Influence Of Nb Research Articles

Influence of lanthanum and niobium doping on the relaxor behaviour of (Pb 0.75Ba 0.25)(Zr 0.70Ti 0.30)O 3 ceramics

The lead–barium–zirconate–titanate (PBZT) ceramics of composition (Ba/Zr/Ti: 25/70/30) exhibit classical relaxor ferroelectric behaviour similar to other complex lead perovskites such as lead–lanthanum–zirconate–titanate or lead–magnesium–niobiate. Influence of Nb or La admixture on grain structure, dielectric and pyroelectric properties was showed earlier. The effect of simultaneously lanthanum and niobium modified PBZT 25/70/30 ceramics on properties have been studied and compared with earlier results. The influence of the additives on the values of characteristic parameters describing the relaxor behaviour of the studied ceramics ( ε ′ max , T m, T f, T B) was determined.

High power laser welding of Nb microalloyed steel plates

Laser welding studies on 12 mm thick Nb microalloyed steels were done using a 25 kW CO2 laser at welding speeds of up to 3 m min−1 with the aim of identifying the influences of Nb and carbon on laser weldability and weld properties. Welds were examined for solidification flaws, penetration characteristics, microstructure and mechanical properties. Solidification cracking did not appear to be influenced by carbon or Nb in the ranges studied when welding at power levels between 22 and 25 kW. The area fraction of martensite was shown to increase with decreasing energy input and increasing carbon content. Weld metal toughness was improved by reducing carbon content in the range 0·08–0·05%C but was little influenced by Nb. Weld metal and heat affected zone hardness levels were reduced, as expected, by reducing carbon content. The results show that increasing Nb content leads to higher strength material without significant loss of toughness, while lowering carbon content can improve toughness without loss of strength. Thus low carbon Nb microalloyed steels with about 0·05%C can achieve a good combination of parent plate and laser weld properties and appear to be suitable for high power laser welding situations.

On-line measurement of gamma radiation-induced absorption in A3+-codoped PbWO4: Mo crystals

The radiation hardness of the set of seven samples of Mo-doped PbWO4 crystals (from 0 up to 10,000ppm) and further codoped by Y, La, Nb, is investigated. With increasing Mo concentration above 1000ppm radiation hardness increases. Codoping by Y, La can still decrease radiation-induced absorption about several tens percent at least, while influence of Nb is not clear. Induced absorption increases with the dose rate, for dose rates higher than 0.35Gy/min it achieves saturation level. As it is planned to use PbWO4 scintillating crystals at lower temperature in ALICE experiment in CERN, some measurements were performed at temperature −15°C too. Induced absorption coefficient at low temperature is 2–4 times higher with respect to room temperature and kinetic of recovery processes gets slower.

Photoluminescence properties of yttria-stabilized zirconia single crystal

The photoluminescence (PL) and PL excitation spectra of the single-crystal samples of yttria-stabilized zirconia (YSZ) were measured. We found that the PL spectra of two samples for the 280-nm excitation significantly differ from one another in intensity, although the two samples have the same macrostructure and the same chemical composition. These results indicate that PL spectroscopy is a useful method for studying the microstructure of YSZ. The result of the trace-impurity analysis suggests that the large difference in PL intensity between the two samples can be explained by considering the influence of Nb in the YSZ sample. It seems that Nb in YSZ caused an yttria-associated defect. The broad emission band around 550 nm would be attributed to this defect. These results suggest that information can be obtained from its PL measurement not only on the yttria-associated defect, but also on the trace impurity in the YSZ.

Influence of Nb on the first stage of crystallization in Fe86−xNbxB14 amorphous alloys

Abstract The kinetics of the first stage of crystallization (nanocrystallization) in the Fe 86− x Nb x B 14 amorphous alloys was studied by applying differential scanning calorimetry and magnetic balance techniques. It was shown that the nanocrystallization temperature increases with increasing Nb content by more than 80 K. Activation enthalpy of the nanocrystallization process increases from 2 eV for 2 at.% of Nb to 4 eV for 5–8 at.% of Nb. The results obtained by the mentioned experimental techniques are also discussed from the methodological point of view.

Solidification microstructures and mechanical properties of vertical centrifugal cast high speed steel

This study was undertaken to investigate the influence of Nb and V alloying elements and manufacturing conditions on the microstructural behaviour and mechanical characteristics of HSS (high speed steel) roll manufactured by a VCC (vertical centrifugal casting) process. In the Fe - 2C - 6Cr-1.5W - 3Mo - 4V alloy, the amount of MC carbide was increased and the the amount of M7C3 carbide decreased with an increase in V and Nb content. In steel containing 3%Nb, primary NbC carbide was formed within the cell in the matrix. The hardness of steel containing 6.5%V but no Nb was increased a little but when 9%V was added, the hardness decreased in the specimen owing to the soft ferritic matrix. The hardness of the matrix in steel containing 1.5%Nb increased, but decreased for 3%Nb addition. In wear tests, wear loss decreased with increasing rotational wear speed.

Influence of Nb, V and Ti on peak strain of deformed austenite in Mo-based micro-alloyed steels

In this paper, the influence of Nb, V and Ti on the peak strain of deformed austenite in Mo-based micro-alloyed steels has been studied. Four steels, identified as Mo, Mo+V, Mo+Nb and Mo+Ti, respectively, were heated to 1200 °C and held for 10 min and then the temperature was rapidly reduced to test temperatures and maintained for 40 s. The test temperatures were 950, 1000, 1050, 1100, 1150 and 1200 °C at the strain rates of 0.05, 0.1, 0.5, 1 and 5 s −1, respectively. Results indicate that the presence of Nb, Ti, and V affects significantly the value of peak strain ( ε p), especially Nb which has a significant effect on the start of the dynamic recrystallisation. For all the steels studied, the peak strain ε p was modelled as a function of the Zener–Hollomon parameter and the austenite grain size.

Effects of Nb and Al on the microstructures and mechanical properties of high Nb containing TiAl base alloys

The influence of Nb and Al contents on the microstructure and yield strength of high Nb containing TiAl base alloys was investigated. The experimental results show that the yield strength at 900 °C of the alloys with the same type of microstructure, such as fully lamellar (FL), nearly lamellar (NL) and degraded fully lamellar (DFL), increases with increasing Nb content and decreasing Al content in the composition range of 0–10 at.% Nb and 44–49 at.% Al. DFL is the degraded form of FL microstructure after exposure at 1050 °C for 30 h. It is shown that the Nb addition in the alloys increases the value of the σ 0 term in the Hall–Petch relation of yield stress vs. lamellar spacing. This result has been related to TEM observations of dislocation structure in deformed specimens. The observations indicated that high level of Nb solute in the γ-TiAl matrix leads to a high critical resolved shear stress (CRSS) of dislocation loops. High Nb addition also reduces the degradation rate of FL microstructure after exposure at 1050 °C for 30 h. Both effects of high Nb addition are related to the change of the directionality of Ti–Ti (Nb) and Nb–Al bonds in the lattice. The decrease in Al content results in an increase in the volume fraction of α 2 phase, which leads to a decrease in the lamellar spacing of the lamellar structure. The high temperature strength of the alloys is determined by the lamellar spacing λ through the Hall–Petch equation k λ λ −1/2.

Influence of Nb content on the corrosion resistance and saturation magnetic density of FeCuNbSiB alloys

Nanocrystalline FeCuNbSiB alloys obtained from the partial crystallization of amorphous alloys have attracted technological attention due to their excellent magnetic properties, but the relationship between corrosion resistance and magnetic properties is not well established. The influence of Nb as an alloying element and effect of partial crystallization on the corrosion resistance of Fe 73.5Si 13.5B 10Cu 1, Fe 73.5Si 13.5B 7Nb 3Cu 1 and Fe 73.5Si 13.5B 5Nb 5Cu 1 amorphous alloys were studied and the effect of corrosion on magnetization saturation flux density, B s, was investigated. The addition of niobium on amorphous alloys increases the corrosion resistance. The raise of Nb content from 3 to 5% increases the corrosion resistance also. A partial crystallization increases the corrosion resistance of the samples with Nb. However, in the samples without Nb, the partial crystallization diminishes the corrosion resistance. The values of B s depend on the alloy corrosion resistance.

The influence of Nb + and Al + implantation on the oxidation behavior of Ti-60 alloy

The metal vapor vacuum arc (MEVVA) source ion implantation method was used to improve the oxidation resistance of Ti-60 alloy (Ti–5.6 Al–4.8 Sn–2.0 Zr–1.0 Mo–0.85 Nd–0.34 Si). The influence of Al + and Nb + implantation on the isothermal oxidation behavior of Ti-60 alloy was investigated. A detailed investigation of the microstructure, composition and oxidation kinetics of implanted and non-implanted Ti-60 alloy indicated that Nb + implantation deteriorates the oxidation behavior of Ti-60 alloy while the implantation of Nb + and Al + improves its oxidation resistance. The enhanced oxidation resistance in Nb+Al-implanted specimens could be attributed to the presence of protective layers.

Effect of Nb content on the structural and magnetic properties of amorphous Co 21Fe 64− xNb xB 15 alloys

The influence of Nb on nanocrystallization of amorphous Co 21Fe 64− x Nb x B 15 alloys has been studied. Increase in Nb content causes higher disorder in the atomic structure as well as in the spin texture of as-quenched alloys. The first step of crystallization leads to the formation of Fe 3Co phase embedded in residual amorphous matrix. In the second step of crystallization (FeCo) 2B phase is formed. Mössbauer measurements show that Fe 2B phase is not formed in the specimen with x=7, a non-magnetic phase is formed.

The influence of Nb and C on the solidification microstructures of Fe-Ni-Cr alloys

Mill products, such as sheets, usually show obvious anisotropy in their mechanical properties, which greatly affects both their applications and workability. In this study, the orientation-dependent tensile and creep behaviors of Inconel 625 alloy sheets with weak local textures were systematically investigated at 650 °C. The results showed that Inconel 625 superalloy exhibits nearly isotropic tensile properties; however, obvious creep anisotropy appears when loading along different directions. Creep life in the rolling direction (150 ± 5 h) was approximately 4.5 times longer than in the transverse direction (33 ± 1 h). Severe creep anisotropy was found to be determined by two aspects: (i) the change in deformation mechanisms along the rolling direction (a combination of boundary sliding, dislocation slipping, and twinning) and the transverse direction (dislocation slipping). Stronger impingement of slip bands on grain boundaries accelerated intergranular crack initiation and propagation during loading along the transverse direction, which resulted in a short creep life. (ii) The differences in strain compatibility at grain boundaries (i.e., creep loading along the transverse direction resulted in the initial grains forming strong Brass, Cu, and S textures). Creep cracks preferentially nucleated at the junctions between Cu/Brass texture grains, as these interfaces exhibit the worst strain compatibility (Luster–Morris parameter m′ ≤ 0.22). Furthermore, pre-stress aging (PSA) treatment is proposed as an efficient method to suppress creep anisotropy. The discrepancy rate of creep life was found to be reduced by nearly 50% after PSA treatment.

Solidification of Nb-bearing superalloys: Part I. Reaction sequences

The solidification reaction sequences of experimental superalloys containing systematic variations in Fe, Nb, Si, and C were studied using differential thermal analysis (DTA) and microstructural characterization techniques. The reaction sequences responsible for microstructural development were found to be similar to those expected in the Ni-Nb-C ternary system and commercial superalloys of comparable composition. The solute-rich interdendritic liquid generally exhibited two eutectic-type reactions at the terminal stages of solidification: L → (γ+NbC) and L → (γ+Laves). The Ni-base alloys with a high C/Nb ratio represented the only exception to this general solidification sequence. This group of alloys terminated solidification with the L → (γ + NbC) reaction and did not exhibit the γ/Laves constituent. At similar levels of solute elements (Nb, Si, and C), the Fe-base alloys always formed more of the γ/Laves eutectic-type constituent than the corresponding Ni-base alloys. Silicon additions also increased the amount of the γ/Laves constituent that formed in the assolidified microstructure, while C additions promoted formation of γ/NbC. The influence of Nb was dependent on the C content of the alloy. When the C content was low, Nb additions generally promoted formation of γ/Laves, while Nb additions to alloys with high C led to formation of the γ/NbC constituent. The results of this work are combined with quantitative analyses for developing γ-Nb-C pseudoternary solidification diagrams in a companion article.

Nb and the Transformation from Deformed Austenite

The influence of Nb on the transformation behaviour depends on the thermal and mechanical history of the steel. In this paper experiments are described which were performed to study the relation between deformation and transformation behaviour in a typical HSLA steel. It was found that Nb in solution raises the start temperature of transformation but delays the transformation kinetics. Retained strain also raises the start temperature and has a small reducing effect on the temperature range of transformation. The competition of ferrite formation and Widmanstatten formation is influenced by the amount of Nb in solution. More Nb in solution leads to a larger fraction of Widmanstatten ferrite.

Effect of niobium on cast structure of high speed steel

The major objective of the present work is to design a high speed steel composition for tool casting. The effect of replacement of V and W by Nb as a modifier of the structure and properties of cast S 2-9-2 (AISI M7) high speed steel has been investigated with the aid of EDX and WDX attached to the scaning electron microscope. The influences of Nb on eutectic cell size, eutectic volume percentage and eutectic carbide shapes and types were determined. The values of hardnesses of steels under investigation after various heat treatment operations were studied so that the optimum value of substitutional niobium could be determined. The results show that increasing Nb can decrease the volume fraction of eutectic cell size, however the maximum hardness of the heat treated samples can be achieved in the presence of 1.8% of Nb. Das vorrangige Ziel dieser Arbeit besteht darin, eine geeignete chemische Zusammensetzung für einen Werkzeugstahl zu ermitteln. Anstelle der bei Schnellarbeitsstahl häufig verwendeten Elemente V und W wurde hier Nb als eingesetzt. Dessen Wirkung auf Gefügeveränderungen und Eigenschaften des gegossenen Schnellarbeitsstahls S 2-9-2 (AISI M7) wurde mit Hilfe von EDX und WDX am Rasterelektronenmikroskop untersucht. Bestimmt wurden der Einfluß von Niob auf die Größe der eutektische Zelle, Volumenanteile sowie Carbidform und -typen bei der eutektischen Zusammensetzung. In Abhängigkeit von verschiedenen Wärmebehandlungen wurden Härtewerte der untersuchten Stählsorten ermittelt, bis der optimale Substitutionsgehalt an Niob bestimmt war. Die Ergebnisse zeigen, daß mit steigendem Niobgehalt der Volumenanteil der eutektischen Zelle abnimmt; das Härtemaximum der wärmebehandelten Proben ließ sich bei 1.8% Nb ermitteln.

The Influence of Nb and Ti on the Recrystallization of UHP Iron

The influence of Nb and Ti in solid solution on the recrystallization mechanisms and textures of cold rolled high purity iron has been studied by optical metallography, SEM, microtexture (EBSD) and macrotexture (X-ray) measurements. Two UHP iron based alloys (Fe-0.08 wt% Nb and Fe-0.04 wt% Ti) together with two reference samples of UHP Fe and electrolytic iron, were treated to form an equiaxed grain structure then rolled 81 % to develop standard bcc rolling textures. The recrystallization mechanisms were then studied by partial recrystallization anneals in the temperature range 475 -800°C. The orientations of the new recrystallized grain were essentially a mixture of {111} and {100} parallel to the sheet planes. Carbon, Ti and to a lesser extent, Nb favour the nucleation and growth of {111} planes grains along prior grain boundaries.

特集 メカニカルアロイング Ｎｉ３Ｓｉ系金属間化合物の機械的性質と耐硫酸性能に及ぼすＮｂとＢの添加の影響

In order to obtain a good hot workability and excellent corrosion resistance in sulphuricacid solution of Ni3Si intermetallic compounds, a process involving a mechanical alloying(MA) method was investigated. However, it was necessary for practicality to improve ductility at room temperature.This paper reports an investigation to improve ductility of Ni3Si intermetallic compounds at room temperature while maintaining good corrosion resistance. The Influence of Nb and B additions on mechanical properties and sulphuric-acid corrosion resi-stance of these compounds was investigated by MA -hot extrusion -heat treatment method. The results showed that Ni3Si intermetallic compounds with 77.5mol%Ni-20.8mol%Si-1.7 mol%Nb-0.024mol%B composition had high ductility and high corrosion resistance. This compound has more than 4% elongation from tensile test at room temperature. The reason why this compound has high ductility may be due to a high a phase content as well as strengthened grain boundaries, which result from segregated B at the grain boundaries. Moreover, corrosion resistance in sulphuric-acid of less than 0.3mm/year was obtained. This is probably due to an improvment of corrosion resistance in the α- and β- phase in spite of the high α-phase content.

Influence of Nb and N on microstructure and work‐hardening properties of medium manganese Austenitic Steel

AbstractThe form of existance of Nb and N in medium manganese steel and influence of Nb and N on microstuctures and work‐hardening properties have been researched The mechanism of work hardening of austenitic Mn steel has been conducted Experimental results show that when trace Nb and N are added into the steel, they can form carbide, nitride of Nb(Nbc, NbN, Nb(N · C)), and become heterogeneous nuclei of r‐Fe. When addition contents of Nb and N are from 0.15% to 0.25% and 0.03% to 0.05% respectively, grain size can be 6–7 Grade Through ageing treatment, grained and dispersed secondary phases were obtained Nb and N can decrease the stacking faults energy. Under no‐severe impact loading conditions, the structures of Mn 7 is high density dislocation, tangled dislocation, stacking fault and strain‐induced martensite. So that the work hardening of Mn 7 is the combined results of dislocation strengthening and the formation of straininduced martensite.

A Comparative Study on the Influence of Nb and Ti Additions to Different Processed Atomized Nial Powders.

ABSTRACTPrealloyed powders of NiAl, NiAl-5Ti, NiAl-5Nb and NiAl-5Ti-5Nb (at.%) were gas atomized with an average particle size of 90 μm and cooling rates of > 104 K/s. The powders were attritor milled under Ar atmosphere reducing the average particle size to 1.5 μm. Sintering CIP compacts developed microstructure and density distributions, which allowed subsequent containerless HIPing to near full density (>98.5%) and a final grain size < 8 μm. Alloying of NiAl with 5at.% Nb or Ti increased its hardness, Young's modulus, toughness and creep resistance. The room temperature fracture path changed from primarily intergranular (NiAl) to primarily transgranular (Nb, Ti alloyed), increasing the Klc, values from 3.8 to 14.4 and 15.3 MPa√m, respectively. For comparison, HIPed materials from the as-atomized powders were also tested.

Muon diffusion in Nb−H systems

We have studied the muon diffusion in various Nb−HX systems with 0.75 0.9 the muon linewidth as function of temperature has a smooth behaviour and the muon mobility is strongly correlated to the hydrogen diffusion in the beta phase. The activation energy for the μ+ diffusion is 160 meV, which is lower than that for protons. At hydrogen concentrations below 0.9, the muon diffusion behaviour is more complicated, and the influence of Nb−H phase transitions is evident. The implications for the local environment of the muon are discussed.