Nb Powder Research Articles

Microstructure and properties of laser clad Fe-based amorphous alloy coatings containing Nb powder

Fe-Cr-Mo-Co-C-B-Nb coatings with the Nb mass fractions of 0, 2, 4 and 6% were prepared on 45 steel by laser cladding. The surface and microstructural evolution, chemical compositions, phases and thermal behavior of the obtained coatings were analyzed using a scanning electron microscope (SEM) equipped with energy disperse spectroscopy (EDS), Electron Probe Microanalyzer (EPMA), x-ray diffraction (XRD), and differential scanning calorimeter (DSC), respectively. The effects of element Nb addition on the glass forming ability (GFA), microhardness and corrosion behavior of coatings were investigated. The results show that the addition of Nb improves the surface properties, corrosion resistance and GFA of the material significantly, but the presence of excessively high Nb elements will generate Nb-Mo phase, which reduces the plasticity of the coating. Besides, by analyzing the properties of the coating, the optimum mass fraction of Nb was determined to be 4%.

Strengthening mechanism and micropillar analysis of high-strength NiTi–Nb eutectic-type alloy prepared by laser powder bed fusion

Although laser powder bed fusion (LPBF) can produce complex structures with promising properties, there still exists a concern on the diversity in materials, especially composites, for LPBF. This work innovatively used NiTi and Nb powders to prepare NiTi–Nb eutectic-type alloy by LPBF, which provides a new method to prepare NiTi–Nb shape memory alloy and could be an alternative for tailoring microstructure. The semi-molten Nb particle phase was retained during LPBF, so that β-Nb and the eutectic structure display a gradient distribution in the Nb diffusion concentration. The heat treatment process (annealed at 850 °C for 0.5 h) makes NiTi–Nb samples have high yield strength (~1640 MPa), high compressive strength (~2380 MPa), and high compressive strain (~39%), which are superior to the corresponding ones of its as-built and as-cast counterparts. Large Nb phase particles with a size of 10–30 μm are retained and accelerated the formation of eutectic phase and β-Nb precipitate phase. Overall, the presence of β-Nb phase has a beneficial effect on the alloy, and a large number of intertwined dislocations and stacking faults around the β-Nb phase promote the formation of martensite under stress loading. The eutectic phase makes an important contribution to the high strength and plasticity of the NiTi–Nb alloy.

A novel surface design for preparing a Mo-10%Nb sputtering target with ultra-low oxygen content: Coating a NbC layer on Nb powder particles via chemical vapour reaction under CH4 atmosphere

Mo-10%Nb sputtering target has broad application prospects in thin-film solar cells and displays. However, the absorption of oxygen by Nb powders during the sintering process leads to a high oxygen content and low density of the sintered Mo-Nb billet. In this study, Nb powder covered with a niobium carbide (NbC) layer was prepared via chemical vapour reaction under CH4 atmosphere for the first time. The NbC layer not only helps prevent oxygen absorption, but can also be completely consumed by reaction with oxygen at the desired temperature. The effects of the preparation method, reaction medium, and reaction parameters on the properties of the NbC layer were investigated, and optimised parameters were found to be a temperature of 600 °C, reaction time of 270 min, and gas pressure of 0.04 MPa. The surface morphology, chemical composition, and the distribution and uniformity of the layer were characterised by scanning electron microscopy, X-ray photoelectron spectroscopy, electron probe microanalysis, Raman spectroscopy, and atomic force microscopy. The oxygen and carbon contents were determined using ONH and CS analysers. The surface-modified Nb powder was mixed with a Mo powder and sintered under vacuum to obtain a sintered Mo-10%Nb billet with an oxygen content of 190 ppm, carbon content of 290 ppm, and relative density of 93%. The quality of this billet is significantly better than that of a billet prepared using a non-surface-modified Nb powder.

Variation of Structural and Hyperfine Parameters of (Fe0.70Al0.30)1-xNbx, with x=0, 0.05, 0.10 and 0.20 System

Fe0.70Al0.30 alloy is a bcc and ferromagnetic phase, being the Al atoms magnetic dilutor. In this work, we study the effect of the Nb on the structural and hyperfine behavior of the Fe0.70Al0.30 alloy when atoms of Nb substitute atoms of Fe or Al. The nanostructured system of (Fe0.70Al0.30)1-xNbx (x = 0, 0.05, 0.10, 0.20, at. %) was obtained by alloying Fe, Al and Nb powders in a planetary ball mill during 12 h, 24 h and 36 h, and a ball mass to powder mass relation of 10:1. The magnetic and hyperfine properties of the samples were studied by X-ray diffraction (XRD) and Mössbauer Spectrometry (MS) at room temperature, respectively. The X-ray diffraction patterns for x=0 showed the bcc-α FeAl structure and its lattice parameter is approximately constant with milling times (∼ 2.91 Å). For x=0.05, 0.10 and 0.20 the patterns showed the coexistence of the α-FeAl, Nb(Fe,Al)2 structural phases with an amorphous component. The Mössbauer spectra of x=0 samples were fitted using hyperfine magnetic field distributions (HMFDs), and the obtained mean hyperfine fields (MHF) were 23.4, 24.2, and 24.3 T for 12, 24, and 36 h of milling time, respectively, which correspond to the α-FeAl structure. The spectra of the samples with x=0.05 and 0.10 were fitted using a model with two components, the first one is a HMFD attributed to the bcc-FeAlNb structure and the second with two doublets attributed to the Nb(Fe,Al)2 structure. When atomic percentage of Nb increases up to 20 at. % the ferromagnetic behavior is diluted due to substitution of Fe-atoms by Nb and Al atoms in the bcc-FeAlNb structure. The magnetic behavior becomes paramagnetic at x=0.20, the spectra were fitted with three doublets, one of them related with bcc-FeAlNb structure and the others to the Nb(Fe,Al)2 structural phase. The alloying of Nb to the Fe0.70Al0.30 system destroyed the magnetism due the substitution of Fe by Nb atoms and generates an amorphization into the system.

Superelastic Behavior of Ti-Nb Alloys Obtained by the Laser Engineered Net Shaping (LENS) Technique.

The effect of Nb content on microstructure, mechanical properties and superelasticity was investigated for a series of Ti-xNb alloys, fabricated by the laser engineered net shaping method, using elemental Ti and Nb powders. The microstructure of as-deposited materials consisted of columnar β-phase grains, elongated in the built direction. However, due to the presence of undissolved Nb particles during the deposition process, an additional heat treatment was necessary. The observed changes in mechanical properties were explained in relation to the phase constituents and deformation mechanisms. Due to the elevated oxygen content in the investigated materials (2 at.%), the specific deformation mechanisms were observed at lower Nb content in comparison to the conventionally fabricated materials. This made it possible to conclude that oxygen increases the stability of the β phase in β–Ti alloys. For the first time, superelasticity was observed in Ti–Nb-based alloys fabricated by the additive manufacturing method. The highest recoverable strain of 3% was observed in Ti–19Nb alloy as a result of high elasticity and reverse martensitic transformation stress-induced during the loading.

Sıcak Presleme Ve Yüksek Sıcaklık Sinterleme Kombinasyonu İle Β Tipi Biyomedikal Ti74Nb26 Alaşımının Üretimi

Titanium (Ti)-Niobium (Nb) alloys are generally produced by casting methods. Since themelting temperatures of pure Ti and Nb are quite high, their fabrication by casting techniques is costly.On the other hand, it is possible to produce these alloys economically at much lower temperatures (lessthan melting temperature of Ti), completely in solid state using powder metallurgy. In the present study,Ti74Nb26 alloys were produced using pure Ti and pure Nb powders by combination of hot pressing andhigh temperature sintering for the first time. The influences of processing temperature and time ondensity, microstructure, and mechanical behavior were investigated. Density measurements showed thathot pressing at 800 °C provided full density. XRD and SEM investigations revealed that amount of β phaseformed increased with increasing sintering time. In addition to main phase β, little amount of α phase anda very small amount of pure Nb were observed in the microstructure. Mechanical properties weremeasured by means of uniaxial compression and micro Vickers indentation tests. The results indicatedthat 4 h of sintering at 1200 °C exhibited the highest value of hardness (336 HV), elastic modulus (44 GPa),yield strength (894 MPa), and compressive strength (1178 MPa).

Interfacial Characterization and High‐Temperature Property of NbB2+NbC Nanoparticles‐Reinforced 2219Al Matrix Composite Synthesized by Melt Spinning

Particle‐reinforced Al metal matrix composites attract more attention due to their excellent properties. The size of the reinforcing particles and their distribution in the matrix are the key factors determining their properties. In situ NbB2 and NbC nanoparticles are prepared using Al–Nb and B4C powders as raw materials by melt spinning and used to reinforce 2219Al. To improve the distribution of nanoparticles in the matrix, the melt is subjected to ultrasonic vibration during the preparation of NbB2–NbC/2219Al composites. After adding the reinforcement nanoparticles and ultrasonic vibration treatment, the grain sizes of 2219Al are decreased. Scanning electron microscope (SEM) test results showed that most of the reinforcing particles are uniformly distributed in the matrix. The high‐resolution transmission electron microscope (HRTEM) image and selected‐area electron diffraction (SAED) pattern show that the reinforcing particles and α‐Al form coherent and semicoherent interfaces with direct atom bonding. The results of mechanical properties’ research show that the addition of NbB2 and NbC nanoparticles is beneficial to the room‐ and high‐temperature properties of the alloy.

Benefits in oxygen control and lowering sintering temperature by using hydride powders to sinter Ti–Nb–Zr SMAs

Abstract The Ti-(11–15)Nb–18Zr (at.%) alloys with low oxygen content and fine grain microstructure were successfully prepared by low temperature sintering after dielectric barrier discharge plasma (DBDP) milling of hydride (TiH2, ZrH2) and Nb powders. Hydride powders effectively reduced the oxygen content and lower the sintering temperature of Ti- (11–15) Nb–18Zr alloys. DBDP milling quickly refined and activated the TH2-Nb-ZrH2 powders without increased contamination by oxygen. The decrease in sintering temperature (as low as 1000 °C) helped to reduce the grain size of the Ti-(11–15)Nb–18Zr alloys to 3–8 μm, which has significantly increased the strength of the alloys. The reduction of oxygen content (as low as 0.4 wt%) in the Ti-(11–15)Nb–18Zr alloys benefited the superelasticity of the alloys. Among them, the Ti–12Nb–18Zr alloys presents an excellent superelasticity of about 1.5%, which is the highest value ever reported in the sintered Ti–Nb based SMAs.

Development of V-free porous Ti-A356-Nb alloy by liquid sintering of compacted powders and its oxidation behaviour

Porous Ti-Al-Si-Nb alloy was developed through a mixture of Ti, A356 Al alloy and Nb powders followed by compaction and sintering. The sintered Ti-Al-Si-Nb alloy was comprised of the α and β-phases after sintering. The Nb content was predominately found in the β-phase. XRD technique has detected the FCC phase (5.750 Å), the HCP (5.140 Å; c = 9.480 Å) and tetragonal Ti3Al (4.585 Å; c = 2.960 Å) phases. Upon cyclic oxidation conducted at 900 °C, the porous Ti-Al-Si-Nb alloy showed a progressive gain in weight of ∼3 wt% 100 h to ∼12 wt% after 900 h. EDS analysis confirmed the presence of O and N around the pores on the 800 °C and 900 °C annealed samples. The density of the porous Ti-Al-Si-Nb alloy increased with the holding time during cyclic oxidation.

Microstructure and elevated-temperature mechanical properties of in situ Ti2AlNb-reinforced TiAl-matrix composite prepared by powder metallurgy

An in situ Ti2AlNb-reinforced Ti–45Al–5Nb–0.3 W-based intermetallic composite was prepared using 2 vol. % Nb powder and TiAl pre-alloy powder. The microstructure evolution and elevated-temperature mechanical properties of the Ti2AlNb/TiAl composite were investigated. The results show that during the hot isostatic pressing (HIP) process, Nb diffused into the TiAl matrix, and formed Nb-rich particles in which an Nb-rich-region and the coarse rod-like Ti2AlNb phase existed. After hot extrusion, the Nb-rich particles elongated along the direction of extrusion. Further, the mean diameter of the Ti2AlNb phase regions decreased, and the Ti2AlNb content increased. After heat treatment at 1280 °C for 1 h, the rod-like Ti2AlNb phase regions in the extruded specimen transformed into needle-like and fine lath-like structures, and the proportion of Ti2AlNb in the Nb-rich-regions increased. The extruded Ti2AlNb/TiAl specimen shows a high tensile elongation (TE), and the heat-treated specimen shows a high yield strength (YS) and ultimate tensile strength (UTS) at the test temperatures of 750 °C–900 °C. In particular, the extruded specimen shows excellent strength–ductility product (UTS × TE) values of 38.8 GPa% and 46.9 GPa% at 800 °C and 850 °C, respectively. The high toughness of TiAl intermetallic composites was because of the fibrous tough Nb-rich-regions that contained the fine Ti2AlNb phase.

Effect of sintering time on corrosion behavior of an Ag/Al/Nb/Ti/Zn alloy system

High-entropy alloys are interesting for both aerospace and biomedical applications. Additionally, their application into a corrosive environment is also demanded. Investigations concerning to the effects in the sintering time on the microstructural features of an AgAlNbTiZn alloy system and correlating with corrosion behavior are scarce. This investigation is focused on the evaluation of the corrosion behavior of an AgAlNbTiZn alloy system in a 0.5 M NaCl solution at 25 °C. Experimental and simulated EIS parameters and potentiodynamic polarization curves are discussed. It is found that both the dispersed-Nb particles and the TiAl intermetallics constitute the microstructural arrays affecting significantly the cathode-to-anode area ratio. Consequently, the corrosion behavior is also substantially modified. It is also found that the sintered sample during 12 h reveals some colonies of the TiAl intermetallic interfacing with the Nb powder particles. These are lower (∼3x) than the sintered sample for 24 h. This evidences that the microstructural array has an important role on the corrosion current density and polarization resistance of the samples examined.

Properties of a rapidly solidified Ni–Nb layer prepared using a high-current pulsed electron beam

In this study, the surface of a bulk crystalline Ni–Nb powder metallurgy (PM) sample of a glass-forming composition was investigated using high-current pulsed electron-beam (HCPEB) irradiation, which also improved the surface properties. Unlike the original crystalline sample, X-ray diffraction (XRD) of the surface shows an amorphous phase following HCPEB exposure. Transmission electron microscopy (TEM) reveals that, after the Ni–Nb PM samples were exposed to 20 or 30 pulses of HCPEB irradiation, the re-melted layer contains localized nanocrystalline regions within an amorphous matrix. The scanning electron microscopy (SEM) results indicate that, after 30 pulses, a re-melted layer about 5 μm in thickness forms on the surface of the Ni–Nb PM samples. Meanwhile, a large number of cracks and craters were observed on the re-melted layer. In addition, the micro-hardness tests reveal that the micro-hardness improves significantly after HCPEB irradiation. The microhardness of the sample was the highest after the 30 pulses, which was 1.5 times that of the original sample. Furthermore, potentiodynamic polarization tests indicate that the irradiated samples of corrosion resistance were not enhanced compare to the initial samples, due to the formation of cracks providing a Cl− etching channel that accelerates the corrosion rate.

Preparation of Ti-22Al-25Nb solid solution powders using mechanical alloying and solid solution mechanism analysis

Solid solution powders of Ti-22Al-25Nb (at.%) were successfully prepared with Ti, Al, and Nb elemental powders via mechanical alloying (MA). The effects of milling time, stearic acid process control agent and Al2O3 reinforced particles on the morphology evolution, average particle size, crystallite size, solid solution and phase of mixed powders were studied. The solid solution mechanism and strengthening mechanism of Ti, Al and Nb mixed powders during MA were revealed. In addition, the strengthening effect of Al2O3 reinforced particles was clarified. The mixed powders at different milling times were characterized by X-ray diffraction and scanning electron microscopy. The microhardness of the solid solution powders was investigated, and the solid solubility of Al and Nb atoms in the Ti matrix was quantitatively calculated. The results revealed that the crystallite size of mixed powders without the addition of Al2O3 reinforced particles decreased with the increase of MA time, and was 18 nm after MA for 60 h. The solid solubility values of Al and Nb in the Ti matrix were 22.68 at.% and 9.49 at.%, respectively. The addition of Al2O3 reinforced particles could effectively refine the mixed powder particles, but had no obvious effect on the evolution of particle morphology; the values of load-bearing effects (ΔσLoad) and orowan strengthening (ΔσOrowan) were determined to be 27.5 MPa and 88.4 MPa, respectively. The microhardness values of the Ti-22Al-25Nb solid solution powders and Ti2AlNb-5 wt% Al2O3 nanocomposite powders were 435 HV and 465.8 HV, respectively. Compared to Al2O3 reinforced particles, stearic acid process control agent could significantly inhibit the welding between Ti, Al and Nb powders, making the powders more prone to disperse and break into small flakes with a smaller average particle size of 10 µm at 60 h. With the addition of stearic acid, the mechanical alloying process of Ti, Al and Nb element powders was inhibited, and the solid solubility of Al in the Ti matrix and the microhardness of the mixed powders after MA for 60 h were reduced to 16.31 at.% and 330 HV, respectively.

Effects of trace Nb addition on microstructure and properties of Ti–6Al–4V thin-wall structure prepared via cold metal transfer additive manufacturing

To refine the coarse columnar prior-β grains across the layers in the cold metal transfer additive manufacturing (CMTAM) of a Ti–6Al–4V thin-wall structure, the addition of trace Nb, which functioned as heterogeneous nuclei, is proposed. After the addition of trace Nb powder, intra-layer bands were obtained in each layer of the Ti–6Al–4V wall, which divided each layer into two parts according to the existing forms of Nb, including a rich unmelted-Nb-powder zone and a (β-Ti, Nb)-phase-rich zone. The unmelted Nb powder with an average diameter of 170 nm—which acted as heterogeneous nuclei, promoting the columnar-to-equiaxed transition of prior-β grains—mainly existed in the lower zones of the layers. A random distribution of (β-Ti, Nb) phases was observed in the upper zones of the layers, which experienced the highest loads (398.8 mN) with indentation displacement of 2000 nm in nanoindentation tests. The trace Nb addition affected the interplanar distances of (β-Ti, Nb) phases and changed the solidification mode from planar to cellular. Tensile tests revealed that the average ultimate tensile strength increased from 990 to 1149 MPa, as the solution strengthening of the (β-Ti, Nb) phases played the dominant role in strengthening, while the average strain decreased from 7.69% to 5.5%. The unmelted Nb powder was the cause of the change in the fracture modes from ductile behavior to mixed behavior of cleavage and ductile fracture. During the CMTAM process, the possible thermal cycles for as-built and trace-Nb-addition specimens were analyzed.

Superelastic behavior of in-situ eutectic-reaction manufactured high strength 3D porous NiTi-Nb scaffold

NiTi-Nb porous shape memory scaffold was in-situ sintered by eutectic reaction using NiTi powder, Nb powder and Ti wire at 1180 °C. Ti2Ni and Ni4Ti3 phases are precipitated between the eutectic region and Ti wire, while the R martensite phase and Nb-Rich phases are formed in both eutectic region and the pre-eutectic region. Moreover, the stacking faults and micro-twinning in the eutectic region are beneficial to nucleation of R-phase martensite. All results demonstrate that the eutectic reaction combined with the interaction of Ti wire, NiTi powder and Nb powder contribute to tremendous increase in compressive strength up to 350 MPa.

In situ synthesis of a binary Ti–10at% Nb alloy by electron beam melting using a mixture of elemental niobium and titanium powders

Abstract This study reports the results of the preliminary assessment to fabricate Ti-10at% Nb alloy by electron beam melting (EBM®) from a blend of elemental Nb and Ti powders. The microstructure of the EBM-manufactured Ti-10at% Nb alloys is sensitive to the following factors: different sintering properties of Nb and Ti powders, powder particle properties, material viscosities at varying melt pool temperatures, β-stabilizer element content and the EBM® process parameters. Three phases were observed in as-manufactured Ti-10at% Nb alloy: μm-size Nb phase, a Nb-rich β-solid solution surrounding Nb phase, lamellar structured α-phase and β-solid solution with different distribution and volume fraction. Thus, the combination of powder particle characteristics, very short time material spends in molten condition and sluggish kinetics of mixing and diffusional process in Ti-Nb alloy results in heterogeneous microstructures depending on the local Nb content in the powder blend and the EBM® process conditions.

Effect of Nb addition on mechanical properties and corrosion behavior of Ti6Al4V alloy produced by selective laser melting

Abstract

Influence of Mechanical Alloying and Sintering Temperature on the Microstructure and Mechanical Properties of a Ti-22Al-25Nb Alloy

In this research, a fine-grained Ti-22Al-25Nb (at.%) alloy was fabricated from the powders of Ti, Al and Nb by mechanical alloying (MA) and subsequent spark plasma sintering (SPS). The effects of MA and SPS parameters on the microstructure, micro-hardness and tribological properties of the sintered compacts were investigated and discussed. The single phase of (Ti, Al, Nb) bcc solid solution with the chemical composition of Ti-22Al-25Nb was produced by MA for 5-20 h and the rotation speed of 500 rpm. The mechanically alloyed powders for 5, 10, 15 and 20 h were subsequently consolidated by SPS at the temperature range of 1000-1300 °C for 60 min, respectively, followed by furnace cooling. The microstructures from the sintered compacts showed that the fine equiaxed B2 phase, the lamellar or equiaxed O phase, and the equiaxed α2 phase were present in all the sintered compacts. The highest micro-hardness value of 1840 HV0.3 and the smallest wear rate of 1.59 × 10−3 mm3/m were exhibited in the Ti-22Al-25Nb alloy sintered at 1100 °C/60 min/50 MPa.

Evolution of Nb oxide nanoprecipitates in Cu during reactive mechanical alloying

Abstract

Microstructure and formation mechanisms of TiNiNb amorphous powder prepared by mechanical alloying

Three high-purity (pure ≥99%) metal powders of Ti, Ni, and Nb (the atomic ratio of Ti, Ni, and Nb is Ti:Ni:Nb = 47%:44%:9%) were subjected to high-energy ball milling to explore the mechanical alloying process of TiNiNb alloy. Then, the phase transformation, microstructure and crystallization characteristics of the alloy powders were investigated and analyzed. The results show that the amorphous phase began to appear when the time reached 30 h. With the increase of milling time, the amorphous content gradually increased and tended to be stable, when the milling time reached 50 h. As for particle size, in the initial stage of ball milling, the powder particles were not obvious refined. Nevertheless, when the powder was milled for 30 h, the powder particles were significantly refined, the particle agglomeration was weakened, and the particle size became more uniform. When the ball milling reached 70 h, the average size of powder particles gradually reached stabilization.