Nb Ta Research Articles

Direct selective laser sintering of high-entropy carbide ceramics

The direct selective laser sintering (SLS) process was successfully demonstrated for additive manufacturing of high-entropy carbide ceramics (HECC), in which a Yb fiber laser was employed for ultrafast (in seconds) reactive sintering of HECC specimens from a powder mixture of constitute monocarbides. A single-phase non-equiatomic HECC was successfully formed in the 4-HECC specimen with a uniform distribution of Zr, Nb, Hf, Ta, and C. In contrast, a three-layer microstructure was formed in the 5-HECC specimen with five metal elements (Zr, Nb, Hf, Ta and Ti), consisting of a TiC-rich top layer, a Zr–Hf–C enriched intermediate layer, and a non-equiatomic Zr–Ta–Nb–Hf–C HECC layer. Vickers hardness of 4- and 5-HECC specimens were 22.2 and 21.8 GPa, respectively, on the surface. These findings have important implications on the fundamental mechanisms governing interactions between laser and monocarbide powders to form a solid solution of HECCs during SLS.Graphical abstract

Machine learning accelerated design of non-equiatomic refractory high entropy alloys based on first principles calculation

The properties of High Entropy Alloys (HEAs) strongly depend on the composition and content of elements. However, it was difficult to obtain the optimized element composition through the traditional "trial and error" method. The non-equiatomic HEAs have a large range for composition exploration by changing the content of elements, but the current research methods are difficult to analyze comprehensively. In this work, the prediction model with high accuracy is established by mixture design, the first principles calculation and machine learning. The model is used to predict the elastic properties and Poisson's ratio of non-equiatomic Mo–Nb–Ta–Ti–V HEAs, and the prediction results agree well with experimental data. The optimal element composition range of elastic properties and Poisson's ratio could be obtained. The influence of elements on the elastic properties and Poisson's ratio is analyzed through the calculation of features' importance. The results show that the content of Ti has the greatest contribution to the elastic properties and Poisson's ratio of the alloy. This model can not only obtain a large amount of data quickly and accurately but also help us to establish the relationship between element content and mechanical properties of non-equiatomic Mo–Nb–Ta–Ti–V RHEAs and provide theoretical guidance for experiments.

AI-accelerated materials informatics method for the discovery of ductile alloys

In computational materials science, a common means for predicting macroscopic (e.g., mechanical) properties of an alloy is to define a model using combinations of descriptors that depend on some material properties (elastic constants, misfit volumes, etc.), representative for the macroscopic behavior. The material properties are usually computed using special quasi-random structures (SQSs), in tandem with density functional theory (DFT). However, DFT scales cubically with the number of atoms and is thus impractical for a screening over many alloy compositions. Here, we present a novel methodology which combines modeling approaches and machine-learning interatomic potentials. Machine-learning interatomic potentials are orders of magnitude faster than DFT, while achieving similar accuracy, allowing for a predictive and tractable high-throughput screening over the whole alloy space. The proposed methodology is illustrated by predicting the room temperature ductility of the medium-entropy alloy Mo-Nb-Ta.

Subduction‐related mafic to felsic magmatism in the Xiangpishan concentric calc‐alkaline complex, Northeast Tibetan Plateau

The Xiangpishan complex in the Zongwulong‐Qinghainanshan Tectonic Belt, Northeast (NE) Tibetan Plateau, is a composite concentric pluton consisting of a felsic core (granodiorite) surrounded by quartz diorite in the middle to diorite and minor gabbro at the margin with locally less volume of monzogranite. Many dioritic enclaves are unevenly distributed within host granitoids. We evaluate the petrogenesis of the complex by geochemical, geochronological, and Hf isotopic data in tandem with regional data in the belt. The results show that felsic rocks were emplaced during the Late Permian (ca. 262–256 Ma); whilst gabbros yielded a younger age of ca. 249 Ma. As the hybrid phase from mixing between felsic and mafic magmas, enclaves and diorites have analogous ages (ca. 257–254 Ma) to both. Zircons from gabbro and enclaves are marked by higher εHf(t) value up to +1.82; whilst granodiorites have lower εHf(t) value of −5.48, consistent with hybrid diorites possessing intermediate εHf(t) values of −3.14 to 0.34. Furthermore, the quantitative calculation from Mass Balances Modelling suggests that the mass of mafic magma (ca. 67%–79%) is involved to achieve the hybridization. Geochemically, these rocks crystallized from calc‐alkaline magma with different sources, but demonstrated consistent arc‐like signatures, as they are enriched in large‐ion lithophile elements and light rare earth element (LREE), and depleted in high‐ field‐strength elements and heavy rare earth element (HREE). Besides, they present negative Nb–Ta anomalies together with significant P and Ti troughs. Finally, an evolutional model has been proposed that the asthenosphere‐lithosphere interaction played an important role during the emplacement of the complex, where the limited volumes of mantle‐derived melt act as the suppliers of heat and mass (mainly volatile components) to induce partial melting of the juvenile mafic lower crust and mixed (or mingled) with the produced crust‐derived magma during the oceanic subduction, which led to the generation of diorites as well as mafic microgranular enclaves.

Heat treatment effects on microstructure and mechanical properties of TiZrNbTa high-entropy alloy

Microstructure and mechanical properties of TiZrNbTa high-entropy alloy (HEA) in the as-cast and annealed states are systematically investigated. The yield strength of TiZrNbTa HEA strongly depends on the heat treatment temperatures. With the increase of heat treatment temperature, the yield strength of TiZrNbTa increases first and then decreases. When the heat treatment temperature reaches 600 ℃, the yield strength and uniform strain of TiZrNbTa HEA are 1583 ± 55 MPa and 20.5% ± 1.8%, respectively. Compared with the as-cast state TiZrNbTa, the yield strength of TiZrNbTa HEA after simple heat treatment, i.e., 600 ℃ for 1 h improves by 47%, which is attributed to the spinodal decomposition strengthening. By comparing the contribution of grain boundary strengthening for the TiZrNbTa HEA before and after annealing, the significant decrease in the yield strength of the TiZrNbTa HEA is not caused by grain coarsening after heat treatment at 800 ℃, but by the formation of a vein-like phase in grain boundaries. The Ti(Zr)-rich and Nb(Ta)-rich phases in TiZrNbTa HEA exhibit different performances in large compressive strain conditions. The Ti(Zr)-rich phase exhibits good compressive plastic deformation ability, and the Nb(Ta)-rich phase has a higher strength. The TiZrNbTa HEA after one-step simple heat treatment displays excellent mechanical properties, which significantly improves the possibility of clinical application as a new orthopedic-implant alloy.

Quaternary post-collisional high Nb-like basalts from Bijar-Qorveh, NW Iran: A metasomatized lithospheric mantle source

The Quaternary Bijar-Qorveh mafic volcanic rocks (BQMVR) occur in the Sanandaj-Sirjan Zone (SSZ) of Iran, a segment of the Alpine-Himalayan Orogeny with a Gondwana-affinity basement. Phases 1 and 2 of BQMVR are silica-undersaturated (basanite, tephrite, and phonotephrite) and form a highly alkaline or HA suite. The last phase, phase 3, of BQMVR is silica-saturated (alkali olivine basalt and hawaiite) and is called the mildly alkaline or MA suite. BQMVR share well-known subduction-related negative Nb Ta anomalies, and their Nb abundances are high enough to be classified as ‘high-Nb like basalts’. However, they do not show geochemical characteristics of typical high-Nb basalts. Trace element abundances and patterns of the MA suite mimic garnet-bearing spinel peridotite partial melts, whereas the HA suite is too rich in incompatible trace elements to match normal mantle partial melts. Enriched trace element patterns of the HA suite are akin to hornblendite experimental partial melts, and are likely derived from a garnet-amphibole peridotite source. Sr-Nd-Pb isotopic characteristics of the BQMVR indicate a subcontinental lithospheric mantle affinity. The HA suite tends toward the EM1 array, whereas the MA suite follows the EM2 array. The highly radiogenic Sr Nd isotopes of the MA suite indicate significant crustal contamination. Lithospheric delamination beneath the SSZ that followed Arabia-Eurasia collision, triggered garnet-amphibole peridotite partial melting that interacted with 10–30% of the asthenospheric component to have formed the HA suite. Mantle melting at shallower lithosphere depths followed and produced the MA suite. MELTS modeling shows the BQMVR underwent fractional crystallization of clinopyroxene ± olivine. Whole-rock thermobarometric calculations suggest derivation of the primary melts at a depth of ~97 km, however the Cpx-thermobarometer indicates that such melts equilibrated at lower crust depths at a depth of 45 km close to the Moho. The present Quaternary volcanostratigraphic study provides substantial clues for major post-collisional alkaline high-Nb mafic volcanism bearing signatures of two distinct magmatic stages; an early phase (phases 1 and 2) rooted in a deeper garnet amphibole peridotite followed by phase 3 rooted in a garnet-poor spinel peridotite. • Quaternary alkaline mafic volcanism in western Iran is post collisional. • Highly alkaline (HA) suite is derived from juvenile amphibole rich mantle. • Mildly alkaline (MA) suite is derived from shallower, ancient lithospheric mantle. • EM1 and EM2 affinities of the HA and MA suites respectively comply with the SCLM. • MELTS and isotopes revealed FC and AFC roles for HA and MA suites respectively.

A novel Ti42.5Zr42.5Nb5Ta10 multi-principal element alloy with excellent properties for biomedical applications

Body-centered cubic (BCC) Ti–Zr–Nb–Ta multi-principal element alloys (MPEAs) have drawn extensive research attention as orthopedic implant materials. In this work, a novel Ti42.5Zr42.5Nb5Ta10 multi-principal element alloy was developed for biomedical applications in terms of its microstructure, mechanical properties, wear performance, corrosion behavior, and in vitro biocompatibility. The Ti42.5Zr42.5Nb5Ta10 alloy after cold rolling followed by annealing at 880 °C (TZNT-880), possessed excellent mechanical properties combination, with a yield strength of 839.5 MPa, elongation at fracture of 22.6%, and Young's modulus of 63.2 GPa, superior to most of the currently existing biomedical BCC MPEAs. Meanwhile, TZNT-880 alloy exhibited higher wear resistance compared with commercial CP-Ti and Ti6Al4V, which is strongly related to its high H/E and H3/E2 values. Also, TZNT-880 alloy showed good corrosion resistance, as revealed by a nobler corrosion potential, lower corrosion current densities, and higher passivation stability, which is attributed to the formation of passivation films consisting of TiO2, ZrO2, Nb2O5, and Ta2O5. The in vitro biocompatibility tests demonstrated that the TiZrNbTa alloys can support cell adhesion and proliferation with high biocompatibility comparable to that of CP-Ti and Ti6Al4V, indicating their potential as a candidate for implant material.

Newly-recognized Triassic highly fractionated leucogranite in the Koktokay deposit (Altai, China): Rare-metal fertility and connection with the No. 3 pegmatite

Rare-metal granitic pegmatites are commonly associated with granites. However, for the Koktokay No. 3 pegmatite in the Chinese Altai, hosting a giant Li–Be–Nb–Ta–Cs–Rb–Hf deposit, the parental granites have not yet been found. Here we first recognized the ore-bearing leucogranites at Koktokay, in which the beryl (Be) and coltan (Nb–Ta) occur. Six coltan U–Pb ages of the leucogranites fall in a narrow range of 224.2 ± 2.7–220.7 ± 4.0 Ma which are in good agreement with our new coltan U–Pb age of 219.8 ± 1.3 Ma of the No. 3 pegmatite. Four muscovite 40Ar/39Ar ages from the same samples are from 181.1 ± 1.4 Ma to 177.2 ± 1.2 Ma which are consistent with published 40Ar/39Ar age results (182.1–179.7 Ma) from the No. 3 pegmatite. Thus, the emplacement of the leucogranites and associated mineralization occurred in late Triassic which was followed by a new mineralization at early Jurassic. The leucogranites, consisting of muscovite albite granite and minor albite granite, are characterized by high Al2O3 and Na2O and show well-developed convex tetrad effect. They are peraluminous S-type granites and were formed by highly fractional crystallization and melt-fluid interaction. The leucogranites are enriched in volatile elements (B, F, P, and H2O) and lithophile (Li, Be, Nb, Ta, Cs, and Na) with very low Zr/Hf (8.2–13.8) and Nb/Ta (0.8–5.9) ratios, indicating a fertile rock. The similar petrographic, geochemical and geochronological data between the leucogranites and the No. 3 pegmatite indicate that they are contemporaneous and cogenetic, implying a common magmatic source. A much larger, unexposed parental granite, from which the leucogranite and No.3 pegmatite have fractionated, is present at depth. A granite-pegmatite model is established that the parental granite at depth is connected with leucogranite and pegmatite at shallow which is likely responsible for the formation of the giant Koktokay No. 3 pegmatite.

Trace element composition of quartz from alkaline granites – A factor supporting genetic considerations: Case study of the Pitinga Sn–Nb–Ta–Th-cryolite deposit

The Madeira pluton, bearing the world-class tin-cryolite deposit of Pitinga, and the closely associated Europa pluton lie in the central part of the Amazon craton, Brazil. The Madeira pluton consists of four principal rock types: early metaluminous porphyritic amphibole-biotite granite with rapakivi texture, metaluminous biotite granite, metaluminous hypersolvus porphyritic granite, and peralkaline albite granite, while the Europa pluton consists of peralkaline riebeckite-biotite alkali feldspar granite. Texture and chemical composition of quartz from all mentioned rock types was evaluated in order: (i) to estimate the contents of trace elements in quartz from peralkaline granites, (ii) to define major differences in the uptake of trace elements into quartz in peraluminous vs. peralkaline conditions, (iii) to better constrain the evolution of the composite Madeira pluton. The contents of Li, Be, B, Na, Al, P, K, Sc, Ti, Mn, Fe, Ga, Ge, Rb, Sr, Zr, Nb, Sn, Sb, Ce, Yb, Hf, Ta, Th, and U in quartz were analyzed using laser-ablation ICP-MS. Quartz from the studied metaluminous and peralkaline granites of the Madeira and Europa plutons is poor in Al (<150 ppm Al) and Li (mostly <20 ppm Li) but enriched in Ge (max. 10 ppm), Sc (max. 6 ppm), and Ga (max. 13 ppm). As suggested by the TitaniQ thermobarometer, the Madeira biotite granite crystallized between ca. 700 and 650 °C at a nearly constant pressure of 3 kbar, while the hypersolvus granite crystallized between 800 and 700 °C at 15–20 to 2 kbar. Textural and chemical data on quartz are in agreement with previous geochronological data: the Madeira pluton comprises two older pulses of less evolved, mostly metaluminous biotite-hornblende and biotite granites, and two younger pulses of mutually mingled metaluminous hypersolvus granite and rare metal-enriched peralkaline albite granite. Differences in texture and composition of quartz do not support direct relations between the hypersolvus granite and the albite granite via magmatic fractionation, but exposure to similar metasomatic processes after their mingling is highly probable. Typical chemical features of quartz from peralkaline granites are relative high contents of Ti and Ge accompanied by low contents of Al and Li, forming an array along the Ti–Ge join in the Ti–Al–Ge ternary diagram.

Rare-Metal Enrichment and Nb–Ta Fractionation during Magmatic–Hydrothermal Processes in Rare-Metal Granites: Evidence from Zoned Micas from the Yashan Pluton, South China

Abstract Rare-metal mineralization in aluminous granites (i.e. rare-metal granites, RMGs) is usually associated with high degree of magma fractionation, strong enrichment in fluxing elements (Li, B, P, and F), and the operation of both magmatic and hydrothermal processes. Experimental data have established the theoretical basis for melt- or fluid-driven rare-metal mineralization. To investigate these mechanisms in natural samples, this paper presents detailed textural and compositional variations for zoned micas and rare-metal minerals from rocks of the Late Jurassic Yashan rare-metal granitic pluton, South China. This pluton preserves an evolutionary sequence from ore-barren rocks to those containing ores formed by Ta–Nb–Li mineralization during magmatic–hydrothermal processes. Three main units of the Yashan pluton are exposed: from bottom to top, these comprise protolithionite–muscovite granite (Unit I), Li-mica granite (Unit II), and topaz–lepidolite granite (Unit III), representing crystallization from successive magma batches from a deep-level magma chamber. The gradual decrease in Nb/Ta and K/Rb in both whole rocks and micas from units I to II to III illustrates fractionation within the magma chamber, accompanied by successive enrichment of incompatible elements in the residual melt. Furthermore, the strong enrichment of fluxing elements such as Li, P, and F in Unit III likely led to lower magma viscosity, which may have helped to expulse interstitial residual melt from the magma chamber. Zoned micas from the Yashan pluton are composed of Li-phengite or lepidolite inner cores and muscovite rims. Cores show increasing Li, F, and rare-metal elements from units I and II to Unit III, consistent with the trend of magmatic fractionation. In contrast, rims that formed in the residual hydrosilicate melt show marked decrease in F and rare metals (i.e. Li, Cs, Rb, Nb, Ta, Sn, and W). Chemical variations of the zoned micas and rare-metal minerals were used together with Rayleigh fractionation modeling calculations to reconstruct the contribution of melt–fluid immiscibility to the crystallization of rare metals, which took place via the combination of melts enriched in high-field-strength elements (e.g. Nb and Ta) and fluids enriched in mobile elements (e.g. Mn, Fe, W, and Cs). Strong fractionation of Nb and Ta, along with extreme enrichment of Ta, in RMGs is caused mainly by the crystallization of micas and columbite-group minerals, and also depends on the degree of fractional crystallization. The subsolidus alteration of micas by acidic fluids may have leached some Nb rather than Ta during chloritization, which could have partly contributed to the enrichment of rare metals and fractionation of Nb–Ta. It is concluded that magmatic–hydrothermal processes, including magmatic evolution and fluid exsolution, are critical for rare-metal enrichment and Nb–Ta fractionation in RMGs.

Critical element (Nb-Ta-Zr-Hf-REE-Ga-Th-U) mineralization in Late Triassic coals from the Gaosheng Mine, Sichuan Basin, southwestern China: Coupled effects of products of sediment-source-region erosion and acidic water infiltration

The Nb-Ta-Zr-Hf-REY-Ga mineralization in the Late Permian coals in southwestern China has been well investigated by several studies and has generally been attributed to alkaline pyroclastics coupled with input from hydrothermal fluids. The Late Triassic is one of the important coal-forming periods but the critical element mineralization in coals of this geological age has not been well documented. In this paper, the mechanism of Nb-Ta-Zr-Hf-REE-Ga-Th-U mineralization in the K5 coal seam of the Upper Triassic Xujiahe Formation from the Gaosheng Mine, Sichuan Basin, southwestern China, was investigated. The K5 coal is a high-ash, low-sulfur, and low-volatile bituminous coal. The minerals in this coal include illite, kaolinite, quartz, and, to a lesser extent, anatase, calcite, chamosite, bassanite, and pyrite, along with traces of ankerite, rutile, and zircon. Compared with the averages of common world hard coals, the studied coals are enriched in critical elements including Zr (247 ppm), Hf (5.56 ppm), Nb (23 ppm), Ta (1.55 ppm), rare earth elements and yttrium (REY, 168 ppm), Ga (18.3 ppm), Th (14.1 ppm), and U (6.18 ppm) (all on a whole coal basis). The Al2O3/TiO2 ratios, Eu anomalies, and the relationships of Al2O3/TiO2 vs. Zr/TiO2 and Nb/Yb suggest that the sediment-source rocks of the Gaosheng coals were Neoproterozoic and Early-Middle Triassic felsic-intermediate igneous rocks from the southeastern Qinling and Longmenshan Orogens, along with the Hannan and Micangshan-Dabashan Uplifts. Other probable sources are contemporaneous felsic-intermediate pyroclastics from the Late Triassic volcanic areas around the Sichuan Basin (i.e., East Kunlun Orogen, West Qinling Orogen, and East Tibetan Plateau). The relationships of Al2O3/TiO2 vs. Zr/Al2O3, Al2O3/TiO2 vs. Nb/Al2O3, Ga/Al2O3, and Al2O3/TiO2 vs. LREY/Al2O3 further indicate that the elevated concentrations of Nb(Ta)-Zr(Hf)-REY-Ga in the Gaosheng coal are probably sourced from both the erosion of sediment-source regions and contemporaneous pyroclastics. The illite-kaolinite aggregates with a vermicular texture and authigenic illite, quartz, anatase, pyrite, calcite, ankerite, barite, and REE-rich minerals, REY distribution patterns, as well as elemental variation trends of the coal seam, collectively indicate that the studied coals were likely influenced by multiple-stage infiltration of various solutions. These solutions leached the fresh pyroclastics and products of erosion derived from granites in the sediment-source regions, leading to redistribution of the critical elements (e.g., Zr, Nb, and HREY) between the roof, floor, and parting mudstones and the coal benches. The concentrations of (Nb,Ta)2O5, (Zr,Hf)2O5, and Ga in the coals are 107, 1093, and 57.6 ppm, respectively, close to or higher than the marginal grade of conventional ore deposits for these elements, and thus the Gaosheng coals have potential as raw materials for the recovery of the critical metals Nb, Ta, Zr, Hf, and Ga.

Mafic to felsic dyke swarms in coastal Guangdong, China: geochemical and geochronological constraints on the latest Mesozoic geodynamics on the southern margin of the South China Block

AbstractThe coastal region of Guangdong Province, China, is characterized by well-developed dyke swarms. The dykes with widths of decimetres to metres and lengths of tens of metres occur along straight and planar fractures cutting granites or volcanic rocks with Jurassic to Early Cretaceous ages. They show steep attitudes with strikes varying from NNW to NNE and from NE to SE, consistent with a stress regime transition from E–W to N–S extension. Major-element analysis on representative dyke samples reveals a composition range from basaltic to andesitic with a few dacitic outliers. Trace elements of most samples show notable Nb–Ta negative anomalies and Pb positive anomalies on the primitive mantle normalized spidergrams, characteristic of arc-related rocks. Among these, several dacite samples show notable fractionated medium rare earth elements and heavy rare earth elements and high Sr/Y (47–74) and La/Yb (15–21) ratios indicative of adakitic affinity. A few samples lack anomalies in Nb and Ta and have primitive trace-element ratios (e.g. Nb/La and Sr/Nd) or initial ϵNd values resembling ocean island basalt-like rocks. Rare earth element distribution patterns of all samples are right inclined and generally absent of Eu anomalies, which together with other trace-element indexes indicate an origin from heterogeneous mantle sources with depths below the stability field of plagioclase. Radiogenic isotopes, especially those of Nd and Sr (or Nd–Pb), define an array extended from the depleted to enriched mantle (EMII) provenance. LA-ICP-MS dating of zircon obtains ages between 110 and 70 Ma indicating emplacement of these dykes in latest Early to Late Cretaceous time, a time just before initiation of the South China Sea basin. In the context of regional geodynamics, it is proposed that these dykes were formed in a tectonic setting transiting from a Pacific-related back-arc to a passive continental margin pertaining to the development of the South China Sea basin.

Migration and tectonic implications of Late Jurassic mafic magmatism in South China

The Jurassic magmatism in the southeastern South China Block has been interpreted as extension-related, yet its tectonic drivers remain unclear. Tectonic models vary between two end-members: (1) Palaeopacific subduction-related; and (2) intracontinental extension-related. This study presents new geochronological and geochemical data for the Late Jurassic mafic rocks in the southeastern South China Block that allow us to differentiate between these tectonic models. The Late Jurassic mafic rocks yielded crystallization ages of 162–157 Ma. Our new geochemical data, together with previously published data, can be divided into three groups: group A with variable ε Nd ( t ) (+0.1 to +3.4) and zircon ε Hf ( t ) (−4.1 to +15.9) values has slightly negative Nb–Ta anomalies; group B is characterized by negative Nb–Ta anomalies with varying ε Nd ( t ) (+1.4 to +1.5) and ε Hf ( t ) (–3.0 to +2.6) values; and group C displays significant Nb–Ta anomalies with high ε Nd ( t ) (+4.5 to +6.6) and ε Hf ( t ) (+6.4 to +14.4) values. The geochemical characteristics suggest that groups A and B are mainly the products of asthenosphere–lithosphere interactions and group C was derived from the asthenosphere. Our new data, together with geological observations, suggest that the Late Jurassic magmatism in the southeastern South China Block probably resulted from asthenospheric upwelling in an intracontinental extension setting due to the far-field effects of the subduction of the Palaeopacific Ocean. Supplementary material: Tables of geochronological data, geochemical data, and additional figures are available at https://doi.org/10.6084/m9.figshare.c.6080871

Magnesium and Calcium Isotopic Geochemistry of Silica‐Undersaturated Alkaline Basalts: Applications for Tracing Recycled Carbon

AbstractCarbon plays important roles in the evolution of the atmosphere and biosphere, and geochemical differentiation in Earth's interior. Most subducted C is recycled to the deep mantle and returns to the surface by degassing from erupted basalts and associated fluids. The Mg–Ca isotopic systems have been widely used in tracing recycled C. However, the idea that these geochemical proxies truly reflect the deep C cycle has been challenged. Here we present whole‐rock geochemical and Mg–Ca isotopic compositions of Miocene silica‐undersaturated alkaline basalts of the Western Qinling orogen, China. These alkaline basalts are associated with carbonatites and are characterized by low SiO2 (39.0–43.2 wt.%) and Al2O3 (6.98–9.15 wt.%) contents, high CaO/Al2O3 ratios (1.4–1.8), and positive Nb–Ta and negative Pb–Zr–Hf–Ti anomalies, suggesting they were derived by partial melting of carbonatite‐metasomatized asthenospheric mantle. The studied samples have δ26Mg values of −0.24‰ to −0.44‰, ranging from mantle‐like values (δ26Mg = −0.25‰ ± 0.07‰) to lower values. This implies that carbonatite metasomatism does not always produce low‐δ26Mg anomalies. The samples have δ44/40Ca values (0.59‰–0.77‰; relative to the standard SRM915a) that are lower than Bulk Silicate Earth (0.94‰ ± 0.05‰), which are attributed to the involvement of low δ44/40Ca recycled carbonate in the mantle source. We suggest that the shift in mantle δ26Mg values during carbonatite metasomatism is controlled by the type and amount of carbonatite involved, while Ca isotope variations depend largely on the δ44/40Ca values of subducted carbonates. Mg or Ca isotopes alone, however, may not be sufficient to track the deep carbon cycle.

Phase Decomposition and Elevated Temperature Mechanical Properties of Zr–Ti–Nb–Ta–Sn Complex Concentrated Alloy Annealed at Intermediate Temperatures

Phase Decomposition and Elevated Temperature Mechanical Properties of Zr–Ti–Nb–Ta–Sn Complex Concentrated Alloy Annealed at Intermediate Temperatures

Elastic properties of a Sc–Zr–Nb–Ta–Rh–Pd high-entropy alloy superconductor

We report a comprehensive study on the elastic properties of a hexanary high-entropy alloy superconductor (ScZrNbTa)0.685[RhPd]0.315 at room and cryogenic temperatures, by Resonant Ultrasound Spectroscopy experiments. The derived elastic constants are bulk modulus K=132.7GPa, Young’s modulus E=121.0GPa, shear modulus G=44.9GPa, and Poisson’s ratio ν = 0.348 for room temperature. The Young’s and shear moduli are ∼10% larger than those in NbTi superconductor with similar Tc, while the ductility is comparable. Moreover, the mechanical performance is further enhanced at cryogenic temperature. Our work confirms the advantageous mechanical properties of high-entropy alloy superconductors and suggests the application prospects.

Tectonic affinity of the Zhusileng–Hangwula Belt in the northern Alxa area: Evidence from the zircon U–Pb ages and Hf isotopic compositions of the Mesoproterozoic (~1.4 Ga) igneous rocks

Precambrian rocks are necessary to understand the tectonic and crustal evolution of the Central Asian Orogenic Belt, especially the tectonic affinities of embedded microcontinents. We conducted a combined analysis of whole‐rock geochemistry, zircon U–Pb geochronology, and Hf isotope on the Mesoproterozoic igneous rocks from the Zhusileng–Hangwula Belt of the northern Alxa area to investigate its tectonic affinity. The zircon ages show that the gneissic granites, metagabbro, and amphibolite formed at 1,433–1,424 Ma, 1,383, and 1,373 Ma, respectively. Furthermore, zircon xenocrysts from the rhyolite in the Zhusileng area exhibit a206Pb/238U ages cluster at about 1.4 Ga. Geochemically, the gneissic granites are high‐potassium calc‐alkaline granitoids and exhibit light rare earth element‐enriched pattern, pronounced significant negative Eu anomalies, negative Nb–Ta anomalies, positiveεHf(t) values (3.2–11.3), and young two‐stage model ages (2.21–1.46 Ga), indicating that they were derived from a magma source of rapid reworking of juvenile mantle‐derived materials with a limited ancient crustal contamination. The FeOT, CaOm and MgO contents of mategabbros and amphibolite are high, but their total rare earth elements are relatively low (TREE = 31.45–32.74). They are characterized by relatively positive zirconεHf(t) values (5.3–11.0), and very young two‐stage model ages (1.98–1.49 Ga), indicating that they were generated from the depleted mantle. Our geochemical data suggest that these Mesoproterozoic rocks in the Zhusileng–Hangwula Belt are consistent with the formation period and tectonic environment of juvenile basement rocks from the Central Tianshan Arc and southern Beishan Orogenic Belt, whereas a Mesoproterozoic correlation with the Tarim Craton is highly unlikely. Thus, we believe that the Zhusileng–Hangwula Belt has an analogous tectonic evolution and a close affinity with the Central Tianshan Arc and southern Beishan Orogenic Belt during the Mesoproterozoic.

Consolidation and high‐temperature properties of ceramics in the TaC–NbC system

AbstractIn this study, we explored the consolidation, solid‐solution formation, and high‐temperature properties of carbides in the Ta–Nb–C system. The tantalum niobium carbide bulks can be consolidated by spark‐plasma sintering only at a temperature of 2200°C using a 30‐min dwell. The ceramics were homogeneous solid solutions and a linear dependence of the lattice parameters on the NbC content was observed. The average grain size varied between 10 and 30 μm, while the reference monolithic tantalum carbide consolidated under similar conditions had a grain size exceeding 40 μm. The room temperature strength linearly decreased from TaC to NbC. The 75 mol% NbC ceramic showed almost an unchanged strength up to 1600°C (450 ± 20 MPa), following the linear decrease in strength to 290 MPa at 2000°C. The monolithic tantalum carbide had showed the lowest strength at 2000°C among the studied ceramics.

Wear behavior of (Mo–Nb–Ta–V–W)C high‐entropy carbide

AbstractWear characteristics of an (Mo–Nb–Ta–V–W)C high‐entropy carbide were investigated using ball‐on‐flat technique. The experimental material with a high relative density of 99.0%, single phase, average grain diameter of 10.7 μm, and nanohardness of grains 28.6 GPa was prepared by ball‐milling and two‐step field‐assisted sintering. The tribological test was realized during dry sliding in air with the SiC ball as tribological partner at applied loads 5, 25, and 50 N. The microstructure, deformation, and damage characteristics were studied using scanning electron microscopy and confocal electron microscopy. The friction coefficient values during the test with 5 and 25 N were very similar and stable, with a value of approximately .4, whereas during the test with 50 N, it decreased from the value of .48–.42. The specific wear rate increased with increasing load from 3.71 × 10–7 mm3/N m at 5 N to 2.59 × 10–6 mm3/N m at 50 N. The dominant wear mechanism was mechanical wear with intensive grains pullout, fracture, and powder formation, without visible tribochemical reactions and tribo‐layer formation. The wear rate decreased due to the created rolling contacts among the tribopartners thanks to the hard and spherical nanopowders present.

Effect of Zr addition on the local structure and mechanical properties of Ti–Ta–Nb–Zr refractory high-entropy alloys

Solid solution strengthening is the major strengthening mechanism that accounts for the high strength of single-phase body-centered cubic (BCC) refractory high-entropy alloys (RHEAs). Local lattice distortion (LLD), often regarded as one of the core effects of HEAs, is generally believed to be deterministic in solid solution strengthening for RHEAs since the loosely packed BCC crystal structure can accommodate significant LLD. To systematically investigate the effect of LLD on solid solution strengthening, the present study deliberately introduced different degrees of LLD in the experimentally fabricated BCC Ti65-xTa25Nb10Zrx (x = 0, 5, 10, 15, and 20) RHEAs by varying the Zr content. Subsequently, by combining experimental analysis, first-principles calculations, and theoretical modeling, it is found that yield strength, hardness, atomic radii, and LLD increase with the increase of Zr content. Moreover, through quantitative solid-solution strengthening analysis, it is demonstrated that the modulus mismatch dominates solid solution strengthening over LLD even for severely distorted Zr-containing RHEAs, contrary to the generally accepted assumption that solid solution strengthening is mainly from LLD effect. What's even more surprising is that the increase of Zr content accelerates grain growth, opposite to the sluggish diffusion effect proposed for HEAs. Our results shall guide the elemental selection for the design of high-strength RHEAs eradicating the random sampling in the endless compositional pool.