Combination Of Nb Research Articles

Corrosion and abrasion behavior of high-temperature carburized 20MnCr5 gear steel with Nb and B microalloying

This paper investigates the effect of Nb and B microalloying on the wear and corrosion resistance of 20MnCr5 steel after high-temperature carburization at 950 °C. The abrasion and corrosion performance of the steel was compared using electrochemical experiments and dry sliding wear tests. The results show that Nb microalloying reduces the size of residual austenite, thereby improving the wear resistance of 20MnCr5 steel. Furthermore, the combination of Nb and B microalloying reduces the amount of residual austenite, leading to further improvements in wear resistance. Both microalloying methods reduce the wear scar depth and debris accumulation. The corrosion potentials of 20MnCr5, 20MnCr5Nb, and 20MnCr5NbB are 0.645 V, 0.627 V, and 0.675 V, respectively. The addition of Nb to 20MnCr5 steel results in higher corrosion resistance after carburization due to the refinement of needle-like martensite. However, 20MnCr5NbB steel exhibits low corrosion resistance due to the coarsening of needle-like martensite caused by B microalloying. In summary, this study provides new insights into the effects of microalloying elements on the properties of steel. The findings contribute to a deeper understanding of how to design and manufacture gears and other components with superior wear and corrosion resistance.

Effect of Nb and Mo on Austenite Microstructural Evolution During Hot Deformation in Boron High Strength Steels

This work has focused on the study of hot working behavior of boron high strength steels microalloyed with different combinations of Nb and/or Mo. The role of Nb and Mo during the hot deformation of low carbon steels is well known: both mainly retard austenite recrystallization, leading to pancaked austenite microstructures before phase transformation and to refined room temperature microstructures. However, the design of rolling schedules resulting in properly conditioned microstructures, requires microstructural evolution models that take into account the effect of the different alloying elements. In this specific case, the effect that high levels of molybdenum (0.5 pct) have in the recrystallization delay was evaluated. In that respect, hot torsion tests were performed in this work to investigate the microstructural evolution during hot deformation of four boron steels, with different Nb (0.025 pct) and Mo (0.5 pct) combinations. The retardation in recrystallization kinetics was modeled in all cases and measured kinetics agree with those predicted by equations previously developed for Nb–Mo microalloyed steels with lower Mo concentrations (< 0.3 pct). The strain-induced precipitation in the Nb and Nb–Mo bearing steels was also characterized. Finally, the fractional softening evolution during multipass rolling simulations was compared with MicroSim® model predictions, showing a good agreement with experimental results.

Synthesis and characterization of ternary layered Nb2SB ceramics fabricated by spark plasma sintering

In this paper, B-containing MAX phase of Nb2SB ceramics with high purity of 96 wt% (4 wt% NbB impurity) was successfully synthesized using the molar ratio of Nb: S: B = 2: 1.3: 1 by spark plasma sintering at 1350 °C under 30 MPa. The reaction path, microstructure, physical and mechanical properties were systematically studied. It is found that the formation of Nb2SB is from the combination of Nb, NbS2, and Nb5B6, or NbB and NbS. The full dense sample (RD 99.7%) possesses the fine grains about 6 µm in length and 3.6 µm in width. The grains of Nb2SB show a layered structure, which is same to other MAX phases. The thermal expansion coefficient is 7.1 × 10−6 K−1 in the range of 24–1100 °C. In the temperature range of 25–800 °C, the thermal diffusivity of Nb2SB ceramic increases from 5.58 mm2/s to 7.07 mm2/s. At 25 °C, the heat capacity is 0.36 J·g−1·K−1, the thermal conductivity is 13.79 W·m−1·K−1, and the electrical conductivity is 1.17 × 106 Ω−1·m−1. Additionally, the obtained Nb2SB ceramics exhibit excellent mechanical properties of Vickers hardness of 11.89 GPa (10 N load), flexural strength of 249 MPa, fracture toughness of 4.76 MPa·m1/2, and compressive strength of 1157 MPa.

Longevity can mask low Nb if only Ne of mixed-age samples is estimated in threatened and mobile species

Knowing about a threatened species’ effective population size (Ne) is vital to assess population trends and guide conservation efforts. Highly mobile and migratory species are some of the most threatened yet hardest to monitor groups. Recently, a conversion has been proposed to convert estimates of the effective number of breeders (Nb) to Ne using two life history traits. We evaluated current methods to estimate Nb and Ne to inform conservation management using the black-fronted tern/tarapirohe (Chlidonias albostriatus) as a case study. Black-fronted terns are endangered, highly mobile and traditional monitoring methods have proven difficult. Based on 17 microsatellites and extensive sampling throughout the breeding range, we estimated mean Nb ca. 700 based on sibship assignment and linkage disequilibrium (LD) methods. Mean estimates of LD Ne based on the conversion of Nb and two life history traits was 668, while LD Ne based on samples of chicks and adults was 3216. The low ratio of Nb/Ne when using the Ne estimate based on mixed-age samples is probably driven by a combination of Nb being more sensitive to the large recruitment failure of individuals, large variation compared to mean reproductive success between same-age and same-sex individuals, and the ongoing overall population decline. We highlight that in relatively long-lived and threatened species, a combination of Nband Ne estimates are more appropriate to assess the population status rather than solely relying on Neof mixed-age samples. For black-fronted terns, we recommend increased conservation management and genetic monitoring based on Nb and Ne.

Effect of the Time between Last Deformation Pass and Accelerated Cooling on the Mechanical Properties in Nb and Nb-Mo Microalloyed Steels

The microstructural refinement induced when the holding time between last deformation pass and accelerated cooling is reduced, affects the mechanical properties in low carbon Nb and Nb-Mo microalloyed steels. Plane strain compression tests were performed and mechanical property samples machined in order to quantify this effect using tensile and Charpy impact tests. A complete microstructural characterization was carried out using electron backscattered diffraction (EBSD) measuring unit size distributions and homogeneity of complex microstructures. The synergetic combination of Nb and Mo elements modifies the final microstructures and, therefore, affects the contribution of different strengthening mechanisms, such as substructure, precipitation hardening and dislocation density. Even though strength is not clearly affected by the reduction of the holding time after the last deformation pass, Charpy properties are considerably improved in the case of the Nb steel. The presence of MA islands in the Nb-Mo steel limits the beneficial effect of the microstructural refinement and toughness remains unmodified.

Analysis of local bond-orientational order for liquid gallium at ambient pressure: Two types of cluster structures.

In terms of the local bond-orientational order (LBOO) parameters, a cluster approach to analyze local structures of simple liquids was developed. In this approach, a cluster is defined as a combination of neighboring seeds having at least nb local-orientational bonds and their nearest neighbors, and a cluster ensemble is a collection of clusters with a specified nb and number of seeds ns. This cluster analysis was applied to investigate the microscopic structures of liquid Ga at ambient pressure (AP). The liquid structures studied were generated through ab initio molecular dynamics simulations. By scrutinizing the static structure factors (SSFs) of cluster ensembles with different combinations of nb and ns, we found that liquid Ga at AP contained two types of cluster structures, one characterized by sixfold orientational symmetry and the other showing fourfold orientational symmetry. The SSFs of cluster structures with sixfold orientational symmetry were akin to the SSF of a hard-sphere fluid. On the contrary, the SSFs of cluster structures showing fourfold orientational symmetry behaved similarly as the anomalous SSF of liquid Ga at AP, which is well known for exhibiting a high-q shoulder. The local structures of a highly LBOO cluster whose SSF displayed a high-q shoulder were found to be more similar to the structure of β-Ga than those of other solid phases of Ga. More generally, the cluster structures showing fourfold orientational symmetry have an inclination to resemble more to β-Ga.

Evolution of Si-2N2Nb island configuration on NbN (0 0 1) surface: A first-principles calculation

The separation and aggregation of Nb, Si, and N atoms around the NbN grain during the deposition of the Nb–Si–N nanocomposite film were discussed. The evolution behavior of the 2N2Nb island and the adsorption and diffusion energy of Nb, Si, and N atoms around the island on the NbN (001) surface were investigated using the first-principles method based on density functional theory. Results indicated that the most stable configuration of the Nb–Si–N island was the combination of Nb and N atoms to form the island and the possible aggregation of the Si atom to diagonal Nb atom outside the island. Substitution solid solution was eventually formed, in which the Nb atom of the 2N2Nb island was replaced by the Si atom during deposition. However, the Si atom was easily replaced by the Nb atom at the site with abundant Nb atoms. The diffusion energy of the evolution from Nb-2N1Nb1Si to Si-2N2Nb was 1.58eV, and the total energy of the configuration decreased. Moreover, the interface of Si and NbN grains tended to separate. The highest energy adsorption sites for Nb, Si, N atoms adsorbed on the NbN (001) surface around the 2N2Nb island were P3, P1, and P2, respectively. The adsorption energies of Nb, Si, and N atoms on the NbN (001) surface around the 2N2Nb island were 7.3067, 5.3521, and 6.7113eV, respectively, and their diffusion energies around the 2N2Nb island were 2.62, 1.35, and 5.094eV, respectively. The low adsorption and diffusion energies of active Si atoms promoted the distribution of Nb and N atoms during deposition. Furthermore, the NbN grain was easily separated through Si atom diffusion into the 2N2Nb island. The grain was refined, and its growth was inhibited by the Si atom during deposition.

Quasi-static and dynamic response of explosively consolidated metal–aluminum powder mixtures

Nearly fully dense (>96% theoretical maximum density) powder mixture compacts with combinations of Nb, Ni, Mo, W, and Ta, with Al, were produced by explosive consolidation. The quasi-static and dynamic behavior and failure mechanisms were investigated experimentally and computationally. For two mixtures (Ni+Al, W+Al) the Al phase was continuous, while for the other three mixtures (Nb+Al, Ta+Al, Mo+Al), the Al phase was discontinuous. It was found that the continuous phase significantly influenced the mechanical response (in compression) and determined the fracture morphology of the compacts. Accordingly, the mixtures with continuous Al phases had the lowest compressive strength. Two distinct failure mechanisms, axial splitting and shear failure, were observed. Axial splitting occurred when the Al phase was continuous (Ni+Al, W+Al); shear failure was primarily associated with extensive deformation of the Nb, Ta and Mo continuous phases. Finite element simulations provide valuable help in interpreting the experimental results and predicting mechanical strength and failure mechanisms akin to those observed. The interfacial bonding strength is shown to be an important parameter in determining the mechanical response of the compacts.

Non-Isothermal Austenite Grain Growth Kinetics in the HAZ of a Microalloyed X-80 Linepipe Steel

Non-isothermal austenite grain growth kinetics under the influence of several combinations of Nb, Ti and Mo containing complex precipitates has been studied in a microalloyed linepipe steel. The goal of these studies is the development of a grain growth model to predict the austenite grain size in the weld heat affected zone (HAZ). A detailed electron microscopic investigations of the as-received steel proved the presence of Ti-rich, Nb-rich and Mo-rich precipitates. Inter and intragranular precipitates of ~5-150 nm have been observed. The steel has been subjected to austenitizing heat treatments to selected peak temperatures of 950, 1150 and 1350°C at various heating rates of 10, 100 and 1000°C/s. Thermal cycles have been found to have a strong effect on the final austenite grain size. The increase in heating rate from 100 to 1000°C/s has a negligible difference in the austenite grain size irrespective of the austenitizing temperature. However, the increase in grain size has been noticed at 10°C/s heating rate for all the austenitizing temperatures. The austenite grain growth kinetics have been explained taking into account the austenite growth in the presence of precipitates.

Nonisothermal Austenite Grain Growth Kinetics in a Microalloyed X80 Linepipe Steel

Nonisothermal austenite grain growth kinetics under the influence of several combinations of Nb, Ti, and Mo containing complex precipitates has been studied in a microalloyed linepipe steel. The goal of this study is the development of a grain growth model to predict the austenite grain size in the weld heat affected zone (HAZ). Electron microscopy investigations of the as-received steel proved the presence of Ti-rich, Nb-rich, and Mo-rich precipitates. The steel has then been subjected to austenitizing heat treatments to selected peak temperatures at various heating rates that are typical for thermal cycles in the HAZ. Thermal cycles have a strong effect on the final austenite grain size. Using a mean field approach, a model is proposed for the dissolution of Nb-rich precipitates. This model has been coupled to a Zener-type austenite grain growth model in the presence of pinning particles. This coupling leads to accurate prediction of the austenite grain size along the nonisothermal heating path simulating selected thermal profiles of the HAZ.

BaNbO(IO3)5: A New Polar Material with a Very Large SHG Response

By combination of Nb(5+) (having a d(0) electronic configuration) and the lone-pair-containing iodate anion, a new SHG material, BaNbO(IO(3))(5), has been prepared. It exhibits a very large SHG response (approximately 14 times that of KH(2)PO(4) and approximately 660 times that of alpha-SiO(2)) and is phase-matchable. The material has high thermal stability and a wide transparent region.

Effects of Nb and Si on high temperature oxidation of TiAl

The isothermal oxidation behavior of TiAl based alloys at 900 °C in air with a combination of Nb (5%-10%, mole fraction) and Si (1%-5%, mole fraction) was investigated. The microstructure and the composition of the oxidation scale were studied by using XRD, TEM and EPMA. The results show that the combination of Nb and Si can improve the oxidation resistance of the alloys significantly. The element Si can change the typical microstructure of oxidation scale on TiAl based alloys. In alloys with Si addition, the compact Al 2O 3 forms in the interior side of oxidation scale. When x(Si)>3%, the Ti 5Si 3 phase forms and the coarse crystal TiO 2 forms on Ti 5Si 3 phase after oxidation. The increase of Nb content in the TiAl based alloys impedes the growth of Ti 5Si 3 phase, and the formation of TiO 2 on surface and on Ti 5Si 3 phase is also impeded.

Nippostrongylus brasiliensis can induce B7-independent antigen-specific development of IL-4-producing T cells from naive CD4 T cells in vivo.

Th2 immune responses to a number of infectious pathogens are dependent on B7-1/B7-2 costimulatory molecule interactions. We have now examined the Th2 immune response to Nippostrongylus brasiliensis (Nb) in B7-1/B7-2(-/-) mice and show that Th2 effector cells develop that can mediate worm expulsion and produce substantial Th2 cytokines comparable with wild-type infected mice; however, in marked contrast, B cell Ag-specific Ab production is abrogated after B7 blockade. To examine the mechanism of T cell activation, OVA-specific DO11.10 T cells were transferred to recipient mice, which were then immunized with a combination of Nb plus OVA or either alone. Only the combination of Nb plus OVA triggered T cell differentiation to OVA-specific Th2 cells, suggesting that Nb acts as an adjuvant to stimulate Ag-specific naive T cells to differentiate to effector Th2 cells. Furthermore, using the DO11.10 TCR-transgenic T cell adoptive transfer model, we show that blocking B7-1/B7-2 interactions does not impair nonparasite Ag-specific DO11.10 Th2 cell differentiation; however, DO11.10 T cell cycle progression and migration to the B cell zone are inhibited.

Hot Ductility of Certain Microalloyed Steels under Simulated Continuous Casting Conditions

The hot ductility of steels containing 0.014-0.017%Ti, 0.34-0.72%Ni and various combinations of Nb, V and Cu has been investigated by tensile testing over the temperature range of 600-1050°C. The in-situ melting procedure was employed, followed by subsequent cooling at three different rates to the selected testing temperature. Two strain rates, 0.005 and 0.05 s -1 were used. The results show that a ductility trough exists in all the steels in the temperature range of 700-950°C, and the lowest ductility in terms of reduction of area (RA) is at 750°C. Markedly lower RA and elongation to fracture values were obtained at the lower strain rate. The ductility trough was quite similar in Nb bearing and V or Cu containing steels, especially at the high cooling rate of 4°C/s and with a Ti/N ratio of about 2.8. Reducing the cooling rate from 4 to 1 °C/s makes the ductility trough narrower and shallower in the Nb-bearing steels, but has little effect in the Nb-free steels. Increasing Ca/S ratios in the range 0 to 1.25 improve the ductility minimum especially at the lower cooling rate of 1°C/s. Low N and high Ti/N ratio may also improve the minimum ductility at lower cooling rates.

Extensions of string theories

With the motivation that critical dimensionsD≠4 might be suggesting that string theories have not been completely formulated, we study more general alternatives. We first consider a direct extension in the world-sheet formulation withNB bosons andNF fermions and analyze the conditions for canceling the anomaly in all possible combinations ofNB,NF andD. Later on we incorporate degrees of freedom of antisymmetric tensors to the previous model. The only possibility to cancel the anomaly in this case is withNB=NF=1 and the our everyday spacetime dimensionD=4.

Interface electronic states of V(100) in M1-V-M2

The variation of the electronic structure of V(100) slabs in sandwich-type M1-V-M2 systems is studied by using the Green function matching method and empirical tight binding with s, p and d bands. Combinations of Nb, Cr, Mo and Ta are used for M1 and M2. The author chooses to study mainly the local density of states for each V interface as a function of V slab size. For the slab sizes studied he finds that the properties for the sandwich system are reduced to those of uncoupled interfaces of two semi-infinite media in contact.

Computer Model for Prediction of Carbonitride Precipitation during Hot Working in Nb-Ti Bearing HSLA Steels.

A computer model which predicts complex precipitation behavior quantitatively in Nb-Ti bearing steel has been developed on a theoretical basis. The solubility and composition of the complex precipitates, and the chemical driving force of the precipitates from supersaturated austenite are estimated by means of thermodynamic analysis of regular solution composed of four-binary compounds. The change in dislocation density which acts as a nucleation site during hot working is calculated by using dislocation theory. And the time dependence of volume fraction and the particle radius of strain induced precipitation are also predicted on the basis of classical nulceation theory. In order to estimate the effect of deformation on nucleation, the change in elastic energy of dislocation with nucleation is calculated.Experimental results showed that combination of Nb and Ti addition, decreased the solubility of carbonitrides and accelerated the precipitation rate from supersaturated austenite because of the formation of complex precipitates. Such experimental results are in good agreement with the prediction by the present model. And both the acceleration of precipitation rate and the refinement of precipitates particles due to hot deformation are also quantitatively explained.

HAZ fracture toughness of titanium containing steels

AbstractSteels containing various combinations of microalloying elements (Nb, V, and Ti) were welded at heat inputs from 3 to 6 kJ mm−1. It was shown by detailed crack tip opening displacement fracture toughness testing of coarse grained heat affected zone (HAZ) regions in single pass weld deposits that the poorest toughness properties were exhibited by steel containing a combination of Nb, V, and Ti. Steel microalloyed with only titanium had the best HAZ fracture toughness at all heat input levels. Detailed microstructural analysis, grain size measurement, hardness, and precipitation in HAZ regions were evaluated to explain the fracture toughness properties observed.MST/887

薬物の経皮吸収におけるレシチンの効果(第1報)インドメタシンゲル軟膏のラット背部経皮吸収と排泄

The effect of benzyl nicotinate (NB) and/or lecithin (PC) on the absorption of indomethacin (IM) through rat back skin were studied by using the 14C-IM gel ointment preparations containing 0.5%NB and/or 2%PC. The absorption of IM estimated from the amount remained both on the plaster and on the surface of skin was increased slightly by NB or PC and significantly by the combination of NB and PC. The radioactivity excreted in the urine and feces was much higher in the preparations containing PC than control 120h after a topical application for 7h. Comparing with the pharmacokinetic parameters of IM from control, those from the preparation containing PC were significantly affected ; plasma AUC was higher, MRT was shorter, and VRT was larger. NB was fastly absorbed and disappeared from skin, but the disappearance of PC was not so remarkable as NB. The skin level of IM from the preparation containing both NB and PC was higher in the carrageenin induced edema than in the intact skin. It is suggested that the enhancement of transdermal absorption of IM and the acceleration of excretion of IM by PC may be due to the alteration of permeability by the interaction of skin membrane with PC.