Nb Addition Research Articles

Evaluation of Forged TiAl Alloy Usefulness Based on Their Impact Resistance

The purpose of this study is to determine if forged TiAl alloys are worth using for small parts such as jet engine turbine blades. As part of this goal, this study investigated ways to improve the impact resistance of forged TiAl alloys and compared them to cast TiAl alloys. The effects of additive elements and microstructure on the impact resistance of forged ternary TiAl alloys of 43.5 at. % Al were evaluated using the Charpy impact test on specimens heated to 500 °C prior to testing. The impact resistance of the forged alloys improved with the addition of Cr, V, and Mn and deteriorated with the addition of Nb. The impact resistance of the microstructure containing a β-phase, a common microstructure in forged TiAl alloys, was significantly lower. The fully lamellar structure obtained at the expense of forgeability showed much higher impact resistance than this. However, even the best impact resistance of the forged alloys was significantly inferior to that of cast ternary alloys of 46.5 at. % Al prepared with the same additive content. Combined with the high cost and low high-temperature strength of the forged TiAl alloys, it is concluded that it is pointless to use forged TiAl alloys for small parts that can be made via casting.

Performance of Zr/3C-SiC interfaces modified by additions of Nb, Cr, Ni, Sn and Fe: First-principles studies

Coexisted covalent, metallic and ionic bonds increase difficulty in tailoring the properties of Metal/SiC interfaces by addition of alloying elements. Herein, we revealed the origin of Zr/SiC performance impacted by doping elements (X = Nb, Cr, Fe, Ni and Sn) using density functional theory. We found and clarified weighting of diverse chemical bonds acting on interfaces with different SiC terminations. Interface jointed by strong covalent bonding disadvantages vacancy formation, whereas favors the solution of doping elements, some of which even enhance the interface in turn. Synergy from covalent bonding, ion interaction and structural deformation is important in interfacial adhesion for the other interfaces jointed by weakly covalent bonding. Tensile performance cannot be deducted from the interfacial adhesion as cleavage is ignited from the weakest Zr-X metallic bonds on the side of Zr. An effort of this work aims to establish fundamental rules to help survey and improve Metal/SiC interfaces by screening alloying elements.

The Influences of Nb Microalloying and Grain Refinement Thermal Cycling on Microstructure and Tribological Properties of Armox 500T

This study aims to investigate the combined effect of niobium (Nb) microalloying and austenite grain refinement, using a specific heat treatment cycle, on the microstructure and tribological properties of Armox 500T steel. In this work, Nb addition and thermal cycling were utilized for grain refinement and enhancement of the mechanical properties of Armox 500T alloy, to provide improved protection via lightweight armor steel components with a high strength-to-weight ratio. The kinetics of transformation of the developed Armox alloys were studied using JMATPro version 13.2. The samples were subjected to two austenitizing temperatures, 1000 °C and 1100 °C, followed by 4 min of holding time and three consecutive thermal and rapid-quenching processes from 900 °C to room temperature. Scanning electron microscopy with energy dispersive X-ray analysis (SEM-EDX) was employed to analyze the microstructure, which primarily consists of four types of martensite: short and long lath martensite, blocky martensite, and equiaxed martensite. Additionally, a small percentage (not exceeding 3%) of carbide precipitates was observed. The wear characteristics of the investigated alloys were evaluated using a pin-on-disc tribometer. The results demonstrate that alloying with Nb and grain refinement using a thermal cycle significantly reduce the wear rate.

Mechanical and corrosion properties of highly porous Ta-Nb-Sn alloy for intervertebral disc in spinal applications

Abstract In this study, low Young’s modulus, highly porous Ta-Nb-Sn alloy foam was manufactured by using the space holder method. The aim of this study is development of an alloy with high wear resistance, with Young’s modulus, with good imaging (MRI, CT) properties, and with high bioactivity. Ta alloy foam can be used in spinal applications (intervertebral disc) or dental applications. The space holder method enables the manufacturing of open-cell foam with a low elastic modulus. Powder mixtures were prepared through mechanical alloying. Carbamide was used to form pores. Ta has suitable strength, ductility, corrosion resistance, and biocompatibility. Ta has high price, however, and a high melting temperature, high activity, and high density. Nb addition lowered the melting temperature, elastic modulus, and cost of using Ta. The sinterability of Ta was enhanced by Sn addition. The corrosion behaviour of Ta alloy was examined. Young’s modulus was determined by compression and ultrasonic tests. Tomography and radiography tests were also used.

He bubbles inhibition and abnormal hardening in GH3535 alloy by niobium element addition

GH3535 and 2 wt.% Nb-modified GH3535 (Nb-GH3535) alloys were irradiated with 1.2 MeV He ion at fluences of 1 × 1016, 3 × 1016 and 1 × 1017 ions/cm2 at 750 °C. Microstructural changes, including the formation of He bubbles and superlattice phases, as well as the irradiation-induced hardening, were investigated by TEM and nanoindentation. Notably, Nb-GH3535 exhibited a smaller size and lower number density of He bubbles, especially at higher fluences, indicating the inhibitory effect of Nb on bubble evolution. First-principles calculations revealed that the presence of Nb inhibits the combination of He atoms and vacancies, reducing their diffusion rate and consequently impeding the nucleation and growth of He bubbles. Furthermore, the addition of Nb facilitates the irradiation-induced precipitation of the superlattice phase, leading to a higher degree of total hardening in Nb-GH3535 alloy.

Effect of Mo and Mo+Nb Additions on the Phase Transformation and Microstructure of a Developed Low-Carbon CrNiMnB Ultrahigh-Strength Steels with a Preceding Hot Deformation

The influence of molybdenum, and molybdenum with niobium addition on the phase transformation behaviour of a developed low-carbon CrNiMnB ultrahigh-strength steels, was investigated. Gleeble 3800 thermomechanical simulator was employed to simulate the hot-rolling process and to get the dilatation curves. After austenitization at 1250 °C for the complete dissolution of carbides, specimens received 0.6 total strain (i.e., 0.2 at 1100 °C and 2 x 0.2 at 900 °C) followed by cooling at various cooling rates (CRs) in the range of 2-60 °C/s. The final microstructures were investigated using laser scanning confocal microscopy, field emission scanning electron microscopy, and hardness measurements. Then the continuous cooling transformation diagrams were constructed based on the dilatation curves, microstructure, and hardness values. The electrolytic extraction method was used to assess the elements' distribution and the composition of the forming precipitates. The addition of Mo increased the hardenability, decreased the transformation temperatures, and promoted the formation of low-temperature transformation products i.e., martensite and bainite ferrite, at different CRs and inhibit the formation of polygonal ferrite. The formation of coarse precipitates neglected the effect of Mo+Nb addition, decreased the hardenability and expanded the region of BF formation to high CRs. The variation in the hardness with microstructural changes was discussed.

The Effect of Niobium Addition on Properties of Titanium-Based Alloy Fabricated via Mechanical Alloying

The aim of this study was to investigate the effect of niobium addition on phase formation, densification, microhardness and compressive properties of Ti-Nb alloys that possess suitable characteristics as bone fixation device. The mixture of Ti and Nb powders was mechanically alloyed (MA) in a planetary mill for two hours. The effect of Nb addition to Ti was investigated by x-ray diffraction (XRD) analysis. In addition, density, microhardness and compressive behavior of the sintered alloy were also determined by the principle of Archimedes, Vickers microhardness test and compression test, respectively. The results suggested that Nb addition has changed the phase from α-Ti to β-Ti. As the Nb addition was increased from 0 wt.% to 40 wt.%, it is observed that the density of alloy increased from 4.17 g/cm3 to 5.24 g/cm3. The microhardness and compressive modulus were 306.92 HV and 57.06 GPa for Ti-0Nb (wt.%), while the mechanical properties of the alloy dropped to 218.23 HV and 25.88 GPa when the Nb addition was up to 40 wt.%. This trend is similar to the compression strength, which the compression strength for Ti-0Nb (3221 MPa) decreased to 2123 MPa as Nb was incorporated into Ti up to 40 wt.%. It is found that Ti-40Nb possess close resemblance to the Young’s modulus of human cortical bone which lies in the range of 7-30 GPa and exhibit suitable characteristics as bone fixation device.

Ab initio stability prediction of [formula omitted] titanium and [formula omitted] and [formula omitted] precipitates in [formula omitted] titanium matrix for titanium alloys using density functional theory and micromechanics

β titanium alloys have a wide range of applications, including in aerospace and transport. The β phase is stable only at high temperatures, and the phase stability can be improved by adding stabilizers. However, the β-phase-stabilization effects of β stabilizers have not yet been clearly elucidated. Here, I report the ab initio prediction of the energetic phase stability of β titanium alloys with Mo, V, W, Nb, and Ta as additive β stabilizer elements. The stability is predicted using a combination of atomistic simulation via density functional theory and continuum micromechanics (Eshelby’s ellipsoidal inclusion analysis). In particular, I consider the heterogeneity of the secondary ω and α phases (precipitation) in the β matrix. All β stabilizer species led to a significant energetic and elastic stabilization of the β phase. Mo and W additives stabilized the β phase relatively stronger and secondary ω and α precipitates may hardly nucleate in β phase in high concentrate condition. Although V, Nb, and Ta additives stabilized the β phase significantly, the β phase remained metastable. Regarding the morphology of these secondary phases, V helped α precipitation and Ta helped ω precipitation. The possibility of a coexistence of ω and α in the β matrix was suggested for Nb addition. The strain fields around the precipitates were also investigated and the results suggested that α precipitates cause a large residual strain around it though ω precipitates do not.

Development of a Cr-Ni-Mo alloyed stress corrosion-resistant anchor bolt steel

PurposeThe purpose of this paper is to develop new types of anchor bolt materials by adding corrosion-resistant elements for alloying and microstructure regulation.Design/methodology/approachThree new anchor bolt materials were designed around the 1Ni system. The stress corrosion cracking resistance of the new materials was characterized by microstructure observation, electrochemical testing and slow strain rate tensile testing.FindingsThe strength of the new anchor bolt materials has been improved, and the stress corrosion sensitivity has been reduced. The addition of Nb makes the material exhibit excellent stress corrosion resistance under –1,200 mV conditions, but the expected results were not achieved when Nb and Sb were coupled.Originality/valueThe new anchor bolt materials designed around 1Ni have excellent stress corrosion resistance, which is the development direction of future materials. Nb allows the material to retain its ability to extend in hydrogen-evolution environments.

Enhancing electrochemical and passive behavior of Ti-based medium entropy alloys in proton exchange membrane water electrolysis anodic environment through Zr and Nb synergy

The synergistic effect of Zr and Nb on the passive behavior of non-equiatomic Zr-Ti-Nb as bipolar plates in proton exchange membrane water electrolysis (PEMWE) was investigated. The experiment revealed that the complementary change of Zr and Nb content resulted in the corrosion resistance sequence of Z40 > Z20 > Z26 > Z34. The primary constituents of the passive films predominantly comprised ZrO2, TiO2, and Nb2O5. The relative content of ZrO2 and Nb2O5 exceeded the atomic proportions of Zr and Nb in the substrate. Additionally, higher potentials had a significant impact on reducing the number of point defects in the passive films while increasing their thickness. The addition of Zr and Nb inhibited the formation of defects in the passive film. The study also investigated operation-induced passive behaviors. Accelerated stress tests were conducted using two square ripple potentials to simulate overload operating conditions. The findings indicated that the lower upper limit potential was insufficient to establish stable passivation.

Influence of TM elements on the mechanical and thermodynamic properties of Hf2Si intermetallics

In order to improve the properties of Hf2Si, we design six transition metals (TM = Zr, Nb, Mo, Tc, W and Re) doped in Hf2Si. The effect of TM elements on the properties of Hf2Si was studied using the first-principles calculations. The results of formation enthalpy and phonon dispersion confirm that TM-doped Hf2Si are thermodynamically stable and dynamically stable. The addition of the TM element will enhance the compression resistance of Hf2Si along the c-axis. W-doped Hf2Si has the strongest tensile strength. In particular, the addition of Nb, Mo, Tc, W and Re elements enhances the bulk (B), shear (G) and Young's modulus (E) of Hf2Si. The brittle property of Hf2Si is improved and the hardness of the material is reduced. Based on the improvements in mechanical properties, we make further explanations according to the electronic properties.

Enhanced activity and SO2 tolerance in low-temperature NH3-SCR of NOx over MnCr catalyst by hetero-oxide modification

Developing NH3-SCR catalysts with high humid-SO2 resistance is of great significance for NOx emission control of the two-stroke low-speed ship. For further optimizing the catalytic performance and SO2 tolerance of Mn-Cr catalyst, Al2O3, CeO2 and Nb2O5 were doped by coprecipitation. Through structural analyses, it was determined that the incorporation of Al and Ce effectively increased the surface area of the catalysts and promoted the dispersion of various components throughout them. Moreover, the introduction of Nb led to the formation of secondary particle aggregates, ultimately strengthening the structural stability of the catalysts. The catalytic performance, N2 selectivity and SO2 tolerance of the co-doped catalyst containing Al2O3, CeO2 and Nb2O5 showed remarkable improvement. The NOx conversion of MnCrCeAlNb was exceeding 90% and N2 selectivity above 97% at 175–300 °C and remained around 88% after 10 h reaction under 150 ppm SO2 and 10 vol% H2O at 225 °C. Co-doping Al2O3, CeO2 and Nb2O5 greatly improved the reducibility and significantly increased the number of surface acid sites. And the XPS results demonstrated that the addition of niobium enhanced the redox properties and adsorbed oxygen through the electron transfer between Mn4+ and Cr3+, resulting in a significant promotion in the NH3-SCR performance and humid-SO2 tolerance. In particular, the cause of the excellent humid-SO2 tolerance of the MnCrCeAlNb was investigated by TG and FT-IR, demonstrating that the Nb addition significantly reduce the formation of (NH4)2SO4, NH4HSO4 and sulfate on the surface of MnCr catalyst. These results suggested that the doping of Hetero-oxide greatly enhanced the low-temperature NH3-SCR and SO2 tolerance of Mn-Cr based catalysts.

Enhancement of Fe-Nb interaction by acid modification over SO42--FeOx-Nb2O5 catalyst for NH3 selective catalytic reduction of NOx

A series of iron-based composite oxide catalysts, modified with acid and niobium, were produced for the purpose of selective catalytic reduction of NOx with NH3 (NH3-SCR) via co-precipitation. The obtained SO42--FeOx-Nb2O5 (S-FeNbOx) catalyst exhibited significantly better SCR performance than the unmodified FeOx catalyst, with a NOx conversion above 90% and N2 selectivity higher than 95% in the temperature range of 275–450 °C. The characterization results suggest that the addition of Nb not only modifies the electronic structure and alleviates the reducibility but also enhances the surface acidity of the catalysts. The sulfuric acid modification of FeOx-Nb2O5 catalyst promotes the formation of redox-acid sites. The in situ Diffuse Reflectance Infrared Fourier Transform spectroscopy (DRIFTs) results revealed that the combining sulfuric acid and niobium modifications resulted in a significant increase in the amount of Brønsted acid sites, and also led to a blue shift of the band related to the Lewis acid sites, implying the existence of a synergistic effect of the two modification methods. The creation of redox-acid sites significantly enhances the adsorption and activation capacity of NH3 on the catalyst surface. These results suggest that the NH3-SCR reaction to primarily follow the Eley-Rideal (E-R) mechanism on the catalyst.

The Effect of Niobium on <i>In Situ</i> Synthesis of Titanium Carbide in Composite Hardfacings

Niobium (Nb) and titanium (Ti) react with carbon to form high-melting-point and high-hardness MC-type carbides. This study explores the in-situ synthesis of mixed NbC-TiC carbides during plasma transferred arc welding of a steel-based hardfacing. Feedstock powders consisted of stainless steel AISI 316L, TiO2, and graphite with and without 5 wt.% Nb addition. Feedstock powders were ball milled for 72 hours, then mixed with paraffine and pre-placed on the S235 steel. The cladding current was 125 A, and the plasma torch travel velocity was 1 mm/s and 0.7 mm/s. The effect of Nb on TiC generation was examined using scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS). Vickers hardness was also measured at the surface of hardfacings. Results show that previously formed NbC grains acted as nucleation sites for TiC precipitation. Increased torch velocity has resulted in improving distribution and decreasing agglomeration of carbon phases. Hardness tests showed that Nb and Ti increased the hardness resistance of the substrate steel.

Dissolution of Nb-doped hydroxyapatite prepared via low-temperature mechanochemical method: Spectroscopy studies

Calcium phosphate glass ceramics with nominal hydroxyapatite stoichiometry doped with niobium were synthesized using simple as well as low-temperature mechanochemical method and then in the form of compressed pellet were submitted to the static dissolution process in distilled water for one month. The results of structural analysis, performed mainly on the base of spectroscopic methods such as: infrared absorption spectroscopy, energy-dispersive X-ray spectroscopy, photoelectron spectroscopy as well as soft and tender X-ray absorption spectroscopies, indicate that during the dissolution process the presence of niobium reduced the dynamics of the calcium phosphate new layer formation, without a significant impact on the morphology and stoichiometry of this layer. Moreover, the Nb addition favored the formation of hydroxyapatite and Ca-deficient hydroxyapatite, both during the synthesis and dissolution processes, and facilitated the incorporation of the CO3-2 groups into the ceramic matrix, leading to the formation of B-type carbonated apatite.

Improvement of mechanical, biological, and electrochemical properties of Ti6Al4V alloy modified with Nb and Ag for biomedical applications

This study aims to evaluate the mechanical and biological properties of a spark plasma-sintered (SPS) Ti6Al4V alloy modified with 5 and 10 wt% niobium (Nb) together with 2 wt% Ag. Five batches of Ti6Al4V, Ti6Al4V-5 Nb, Ti6Al4V-10 Nb, Ti6Al4V-5 Nb-2Ag, and Ti6Al4V-10 Nb-2Ag were sintered using SPS at 1400 °C for 5 min. X-ray diffraction (XRD) analysis was used to identify the phases of the specimens. Scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), and X-ray mapping analyses were also utilized to study the powder morphology, microstructure, and fractured surfaces of the samples. Three-point flexural strength and Vickers microhardness tests were performed and the fracture toughness (K1 C) was calculated subsequently. The bulk parts showed a very high building density, which means that the plasma sintering parameters were optimal. X-ray diffraction (XRD) analysis confirmed the existence of alpha and beta phases by adding niobium and silver. Potentiodynamic, electrochemical impedance spectroscopy, MTT assay, and antibacterial tests were also conducted to evaluate the biological properties of the sintered samples. The maximum values of flexural strength and K1 C were obtained for Ti6Al4V-5 Nb samples up to 1943 ± 12 MPa and 63 ± 1.1 MPa.m0.5, respectively. The hardness values of samples showed no significant difference by adding Nb and Ag. The samples containing Nb exhibit a lower passive current density compared to the pure Ti6Al4V alloy, suggesting that the addition of Nb positively influences corrosion resistance. According to the results of the antibacterial test, Nb slightly deteriorated the antibacterial properties, while after adding Ag, this property improved. The results of the MTT assay revealed that adding niobium and silver had no toxic effect on the samples.

Site-specific analysis of precipitates during the coiling of an HSLA steel containing V and Nb

Precipitation in a high-strength low-alloy steel containing V and Nb additions during coiling at 500 °C, was investigated by advanced characterization techniques including electron backscattered diffraction, focused ion beam, transmission electron microscopy and atom probe tomography. During coiling, nano precipitates were preferentially formed around dislocations and grain/sub-grain boundaries in the high Kernel Average Misorientation (KAM) areas associated with bainite. Precipitates were frequently observed around cementite in the low KAM areas with cementite which were identified as granular bainite. Interphase clusters were found in the low KAM areas associated with ferrite. The site-specific methods reveal the co-existence of different kinds of precipitates. Analysis of the results indicates that the precipitation of microalloy particles close to cementite could lower the precipitation hardening contribution that could be achieved through microalloying.

Effects of Nb addition on the microstructure and low-cycle fatigue properties of heat-resistant stainless steel

This study aims to improve the quality and durability of materials used in turbocharger housing, particularly to limit the degradation of automobile engine parts. As a result, niobium (Nb)-bearing heat-resistant cast austenitic stainless-steel samples have been explored. Two distinct steel samples, denoted as Alloy-A (with 0 wt.% Nb) and Alloy-B (with 1.5 wt.% Nb), were fabricated by centrifugal casting for investigating the effects of Nb content on the corresponding microstructure and low-cycle fatigue properties of these samples. The phases formed within these alloys were predicted by thermodynamic calculations using the Thermo-Calc software, with the results aligning well with the experimental results. The addition of Nb promoted the formation of niobium carbide, resulting in increased hardness and greater area fraction of the carbides present in the steel samples. Alloy-B displayed enhanced high-temperature strength over Alloy-A, while the low-cycle fatigue resistances of the two alloys were similar. Fatigue cracks predominantly initiated at the outer surface of the specimens, mainly in the carbide regions, due to the mismatch between the matrix and carbide hardness. This paper is the first to report the effect of Nb addition on the microstructure and low-cycle fatigue properties of heat-resistant cast austenitic stainless steel.

Nb-content-dependent passivation behavior of Ti–Nb alloys for biomedical applications

Ti–Nb alloys have the advantages of non-toxicity, low elastic modulus, high strength, and good biocompatibility. However, the effect of Nb content on its passivation behavior in Hank's solution still needs to be investigated. This work investigated the microstructure, hardness, and corrosion behavior of Ti-xNb (x = 5, 15, 25 wt%) alloys. The β phase gradually increases associated with the increasing Nb content in Ti–Nb alloys, resulting in the dispersion strengthening of alloys. Moreover, with the increased Nb content, the samples show higher open circuit potential, lower passivation current density, and higher charge transfer resistance in Hank's solution at 37 °C. When the passive films of Ti–Nb alloys are formed under the high potentials of 1 V and 2 V, the passive films gradually dissolve after the withdrawal of applied potential, representing the decrease in the total impedance of the passive film. The reason for this phenomenon is the addition of Nb substantially decreases the oxygen vacancies in the passive film formed on the samples. Therefore, the impedance of the passive film is increased.

Effects of Mo and Nb on the microstructure and high temperature oxidation behaviors of CoCrFeNi-based high entropy alloys

A series of CoCrFeNi(Mo, Nb) high entropy alloys (HEAs) were prepared using vacuum arc-melting. The effect of Nb and Mo on the microstructure and high temperature anti-oxidation properties of HEAs was investigated. The addition of only Mo was found to not cause formation of new phase, but did increase the lattice distortion. After the addition of Nb, as-prepared CoCrFeNiMo0.2Nb0.1 and CoCrFeNiMo0.2Nb0.2 alloys are characteristic of duplex-phase structures of FCC and Laves, in which the Laves phase is semi-coherent with FCC matrix. Our studies also revealed that the oxidation kinetics of the alloys followed parabolic rate law and the corresponding oxidation rate constants were calculated. Due to the synergistic effects of Mo and Nb, the anti-oxidation properties of HEAs improved significantly. It was also discovered that the new Laves phase containing Mo and Nb at the inner oxidation layer hindered the outward diffusion of active metal cations, ergo improving the oxidation resistance of HEAs. With increase of Nb content, it was further recognized that the layered structure of Laves phase was thinner and denser. Therefore, the oxygen ion diffusion process in the CoCrFeNiMo0.2Nb0.2 alloy can be inhibited effectively by the new formation of duplex-phase structures with undulated Laves phase and FCC matrix.