Effect Of Nb Content Research Articles

Effect of Nb content on microstructure and properties of laser cladding FeNiCoCrTi0.5Nbx high-entropy alloy coating

FeNiCoCrTi0.5Nbx (x = 0.25, 0.50, 0.75, 1.00) high-entropy alloy coatings are prepared by laser cladding. The phase, microstructure, hardness and wear resistance of each coating are analyzed. The results show that each coating has BCC, FCC and Laves phase and the content of Laves phase increases with the increase of Nb content. The microstructure of those coatings are obviously different with the change of Nb content. The top and bottom of each coating are composed of equiaxed crystals and columnar crystals with preferential orientation, respectively. While the middle part of coatings shows different forms of dendrites, equiaxed cellular dendrites and short strips structure. The hardness of each FeNiCoCrTi0.5Nbx coating is much higher than that of the substrate. FeNiCoCrTi0.5Nb0.5 coating has the highest average hardness of 766.62 HV. Furthermore, the highest hardness measured of FeNiCoCrTi0.5Nb0.5 coating reaches up to 852.5 HV, which is about 2.9 times the hardness of the matrix. Each FeNiCoCrTi0.5Nbx coating produces abrasive wear. The worn surface of FeNiCoCrTi0.5Nb0.5 coating is smoother, the degree of wear is lower and the corresponding wear rate is the lowest. The FeNiCoCrTi0.5Nb0.5 coating has the highest hardness and the best wear resistance.

Effects of Nb Content on the Mechanical Alloying Behavior and Sintered Microstructure of Mo-Nb-Si-B Alloys

Different from conventional Mo-Si-B-based alloys consisting of Moss, Mo3Si, and Mo5SiB2, Mo3Si-free Mo-Si-B-based alloys (Moss+Mo5Si3+Mo5SiB2 or Moss+Mo5SiB2) show great potentials for more excellent oxidation resistance and elevated temperature strength. In the present work, alloying element Nb was added to Mo-12Si-10B (at.%)-based alloy to suppress the formation of the Mo3Si phase. Mo-12Si-10B-xNb (x = 10, 20, 22, 24, 26, 28, 30, and 40) bulk alloys were fabricated using mechanical alloying followed by cold pressing and then sintering at 1773 K for 2 h. Effects of Nb content on the mechanical alloying behavior and then sintered microstructure were studied. The addition of Nb with an amount less than 30 at.% accelerated the mechanical alloying process, but 40 at.% Nb addition decreased the process due to excessive cold welding and high powder volume. For the sintered bulk alloy prepared from the mechanically alloyed powders milled for 30 h, a critical Nb content between 24 and 26 at.% was found to suppress Mo3Si production and γNb5Si3 phase formed in the alloys with the addition of Nb content more than 26 at.%. Prolongation of a prior milling process could facilitate the suppression of Mo3Si and delay the formation of niobium silicides.

Effect of Nb additions on microstructure and properties of γ-TiAl based alloys fabricated by selective laser melting

Abstract The γ-TiAl based Ti–Al–Mn–Nb alloys with different Nb additions were fabricated by selective laser melting (SLM) on the TC4 substrate. The effects of Nb content on microstructure and properties of the alloys were investigated. The results reveal that the alloys consist of γ-TiAl phase with tetragonal lattice structure and α2-Ti3Al phase with hcp lattice structure, and show a sequential structure change from near full dendrite to near lamellar structure with the increase of Nb addition. Owing to the higher Nb content in γ-TiAl phase and the formation of near lamellar structure, the alloy with 7.0 at.% Nb addition has the best combination of properties among the studied alloys, namely, not only a high hardness of HV 2000, a high strength of 1390 MPa and a plastic deformation of about 24.5%, but also good tribological properties and high-temperature oxidation resistance.

The effect of Nb content on precipitates, microstructure and texture of grain oriented silicon steel

Abstract Niobium has the potential as an inhibitor forming element in grain oriented silicon steel. The grain oriented silicon steels with different Nb contents (0.028 wt% and 0.052 wt%) were prepared, and the effect of Nb content on the evolution of precipitates, microstructure and texture were investigated by the various analysis methods and thermodynamic calculations. The results show that the smaller size and larger number density of precipitates were obtained in the sample with low Nb steel after hot rolling. In the process of normalization, Nb(C, N) are more inclined to precipitate along the dislocations caused by hot rolling, contributing to finer and more dispersed precipitates in normalized bands. The finer and more dispersed precipitates in 0.028% Nb containing silicon steel perform a stronger pinning force during whole heat treatment processes, resulting in the smaller grain size and higher intensity of Goss texture in the specimen containing 0.028%Nb. After normalization, the intensities of Goss texture in both steels decrease.

Microstructure, phase composition and mechanical properties of new, low cost Ti-Mn-Nb alloys for biomedical applications

A group of new Ti-7Mn-xNb alloys with Nb contents varying from 0 to 10 wt% were fabricated by conventional press and sinter powder metallurgy processing from blended elemental powders. The effect of Nb content on the sintering and phase stability as well as microstructure and mechanical characteristics of the alloys was investigated. Microstructural studies and phase analysis showed a two-phase microstructure composed of α and β phases in all alloys. However, addition of Nb up to 10 wt% enhanced the stability of the β phase hindering the transformation to α during furnace cooling and increasing the proportion of retained β. Sintering and densification of the Ti-7Mn-xNb alloys was enhanced by the fast diffusing Mn and negatively impacted by the slow diffusing Nb due to the reliance of solid sintering processes on diffusion. Nonetheless, the relative densities of the Ti-7Mn-xNb alloys with up to 10 wt% Nb were higher than that of the sintered CP-Ti. The compressive strength and hardness of the alloys varied in the range of (1842–2127 MPa) and (341–375 Hv) respectively. It was also observed that with increasing Nb contents, the elastic modulus decreased, while compressive strain increased due to stabilisation of a greater proportion of the β phase. The results showed that the low-cost Ti-7Mn-xNb alloys possess superior properties to those of CP-Ti and a number of other Ti based alloys developed for biomedical implant applications.

Characterization of Ti-xNb (x = 25 – 35) Alloys in as Melt and Annealed States

The effect of Nb content on microstructure, mechanical properties and phase formation in as-melt and annealed binary Ti-Nb alloys were investigated using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analysis. The content of Nb varied in the range 25-35 mass % leading to significant changes in the microstructure. The annealed and furnace-cooled binary Ti-Nb samples exhibited HCP martensitic α` phase at a Nb content below 27.5 mass % and metastable BCC β phase at higher contents of Nb. The mechanical properties of alloys depended strongly on the Nb content and type of the dominating phase.

High-throughput fabrication of nickel-based alloys with different Nb contents via a dual-feed additive manufacturing system: Effect of Nb content on microstructural and mechanical properties

Laves phase segregation is a universal phenomenon in additive manufactured or as-cast Inconel 718 alloy, and the Laves phase usually degrades the mechanical properties of the matrix. In this work, nickel-based alloys designed with different Nb contents were successfully fabricated by laser metal deposition (LMD) via a dual-feed system, and the Laves phase distribution at the macro level was relatively uniform. The effects of Nb content on the microstructure, mechanical properties and surface potential of the as-received and heat-treated nickel-based alloys were investigated. The grain size of the as-received LMD nickel-based alloys decreased with the Nb content, and the Laves phase exhibited a universally higher nano-hardness but lower surface potential than the γ matrix. The nano-hardness of the Laves phase linearly increased, whereas the Volta potential decreased with the Nb content. The strength improvement for the as-received LMD nickel-based alloys with different Nb contents was equally attributed to grain refinement and enhancement of the Laves phase (both hardness and content), while the increase in the precipitate content (main γ″) as a function of Nb content contributed to the substantial improvement in hardness for the heat-treated LMD nickel-based alloys and the grain refinement strengthening effect was comparative minor after aging treatment.

Effect of Nb Content in the Microstructural and Thermal Characteristics of NiTiNb Shape Memory Alloys

The influence of Nb content variation on the microstructural and thermal characteristics of NiTiNb alloys was evaluated since these aspects are relevant to the control and adequacy of its shape memory properties for application purposes. The aim of this study was to observe how the Nb content acts in the formation of Nb-rich precipitates and the eutectic structures, which can make this alloys more complex. Microstructural characterization of the alloys was performed by X-ray diffraction (XRD), scanning electron microscopy (SEM) and microanalysis by energy-dispersive X-ray spectroscopy (EDS), besides the thermal characterization by differential scanning calorimetry (DSC), and the comparison between the Nb alloys and the NiTi binary alloy. The results demonstrated a proportional dependence between the amount of β-Nb phase in the microstructures and the amount of Nb dissolved in the NiTi matrix with the Nb content. Although it was found that the increase in the Nb content causes the decrease of the martensitic (Mi) and reverse (Ai) transformation temperatures, the magnitude of thermal hysteresis was not significantly changed.

Effect of Nb content on corrosion behavior of Ti-based bulk metallic glass composites in different solutions

The effect of Nb content on the corrosion behavior of in-situ (Ti0.45Zr0.31Be0.17Cu0.07)100−xNbx (x = 4, 6, 8, 10, and 12) was evaluated in 0.5 mol/L H2SO4, 0.6 mol/L NaCl, and 1 mol/L NaOH solutions. A dual-phase microstructure which composed of an amorphous matrix and dendrites was observed. Electrochemical measurements in each corrosion medium showed the same trend. The corrosion resistance first increased and then decreased with the addition of Nb content from 4 to 12 at.%. The results show the best corrosion resistance in terms of × = 8 for the alloys. Notably, Nb addition improved the pitting-corrosion resistance of samples in a chloride-containing solution, whereas spontaneous passivation occurred in chloride-free solutions. A preferential solution was observed in the amorphous matrix region in NaCl solution, but a part of dark spots and dents appeared on the surface after the polarization in chloride-free solutions. X-ray photoelectron spectroscopic measurements showed that Nb addition promoted the formation of metal oxide on the surface film, thus inducing a superior corrosion resistance for the bulk metallic glass matrix composites.

Effect of Nb content on the evolution of β-Zr and Mo2Zr phase in Zr-Nb-Mo alloy during high energy ball milling and annealing

A Zr based alloy has been developed with a β phase (BCC) dominated microstructure by adding Nb and Mo as alloying elements. Effect of Nb has been highlighted throughout the study due to its effectiveness on volume fraction of β-Zr and Mo2Zr as well as on transformation temperature. It has been found that increment of Nb concentration enhances the β-phase volume fraction through the reduction of α→β transformation temperature. Detail TEM analyses elucidates the above explanation.

Effect of Nb Solute Concentration on Crystallite Size Refinement and Strength Enhancement in Mechanically Alloyed Cu-Nb Alloys

Cu-Nb alloys with a Nb concentration range of 0 wt%∼30 wt% were prepared by mechanical alloying (MA) at room temperature. The effects of Nb content on the crystalline refinement process and mechanical properties of the immiscible Cu-Nb system were investigated by X-ray diffraction (XRD), optical microscopy (OM), scanning electron microscopy (SEM) with energy-dispersive X-ray detection (EDX), transmission electron microscopy (TEM) and microhardness measurement. Results show that the completed dissolution of Nb in Cu can be achieved in the samples with Nb content less than ∼11 wt% after 100 h milling, although the equilibrium solubility level is nearly zero. The grain size refinement capability of MA-ed Cu-Nb powder is enhanced with increasing Nb content up to 30 wt%. This is because the susceptibility to recovery process becomes reduced, when the amount of Nb solutes segregated into the dislocation of Cu phase is increased. Cu-30wt%Nb powder milled for 100 h, the average Cu grain size is only ∼6 nm. The microhardness of the samples shows an enhancement with increasing Nb concentration. The main strengthening mechanisms of the MA-ed Cu-Nb alloys are linked to the grain size reduction and the dissolution of Nb into Cu matrix.

Study of martensitic transformation in TiNiCuNb shape memory alloys using dynamic mechanical analysis

In present work, effect of Nb content on martensitic transformation and damping behavior of (Ti50Ni38Cu12)100-xNbx (x = 0, 5, 10, 15at.%) shape memory alloys was investigated by means of X-ray diffraction, differential scanning calorimetry and dynamic mechanical analysis. As a result, the transformation sequence of TiNiCuNb alloys is found to be B2→B19→B19′ upon cooling. Two different damping peaks are observed, one is related to B2→B19 transformation and the other one is related to the overlapping of twin relaxation-type and B19→B19′ transformation. With increasing Nb content to 15 at.%, the peak value of damping capacity of B2→B19 transformation slightly decreases.

Comparison of Mechanical Properties and Microstructure of Annealed and Quenched Ti-Nb Alloys

The effect of Nb content on microstructure, mechanical properties and phase formation in annealed and quenched binary Ti-Nb alloys were investigated using scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDX) and X-ray diffraction (XRD) analysis. The content of Nb varied in the range 0-37 mass % leading to significant changes in the microstructure. The annealed and furnace-cooled binary Ti-Nb samples exhibited HCP martensitic α` phase at a Nb content below 14 mass % and stable BCC β phase at higher contents of Nb. The structure of the quenched samples changed with increase of Nb content in the following order: coarse primary martensite → fine acicular (α`+α``) martensite → single β phase structure. The mechanical properties of alloys strongly depended on the Nb content and type of the dominating phase.

Effect of Nb content on the microstructure and corrosion resistance of the sputtered Cr-Nb-N coatings

Thin Cr-Nb-N films with Nb content ranging from 5.1 to 19.5 at.% were prepared onto the AISI 440C substrates by reactive magnetron sputtering of the Cr and Nb in Ar-N2 gas mixture. The effects of the Nb content on the microstructure and the corrosion behavior in 3.5 wt% NaCl solution were investigated. All the deposited films showed a typical surface feature of granular structure. The Cr-Nb-N films with 5.1 at.% and 10.9 at.% Nb showed a duplex layers consisting of a dense and coherent layer near film-substrate interface, followed by a columnar layer differed from the uniform columnar structure for pure CrN. While for Cr-Nb-N films with higher Nb content, there was no obvious dense layer but a columnar structure. The low Nb content Cr-Nb-N coated samples showed a positive shift of both corrosion potential and the pitting potential compared to the pure CrN coated sample while the pitting potential decreased for high Nb content Cr-Nb-N coated samples. The Cr-Nb-N film with Nb content of 10.9 at.% possesses the best corrosion resistance due to the high polarization resistance resulted from the modification of the microstructure by the Nb incorporation.

Effects of Nb Content on the Ferroelectric and Dielectric Properties of Nb/Nd-Co-doped Bi4Ti3O12 Thin Films

Nd/Nb-co-substituted Bi3.15Nd0.85Ti3−x Nb x O12 (BNTN x , x = 0.01, 0.03, 0.05 and 0.07) thin films were grown on Pt/Ti/SiO2/Si (100) substrates by chemical solution deposition. The effects of Nb content on the micro-structural, dielectric, ferroelectric, leakage current and capacitive properties of the BNTN x thin films were investigated. A low-concentration substitution with Nb ions in BNTN x can greatly enhance its remanent polarization (2P r) and reduce the coercive field (2E c) compared with those of Bi4Ti3O12 (BIT) thin film. The highest 2P r (71.4 μC/cm2) was observed in the BNTN0.03 thin film when the 2E c was 202 kV/cm. Leakage currents of all the films were on the order of 10−6 to 10−5 A/cm2, and the BNTN0.03 thin film has a minimum leakage current (2.1 × 10−6 A/cm2) under the high electric field (267 kV/cm). Besides, the C–V curve of the BNTN0.03 thin film is the most symmetrical, and the maximum tunability (21.0%) was also observed in this film. The BNTN0.03 thin film shows the largest dielectric constant and the lowest dielectric loss and its maximum Curie temperature is 410 ± 5°C.

Effects of Surface Tension Driven Convection Upon Crystal Growth of KTa1‐xNbxO3

AbstractThe surface tension driven convection, together with the rotating crystal growth process of potassium tantalate niobate (KTa1‐xNbxO3, KTN) crystals from unstirred melt has been carried out in a high temperature in‐situ observation system. The streamline of the stable convection is found to be in the form of a double loop axially symmetric vortices, which causes the rotation during KTN crystals growth process. The effect of surface tension convection on interfacial heat, mass and momentum transfer are investigated experimentally. The dimensionless parameters of the three transports are calculated. For KTN crystals, velocity and temperature boundary layers are pointless. Solute transfer is the main form of interface transport during crystal growth process. The effect of Nb content x on boundary layer thickness is discussed. There is a critical Marangoni Number . When , the concentration boundary layer becomes thinner with the increase of x as a result of weakened segregation effect. When , a thicker boundary layer emerges due to slower growth velocity under higher Nb contents. When , the influence of the two is comparable and the boundary layer can maintain a relatively steady value under different components.

Contribution of Nb towards enhancement of glass forming ability and plasticity of Ni-Nb binary metallic glass

In this present study, effect of Nb content on glass forming ability and plasticity of Ni-Nb metallic glass has been investigated using molecular dynamics simulation with embedded atom method (EAM). Ni-Nb metallic glass specimens having different atomic percentages of Nb content (i.e. ~15, 20, 25, 30, 38, 40.5, 45 and 50at.%) are prepared by fast cooling process (cooling rate~1012Ks−1) from their liquid phase. It is observed that increase in Nb content up till 38at.% causes improvement of glass forming ability of Ni-Nb binary system. On further increment of Nb content, glass forming ability is found to be slightly reduced or remain almost same. Voronoi cluster analysis has been performed to evaluate the variation in short range ordering with increasing Nb content in Ni-Nb glass. Simulated tensile tests are also performed, and it reveals that higher Nb content actually helps in augmentation of the plastic behavior of the Ni-Nb metallic glass.

Effects of Nb content in Ti–Ni–Nb brazing alloys on the microstructure and mechanical properties of Ti–22Al–25Nb alloy brazed joints

Vacuum brazing was successfully used to join Ti–22Al–25Nb alloy using Ti–Ni–Nb brazing alloys prepared by arc-melting. The influence of Nb content in the Ti–Ni–Nb brazing alloys on the interfacial microstructure and mechanical properties of the brazed joints was investigated. The results showed that the interfacial microstructure of brazed joint consisted of B2, O, τ3, and Ti2Ni phase, while the width of brazing seams varied at different Nb contents. The room temperature shear strength reached 359MPa when the joints were brazed with eutectic Ti40Ni40Nb20 alloy at 1180°C for 20min, and it was 321, 308 and 256MPa at 500, 650 and 800°C, respectively. Cracks primarily initiated and propagated in τ3 compounds, and partially traversed B2+O region. Moreover, the fracture surface displayed typical ductile dimples when cracks propagated through B2+O region, which was favorable for the mechanical properties of the brazed joint.

The effect of Nb on texture evolutions of the ultrafine-grained dual-phase steels fabricated by cold rolling and intercritical annealing

Dual phase (DP) steels with different amounts of Nb were produced by utilizing cold rolling and intercritical annealing of a ferrite-martensite duplex starting structure. The effects of Nb contents (0.00, 0.06, 0.12 and 0.18 wt%) on microstructure and texture evolutions were studied. Addition of Nb promoted formation of ultra-fine grained structures with the ferrite grain size of about ∼1 μm and uniformly-dispersed martensite particles. The results showed increasing the fraction of the high angle grain boundaries and formation of {111} fiber components in the microstructures with increasing Nb content. In addition, the texture power was decreased with the addition of Nb, resulting in random texture components.

Effect of Nb microalloying on the heat affected zone microstructure of girth welded joints

The effect of Nb content in the range 0.07–0.10% on the HAZ microstructure of large diameter pipes is reported in this paper. Results show that Nb is able to influence the size of the bainitic packet and cells in the heat affected zone, i.e. the microstructural parameters affecting impact toughness and hardness behavior. Such an effect leads to an improvement of both toughness and hardness for the steel with higher Nb content.