Ta Content Research Articles

Ti-Ta-Cu Biocompatible Alloy System Development via Selective Laser Melting for Prosthetic Applications

This study investigated the development of Ti-Ta-Cu alloys via selective laser melting (SLM) for potential prosthetic applications. Ti-Ta-Cu alloys with 10, 15, and 20 wt.% Ta were fabricated using in situ alloying of elemental powders. We examined the effects of Ta content and SLM processing parameters on microstructure, phase composition, mechanical properties, and corrosion resistance. X-ray diffraction analysis revealed an increase in β-phase content with increasing Ta concentration. Microstructural analysis showed a dendritic structure in Ta-rich areas, with remelting strategies improving chemical homogeneity and Ta dissolution. The Ti-20Ta-5Cu alloy exhibited the best balance of strength and ductility, with an ultimate tensile strength of 1011 MPa and elongation of 5.7%. All compositions demonstrated lower elastic moduli (103–109 GPa) compared to traditional titanium alloys. Microhardness values were highest for Ti-15Ta-5Cu, ranging from 359 to 410 HV0.5 depending on SLM parameters. Corrosion testing in Hank’s solution showed improved pitting resistance for Ti-15Ta-5Cu and Ti-20Ta-5Cu compared to Ti-10Ta-5Cu. The study demonstrates the feasibility of producing Ti-Ta-Cu alloys with tailored properties via SLM, offering potential for customized prosthetic applications with improved biomechanical compatibility and functionality.

Temperature dependence on γ/γ' partitioning behaviors of alloying elements and γ/γ' interfacial energy of a Mo-rich Ni based single crystal superalloy

Based on three-dimensional atom probe technique and Ardell method, the influences of temperature (850℃∼1150℃) on microstructure, compositions and solid solution strengths of γ and γ′ phases, γ/γ' partitioning behaviors of alloying elements and γ/γ' interfacial energy of a Mo-rich Ni based single crystal superalloy were investigated. After quenching from 1100℃, microstructure was basically similar as heat-treated state. However, after quenching from 1150℃, γ′ phase obviously re-dissolved, and γ channel obviously widened. Meanwhile, with increasing temperature, Co, Cr, Mo and Re contents in γ phase decreased, while Al and Ta contents in γ phase increased. With increasing temperature, Co, Cr and Re contents in γ′ phase slightly decreased, Mo content in γ′ phase significantly decreased, while Al and Ta contents in γ′ phase increased. Meanwhile, with increasing temperature, solid solution strength of γ phase decreased, while solid solution strength of γ′ phase increased. In addition, with increasing temperature, partitioning ratios of Co, Cr and Re elements decreased, partitioning ratios of Mo and Al elements increased, while partitioning ratio of Ta firstly decreased and then increased. Moreover, both γ/γ′ interfacial width and γ/γ′ interfacial energy decreased with increasing temperature.

EFFECT OF MAIZE (<i>ZEA MAYS</i>) COB BASED TOTAL MIXED RATION IN GROWING CALVES

The present study was conducted to study the effect of maize (Zea mays) cob on replacing paddy straw in the Total Mixed Ration (TMR). Twelve cross bred calves of about 5 to 8 months of age with body weight ranging from 41 to 79 kg were divided into two groups of six each in completely randomized design. Five complete diets were prepared (TMR1 to TMR5) using maize cobs at the level of 0%, 25%, 50%, 75% and 100% replacement of paddy straw in the diets containing 12 % CP and 60 % TDN of 50:50 concentrate to roughage ratio. There was significant (P<0.01) differences among the diets in OM, CF, NFE, TA, AIA, NDF, ADF, Lignin, Hemicellulose and Cellulose contents. In vitro rumen fermentation study showed significantly (P<0.01) higher total gas (ml/200 mg/48 h), in vitro dry matter and organic matter degradability in maize cob based ration than paddy straw contained ration (51.17 vs 36.00; 62.87 vs 57.25; 64.80 vs 59.93). Paddy straw (100%) based diet as control ration and maize cob (100 % replacement of paddy straw) based diet as treatment ration fed to growing calves for sixty days in growth trial. A seven day digestion trial was conducted in the middle of the experiment. The digestibility (%) of DM, OM, CP, EE, CF and NFE were significantly (P<0.01) higher in the maize cob based diet fed group than paddy straw based diet fed group. The average body weight gain (kg) and FCR (kg DMI/ kg gain) were significantly (P<0.05) higher in maize cob fed animals (19.47; 6.10) than paddy straw fed animals (16.02; 7.34). The feed cost per unit of weight gain in calves fed paddy straw based diet was numerically higher (30.78 %) than calves fed on maize cob based ration. It could be concluded that maize cob based ration could replace paddy straw at 100 % level in total mixed ration without affecting feed intake and nutrient digestibility and may also improve the body weight gain and reduce feed cost in growing calves.

Effects of Ta on the high temperature creep behavior and deformation mechanism of a Ni-based single crystal superalloy

The effects of Ta on the high temperature creep behavior and deformation mechanism in a Ni-based single crystal (SX) superalloy were investigated at 1120 °C/137 MPa. Ta was regarded as an essential strengthening element of the γʹ phase in the alloy, and the results indicated that the increase of Ta prolonged the creep rupture life. In this work, the addition of Ta increased the volume fraction of the γʹ phase and narrowed the γ channels, making the dislocation bowing out at the primary stage of creep more difficult. As creep continued, with a lower effective diffusion coefficient of alloying elements and larger γʹ raft thickness, the alloy with 6.5 wt% Ta addition was considered to possess the lower dislocation climbing rate, which reduced the minimum creep rate of the alloys. Subsequently, it was noted that the density of superdislocations in γʹ phase was clearly reduced with the increase of Ta. This was supposed to be the elevated Ta content in the alloy, which increased the lattice misfit and led to the formation of a denser dislocation network, thereby enhancing the interfacial strengthening effect and effectively preventing the cutting of superdislocations. The Ta effect on high-temperature creep was systematically summarized in this study, which was an important guideline for further composition design and optimization of Ni-based SX superalloys.

Geochemistry and Petrology of post-Archean dolerite intrusions in the Elogo Complex in the Ivindo Basement northwest of the Congo Craton

Geochemical and tectono-metamorphic study of post-Archean dolerite intrusions is carried out to reconstruct the petrogenesis and geodynamics of post-Archean intrusive mag- matism in the Congo Craton. Dolerites and hornblendites of the Elogo complex are characterized by a low-pressure greenschist metamorphism controlled by brittle micro tectonics and are metaluminous (A/NK: 4.47 and 7.84; A/CNK: 1.02 and 1.37) with a dominant tholeiitic affinity and affected by hydrothermal alteration (LOI = 1.13 – 8.7 %). LREE and Th enrichment, negative Nb and Ti anomaly, low Nb/Th, (Nb/La)PM < 1, Ti/Yb, Ce/La < 0.85, Nb/La < 1, and Ta/Th < 1 ratios, and high (La/Yb)n > 1 and (La/Sm)n > 1 define the dolerites geochemical signature as crustal contaminated. Al2O3/TiO2 (12.17 to 19.65), CaO/Al2O3 (0.60 to 0.78), (Gb/Yb)PM > 1 ( 1.15 to 1.32), and (Tb/Yb)n (1.13 to 1.29) ratios associated with the lack of HREE fractionation (Yb = 11.24 to 18. 01 ppm) characterize a shallow (1073.03 to 1189.92°c) spinel lherzolite-type mantle source with low melt rate (f = 10 to 20%), outside the garnet stability field [(Th/Ta)n < 1]. The negative Nb, Ti, Zr, Rb, and Ba anomalies, positive Hf, Th, and U anomalies, the moderate Cs and LREE (La and Ce) enrichment, and the REE fractionation [(La/Yb) n >1], associated with the high Ta contents, define an extensive intracratonic rift-type setting. The vein rocks originate from an asthe- nospheric uplift marked by lithospheric thinning in a Mezo-Neoproterozoic rift system that dislocated the Congo Craton inducing the genesis of the tholeiitic dolerites (1167 Ma and 850 Ma) of Nola in RCA and Yokadouma in Cameroon.

Blue maize with pigmented germ: Phytochemical compounds and tortilla color

Blue maize is used in the production of various traditional foods, and its phytochemical composition has been claimed to possess health benefits. In this study, two blue maize hybrids with pigmented germ grown in five environments were studied under the hypothesis that the germ could have a different anthocyanin profile from that of anthocyanins synthesized in the aleurone layer, and that those in the germ could increase the total anthocyanin content in the whole grain. The percentage of pigmented germ, total anthocyanin content (TA) and total soluble phenols in the germ, whole grain and tortilla were evaluated to determine how tortilla color is modified. For the first time, the anthocyanin and fatty acid profiles of pigmented germ were determined. In the anthocyanin profile, anthocyanins derived from peonidin stood out, making 50.7 %. The most abundant fatty acid was linoleic acid (40.6 %). Whole kernel TA content increased when the maize had a higher percentage of pigmented germ, with minimal changes when grain was transformed to tortilla, resulting in darker tortillas. The large variation in TA among environments highlights the importance of identifying the environments that most favor anthocyanin synthesis.

Ta5+-substitution effects on crystal structure and ferroelectric property in HfO2-based films

To investigate the Ta5+-substitution effects on crystal structure and ferroelectric property in HfO2-based films, Ta x Hf1−x O2+δ films with various film thicknesses and Ta content were prepared. The ferroelectric orthorhombic phase was formed in a wide film thickness range of 20–100 nm while in a narrow composition range of x = 0.10–0.14. These thickness-insensitive and composition-sensitive characteristics of Ta5+-substituted HfO2 film are similar to Y3+ rather than Zr4+. The X-ray photoelectron spectroscopy measurement suggests that the ionic state of Ta is not reduced and Ta x Hf1−x O2+δ film has an excess oxygen state. The excess oxygen may consist of a combination of oxygen vacancies and more interstitial oxygens. These defects facilitate the formation of the ferroelectric phasebut also decrease the breakdown voltage and increase the leakage current in Ta5+-substituted HfO2 films. On the other hand, the generation of excess oxygen indicates the possibility of controlling oxygen vacancies which deteriorate fatigue and retention properties.

Processing of mineralized microgranite dike for the recovery of niobium, tantalum, and rare earth elements using 1, 2-propyleneglycol extractant

ABSTRACT A number of strategic and economic rare-metal and Rare Earth Elements (REEs)-bearing minerals were recorded in mineralized microgranite dike (MMGD) from Ras Abdah area located in the Northern Eastern Desert of Egypt. Firstly, by sulphuric acid digestion at 300 °C, 3 h, 1/3 ore/Acid ratio, the RE, Nb, and Ta present in the MMGD can be efficiently extracted into the leach solution while Zr, Fe, and Th remained in the unattacked residue. The experimental digestion proved the dissolution of 98.9, 99.2, and 96 % for Nb, Ta, and REEs, respectively. In this study, a novel method was used to selectively recover Nb and Ta content from REEs in the digested concentrate sulphate solution. Solvent extraction using 1, 2-propyleneglycol was applied for the first time to achieve this secondary recovery process. From infrared and 1H-NMR data, the extraction was achieved, and the extractant bonded to Nb and Ta through glycol and alcoholic oxygen atoms. Niobium and Tantalum ions were stripped with water for Ta and 1M HF for Nb, achieving 98.6 and 98.8 % stripping efficiency, respectively. By employing an oxalic acid precipitation technique, a precipitate of extremely pure REEs was extracted from the raffinate solutions.

Rheology, stability, and physicochemical properties of NaOH-tannic acid solvent for β-chitin dissolution

The applicability of chitin in food systems is limited by its poor solubility in ordinary solvents. This study explores a novel solvent system composed of sodium hydroxide and tannic acid (NaOH/TA) in combination with a repeated freeze-thaw process for dissolving chitin. The highest chitin solubility in 8% NaOH/0.3% TA and 10% NaOH/0.3% TA was 2.1% and 2.3% (w/v), respectively. The lower NaOH and excessive tannic acid content may lead to reduction of chitin solubility. We also observed a unique rheological property of the chitin/NaOH/TA system. A higher concentration of TA reduced the chitin solution's shear viscosity, storage modulus, loss modulus, and gelling temperature. Its shear viscosity decreases with increasing shear rate, showing a shear thinning behavior. When the chitin/NaOH/TA solution system was stored at 30oC, the crystalline degree of chitin decreased, and the diffraction peak shifted, suggesting the formation of different intermolecular forces. The TA contents show no significant effect on the crystallinity of chitin. With increased storage time, the molecular weight of chitin decreased, and the degree of deacetylation (DD) increased. These results underscore the potential applications of the chitin/NaOH/TA system in the food industry.

Platinum-Group Elements and Nb-Ta geochemistry of the Deccan basalts from Kumbharli and other Ghat sections and the Koyna Seismic Zone, Maharashtra (India): Crustal contamination and implication for sulfide saturation of the magma

The Deccan basalts from Kumbharli, Nadlapur, Bijaynagar, Hazarmacchi, and Surli Ghat sections (surface samples) and the Koyna borehole-7 (KBH-7, sub-surface samples) from Maharashtra (western India) demonstrate a two-stage crystallization process. Olivine and chromite were crystallized earlier in a shallow crustal magma chamber while clinopyroxene and plagioclase phenocrysts were crystallized in the sub-volcanic conduits forming the crystal mush, and carried to the surface by the evolved Fe-Ti-rich ascending basaltic magma. The high modal abundance of plagioclase at the top and clinopyroxene at the bottom part of the Kumbharli Ghat section is responsible for an increase in Sr and a decrease in Sc content towards the upper flows. The surface and sub-surface basalt samples contain Pd = 5–31 ppb, Pt = 4–15 ppb, Ir = 1–4 ppb, Ru = 1–3 ppb, and Rh = 3–5 ppb. Negative relations of Pd/Ir, Pd/Ru, and Pd/Rh with MgO from both sets of samples indicate partitioning of Ir, Ru, and Rh to early fractionated cumulus chromite (or olivine). Magnetite is a late crystallizing phase from the evolved Fe-Ti-rich basaltic magma. With an increasing modal abundance of magnetite, there is an increase of FeO total , TiO 2 , and V with Pd indicating fractionation of Pd by magnetite. Geochemical characters show that the surface basalt samples are less contaminated compared to the sub-surface KBH-7 basalts. High Nb (6.8–13.6 ppm) and low Ta (0.2–0.37 ppm) content and elevated Nb/Ta ratios of the surface samples from the ghat sections indicate the possible interaction of the basaltic magma with the carbonate metasomatized subcontinental lithospheric mantle (SCLM). On the other hand, a high degree of partial melting with limited crustal contamination can also elevate the Nb/Ta ratios of the basalts from the ghat sections. Deccan basalts from the study areas do not bear the signature of sulfide supersaturation and subsequent immiscible sulfide segregation. This is evidenced by their high chalcophile element concentrations (Ni = 79–103 ppm, Cu = 121–259 ppm) and ratios like Cu/Zr (≥ 1), Ni/MgO (13.7–21.8) with low Cu/Pd (2140–29938) compared to other Ni-Cu (PGE) sulfide mineralized continental flood basalts. The lack of crustal sulfur in the various contaminants is perhaps the main reason for this sulfide-undersaturated character of the Deccan basalts of the current study.

Non-typical fractionation behaviors in a lepidolite-subtype pegmatite: Implications for the internal evolution of a naturally fluxed system

Despite their relatively rare occurrence, lepidolite-subtype pegmatites host abundant Li–Nb–Ta–Cs–Sn mineralization and represent a high-flux pegmatitic system with abnormally high F and Li activity. Characterization of highly fluxed melts and the impact of fluxes and exsolved fluids on fractionation of peraluminous melts have mainly been studied in experimental systems, with natural system correlations remaining poorly understood. Consequently, we conducted a systematic mineralogical study of a lepidolite-subtype pegmatite in the North Qinling orogenic belt, Central China. An abnormal “concave downward” fractionation trend for primary columbite-group minerals on the quadrilateral diagram is identified, and irregularly zoned columbite crystals coexist with F-rich minerals in one of the core zones have the highest Ta contents (normally 50.17–63.13 wt% Ta2O5) and Ta/(Nb + Ta) ratios (up to 0.65). Despite the consistently Ta-dominated B-site in the crystal lattice of microlite-group minerals, extreme compositional variations at the A- and Y-sites are observed. Compared with microlites in intermediate zones, the abrupt increase in U in microlite crystals in core zones and late units (up to 20.16 wt% UO2), is ascribed to the melt-fluid interaction with exsolved U-rich aqueous fluids. In addition, the fractional crystallization of F-bearing minerals resulted in a gradual decrease in F contents in microlite-group minerals from extremely F-rich (2.68–4.84 wt% F) in intermediate zones to low F species (mainly 0.82–1.71 wt% F) in core and late zones. Moreover, autometasomatism by a late fluxed melt and hydrothermal metasomatism by late aqueous fluids are identified in columbite- and microlite-group minerals. This work highlights that these non-typical fractionation behaviors related to the activity of fluxes (especially F) and the exsolution of aqueous fluids during the internal evolution of pegmatitic melts, are critical for the generation of lepidolite-subtype pegmatites. Fluorine was gradually enriched in the pegmatitic melt, and reached its highest level during crystallization of the (inner) intermediate and core zones. Non-equilibrium crystallization occurred throughout pegmatite evolution, and late units were most probably formed from aqueous fluid-enriched residual melts, rather than by hydrothermal replacement.

Dissolution of Ta–Nb and Nb Minerals in Granitoid Melts

The effective solubilities (maximum contents) of Ta and Nb in model felsic lithium-fluoride melts of variable alkalinity and alumina content were experimentally determined at the dissolution of Ta–Nb and Nb minerals: pyrochlore, microlite, ilmenorutile, and ferrotapiolite at T = 650–850°C and P = 100 and 400 MPa. The Ta and Nb partitioning in the mineral-melt systems was also studied. When pyrochlore is dissolved in granitoid melts at P = 100 MPa and T = 650–850°C, the highest effective solubilities of Nb (0.7–1.8 wt %) are obtained in alkaline melt, and they significantly decrease (to 0.03–0.5 wt %) in subaluminous and peraluminous melts. A temperature increase increases the solubility (content) of Nb in the melt. Similar dependences were obtained for Ta solubility by dissolving microlite. In peraluminous granitoid melt, microlite remains stable, while pyrochlore becomes unstable. A pressure decrease from 400 to 100 MPa in alkaline and subaluminous melts was found out to not significantly affect on the dissolution of microlite and pyrochlore, whereas Ta and Nb contents in the peraluminous melt noticeably decrease. The dependences of Nb solubility and its partitioning between granitoid melts and ilmenorutile on the alkalinity–alumina content of the melt are similar to those for the dissolution of columbite and tantalite. The dependences obtained by dissolving ferrotapiolite, pyrochlore, and microlite differ from them.

Effect of Ta content on microstructure, martensitic transformation, and shape memory effect of (Ni52.2Ti47.8)100-xTax alloys

This work focuses on the effects of Ta addition on the microstructure, martensitic transformation, mechanical properties and shape memory effect (SME) of (Ni52.2Ti47.8)100-xTax alloys with a fixed Ni/Ti ratio of 1.09. The solubility limit of Ta in (Ni52.2Ti47.8)100-xTax alloys is determined to be within 3–4 at%. Excessive Ta leads to the formation of secondary phases, the majority of which are (Ta,Ti)2Ni phases. The addition of Ta can effectively refine the grains of NiTiTa alloys. Transformation temperatures are elevated remarkably until Ta content reaches 4 at% and then increase slightly at higher Ta contents, which is due to the change of valence electron concentration. The thermal hysteresis is widened by adding Ta and applying a constraint stress. The addition of Ta remarkably improves the ductility while decreases the hardness. By modifying the content of Ta, a considerable SME is achieved with the maximum recovery strain up to 7.0 %.

Tunable thermal expansion via the magnetic phase competition in kagome magnets

Negative thermal expansion materials can solve the challenge of mismatched coefficients of thermal expansion of components in precision instruments, thereby improving the thermal shock resistance of devices. The adjustment of negative thermal expansion performance can improve the universality of its application. In this work, tunable thermal expansion has been achieved in Hf1−xTaxFe2 kagome magnets via magnetic phase competition. The transition from ferromagnetism to antiferromagnetism results in a sharp volume shrinkage of Hf0.83Ta0.17Fe2 within a narrow temperature range of 190–230 K, which limits its practical application. As the Ta content decreases, the ferromagnetic ground state becomes more robust and eventually suppresses the antiferromagnetism completely, achieving a negative thermal expansion in Hf0.88Ta0.12Fe2 caused by the ferromagnetic to paramagnetic transition over a wide temperature region and containing room temperature (αV = −37.63 × 10−6 K−1, 250–350 K). This work realizes the regulation of negative thermal expansion through magnetic phase competition, which provides guidance for the regulation of thermal expansion of magnetic materials in the future.

Simultaneous improving high temperature oxidation resistance and room temperature toughness of Nb[sbnd]Si based alloy via appropriate Ta content addition strategy

NbSi based alloys are expected to become the application materials for high pressure turbine blades of aircraft engines. This paper investigates the impact of Ta addition on room temperature fracture toughness and isothermal oxidation behavior at 1250 °C of four NbSi based alloys with compositions of Nb-16Si-20Ti-8Zr-4Hf-1.5Al-xTa (x = 0, 1, 2, and 4 at.%) fabricated through vacuum non-consumable arc-melting. The results show that the room temperature fracture toughness and 1250 °C oxidation resistance of the alloys increase first and then decrease with the addition of Ta element. The room temperature fracture toughness of 1Ta alloy is the best, reaching 17.1 MPa·m1/2. Adding a moderate amount of Ta (1 at.%) significantly enhances the alloy's oxidation resistance, but an excessive Ta content diminishes this enhancement. This research has obtained a Nb-16Si-20Ti-8Zr-4Hf-1.5Al-1Ta alloy with high room temperature fracture toughness and excellent high temperature oxidation resistance simultaneously, which provide an ideal path for designing NbSi alloys with superior comprehensive properties.

A modified maxwell-pulse thermoplastic constitutive model of in-situ Ta-particle reinforced Zr-based bulk metallic glass composites

The impact of different Ta contents on the mechanical properties and thermoplastic forming ability of in-situ Ta-particle reinforced Zr–Cu–Al–Ni bulk metallic glass composites was studied. The composition (Zr55Cu30Al10Ni5)94Ta6 with the best comprehensive performance was chose for a systematic investigation into its thermoplastic behavior in the supercooled liquid region (SLR), with quantitative analysis conducted by the strain rate sensitivity index and activation volume. The steady-state flow stress and the stress overshoot intensity were augmented with deformation temperature decreasing, strain rate increasing, and the addition of the secondary phase, leading to a transition from Newtonian to non-Newtonian flow regime. The addition of the secondary phase deteriorated the rheological properties of the material. To solve the problem that the Maxwell-Pulse constitutive model showed an inability to accurately describe the steady-state flow process. A modified constitutive relationship, introducing the effect of the volume fraction of Ta particles on viscosity and elastic modulus in the steady-state flow process which was ignored in Maxwell-pulse model, was established. The fitting results of the true stress-strain curves of the modified Maxwell-pulse constitutive model were in better agreement with the experimental date than those of the Maxwell-pulse constitutive model, with higher prediction accuracy. The modified constitutive model well predicted the thermoplastic deformation behavior of (Zr55Cu30Al10Ni5)94Ta6. The influence mechanism of Ta particles on the flow behavior was explained that Ta particles increased the viscosity of amorphous matrix, thereby hindering its flow and ultimately leading to an increase in flow stress.

Li-mineralized pegmatite of anatectic origin: Constraints from Li[sbnd]Hf isotopes and geochemical modeling

Pegmatites are important reservoirs of lithium resources. There is an ongoing debate as to whether Li-mineralized pegmatites were generated from evolved granitic systems via extreme differentiation or by direct melting of metasedimentary rocks. The Chinese Altay is one of the largest pegmatite provinces in the world, and includes many rare-metal pegmatites (e.g., Koktokay, Kelumute, Kaluan and Azubai). However, they display significant differences in formation ages and isotopic compositions compared with the neighbouring or potential parental granites. In this contribution, we present a case study of the Kaluan Li ore deposit in the Chinese Altay, elucidating the origins of pegmatites and related Li mineralization. The Kaluan Li-mineralized pegmatites are characterized by high SiO2, K2O, Na2O, Li, Cs, Ta, and Rb contents; low Fe2O3T, MgO, Ba, and Sr contents; and peraluminous signatures. They have homogeneous HfLi isotopic compositions (εHf (t) = −0.6 to +2.5; δ7Li = +1.6 to +5.8‰) that are within the range of HfLi isotopic compositions of the Kulumuti Group schists (εHf (t) = −2.8 to +7.5; δ7Li = −8.6 to +10.8‰). In addition, the chemical compositions of the melt derived from the partial melting of the Kulumuti Group by phase equilibrium modeling are compatible with our analyses of the Kaluan Li-mineralized pegmatites. These similarities suggest that the Kaluan Li-mineralized pegmatites were derived from the partial melting of the Kulumuti Group schists at depths during the Triassic, in a post-orogenic and extensional setting. The generation of these pegmatites was mostly controlled by biotite dehydration melting at relatively high temperatures, rather than by the low-temperature melting of muscovite. Trace elements modeling results show that approximately 33–36% partial melting of the average Kulumuti Group schist may produce melts with maximum Li concentrations ranging from 664 to 751 ppm. Subsequently, a high degree of fractionation exceeding 85%, was required for the Li concentration of the residual melt to reach concentrations suitable for crystallization into albite-spodumene pegmatites. Based on our research, an anatectic origin model may have general applicability in explaining the genesis and mineralization of rare-metal pegmatites in the Chinese Altay.

Influence of initial microstructure on the γ′-coarsening behavior in a corrosion-resistant Ni-based superalloy

To clarify the initial microstructure dependent γ′-coarsening behavior, a corrosion-resistant Ni-based superalloy with the varied γ′-size were prepared by changing the primary aging heat treatment temperature. The microstructural evolution was investigated during long term thermal exposure (up to 3000 h) at 900 °C and 1000 °C, respectively. It was found that Cr, Co, and Mo preferentially partition to γ-matrix, while Ta, Ti, Al, Ni, and W partition to the γ′-phase. The abnormal partition of W to the γ′-phase can be attributed to the low content of Ta in CM247 LC alloy. Furthermore, the γ′-coarsening behavior can be divided into two stages. During the early stage of coarsening (<1000 h), the coarsening rate obeys the classical LSW model with the cube rate law. As the increase of the initial γ′-size, the γ′-coarsening rate obviously increases, which can be mainly attributed to the increased solute diffusion capability in the γ-matrix and the higher γ'/γ interfacial energy. By contrast, there is an apparent γ′-coalescence during the later stage of coarsening (1000 h–3000 h). The temperature plays a more dominant role on the γ′-coarsening rate than the duration times during thermal exposure.

Microstructure and mechanical behavior of TaxHf1−xC–SiC fabricated by reactive hot‐pressing: Effect of Ta:Hf ratio

AbstractTaxHf1–xC are promising candidates for many applications under harsh environments due to their unique properties. Up until now, low‐temperature densification is still a big challenge for these ceramics. Moreover, the effect of Ta:Hf ratio on microstructure development and mechanical behavior of the ceramics is not clear. In this work, highly dense TaxHf1−xC–SiC ceramics (x = 0.2, 0.4, 0.6, 0.8) were fabricated at 1700°C by a novel reactive hot‐pressing processing with 8 wt% Si as sintering aid, which present excellent mechanical properties. Fracture toughness of the ceramics is higher than 6.3 MPa·m1/2, with the highest toughness achieved in Ta0.6Hf0.4C–SiC (8.5 MPa·m1/2). With the increase of Ta content, hardness of the ceramics tends to increase, while the bending strength tends to decrease. The highest bending strength is achieved in Ta0.2Hf0.8C–SiC (637 MPa), and the highest hardness is achieved in Ta0.8Hf0.2C–SiC (17.6 GPa). This work lays the foundation for the composition design of TaxHf1−xC‐based ceramics and composites.

Enhancing microstructural stability and creep properties by Ta addition in Ni-based single crystal superalloys

To investigate influences of Ta content on microstructural stability during thermal exposure at 900 °C (up to 3000 h) and creep properties at 980 °C/163 MPa in Ni-based SX superalloy, alloys with 7Ta, 8Ta and 9Ta (wt.%) were studied utilizing DSC, SEM, TEM, HR-XRD and APT. The results shows that Ta addition enhanced the partitioning behavior of alloying elements. Besides, lattice misfit was controlled by both alloy composition and temperature. Ta addition increased absolute misfit both room temperature and 980 °C. The difference was that the γ/γ′ lattice misfit changed from positive to negative at room temperature. The γ′ coarsening indicated that Ta addition reduced the effective diffusion coefficient and exacerbated W segregation at γ/γ′ interface, which was beneficial to improve the microstructural stability. Merging of several adjacent γ′ precipitates in preferred direction was observed to be delayed with increasing Ta content, which occurred at 500 h for 7Ta alloy, 800 h for 8Ta alloy and 1000 h for 9Ta alloy, respectively. Ta addition affected the diffusion kinetics and greatly prolonged the steady creep duration, and then resulted in longer creep rupture life. It was discussed based on the γ matrix channels, γ′ raft thickness, the perfection degree of γ′ rafts, residual γ′ precipitates, interfacial dislocation networks and solid solution strengthening.