Nb Content Research Articles

Microstructure and Mechanical Properties of Spark Plasma Sintered CoCrFeNiNbX High-Entropy Alloys with Si Addition

Three mechanically alloyed (MA) and spark plasma sintered (SPS) CoCrFeNiNbX (X = 5, 20, and 35 at.%) alloys with an addition of 5 at.% of SiC were investigated. The face-centered cubic (FCC) high-entropy solid solution, NbC carbides, and hexagonal Laves phase already developed during MA. In addition, the SPS compacting led to the formation of oxide particles in all alloys, and the Cr7C3 carbides in the Nb5 alloy. The fraction of the FCC solid solution decreased with increasing Nb concentration at the expense of the NbC carbide and the Laves phase. Long-term annealing at 800 °C led to the disappearance of the Cr7C3 carbide in the Nb5 alloy, and new oxides-Ni6Nb6O, Cr2O3, and CrNbO4-were formed. At laboratory temperature, the Nb5 alloy, containing only the FCC matrix and carbide particles, was relatively strong and very ductile. At a higher Nb content (Nb20 and Nb35), the alloys became brittle. After annealing for 100 h at 800 °C, the Nb5 alloy conserved its plasticity and the Nb20 and Nb35 alloys maintained or even increased their brittleness. When tested at 800 °C, the Nb5 and Nb20 alloys deformed almost identically (CYS ~450 MPa, UTS ~500 MPa, plasticity ~18%), whereas the Nb35 alloy was much stronger (CYS of 1695 MPa, UCS of 1817 MPa) and preserved comparable plasticity.

Impacts of Nb on grain refinement in a simulated coarse-grained-heat-affected-zone of ultra-high-strength steels

ABSTRACT The impact of Nb contents on grain refinement in a simulated coarse-grained heated-affected zone (CGHAZ) in steels was investigated. The austenite grain grew in multiple directions and then impinged against each other during the α→γ transformation. Subsequently, austenite grains coarsened via the coalescence of small grains and boundary migration. With the increased Nb content, the austenite in CGHAZ became coarser due to the decreased quantity and increased size of Nb precipitates. Furthermore, the austenite decomposed into bainite during the cooling process. Compared with the low-Nb specimen, the crystallographic grain size in CGHAZ of high-Nb specimen is slightly coarser, relating to the coarser prior austenite grain. However, higher Nb content delays the bainite transformation start temperature, leading to multiple variants selection of bainite, increasing the refinement ratio.

Electrochemical corrosion behavior in sulfuric acid solution and dry sliding friction and wear properties of laser-cladded CoCrFeNiNbx high entropy alloy coatings

316 stainless steel (SS) was coated with CoCrFeNiNbx (x: atomic ratio, x = 0, 0.1, 0.2, and 0.3) high entropy alloy coatings (HEACs) by laser cladding (LC). The impacts of Nb content on the phase composition, microstructure, microhardness, wear resistance and corrosion properties of CoCrFeNi based HEACs were examined. Different from the canonical dendritic (DR) - interdendritic (ID) microstructure presented by the other three HEACs, the ID of Nb0.3 HEACs also existed nanoscale Nb-rich Laves phase composed of NbNi and NbCo. The inclusion of Nb significantly reduced the average grain size of CoCrFeNi based HEACs from 59.43 μm to 11.38 μm. It also greatly diminished the formation of high angle grain boundaries (HAGBs), increasing the percentage of low angle grain boundaries (LAGBs) from 31 % to 61 %. The microhardness of Nb-containing HEACs was significantly promoted due to the solid solution strengthening and fine grain strengthening caused by large size Nb atoms. Affected by Laves phase with high coordination number and space filling ratio and higher proportion of LAGBs, the microhardness of Nb0.3 HEAC was even as high as 530 HV. The increase in Nb concentration also strengthened the HEACs' resistance to wear. Nb0, Nb0.1, Nb0.2, and Nb0.3 HEACs had corresponding specific wear rates of 0.36, 0.32, 0.23, and 0.20 mm3/Nm. Unlike 316 SS, Nb0 and Nb0.1 HEACs, which had both adhesive wear and abrasive wear, Nb0.2 and Nb0.3 HEACs were mainly wear by abrasive wear. The corrosion behavior of CoCrFeNiNbx HEACs in 0.5 M H2SO4 solution was similar to 316 SS, but the corrosion resistance was stronger than 316 SS. Nb0.3 HEAC with the Ecorr of −164 mV and Icorr of 6.40 × 10−7 A/cm2 showed the best acid corrosion resistance, which could be attributed to the stable and dense passivation film on its surface. Distinct from the intergranular corrosion of other coatings, the corrosion of Nb0.3 HEAC mainly occurred in DR, because the FCC phase acted as the anode site in it when FCC and Laves phase co-existed.

The different responses of trace elements to equilibrium and disequilibrium melting: Implications for crustal differentiation and granite compositions

Equilibrium and disequilibrium meltings are two common mechanisms in the geochemical differentiation of the continental crust. However, responses of trace elements to the two melting processes are still not fully understood in granite petrogenesis. To address this, we conducted trace element modelling of open system melting using phase equilibrium calculations combined with solubility equations for accessory minerals and mineral–melt partition coefficients based on three melt-reintegrated felsic granulite compositions. The results indicate systematic differences between the compositions of disequilibrium (Type I) and equilibrium (Type II) melts involving water-present melting reaction, fluid-absent melting reaction involving biotite, and fluid-absent melting reaction in the absence of biotite. Type I melts generally have higher Rb, Ba, Co, Ni, V, and Cr contents, and Rb/Sr and Nb/Ta ratios, and lower Sr, P, Th, U, and light rare earth element contents than Type II melts. Significantly, disequilibrium melting involving biotite can produce melts with high Nb contents and super-chondritic Nb/Ta ratios, which may be a reservoir for the missing Nb on Earth. Compared with Type II melts, the trace element contents and ratios of Type I melts exhibit a larger range, more complex trends, and are more sensitive to changes in melting reaction types and melt loss. This suggests that, in addition to petrogenetic processes such as crystal entrainment, fractional crystallization and magma mixing, the disequilibrium melting would also contribute to the compositional diversity of granites. The modelling results also show that the trace element signatures of granites that are commonly used to determine their petrogenetic processes and tectonic setting may lead to erroneous conclusions if the granitic melts were produced by disequilibrium melting.

Theoretical study on structural transformation and mechanical properties of Ni3Ti1-xNbx

Using plane wave pesudopotential method based on density functional theory, we studied the structural transition of intermetallic compounds Ni3Ti1-xNbx (0≤x≤1). By constructing and relaxing various Ni3Ti1-xNbx structures, the most stable configurations were obtained. The variations of the Ni3Ti1-xNbx structures with x were fitted based on the calculated results. It can be seen that the Nb concentration will be in the range of 29.5%∼71.2% in ternary D019 phases if they participate from the system. The structural transitions can induce the change of mechanical and electronic properties of the compounds. It is shown that the elastic constants such as C44 and C66, decrease with the increase of x although the elastic constants such as C11 and C13 as well as the B/G ratio increase evidently. It indicates that the possibility of shear deformation of the system increases with the increase of the Nb concentration. The formation of different stacking-faults becomes favorable with the substitution of Nb for Ti, which results in the structural transition of Ni3Ti1-xNbx. The conclusions are further supported by density of states and charge density differences.

W–Ta–Nb solid solutions prepared by vacuum arc melting: Microstructure evolution and mechanical properties

In order to further improve the strength and toughness of W–Ta solid solutions and ensure the high specific gravity characteristics of the material, the effect of low content of Nb on the microstructure evolution and performance of W–30Ta solid solutions was performed. The results showed that the phase composition of W–Ta–Nb alloys was single phase W–Ta–Nb solid solutions. The compressive strength of W–Ta–Nb solid solutions increased first and then decreased upon increasing the Nb content. The amount of solid solution of Nb in W–Ta–Nb solid solutions increased and the interplanar spacing increased upon increasing the Nb content. Nb has the effect of refining the grain of tungsten alloy. The grain size gradually decreased upon increasing the Nb content. The addition of a small amount of Nb can effectively improve the strength and toughness of W–Ta–Nb solid solutions. The addition of a small amount of Nb reduced the energy required for the initiation of ductile dislocations in W–Ta–Nb solid solutions.

Effects of niobium doping on the charge density wave and electronic correlations in the kagome metal Cs(V1−xNbx)3Sb5

The transport and optical properties of the Nb-doped Cs(V$_{1-x}$Nb$_{x}$)$_{3}$Sb$_{5}$ with x = 0.03 and 0.07 have been investigated and compared with those of the undoped CsV$_{3}$Sb$_{5}$. Upon Nb doping, the charge-density wave (CDW) transition temperature $T_{\text{CDW}}$ is suppressed, and the superconducting temperature $T_{c}$ rises. The residual resistivity ratio decreases with Nb doping, suggesting an increase of disorder. For all compounds, the optical conductivity in the pristine phase reveals two Drude components (D1 and D2). The substitution of Nb causes an increase of D1 alongside a reduction of D2 in weight, which implies a change of the Fermi surface. The total Drude weight is reduced with increasing Nb content, signifying an enhancement of electronic correlations. Below $T_{\text{CDW}}$, while the optical conductivity clearly manifests the CDW gap in all materials, the gapped portion of the Fermi surface shrinks as the Nb content grows. A comprehensive analysis indicates that the change of the Fermi surface, the enhancement of electronic correlations, the shrinkage of the removed Fermi surface by the CDW gap, and the increase of disorder may all have a considerable impact on the interplay between the CDW and superconductivity in Cs(V$_{1-x}$Nb$_{x}$)$_{3}$Sb$_{5}$.

Effect of Alloying on the Microstructure, Phase Stability, Hardness, and Partitioning Behavior of a New Dual-Superlattice Nickel-Based Superalloy

A novel γ–γ′–γ″ dual-superlattice superalloy, with promising mechanical properties up to elevated temperatures was recently reported by Mignanelli et al. (in: Proceedings of the 9th International Symposium on Superalloy 718 & Derivatives: Energy, Aerospace, and Industrial Applications, pp 679–690, 2018). The present work employs state-of-the-art chemical and spatial characterization techniques to study the effect systematic additions of Mo, W, and Fe and variations in Nb and Al contents have on the phase fraction, thermal stability, elemental partitioning, and mechanical properties of alloys from this system. Alloys were produced through arc melting followed by heat treatment. Multi-scale characterization techniques and hardness testing were employed to characterize their microstructure, thermal stability, and mechanical properties. Alterations in such properties or in elemental partitioning behavior were then explained through thermodynamic modeling. A modest addition of 1.8 at. pct Mo had a strong effect on the microstructure and thermal stability: it minimized microstructural coarsening during heat treatments while not significantly decreasing the γ′ solvus temperature. A reduction of Nb by 0.6 at. pct strongly reduced the γ″ volume fraction, without affecting the γ′ volume fraction. The reduced precipitate fraction led to a significant reduction in alloy hardness. Fe, added to achieve better processability and reduced material cost, decreased the γ′ solvus temperature and caused rapid microstructural coarsening during heat treatments, without affecting alloy hardness. A reduction of Al by 0.4 at. pct reduced the γ′ volume fraction and the γ′ solvus temperature, also without affecting alloy hardness. The addition of 0.9 at. pct W decreased the γ′ solvus temperature but increased both precipitate volume fractions. These data will be invaluable to optimize current alloy design and to inform future alloy design efforts.Graphical

Doping with Niobium Nanoparticles as an Approach to Increase the Power Conversion Efficiency of P3HT:PCBM Polymer Solar Cells.

Metal additive processing in polymer: fullerene bulk heterojunction systems is recognized as a viable way for improving polymer photovoltage performance. In this study, the effect of niobium (Nb) metal nanoparticles at concentrations of 2, 4, 6, and 8 mg/mL on poly(3-hexylthiophene-2,5-diyl) (P3HT)-6,6]-phenyl C61-butyric acid methyl ester (PCBM) blends was analyzed. The effect of Nb volume concentration on polymer crystallinity, optical properties, and surface structure of P3HT and PCBM, as well as the enhancement of the performance of P3HT:PC61BM solar cells, are investigated. Absorption of the P3HT:PC61BM mix is seen to have a high intensity and a red shift at 500 nm. The reduction in PL intensity with increasing Nb doping concentrations indicates an increase in PL quenching, suggesting that the domain size of P3HT or conjugation length increases. With a high Nb concentration, crystallinity, material composition, surface roughness, and phase separation are enhanced. Nb enhances PCBM's solubility in P3HT and decreases the size of amorphous P3HT domains. Based on the J-V characteristics and the optoelectronic study of the thin films, the improvement results from a decreased recombination current, changes in morphology and crystallinity, and an increase in the effective exciton lifespan. At high doping concentrations of Nb nanoparticles, the development of the short-circuit current (JSC) is associated with alterations in the crystalline structure of P3HT. The highest-performing glass/ITO/PEDOT:PSS/P3HT:PCBM:Nb/MoO3/Au structures have short-circuit current densities (JSC) of 16.86 mA/cm2, open-circuit voltages (VOC) of 466 mV, fill factors (FF) of 65.73%, and power conversion efficiency (µ) of 5.16%.

A novel strategy for architecting low interfacial energy transition phase to enhance thermal stability in a high-entropy alloy

Alloys with high strength and thermal stability are attractive for crucial applications in aerospace and power-generation sectors. In this paper, based on the thermodynamics, the microstructure, hardness, and compressive properties of the (FeCoNiCrCu1.71)96Nb4 and (FeCoNiCrCu1.71)90Nb10 (at%) high-entropy alloys (HEAs) upon high-temperature aging were studied. The results indicate that the addition of Nb increases the amounts of the Nb-rich precipitates and concentration of Nb within the matrix, enhancing the hardness and yield strength. With prolonged aging time, the hardness and yield strength of the (FeCoNiCrCu1.71)96Nb4 and (FeCoNiCrCu1.71)90Nb10 HEAs remain almost unchanged, showing high thermal stability. It is discussed from the synergistic of high-density secondary Cu-rich precipitates and the low-energy Nb-rich precipitate/transition precipitate/matrix and Cu-rich precipitate/matrix interfaces. From a thermodynamical point of view, the free energy of the matrix is decreased to be lower than that of the Nb-rich precipitates, changing the diffusion direction of Nb and forming a gradient distribution of Nb. It provides a convenient strategy to architect an fcc metastable transition precipitate linking Nb-rich precipitates and Cu-depleted matrix, reducing interface energy. Moreover, Cu and the coherent interfaces with low interfacial energy effectively retard the coarsening of the Nb-rich precipitates. It may serve as guidance for the future alloy design strategy of high-entropy superalloys with high thermal stability.

Early Paleoproterozoic tectonic evolution of the Yinshan Block in the North China Craton: Constraints from the geochronology and geochemistry of basic to felsic magmatic rocks in the Guyang area

The earliest Paleoproterozoic magmatic rocks have recorded the transition from the Neoarchean cratonization of the NCC to its post-Archean tectonic evolution, which will provide insight into the onset of the modern-style subduction. This study focuses on the early Paleoproterozoic granodiorite, monzonitic diorite, alkali feldspar granite and gabbro in the Guyang area to decipher the early Paleoproterozoic tectonic evolution of the Yinshan Block. Zircon U–Pb dating indicates that these rocks were emplaced at ca 2.46 – 2.41 Ga. The ∼ 2.46 Ga granodiorite samples have high Sr contents, low Y and Yb contents with high Sr/Y ratios, similar to the characteristics of adakitic rocks. Based on their high Mg# values, Na2O/K2O ratios, Cr, Co and Ni concentrations, and positive εNd(t) values, we propose that the granodiorite was likely produced by partial melting of subducting oceanic slab. The contemporary monzonitic diorite samples are characterized by high Nb concentration, which are similar to those of Nb-enriched basalt/andesite. The monzonitic diorite samples are characterized by LREE-enriched patterns with negative Eu anomalies and have negative εNd(t) values (-0.4 – −1.4), which suggest that they were derived from partial melting of fertile mantle peridotite metasomatized by adakitic melts. The ∼ 2.44 Ga alkali feldspar granite samples have negative εNd(t) values (-4.0 – −1.9) and show geochemical characteristics of A-type granites, indicating an extension background. The distinct geochemical characteristics of ca. 2.46 – 2.44 Ga Guyang adakatic granodiorite, Nb-enriched monzonic diorite and A-type alkali feldspar granite suggest that a slab window was opened in the southern margin of the Yinshan Block. The gabbros were emplaced at ∼ 2.41 Ga revealed by U-Pb dating. The enriched LREEs and relatively flat HREEs patterns with negative Nb-Ta anomalies of gabbros indicate a subducting tectonic setting. Their high Ba/Th and low Nb/Y ratios imply that the mantle source was metasomatized by slab-derived fluids. This special rock association not only constrains the tectonic evolution in the southern margin of the Yinshan Block, but also indicates modern-style subduction operated already in the early Paleoproterozoic.

Two pulses of Mesoproterozoic intra-plate magmatism in the heart of the Palaeoproterozoic Ubendian Domain of northern Malawi

Two Mesoproterozoic anorogenic igneous events are recorded in the Palaeoproterozoic Ubendian Domain in northern Malawi. The oldest is represented by the Mwakikome orthogneiss, a small peraluminous, sub-alkaline and ferroan syenogranite that has a U–Pb zircon emplacement age of 1411 ± 3 Ma, an initial εNd of −4.5 and a Nd TDM2 model age of 2.27 Ga. These data are interpreted to suggest that the Mwakikome intrusion was derived mainly from the melting of the adjacent Palaeoproterozoic country rocks during Kibaran-aged extension. The second anorogenic igneous event is defined by the more widespread Mwenga Suite, a series of small (<100 km2) NW-SE oriented and elongated plutons that occur in a narrow belt in the north of the Ubendian Domain. Seven samples from different intrusions gave U–Pb zircon emplacement ages between ∼1150 and 1110 Ma. The Mwenga Suite is comprised of rocks that are also ferroan, potassic and sub-alkaline in composition and shows a range of major element compositions from monzogranite to alkali-feldspar granite. Nd isotopic data from one sample yielded an initial εNd of −2.2 and a Nd TDM2 model age of 1.88 Ga, suggesting that the suite was also largely derived from melting of the Ubendian host rocks, but with some additions from an enriched mantle source. Both the Mwakikome and Mwenga rocks are characterised by high concentrations of Zr, Hf, Nb, Ta, Y and REE and high Ga/Al, imparting a within-plate, A-type, trace element signature. The rocks have no direct temporal correlatives beyond northern Malawi and SW Tanzania and appear unique to this region. They do, however, build on a theme of long-lived Mesoproterozoic (∼1400–1100 Ma) intra-plate extension, basin formation, and bimodal A-type magmatism that is better established in areas of central Africa located over 500 km NW of the study area.

Wear and corrosion resistance improvement of (CoCrNi)72−xB18Si10Nbx coatings obtained by laser cladding: Role of Nb concentration

Wear and corrosion resistance improvement of (CoCrNi)72−xB18Si10Nbx coatings obtained by laser cladding: Role of Nb concentration

Twinning-induced dislocation and coordinated deformation behavior of a high-Nb TiAl alloy during high-cycle fatigue

The deformation mechanism responsible for the high-cycle rotating bending fatigue of a high-Nb TiAl alloy was investigated. Fatigue deformation in the γ phase was dominated by superlattice dislocations [0 1 1¯] and twinning. Dislocations 〈110〉 in the B2 phase can be induced by twins in the adjacent γ phase, which has a low stacking fault energy owing to the high Nb content. Stress transfer between two adjacent phases can be accomplished through atomic rearrangement of the interface by twinning. The local stresses were accommodated by the continuous dislocation slip of the B2 phase, deformation twins, and twin intersections in the γ phase.

Petrogenesis and Tectonic Implications of the Cryogenian I-Type Granodiorites from Gabgaba Terrane (NE Sudan)

The widely distributed granitic intrusions in the Nubian Shield can provide comprehensive data for understanding its crustal evolution. We present new bulk-rock geochemistry and isotopic (zircon U-Pb and Lu-Hf) data from the Haweit granodiorites in the Gabgaba Terrane (NE Sudan). The dated zircons presented a 206Pb/238U Concordia age of 718.5 ± 2.2 Ma, indicating that they crystallized during the Cryogenian. The granodiorites contain both biotite and amphibole as the main mafic constituents. The samples exhibit metaluminous (A/CNK = 0.84–0.94) and calc-alkaline signatures. Their mineralogical composition and remarkable low P2O5, Zr, Ce, and Nb concentrations confirm that they belong to I-type granites. They exhibit subduction-related magma geochemical characters such as enrichment in LILEs and LREEs and depletion in HFSEs and HREEs, with a low (La/Yb)N ratio (3.0–5.9) and apparent negative Nb anomaly. The positive Hf(t) values (+7.34 to +11.21) and young crustal model age (TDMC = 734–985 Ma) indicates a juvenile composition of the granodiorites. The data suggest that the Haweit granodiorites may have formed from partially melting a juvenile low-K mafic source. During subduction, the ascending asthenosphere melts might heat and partially melt the pre-existing lower crust mafic materials to generate the Haweit granodiorites in the middle segment of the Nubian Shield.

Thermodynamic Study on Initial Oxidation Behavior of TiAl-Nb Alloys at High Temperature

The initial oxidation behavior of TiAl-Nb alloys was systematically investigated against the composition, temperature, and partial pressure of O2 with the CALculation of PHAse Diagrams (CALPHAD) technique. The mole fraction of each oxidation product at the initial oxidation stage of the alloys at the corresponding temperatures was predicted. The initial oxidation products of the alloys are oxides of Al, Ti, and Nb, with the oxidation order of Al, Ti, and Nb. As P(O2) increases, the Ti and Nb oxidation products move towards a high oxygen content, and the mole fractions of the Al and Ti oxides gradually decrease and increase, respectively. It was found that the temperature and partial pressure of O2 determined the types of the oxides and the oxidation order, while the concentration of Nb and Al determined the mole fraction of the oxides. The CALPHAD results are in good agreement with the experiments.

Glass formation ability and physical properties of Fe–B–Y bulk metallic glass alloys with different Nb contents

This study investigated the effects of Nb addition on the glass formation ability, mechanical properties, and microstructural evolution of Fe–Y–B bulk metallic glass (BMG) alloys. The glass formation ability of the alloys with different Nb contents was evaluated by means of X-ray diffraction and differential scanning calorimetry. The mechanical properties of the various BMGs were examined using a universal testing machine (MTS 810) under quasi-static strain rates of 10[Formula: see text]–10[Formula: see text] s[Formula: see text]. The high strain rate mechanical properties of the BMGs were tested using a split Hopkinson pressure bar system under strain rates of [Formula: see text] to [Formula: see text] s[Formula: see text]. Finally, the microstructures of the fracture surfaces of the alloys tested at different strain rates were observed by scanning electron microscopy (SEM).

Petrogenesis and Rb-Sr Isotopic Characteristics of PaleoMesoproterozoic Mirgarani Granite Sonbhadra Uttar Pradesh India: Geodynamics Implication for Supercontinent Cycle

The Rb-Sr whole-rock isochron, age 1636 ± 66 Ma of Mirgarani granite, is the one of the oldest granite dated in the northwestern part of the Chhotanagpur Granite Gneiss Complex (CGGC). The initial Sr ratio is 0.715 ± 0.012 (MSWD = 0.11), showing an S-type affinity. The Mirgarani granite has intruded the migmatite complex of the Dudhi Group and forms the Mirgarani formation comparable to the granites of the Bihar Mica Belt around Hazaribagh (1590 ± 30 Ma). The present studies have established the chronostratigraphy of the Dudhi Group and adjoining areas in CGGC. Petro graphic and geochemical studies revealed that the granite is enriched in Rb (271 ppm), Pb (77 ppm), Th (25 ppm), and U (33 ppm) and depleted in Sr (95 ppm), Nb (16 ppm), Ba (399 ppm) and Zr (143 ppm) contents as compared to the normal granite. The Mirgarani granite is a peraluminous (A/CNK = 1.23), high potassic (K2O 6.42%), Calc-Alkalic to Alkali-Calcic {(Na2O+K2O)-CaO = 6.29} S-Type granite, a feature supported by the presence of modal garnet and normative corundum (2.68%). The Mirgarani granite is considered to have been formed by the anatexis of a crustal sedimentary protolith at a depth of approximately 30 km with temperatures ranging from 685-700 °C during the Co lumbian - Nuna Supercontinent.

The adsorption behavior of niobium (V) on kaolin clay and kaolinite

Niobium (Nb) in kaolin clay usually occurs in the Ti-bearing minerals, such as rutile and anatase. However, the low Ti-bearing minerals contents for some kaolin clay rocks were insufficient to explain the high Nb concentrations. Thus, Nb was widely considered to be adsorbed by clay minerals. However, the adsorption behavior of niobium (V) on clay minerals has not been fully understood. In this study, a series of batch adsorption experiments were carried out on kaolin clay (Kclay) and pure kaolinite (Kaol) using niobium oxalate solutions. The effects of contact time, initial niobium (V) concentration, solution pH, and temperature on the adsorption were investigated. The results showed that Kclay exhibited a higher adsorption capacity than Kaol under the same conditions. The niobium (V) adsorptions on Kclay and Kaol were pH-dependent, and both of them showed declining adsorption capacities from pH 2 to 4. The adsorption behaviors of niobium (V) on Kclay and Kaol conformed to the pseudo-second-order model. The adsorption isotherm of Kclay was a better fit with the Freundlich isotherm model, while the Langmuir isotherm model was a better fit for Kaol. The Langmuir maximum adsorption amount of Kclay and Kaol were 5.42 and 2.25 mg/g, respectively. These results demonstrated that niobium (V) can be adsorbed by kaolin clay and kaolinite.

The Effect of Adding V and Nb Microalloy Elements on the Bake Hardening Properties of ULC Steel before and after Annealing

Bake hardening (BH) is a vital part of special steel production. Studies in this field have focused on steels under homogeneous yielding, but until now, none have been conducted on the phenomena that occur for steels under heterogeneous yielding. In the current study, the effect of adding Nb and V alloying elements on the strength of ultra-low carbon (ULC) steel after bake hardening was investigated. The effects of pre-strain, grain size, and recrystallization annealing temperature were analyzed, as well as the effect of Nb and V on the yield stress caused by the bake hardening process. For this purpose, five types of alloys with different V and Nb contents were melted, cast in an induction furnace, and subjected to hot hammering and hot rolling. Then, cold rolling was applied to the samples by ~80%. To eliminate the effects of cold working, tensile samples were subjected to recrystallization annealing at 750 and 800 °C for 30 min, and the samples were quickly quenched in a mixture of a NaCl solution and ice. The annealed samples were subjected to a pre-tensile strain in the range of 2-12% and then aged in a silicone oil bath at 180 °C for 30 min. Then they were subjected to a tensile test. The obtained results showed that with the increase of the pre-strain and the annealing temperature, the values of baking hardness increased. The presence of V in the composition of steel reduced the annealing temperature.