Increasing Nb Content Research Articles

Failure Analysis of a Chromium Plating Layer on a Piston Rod Surface and the Study of Ni-Based Composite Coating with Nb Addition by Laser Cladding

The failure of a chromium plating layer on the surface of a piston rod was analyzed, and an Ni-based alloy mixed with a niobium (Nb) composite coating was investigated by means of stereomicroscopy, metallographic microscopy, scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD), Vickers hardness testing, and wear testing. The results show that penetrating cracks were present in the chromium layer. Subsequently, the corrosion intensified, resulting in the bubbling, cracking, and peeling of the chromium layer. The cladding layer presented a structure morphology of planar crystalline at the bottom, dendritic at the middle, and equiaxial crystalline at the top. The solidification parameters, which were derived from simulation results, confirmed that the ratios between temperature gradient (G) and solidification speed (S) decreased, and the values of the cooling speeds increased from the bottom to the top of the cladding layer. With an increase in Nb content, the structure became gradually refined and uniformly dense. The cladding layer of the Ni-based alloy mixed with Nb was mainly composed of γ-Ni, Cr23C6, Cr7C3, NbC, and Ni3Nb. NbC could be formed in situ and presented itself in four forms: particles, dendrites, polyhedrals, and networks. The microhardness of the coating with 15% added Nb was enhanced to 400 HV0.2, and the wear resistance thereof was 11.14 times higher than the substrate. After the 15% Nb coating had aged for 16 h, the diffraction peak intensities of Cr23C6 and Cr7C3 significantly increased, and the volume fraction of granular NbC increased from 1.67% to 2.54%. The microhardness was enhanced to 580 HV0.2, and the wear resistance thereof was better than that of the chromium plating layer.

Preparation and characterization of novel as-cast Ti-Mo-Nb alloys for biomedical applications

Ti and its alloys are the most used metallic biomaterials devices due to their excellent combination of chemical and mechanical properties, biocompatibility, and non-toxicity to the human body. However, the current alloys available still have several issues, such as cytotoxicity of Al and V and high elastic modulus values, compared to human bone. β-type alloys, compared to α-type and (α + β)-type Ti alloys, have lower elastic modulus and higher mechanical strength. Then, new biomedical β-type alloys are being developed with non-cytotoxic alloying elements, such as Mo and Nb. Therefore, Ti-5Mo-xNb system alloys were prepared by argon arc melting. Chemical composition was evaluated by EDS analysis, and the density measurements were performed by Archimedes' method. The structure and microstructure of the alloys were obtained by X-ray diffraction and optical and scanning electron microscopy. Microhardness values were analyzed, and MTT and crystal violet tests were performed to assess their cytotoxicity. As the Nb concentration increases, the presence of the β-Ti phase also grows, with the Ti-5Mo-30Nb alloy presenting a single β-Ti phase. In contrast, the microhardness of the alloys decreases with the addition of Nb, except the Ti-5Mo-10Nb alloy, which has its microhardness increased probably due to the ω phase precipitation. Biological in-vitro tests showed that the alloys are not cytotoxic.

Effect of Nb doping on the structural, optical, and photocatalytic properties of SrTiO3 nanopowder synthesized by sol-gel auto combustion technique

ABSTRACT Metal oxide photocatalyst is a promising wastewater treatment process due to its simplicity, high efficiency, and low cost, as well as being environmentally friendly and non-energy consuming. The perovskite structure material, SrTi1− x Nb x O3 (STNO) with x = 0, 0.01, 0.03, and 0.05, was successfully synthesized by the sol-gel auto-combustion method. Samples with a pure phase and cubic perovskite structure were obtained. The Rietveld refinement results showed that the lattice parameter and unit cell density increased as the Nb-doping level increased. The particle size of the STNO decreases with increasing Nb doping content. Photoluminescence was excited at 327 nm, producing violet, green, and blue emissions, while the Nb content asserts an insignificant effect on the bandgap (Eg ). The Nyquist plot and Mott-Schottky analysis were used to determine the photoelectrode performance of the STNO samples. The photocatalytic activity of STNO on the decolorization of methylene blue (MB) under UV irradiation increased with increasing Nb content and optimization at x = 0.05, corresponding to the results obtained from photoluminescence, Eg , Nyquist plot, and Mott-Schottky analyses.

New β-type Ti-Zr-V-Nb alloys used for laser-based direct energy deposition: Design, microstructure, and properties

To develop new titanium alloys for laser-based direct energy deposition, Ti-Zr-V-Nb alloys were designed from a basic Ti60.94Zr39.06 congruent composition alloyed with constant V content and varying Nb contents. The microstructure and properties of the alloys, fabricated by laser-based direct energy deposition, were systematically studied. The results show that all as-deposited alloys consist of near-equiaxed β grains with multiple orientations. The difference is that the lattice parameter of the phase enlarges and its grain size reduces with increasing Nb content, which leads to a continuous increase in hardness, strength, wear and corrosion resistance. But the ductility shows a reverse variation due to the combination of enhanced solid solution strengthening and dislocation strengthening. Owing to the combined effect of fluidity and spreadability of melt, the surface roughness firstly decreases and then increases with the increase of Nb content. The optimized alloy with 3.91 at.% Nb exhibits a good match of mechanical, tribological, and chemical properties compared with Ti60.94Zr39.06 congruent alloy, being a promising candidate used for laser-based direct energy deposition.

Role of Nb content in tailoring the microstructure and magnetic anisotropy of soft magnetic W/CoFeB alloy thin films prepared with varying the substrate temperature

The work describes the role of Nb addition on the magneto-structural properties of magnetron sputtered Si/SiO2/W/(CoFeB)1−xNbx (x = 0, 3, 5 and 10) metal metalloid alloy thin films. Films were grown at substrate temperature (Ts) of RT, 300 °C and 500 °C to realise the influence of Nb content in the amorphous and nano-crystalline states of (CoFeB)1−xNbx thin films. RT deposited films are soft magnetic (coercivity (Hc) ≤ 10 Oe), exhibits amorphous microstructure and display a well-defined uniaxial magnetic anisotropy (UMA) in the film plane. At 300 °C, devitrification occurs, and the film (x = 0) becomes partially crystalline with precipitation of FeCo nano-crystals, and UMA nearly disappears. With increasing Nb content, the mean grain size and amount of FeCo nano-crystals decreases, and partially crystalline CoFeB films transform to a completely amorphous microstructure with the simultaneous appearance of in-plane UMA and systematic improvement in soft-magnetic nature (Hc decreases from~22–5 Oe). Nb addition on at Ts= 500 °C results in grain growth inhibition and magnetically isotropic (CoFeB)1−xNbx films (except x = 3). The present study demonstrates that thermally stable amorphous CoFeB films with desired soft magnetic properties can be prepared by appropriate selection of Nb content and suitable growth temperature.

Effect of Nb Addition and Heat Input on Heat-Affected Zone Softening in High-Strength Low-Alloy Steel.

The effect of both Nb content and heat input on the softening phenomenon of the heat-affected zone (HAZ) of low-alloy high-strength steel was studied through welding thermal simulation experiments. The microstructure evolution, density variation of geometrically necessary dislocation, microhardness distribution and the second phase precipitation behavior in HAZ was characterized and analyzed by combining the optical microscope, scanning electron microscope, high-resolution transmission electron microscope with microhardness tests. The results showed that the softening appeared in the fine-grain HAZ (FGHAZ) of the low-alloy high-strength steel with the polygonal ferrite and bainite microstructure. With an increase in Nb content, the FGHAZ softening was inhibited even with high heat input; however, the hardness shows little variation. On the one hand, the increase in the Nb content increased the volume fraction of high-strength bainite in the FGHAZ. On the other hand, the remarkable strengthening was produced by the equally distributed precipitation nanoparticles. As a result, the two factors were the main reason for the solution of the FGHAZ softening problem in the low-alloyed high-strength steel with the mixed microstructure of ferrite and bainite.

High-Temperature Wear Behavior of CoCr Matrix Coatings Reinforced by Niobium Element From Room Temperature to 1000 °C

Abstract The high-temperature wear resistant CoCr matrix coatings reinforced by the Nb element were fabricated on the Inconel 718 alloy by using the hot-pressed sintered method. The effects of Nb on the microstructure, hardness, and high-temperature tribological performance of coatings are also investigated in detail, and Nb content was further optimized. The tribological properties were investigated by using a ball-on-disk tribo-tester at 23 °C (room temperature), 200 °C, 400 °C, 600 °C, 800 °C, and 1000 °C. The results showed that the Nb element showed the solution strengthening effect and particle strengthening effect. The Nb greatly affected the tribological performance of the coatings. With the increase of Nb content, the wear-rate and friction coefficient initially decreased and then increased. There was a critical value of Nb content for the high-temperature wear behavior of coatings. The coating with 5.0 wt% Nb kept the best tribological properties compared with other specimens, and the wear resistance was 1.4–29 times as high as that of the substrate. It was attributed to the high hardness, high load-bearing capacity of the Nb-rich phases, and oxide lubricating film on the worn surfaces. The corresponding wear mechanism was discussed.

Tuning the texture characteristics and superelastic behaviors of Ti–Zr–Nb–Sn shape memory alloys by varying Nb content

In this study, Ti–20Zr–(8–12)Nb–3Sn (at.%) shape memory alloys were fabricated by arc melting method and their phase constitutions, texture characteristics and superelastic behaviors were investigated by X-ray diffraction (XRD), electron back-scattered diffraction (EBSD) and tensile tests. Main α" martensite and minor β were formed in solution-treated Ti–20Zr–8Nb–3Sn specimen. With increasing Nb content to above 10 at.%, only the β phase was observed. The texture characteristics of these solution-treated Ti–Zr–Nb–Sn alloys were found to be tuned by varying Nb content. A highly dominant {001}β < 110>β recrystallization texture was evolved to dominant Goss texture ((110)β[001]β) and weak γ-fiber texture ((111)β//rolling plane) with increasing Nb content from 9 to 12 at.%. The Goss texture has not previously been reported in Ti–Zr–Nb–Sn alloys. The texture evolutions of the present Ti–Zr–Nb–Sn alloys were related to the strong β-stabilizing effect of Nb. Dominant shape memory effect was observed in Ti–20Zr–(9, 10)Nb–3Sn specimens and room temperature superelasticity was observed in Ti–20Zr–(11, 12)Nb–3Sn specimens. Compared with the Ti–20Zr–12Nb–3Sn specimen, the Ti–20Zr–11Nb–3Sn specimen exhibited superior superelasticity. The simultaneous presence of {001}β < 110>β texture, Goss texture and room temperature superelasticity in the Ti–20Zr–11Nb–3Sn specimen is beneficial to the practical biomedical application.

Microstructure, corrosion and anti-bacterial investigation of novel Ti-xNb-yCu alloy for biomedical implant application

Novel Ti-xNb-yCu alloys containing various Cu and Nb concentrations have been developed through heat treatment and rapid quenching. The effects of Cu and Nb content on microstructure, corrosion properties and bacterial inhibitory ability of the novel alloys have been systematically investigated with various characterisation methods. Results revealed that Ti3Cu alloy showed a typical eutectoid structure (α-Ti and Ti2Cu), Ti10Nb3Cu alloy exhibited three-phase coexistence microstructure (α+β+Ti2Cu), Ti30Nb alloy comprised of α+β phases, and Ti30Nb5Cu and Ti30Nb3Cu alloys comprised of single β phase. The corrosion behaviour of novel Ti-xNb-yCu alloys were studied in details using electrochemical measurements and immersion testing. It has been found that corrosion resistance of novel Ti-xNb-yCu alloys was improved with increasing Nb content, while the addition of Cu exhibited opposite trend on corrosion resistance. Higher Cu content (5%) in Ti30Nb alloy decreased its corrosion resistance while lower Cu content (3%) improved its corrosion resistance, probably due to the single-phase transition and less Cu-containing precipitates on the grain boundary of Ti30Nb3Cu. Besides, Cu-containing Ti alloys exhibited significantly better bacterial inhibitory properties. This study suggests that, Ti30Nb3Cu alloy with high corrosion resistance and excellent bacterial inhibitory property is promising for biomedical implant applications.

Effect of Nb content on the stacking fault energy, microstructure and mechanical properties of Fe-25Mn-9Al-8Ni-1C alloy

In this study, Fe-25Mn-9Al-8Ni-1C-xNb alloys (x = 0, 0.1%, 0.2%, 0.3%, and 0.4%) were prepared by vacuum arc melting, and the effects of Nb content on the stacking fault energy, microstructure, hardness and room temperature tensile properties of the alloys were systematically studied. It is deduced from the literature on the estimation of stacking fault energy that the stacking fault energy of the Fe-25Mn-9Al-8Ni-1 C-xNb alloys increases the increase of Nb content. Within this range of stacking fault energies, twinning-induced plastic deformation is dominant. Microstructure analysis shows that main phases of the series alloys are austenite, ferrite, k-carbide, NiAl intermetallic compound and NbC phase. As the Nb content increases, the NbC quantity gradually increases. With increasing Nb content, the hardness and elongation of the material gradually increase, while the tensile strength first increases and then decreases. When the Nb content is 0.3%, the alloy has enhanced comprehensive properties, and the average tensile strength is about 853 MPa, and its average elongation is about 30%, which about 8 times higher than that of Fe-25Mn-9Al-8Ni-1C alloy.

Corrosion and tribo-corrosion behaviors of nano-lamellar Ni1.5CrCoFe0.5Mo0.1Nbx eutectic high-entropy alloy coatings: The role of dual-phase microstructure

In this work, the effect of the dual-phase microstructure (FCC and Laves phases) of Ni1.5CrCoFe0.5Mo0.1Nbx (x = 0.55 hypoeutectic, 0.68 eutectic and 0.8 hypereutectic) high-entropy alloy coatings on their corrosion and tribo-corrosion behaviors were studied. In a 3.5 wt.% NaCl solution, the FCC phase behaved as anodic sites. With the increase of Nb content, the passive regions of the coatings increased slightly. Mott–Schottky analysis revealed that the improvement in the performance of the passive film is mainly attributed to the reduced point-defect density. The increased Laves phase changed the wear mechanism of the coatings from adhesive to abrasive wear.

The microstructure and properties of Fe55Cr15Ni(30-x)Nbx eutectic high-entropy alloys

The emergence of eutectic high entropy alloys (EHEAs) provides new insights for the design of the next generation structural alloys. In this paper, a set of low-cost Co-free Fe55Cr15Ni(30-x)Nbx (x = 0, 3, 6, 9, 12 and 15 at.%) EHEAs was successfully designed and prepared by vacuum arc melting. With the increase of Nb content, the solidification structure of the EHEAs change from single-phase FCC (x = 0) to divorced eutectic structure (x = 3) containing FCC and Laves phase, hypoeutectic structure (x = 6 and 9) and eventually becomes hypereutectic structure (x = 12 and 15). The FCC phase is rich in Fe, Cr and Ni, and the Laves phase is rich in Nb. The addition of Nb result in the increase of the volume fraction of the hard Laves phase which improved the room temperature strength. Solid solution strengthening and second phase strengthening are the main factors affecting the properties of the alloys. In this study, Fe55Cr15Ni21Nb9 alloy shows the best comprehensive mechanical properties, the compressive fracture strength, fracture strain and yield strength are 1216 MPa, 32% and 749 MPa, respectively. Phenomenologically, when the Nb content is in the range of 0–15 at.%, the yield strength of the alloy is a function of the Nb content: σ0.2=550×ex/15.81−256. For (Co)CrFeNi-based high-entropy alloys, a new phase prediction criterion is proposed in this paper. When the d-orbital energy level of the alloy is Md ≤ 0.92, the atomic radius difference is δ ≤ 2.88 or the mixing enthalpy meets −4.16≤ΔHmix≤0, single-phase FCC will be formed. If this is not the case, the FCC + TCP phase will be formed.

Molten Salt Flux Synthesis, Structure determination, Optical, Impedance and Modulus Spectroscopy Characterization of perovskite compound

The chemical Molten Salt Flux process was used for the synthesis of Ba0.97La0.02Ti1-xNb4x/5O3 polycrystalline sample (well-known as BLTi0.93Nb0.056). Doping with Niobium caused significant alterations in the physical properties of BLT ceramic. The XRD analysis revealed that Nb introduction forms a pure perovskite phase and crystallize in the P4/mmm-tetragonal symmetry. The average crystallite size was proven to decrease with the increase in Nb concentration. TEM image showed the formation of particles, where the average grain size decreased with Nb doping. The Nb incorporation into the BLT host lattice was also confirmed by the optical band gap (Eg) value. The optical properties were strongly influenced by Nb doping. The dielectric parameters were subsequently investigated as a function of frequency and d.c bias voltage. The observed dielectric dispersion was interpreted on the basis of Maxwell-Wagner interfacial model and Koop's phenomenological theory. Overall, Nyquist plot shows both bulk and grain boundary effect. The electrical relaxation process occurring in the material has been found to be d.c bias voltage dependent. Modulus analysis has established the possibility of hopping mechanism for electrical transport processes in the system.

Influence of Nb content on mechanical behavior and microstructure of Ti–Nb alloys

Abstract The effect of Nb content on the mechanical behavior of Ti-(20, 25, 30) at.% Nb alloys has been investigated. Results show that the storage modulus, the tensile strength and elongation at room temperature decrease with increasing Nb content. The Ti-20Nb and Ti-25Nb alloys show double-yielding behavior and they exhibit higher work hardening rate than the Ti-30Nb alloy. The Ti-20Nb alloy deforms by stress-induced β → α″ transformation and the reorientation of the α″ phase. While the Ti-25Nb alloy deforms by stress-induced martensitic transformation and deformation bands that are devoid of ω phase. The Ti-30Nb alloy, which has the highest β phase stability, deforms in a localized mode mainly by dislocation slip. The “marble-like” deformation microstructure previously reported in “gum metal” was observed in severely deformed Ti-25Nb and Ti-30Nb alloys.

Effects of niobium and ultrasonic action coupling on microstructure evolution and mechanical properties of Ti46Al 2.6 C alloy

To refine microstructure, adjust the ratio of γ/α2 and improve the mechanical properties, Ti46Al 2.6 C-xNb (at. %) alloys were prepared by arc melting under the action of ultrasound. The phase composition, lamellar colony size, elements distribution, the kinds and distribution of carbides and compressive properties were investigated. Results show that as the Nb content increases, the relative content of α2 phase and Ti2AlC phase increases, and the relative content of γ phase decreases. TiC phase completely reacts to form Ti2AlC phase and its shape changes from coarse long rod to short rod. The microstructure was refined with the addition of Nb under ultrasound treatment. Lamellar colony size decreases from 36.9 to 21.5 µm, lamellar spacing decreases from 1.6 to 0.8 µm, and the length-diameter ratio of Ti2AlC decreases from 5.4 to 4.0 when the Nb content increases from 0 to 8.0 at. %. During solidification process, not only the component supercooling and heterogeneous nucleation of Nb are increased, but also the crystal grains are broken and the nucleation barrier is reduced under the action of ultrasound to promote the nucleation. The microstructure is refined and the uniformity of the element distribution is improved. Compressive results show that the strength increases from 2074.1 to 2474.2 MPa and the strain increases from 23.4% to 28.0% when the Nb content increases from 0 to 4 at. %. The refinement of lamellar colony and Ti2AlC, the ratio of γ/α2 and solid-solution of Nb are the main reasons for improving compressive properties.

Effect of Nb content on Ti-Mo-Nb alloy materials for neutron high pressure diffraction

Ti-Mo-Nb alloy material, which is a candidate of the zero-scattering material used for neutron diffraction applications, was designed and prepared by the powder metallurgy method. Ti-Mo-Nb alloy containing 10%Nb sintered at 1700 °C for 5 h has a microstructure of single solid solution phase, and has a compressive strength of 1711 MPa and the compression strain of 13.5%. (β-Ti-Mo-Nb)/(β-Ti-Mo-Nb) grain boundaries can be gradually wetted by the α-Ti phase with the increase of sintering temperature and Nb content. The neutron diffraction test of the Ti-Mo-Nb alloy shows that the diffraction intensity is very low and peaks are not obvious, which illustrates that no neutron diffraction appears for this alloy.

ESTUDIO TEÓRICO Y NUMÉRICO DE LA DIFUSIÓN DE HIDRÓGENO EN ALEACIONES BASE Zr-Nb

Within the framework of the delayed hydride cracking phenomena reported for the pressure tubes of CANDU-type nuclear reactors, we study the influence of the Zr-β(∼20 %Nb -∼80 %Zr) continuous phase on the hydrogen diffusion coefficient,DH, through the Zr-α/ Zr-βbiphasic alloy. We propose an improved phenomenological model forDHwithrespect to those found in the literature. Furthermore, we study the influence of the Nb content on DH for the cubic phase Zr-β, employing the transition state theory furnished with ab-initio parameters provided by the SIESTA code. In particular, 9 ordered alloys are considered with different Nb content and effective activation energies are computed by Arrhenius fits for each alloy. We find that activation energies vary in a non-monotonic way as Nb content increases, reaching a maximum value at about Zr-50 %Nb. Finally, we observe that the predicted and measured larger diffusivity along the tube axis vs. the radial direction, is consistent with the material texture. Moreover, we conclude that the loss of continuity of the Zr-βsheets present in the tube microstructure, is consistent with the decrease of DH in time at agiven temperature.

Microstructure evolution and mechanical properties of AlCrFe2Ni2(MoNb)x high entropy alloys

The AlCrFe2Ni2(MoNb)x multiphase high entropy alloys were designed, prepared and characterized. The synergistic effect of Mo and Nb alloying on microstructures and mechanical properties of AlCrFe2Ni2-based high entropy alloy were investigated. By synergistic alloying with Mo and Nb, the volume fraction of the BCC phase increased, and a novel Laves phase with hexagonal close-packed(HCP) structure was formed. With the increase of Mo and Nb content, the alloys dramatically transformed from equiaxed grain with multiple phases to dendrites with the spinodal decomposition structure of the A2 phase and B2 phase, as well as inter-dendrites with the eutectic structure of the FCC phase and Laves phase. Furthermore, the solidification behavior of the alloys varied considerably as the increase of Mo and Nb content. The coexisting solidification microstructure of the eutectic structure and spinodal decomposition structure in the AlCrFe2Ni2(MoNb)0.3, AlCrFe2Ni2(MoNb)0.5 and AlCrFe2Ni2(MoNb)0.7 alloys have hardly been observed in other HEAs. The increase of Mo and Nb elements tends to segregate in the front of the liquid–solid interface, which hinders the growth of the FCC phase and leads to the formation of fine rod-like morphology. The synergistic effect of the fine grain strengthening and the solid solution strengthening resulted in high yield strength and fracture strength of 878 MPa and 2830 MPa, maintaining high plastic strain of 43.7%. Further increasing the content of Mo and Nb would lead to the increase of brittle Laves phase, with the second phase strengthening becoming the dominant strengthening mechanism, resulting in an increase in yield strength to 1549 MPa and a decrease in plastic strain to 8.6%. The investigation results would provide a guide for strengthening the macroscopic mechanical properties of eutectic high entropy alloys through synergistic alloying effect.

Suppression of Sr surface segregation in La0.8Sr0.2Co0.2Fe0.8O3-δ via Nb doping in B-site

Sr surface segregation has been one of the main reasons for the cathode performance degradation during the long-term operation of solid oxide fuel cells (SOFC). Investigation on Sr segregation mechanism and proposing strategies on suppressing the Sr surface segregation are significant for SOFC development. In this paper, La 0.8 Sr 0.2 Co 0.2 Fe 0.8-x Nb x O 3-δ (LSCFNb, x = 0, 0.02, 0.04, 0.06, 0.08 and 0.1) are prepared via sol-gel method. The electrochemical performance and long-term stability are tested through electrochemical impedance spectroscopy (EIS) and constant current polarization. The results show that the long-term stability of LSCFNb cathodes are strongly affected by Nb content. Combining the results of ICP and XPS, it's revealed that the Sr surface segregation can be effectively suppressed with the increase of Nb content. The LSCFNb cathodes gain the optimal electrochemical performance when x = 0.04, with minimum polarization resistance of 0.27 Ω cm 2 at 750 °C and oxygen reduction reaction activation energy of 1.54 eV. After cathodic polarization for 144 h, the polarization resistance and activation energy of LSCFNb4 cathode increase slightly, revealing it a promising cathode material for SOFC research.

Effect of Nb addition on the microstructure and mechanical properties of Inconel 718 fabricated by laser directed energy deposition

To further optimize the microstructure and enhance the mechanical properties of Inconel 718 alloy fabricated via laser additive manufacturing, the Nb-reinforced Inconel 718 composites were fabricated by laser directed energy deposition (LDED) and subsequently subjected to full heat treatment and direct aging treatment. The microstructure and the mechanical properties of the samples with various Nb contents (4.9, 7.0, 8.0, 9.0, 11.0 wt%) under three treated conditions were investigated. The results showed that increasing Nb content led to a more advanced dendrite structure in the as-deposited sample, accompanying with the emergence of fine grains. After undergoing the full heat treatment, the advanced dendrite structure was broken and corresponding recrystallization behavior occurred. The dendrite structure in the directly aged samples was similar to that in the as-deposited sample. Augmenting the Nb content could significantly alter the morphology, the amount, and the size of the Laves phase, γ″ phase, and the δ phase in the three heat-treatment samples. Cracks appeared in the sample with 11.0 wt% Nb. With the increment of Nb, the tensile strength and the microhardness remarkably became enhanced while the elongation decreased in the three heat-treatment samples. The improvement effect of the direct aging on the tensile strength and the microhardness was superior to the full heat treatment. Grain fining and solid solution strengthening were mainly responsible for the enhancement of the strength and microhardness in the as-deposited samples. The variation of the γ″ phase and the δ phase in amount and size jointly improved the heat-treated strength and the microhardness. The 9.0 wt% Nb sample with an excellent tensile strength (1598.3 MPa) which was superior to the currently reported strength, and the microhardness (543.2 HV0.2) can be obtained after direct aging. The fracture morphologies of the samples with various Nb contents were also discussed.