygen in MnS is both the substitutional and interstitial solution. The difference in the surface energies of Mn(S,O) is significantly smaller than that of MnS, this is the root cause for oxygen to spheroidize sulfides.

Laser cladding rapid solidification technique is an effective strategy for manufacturing ultra-high-strength martensitic stainless steels (UHS-MSS). Due to super-saturation solution strengthening of interstitial atoms (IAs), martensitic stainless steels containing IAs exhibit excellent ultra-high strength and toughness and have high tolerance for oxygen impurities. Hence, studying the specific speciation and structural characteristics of IAs is of great significance for guiding laser cladding of ultra-high-strength steels. Herein, we use density functional theory (DFT) computations to analyze the stable occupancies of IAs and their interactions in body-centered cubic iron (BCC Fe). The findings show that single IAs prefer to occupy octahedral sites over tetrahedral sites. Therefore, octahedral sites are selected as the optimal sites for the following double IAs study. For homo IAs, C-C and N-N configurations exhibit greater stability at long-range distances, whereas O-O demonstrate optimal stability at intermediate distances. Crucially, hetero IAs configurations are more stable compared to single IAs and homo IAs, exhibiting a synergistic effect. Especially, the C-O combination shows the highest stability and strongest bonding character. Meanwhile, the dissociation behavior of O indicates that C-O and N-O have higher dissociation temperatures than single O, further verifying the synergistic effect of hetero IAs. This provides a theoretical basis for understanding the interstitial solution strengthening of laser cladding UHS-MSS.

When graphite is dissolved in liquid iron, its microcrystals break down into graphite nanocrystals and carbon atoms. Carbon steel melts consist of iron and graphite nanocrystals, iron and carbon atoms. In carbon steels, structural transformations are mainly nanostructured processes. The elementary components of these processes are iron and graphite nanocrystals. Austenite microcrystals are mainly formed from them. Austenite is not a solid interstitial solution of carbon in γ-Fe. Cementite nanocrystals are formed from iron nanocrystals and austenite graphite, and cementite (iron carbide) molecules are formed from iron and austenite carbon atoms. Ferrite microcrystals are formed from nanocrystals and iron atoms of austenite. Cementite microcrystals are formed from nanocrystals and cementite molecules.

This study is focused on the sorption properties and the changes in the structure and state of Ti-25Al-25Nb (at.%) system alloys under thermal cyclic loading. These samples were produced by combining high-energy processing methods through mechanization and spark plasma sintering in the temperature range of 1100–1300 °C, followed by two-stage heat treatment at temperatures of 800 °C and 1250 °C. Thermal cyclic experiments on hydrogen sorption/desorption with samples of the Ti-25Al-25Nb (at.%) system were conducted at the VIKA experimental installation at a saturation temperature of about 500 °C and a degassing temperature of 610 °C. It took about 41 min to reach pressure equilibrium at 500 °C. The hydrogen diffusion coefficient was calculated based on the Barrer formula and was 9.1 × 10−5 cm2/s at 500 °C. The maximum hydrogen content was recorded after the first sorption/desorption cycle and was 1.91 wt%. Due to the multiple thermal cyclic effects in the hydrogen medium, the predominantly two-phase (O + B2) alloy structure underwent transformation to form a new structure (O-AlNbTi2). In the phase composition of the Ti-25Al-25Nb (at.%) alloy, the formation of hydrides in the form of independent phases as a result of thermal cycling was not detected. Hydrogen absorption is most likely to be associated with the formation of an interstitial solution based on existing crystalline phases.

Ion-exchange membrane (IEM) can be classified into homogeneous and heterogeneous membrane according to the heterogeneity of membrane structure. Results of various studies indicated that the degree of heterogeneity significantly affects the properties and performance of IEMs, such as conductivity, permselectivity, mechanical and chemical stability, energy consumption, and limiting current density. In the case of transport properties, it may be associated with efficacy of Donnan exclusion influenced by the presence of interstitial solution and inert phase in the membrane matrix. Therefore, understanding the effect of heterogeneity on Donnan exclusion is important to provide preliminary information about IEM transport properties. In this paper, the effect of IEC/Wu on Donnan exclusion is discussed. The effect of heterogeneity on Donnan exclusion is expressed as a correlation of IEC/Wu ratio with Donnan equilibrium constant, KD, and transport number of counter-ion, ti.

Improving saline soils’ properties by incorporating limes is a practical technique, generally due to cation exchange, pozzolanic reaction, and carbonation. This study explores how soil salinity, measured by electrical conductivity, affects untreated and lime-treated saline soils. An Algerian sebkha soil (from Ain M’lila) with an original high salinity (ECe3 = 23.2 dS.m−1) was used. The same soil was washed to create medium (ECe2 = 8.3 dS.m−1) and low (ECe1 = 2.32 dS.m−1) salinity soil samples. The results of this study indicate that salinity influenced the shape of the particle size distribution curve, particularly in the silt range. Salinity also had a significant effect on carbonate content (CaCO3) and unconfined compressive strength (UCS). For the untreated soil, when salinity decreased, the UCS and CaCO3 content increased. However, when salinity decreased for the treated soil, the UCS increased, while the CaCO3 content decreased. X-ray diffraction (XRD) analysis of untreated soils showed halite (NaCl) disappearance and gypsum (CaSO4 2H2O) reduction with decreasing salinity in ECe1. In treated soil at ECe3, these mineral phases remained constant. While XRD detected no new cementitious phases in treated ECe3 or ECe1 samples, thermogravimetric analysis confirmed the presence of portlandite in both. As Ain M’lila sebkha is a chloride–sulfate soil, the dissolution of the halite and gypsum phases released more Cl− and SO42− ions into the interstitial solution. In a low fraction of clay, these ions obstructed and slowed the pozzolanic reaction in the ECe3 soil. Identifying the season when this type of soil has lower salinity can be beneficial for treatment from a technical, economic, and environmental point of view.

The effect of thermohydrogen treatment and vacuum ion–plasma nitriding on the determination of the volume and surface structure of ball heads made of Ti–6Al–4V alloy was studied. It was found that the submicrocrystalline structure formed in the head during thermohydrogen treatment makes it possible to achieve hardness values of 39–41 units HRC and a surface roughness of 0.02 μm. It was shown that the creation of a modified layer consisting of ε (TiN) and δ (Ti2N) titanium nitrides on the surface of a ball head and the solid interstitial solution of nitrogen in α-titanium makes it possible to completely eliminate material wear when testing for friction on ultra-high-molecular-weight polyethylene. The equivalent analysis was also conducted with a ball head that had been implanted in a human body for 12 years. It was found that the change in the color of the head, from slightly golden after nitriding to metallic, is due to the formation of an oxynitride nanoscale layer on the surface. It was shown that in contrast with films made of titanium oxide, the film developed in this study has high wear resistance.