Effect Of Nb Content Research Articles

Microstructure and wear properties of Fe–6wt.%Cr–0.55wt.%C–Xwt.%Nb laser cladding coating and the mechanism analysis

Ultra-high performance FeCrC laser cladding coatings with different Nb contents were designed. The effect of Nb content on the microstructure and properties of the coating was researched and the corresponding influence mechanism was analyzed. The microstructure of the coating consists of martensite matrix and MC carbide. With Nb content increases form 0wt.% to 0.71wt.%, the martensite matrix is refined and the amount of MC carbide is increased, so the hardness, strength and wear resistance of the coating improve gradually. When the Nb content is 0.71wt.%, all of the properties are the excellent, in which, the hardness is 620HV, the tensile strength and yield strength are 1588MPa and 1344MPa, respectively, the abrasive wear weight loss is 0.15g/h and the COF of adhesive wear is 0.52. The lattice misfit between (110)NbC//(100)α-Fe is 10.3%, which indicates that NbC act as the heterogeneous nucleus of α-Fe is medium effective. With the increase of the Nb content, the precipitation temperature and precipitation amount of MC carbide both increase, when the Nb content is 1.03wt.%, they are 1072°C and 0.97wt.%, respectively.

Enhancement of relaxor properties by Nb doping in Ba0.8Sr0.12Ca0.08TiO3 lead-free ferroelectric ceramics

Niobium-doped barium strontium calcium titanate (BSCTN) ceramics were prepared using a conventional solid-state reaction method. The effects of Nb contents on crystal structure, microstructure, dielectric properties and ferroelectric relaxor behavior of the BSCTN ceramics were investigated. The BSCTN ceramics showed dense microstructures with uniform crystal grains with Nb doping. It was demonstrated that Nb5+ entered the B-site of the perovskite BSCTN ceramic and substituted for Ti4+, which caused the expansion and distortion of crystal lattice of the tetragonal BSCTN ceramic. Doping of Nb resulted in more diffused phase transition and lower Curie temperature of the BSCTN ceramics. The diffuseness degree indicator γ increased until the addition of Nb dopant exceeded 1.5mol% where a maximum γ of 1.98 was achieved. Among the compositions assayed in this work, the BSCTN ceramics with Nb contents of approximately 1.0–1.5mol% yielded promising relaxor properties that made them alternative sources for development of environmental friendly lead-free relaxor ferroelectric materials.

ωo phase precipitation in annealed high Nb containing TiAl alloys

The ordered ω phases in high Nb containing TiAl (Nb-TiAl) alloys have been garnering increasing attention in the recent years. However, the investigations on the Nb dependence on the ωo precipitation are scarce. In this study, the effect of Nb content on the ωo precipitation in high Nb (6–10 at%) containing TiAl alloys after long-time annealing at 850°C has been studied. The results show that small ordered ω particles in the retained βo phase cannot be discerned under scanning electron microscope (SEM) but can be observed using transmission electron microscopy (TEM). Although the Nb segregation can be eliminated after the homogenization heat treatment, the ωo phase precipitated in all the alloys studied after annealing at 850°C. TEM examination reveals that the orientation relationship between the ωo and α2 phases can be derived as: [0001]ωo//[112̄0]α2; (112̄0)ωo//(0001)α2, which indicates that the ωo phase is directly transformed from the parent α2 phase. Small γ particles are also observed within the ωo areas. The α2→ωo+γ decomposition process is expected during annealing. It is concluded that ωo phase is an equilibrium phase in high Nb-TiAl alloys at 850°C.

Effect of Nb Content on the Impact Toughness of Coarse-Grained Heat-Affected Zone of Pipeline Steels under Large Heat Input

The effect of large heat inputs (200 kJ/cm) on the microstructures and toughness of heat-affected zone of Nb microalloyed X70 pipeline steels were simulated utilizing Gleeble-3800. The microstructures were observed by optical microscope, scanning electron microscope and electron backscattered diffraction technique. Results showed that when the large heat input welding was applied, big austenite grains and coarse microstructures were formed in the coarse-grained heat-affected zone, and thus the toughness of the coarse-grained heat-affected zone was seriously reduced. With the increase of Nb content, the toughness of the CGHAZ did not change remarkably under the large heat input welding.

Optimization of thermal stability and soft-magnetic properties of FeSiBPCuNb alloys by Nb content tuning

The effects of Nb content on the thermal stability, microstructural evolution and soft-magnetic properties of nanocrystalline Fe83−xSi4B10P2Cu1Nbx alloys were systematically investigated. Appropriate Nb addition was found to be effective both in prolonging operative annealing time and annealing temperature range and in improving magnetic softness by tuning the size and distribution of nano-sized α-Fe inclusions. The effective annealing time of 30min over temperature range of 723–793K, in combination with desirable soft-magnetic properties including high saturation magnetic flux density (Bs) of 1.73T, low coercivity (Hc) of 4.5A/m and high effective permeability (μe) of 23,000 at 1kHz, entitles Nb-containing Fe82Si4B10P2Cu1Nb1 nanocrystalline alloy a truly industrial advantage in energy-economic efficiency and great potentials in electromagnetic applications.

The effects of Nb content on microstructure and fracture behavior of near α titanium alloys

Abstract The microstructure and fracture behavior of as-cast Ti-1100 alloys with different contents of Nb were systematically investigated. The results demonstrate that the Nb element added to titanium alloys changes the lattice parameters of α phase. Microstructural observations indicate an obvious reduction in the prior β grain size, α-laths spacing, as well as the thickness of β phase, with the increase of Nb content. It is also observed that Nb addition promotes the formation of ternary (TiZr)6Si3 (S2 type) silicides. The fracture toughness KIC of the alloy increases with increasing content of Nb element, which is primarily attributed to the improved propensity for crack-tip tortuousity caused by the fracture behaviors of the α/β colonies. The fracture morphologies of these alloys reveal cleavage fracture mode.

Effect of Nb content and heat treatment temperature on superelastic properties of Ti–24Zr–(8–12)Nb–2Sn alloys

The effects of Nb content and heat treatment temperature on the superelastic properties of Ti–24Zr–(8–12)Nb–2Sn alloys, developed for potential biomedical applications, were investigated by tensile testing . The Ti–24Zr–10Nb–2Sn alloy exhibited excellent superelastic properties: its superelastic recovery strain increased with increasing heat treatment temperature and reached 7%, which is twice that of other Ni-free Ti-base superelastic alloys. This was explained by the evolution of the strong {0 0 1}〈1 1 0〉 recrystallization texture.

Relationship between Nb concentration and stability of α, ω, β phases in Ti–Nb alloys

The effect of Nb content on the lattice parameters and relative stability of α, β and ω phases in Ti1–xNbx (0<x≤0·30) alloys was investigated using the exact muffin-tin orbitals method in combination with the coherent potential approximation. For ω phase, the value of a increases and c/a decreases almost linearly with increasing Nb concentration. Whereas in the case of α phase, the lattice constant a and the value of c/a increase with the increasing Nb content. The critical Nb concentration for the complete stabilisation of β phase at 0 K is 26 at-%. An approximate composition range in which the ω phase exist is between 17 and 26 at-%Nb. The Nb addition enhances the stability of β phase relative to ω and α.

The Effect of Nb Content on the Thermal, Structural, and Magnetic Properties of FeNbB Ribbons

Amorphous Fe80−xNbxB20 (x = 5, 10, 15) ribbons were prepared by single-roller melt spinning method. The thermal, structural and magnetic properties of Fe80−xNbxB20 (x = 5, 10, 15) ribbons were investigated using di erential thermal analysis, X-ray di raction, and vibrating sample magnetometer. The thermal stability is the lowest for Fe70Nb10B20 ribbon and the highest for Fe65Nb15B20 ribbon. Along with the increase of Nb content, the supercooled liquid region ∆Tx increases, indicating that the amorphous formation ability improves. The primary stages of crystallization of the three ribbons are di erent. The primary devitri cation phases are Fe23B6 type for Fe70Nb10B20 and Fe75Nb5B20 ribbons, and α-Fe type for Fe65Nb15B20 ribbon. Fe80−xNbxB20 (x = 5, 10) ribbons are ferromagnetic and the Fe65Nb15B20 ribbon is paramagnetic. The saturation magnetization (M s) decreases with increasing Nb content.

Composition-Dependent Collapse of β {111} Planes Leading to ω Precipitation in Ti-Nb Alloys: A First-Principles Study

The effects of Nb content on the collapse of β {111} planes leading to ω phase precipitation were investigated in binary Ti-Nb alloys by first-principles exact muffin-tin orbitals-coherent potential approximation (EMTO-CPA) method. In accordance with the accepted mechanism of the beta to omega transformation occurring due to the collapse of the bcc {111} planes, the total energies of β Ti-Nb binary alloys containing multiple states corresponding to different Nb concentration ranging from 20at.% to 30at.% were calculated. The results indicated that the total energies for the same Nb content are not monotonically decreasing with the z (z denotes the degree of collapse of β {111} planes) value increasing, but keeping an energy barrier to cross. The energy barrier increases gradually along with increasing Nb content. The density of states (DOS) was given to elucidate the changes of electronic structure during the collapse of β {111} planes.

Effect of Nb Content on Microstructure and Properties of Microalloyed Rephosphorized Steel

The effects of Nb content on the microstructure and properties of microalloyed rephosphorized steel sheet are investigated by analyzing its microstructure and properties of as hot-rolled and as annealed. The results show that proper coiling temperature for full precipitation increases as Nb content increases. Mechanical properties varies as the annealing temperature increases because of precipitation coarsening behavior, it is bad for mechanical properties stability.

MAGNETIC AND STRUCTURAL TRANSITION PROPERTIES OF NIOBIUM-DOPED BiFeO3 THIN FILMS

Niobium-substituted BiFeO 3( BiFe 1-x Nb x O 3 BFNO ) thin films were successfully deposited on Pt(111)/Ti/SiO2/Si(100) substrates by spin coating with a sol–gel technology and rapid thermal annealing. The effects of Nb content (x = 0~0.08) on the microstructure, magnetic and multiferroic properties of thin films were investigated. The result of X-ray diffraction analysis shows that the BFNO thin films have rhombohedral (R3c) to tetragonal (P4mm) phase transition at x = 0.06. The Nb doping in the B-site of BiFeO 3 could induce the appearance of the spontaneous magnetization and polarization by the phase transition of rhombohedral-to-tetragonal. The BFNO thin films with x = 0.06 exhibits the maximum remanent magnetization (2Mr) of 5.2 emu/g.

Effect of Nb content on hydrothermal stability of a novel ethylene-bridged silsesquioxane molecular sieving membrane for H2/CO2 separation

Abstract Silica-based microporous membranes for the separation of gases with relatively small kinetic diameters, like hydrogen, carbon dioxide, nitrogen and oxygen under harsh industrial processes, will offer great potential for integration in CO2 capture technologies. Development of membranes with integrated performances of permeability, selectivity and stability in the presence of hot vapor, is one of the prerequisites for their successful implementation. Herein, we reported a novel microporous hybrid silica membrane, fabricated through sol–gel deposition of an ethylene-bridged silsesquioxane layer on a multilayer porous support, by adjusting the amount of niobium alkoxide precursor. When the Nb content was less than 50% (in mole), both hybrid siliceous microporous networks and generated Lewis acid sites imparted very low CO2 permeance to the membrane while retaining its comparatively high H2 permeance. Dominant densification shall take effect when Nb content was higher than 50%, which leads to both low H2 permeance and H2/CO2 permselectivity. Hybrid silica membranes with niobium loading amount of 17% and 33% respectively, showed excellent stabilities in the presence of 150 kPa steam under 200 °C, as evidenced by steady H2 permeances and exceptionally high H2/CO2 permselectivities (>700) during long-term stability test up to 300 h, which demonstrating a promising CO2 separation membrane.

Effect of Nb content on deformation behavior and shape memory properties of Ti–Nb alloys

Abstract Deformation behavior and shape memory properties of Ti–(20, 23) at.% Nb alloys in a single α″ martensite state were investigated. The Ti–20Nb alloy exhibited a higher stress for the reorientation of martensite variants when compared with the Ti–23Nb alloy. The recovery strain due to the shape memory effect in the Ti–20Nb alloy was smaller than that in the Ti–23Nb alloy. Transmission electron microscope (TEM) observation revealed that the reorientation of martensite variants occurred by the deformation of {1 1 1} type I and 〈2 1 1〉 type II twins. The Nb content dependence of the deformation behavior and shape memory properties was discussed considering the magnitude of twinning shear of the twins.

Microstructure, corrosion behavior and cytotoxicity of Zr–Nb alloys for biomedical application

In this work, the effects of Nb content on microstructure and corrosion behaviors of biomedical Zr–Nb alloys were systematically studied. The results of XRD analysis and optical microscopy indicated that the experimental Zr–Nb alloys had a duplex structure of α and β phases, and the content of β phase increased with the increase of Nb content. The electrochemical impedance spectroscopy (EIS) studies showed an improvement on the resistance of the spontaneous oxide film with increasing Nb content. The EIS data, fitted by Rs(QpRp) model, suggested a single passive film formed on the experimental material surfaces. Polarization tests in Hank's solution revealed a nobler electrochemical behavior of the Zr–Nb alloys after alloying Nb to pure Zr. The corrosion resistance increased with increasing Nb content, as indicated by lower corrosion current densities and passive current densities and higher pitting potentials. The major components on the surfaces of the corroded Zr–Nb alloy samples detected by XPS were ZrO2 and Nb2O5. The biocompatibility of Zr–Nb alloys was primarily evaluated by culturing L-929 cells in the extraction media of Zr–Nb alloy samples and excellent results were obtained. All of these above results suggested that the Zr–22Nb alloy, among the experimental alloys, showed a promising potential for biomedical applications.

FeNiPBNb bulk glassy alloys with good soft-magnetic properties

The effects of Nb content on glass-forming ability (GFA) and soft-magnetic properties of (Fe0.39Ni0.39B0.16P0.06)100−xNbx (x=0, 1, 1.5, 2, 2.5, 3 and 4) glassy alloys were investigated. By adjusting the Nb content, the GFA and soft-magnetic properties are effectively improved. Bulk glassy alloys with diameters up to 2.5mm were synthesized. The FeNi-based glassy alloys exhibit excellent soft-magnetic properties i.e., low coercivity of 1–1.8A/m and high saturation magnetization of 0.66–0.85T. The [(Fe0.5Ni0.5)0.78B0.16P0.06]97.5Nb2.5 glassy alloy also exhibits high effective permeability of 25,700 with excellent frequency stability. In addition to high GFA and good soft-magnetic properties, the alloy shows a constant differential permeability of about 17,700G/Oe and high fracture strength of 3150MPa.

Microstructure and Magnetic Anisotropy of FeCoNbB Films

Effect of Nb contents on microstructure and magnetic properties of FeCoNbB films has been studied. X-ray diffraction (XRD) analysis reveals that Nb plays a role in refining grain and in facilitating formation of amorphous structure. When Nb content is more than 8 at%, the films transform from crystalline to amorphous structure, accompanied by variations in magnetic properties. An unusual out-of-plane anisotropy component is consequently observed. It can be suggested that the anisotropy induced by increasing Nb contents be attributed to stress-related magnetoelastic anisotropy. The undesirable anisotropy is greatly reduced by thermal annealing, reducing film thicknesses or applying an external magnetic field together with Si addition.

Cold workability and shape memory properties of novel Ti–Ni–Hf–Nb high-temperature shape memory alloys

The effect of Nb content on the cold workability, microstructure and shape memory properties of Ti–Ni–Hf–Nb alloys is investigated. The addition of Nb to Ti–Ni–Hf improves the cold workability due to the formation of a soft Nb-rich phase. The Ti–Ni–Hf–Nb alloys exhibit a high-temperature shape memory effect during heating and cooling cycles under various stress levels. As the Nb content increases, the shape memory properties of the Ti–Ni–Hf–Nb alloys become more stable although the shape recovery strain decreases.

Effect of Nb content on the microstructures and mechanical properties of Zr–Ti–Cu–Be–Nb glass-forming alloys

(Zr 35Ti 30Be 27.5Cu 7.5) 100− x Nb x ( x = 0, 5, 8, 10, 12, 15 at.%) glass-forming alloys were prepared by copper-mould suction casting. The alloys with different Nb contents exhibited different microstructures and mechanical properties. The proper addition of Nb ( x = 5, 8 at.%) to the Zr–Ti–Be–Cu system could ensure the formation of mostly amorphous phase. And excessive amount of Nb favored the formation of the bcc β-Zr solid solution. The alloys with Nb contents of 8 at.%, 10 at.%, and 12 at.% displayed the distinguished plasticity of 11.1%, 7.6%, and 11.0%, respectively.

Effect of Nb Content on Hot Flow Stress, Dynamic Recrystallization and Strain Accumulation Behaviors in Low Carbon Bainitic Steel

Compressive deformation behaviors of low carbon steels with different Nb contents were investigated in the temperature range 900oC to 1100oC and strain rates from 0.05s-1 to 2s-1 by single pass deformation. Multi-pass compressive deformation processes were also carried out to examine strain accumulation under different Nb contents. In single pass deformations, dynamic recrystallization (DRX) can be observed in the case of low strain rate and high temperature, and the higher Nb steel exhibits higher deformation activation energy (Qdef) and critical strain value (εc) for the onset of DRX. However during multi-pass compression process (interval time of 3-4s), the higher Nb steel has larger strain accumulation between passes, so it is easier for high Nb steel that DRX happens during hot strip rolling process, which starts at relative high rolling temperature.