Nb Powder Research Articles

Influence of High Pressure Torsion on structure and properties of Zr-Ti-Nb alloy synthesized from TiH2, ZrH2 and Nb powders

The effects of High Pressure Torsion (HPT) deformation on the microstructure and mechanical properties of a corrosion-resistant, low modulus Zr-Ti-Nb alloy, obtained by vacuum sintering of cold pressed powder are studied. It is shown that HPT treatment leads to the following effects: elimination of the residual chemical heterogeneity of the alloy, significant reduction of the porosity of the material and the pore size and improvement of mechanical properties. The phase composition of the alloy does not change during processing. The results show the potential of the HPT method for the production of alloys with a favorable combination of properties.

Sintering properties of Ti-27Nb alloys prepared by using Ti/TiH2 powders under argon and hydrogen sintering processes

In the present study, Ti-27Nb alloy specimens were prepared from Ti/TiH2 powders using Nb powders through the argon sintering process (ASP) and hydrogen sintering process (HSP). X-ray diffraction and scanning electron microscopy studies were conducted, and the sintered density, Vickers hardness, and Rockwell hardness of the Ti-27Nb alloys produced by different sintering processes, as a function of the vacuum sintering temperature (1350–1450 °C), were measured. The results showed that the Ti-27Nb alloy sintered bodies with the highest density and hardness were obtained by HSP. In addition, the pore size and number of HSP specimens were smaller and less than those of the ASP specimens. It was found that the Ti-27Nb alloy, produced by HSP, can prevent the formation of oxide layers, resulting in enhanced densification and hardness. Furthermore, HSP can also prevent the formation of hydrides and eliminate the dehydrogenation step. At the same time, the problem of brittleness and failure caused by hydride formation could be solved.

Extrinsic p-type doping of few layered WS2 films with niobium by pulsed laser deposition

Doping of few layered 2H WS2 films with Nb by pulsed laser deposition (PLD) using ablation targets fabricated from WS2, S and Nb powders is reported. The undoped controls were n-type, exhibited a Hall mobility of 0.4 cm2/Vs, and characterized by a Fermi level at 1.41 eV from the valence band edge. The latter was determined using ultraviolet photoelectron spectroscopy. Films doped at 0.5 and 1.1 atomic percentages niobium were p-type, and characterized by Fermi levels at 0.31 eV and 0.18 eV from the valence band edge. X-ray photoelectron spectroscopy indicates that Nb substitutes on W lattice sites. With increased Nb doping, the hole sheet concentration increased from 3.9 × 1012 to 8.6 × 1013 cm−2, while the mobility decreased from 7.2 to 2.6 cm2/Vs, presumably due to increased ionized impurity scattering. The approach demonstrates the potential of PLD for controlled doping of transition metal dichalcogenides.

Synthesis of Non-Stoichiometric (TiNb)C0.5 with High Hardness and Fracture Toughness under HTHP

Nonstoichiometric TiC0.5 and (TiNb)0.5 powders were prepared by the mechanical alloying process using Ti, Nb, and TiC powders as raw materials. Furthermore, the as-prepared TiC0.5 and (TiNb)0.5 powders were used as initial materials to fabricate TiC0.5 and (TiNb)0.5 compacts under high pressures and high temperatures (HTHP) of 5.5 GPa and 1200–1550 °C for 5 min. Phase identification and microstructure of the mechanical-alloyed powders and the sintered TiC0.5 and (TiNb)0.5 compacts were realized by an X-ray diffractometer and scanning electron microscope. The results indicate that the as-prepared TiC0.5 and (TiNb)0.5 powders have a similar crystal structure of face-centered cubic (FCC) to TiC. The sintered (TiNb)0.5 compact has good Vickers hardness (~16 GPa), and notably, excellent fracture toughness (~7.3 MPa·m1/2). The non-stoichiometric compound not only reduced the sintering temperature of covalent compounds, but also greatly enhanced the mechanical properties of the materials. Thus, we have provided a novel synthetic strategy for the production of a compound with high-strength covalent bonds.

Overlap Ratio in Wire- and Powder-Based Laser Metal Deposition of H11 + Nb for Hot Forging Dies

AISI H11 tool steel is a complex tool steel alloy used to manufacture hot forging dies. These dies however have a limited life, which depends upon the working conditions, the tool design, the heat treatment, and the quality of tool steels. In this paper, a novel wire-and powder-based laser metal deposition (WP-LMD) process was investigated to deposit H11 wire and niobium (Nb) powder simultaneously and develop a coating on existing forging dies for enhancing their life. The main aim was the development of a novel WP-LMD process, and consequently a new H11 tool steel with improved toughness and hardness. The developed WP-LMD process was later implemented to build a multilayer block made of the modified H11 tool steel. The overlap ratio was optimized in both, horizontal and vertical, directions, and were found to be 30% and 20% respectively in order to achieve a fully dense coating and avoid pores and unmelted Nb particles. The potential of the WP-LMD can be used to fabricate an outer layer of the modified H11 tool steel with improved toughness and hardness, which ultimately enhances the life of hot forging.

NiTi-Nb micro-trusses fabricated via extrusion-based 3D-printing of powders and transient-liquid-phase sintering

We present a novel additive manufacturing method for NiTi-Nb micro-trusses combining (i) extrusion-based 3D-printing of liquid inks containing NiTi and Nb powders, solvents, and a polymer binder into micro-trusses with 0/90° ABAB layers of parallel, ∼600 µm struts spaced 1 mm apart and (ii) subsequent heat-treatment to remove the binder and solvents, and then bond the NiTi powders using liquid phase sintering via the formation of a transient NiTi-Nb eutectic phase. We investigate the effects of Nb concentration (0, 1.5, 3.1, 6.7 at.% Nb) on the porosity, microstructure, and phase transformations of the printed NiTi-Nb micro-trusses. Micro-trusses with the highest Nb content exhibit long channels (from 3D-printing) and struts with smaller interconnected porosity (from partial sintering), resulting in overall porosities of ∼75% and low compressive stiffnesses of 1–1.6 GPa, similar to those of trabecular bone and in agreement with analytical and finite element modeling predictions. Diffusion of Nb into the NiTi particles from the bond regions results in a Ni-rich composition as the Nb replaces Ti atoms, leading to decreased martensite/austenite transformation temperatures. Adult human mesenchymal stem cells seeded on these micro-trusses showed excellent viability, proliferation, and extracellular matrix deposition over 14 days in culture. Statement of SignificanceNear-equiatomic NiTi micro-trusses are attractive for biomedical applications such as stents, actuators, and bone implants because of their combination of biocompatibility, low compressive stiffness, high surface area, and shape-memory or superelasticity. Extrusion-based 3D-printing of NiTi powder-based inks into micro-trusses is feasible, but the subsequent sintering of the powders into dense struts is unachievable due to low diffusivity, large particle size, and low packing density of the NiTi powders. We present a solution, whereby Nb powders are added to the NiTi inks, thus forming during sintering a eutectic NiTi-Nb liquid phase which bonds the solid NiTi powders and improves densification of the struts. This study investigates the microstructure, porosity, phase transformation behavior, compressive stiffness, and cytocompatibility of these printed NiTi-Nb micro-trusses.

Helium irradiation behavior of tungsten-niobium alloys under different ion energies

Tungsten is a primary material in plasma-facing components (PFCs), but several disadvantages limit its application in fusion reactors. This work examined tungsten–niobium (W–Nb) alloys as potential PFC materials and investigated their response to low-energy helium ion irradiation. W–Nb powders were milled for 25 and 36 h, and the W–Nb samples were exposed to 50 and 80 eV helium ion irradiation with a flux of 1.5 × 1022 ions/m2 s at 1230 °C. The sample with a dense structure and obtained after a 25-h milling exhibited enhanced anti-irradiation performance. Sufficient energy can be provided to promote helium ion migration in the matrix, resulting in the formation of nanotendrils. Furthermore, in W–Nb alloys, the Nb-rich regions are more attractive to helium ions and thus provide protection to the tungsten matrix.

Effect of calcium pyrophosphate on microstructural evolution and in vitro biocompatibility of Ti-35Nb-7Zr composite by spark plasma sintering

β-type Ti-35Nb-7Zr alloy has attracted considerable attentions as a bone implant material. The alloy, however, has poor bioactivity, which difficult to form a strong osseointegration between the bone tissues. Combining Ti alloy with a bioactive and biodegradable ceramic has been of interest to researchers. But the large difference in physicochemical property of high-melting metal and ceramic elements would bring the manufacturing restriction. In this work, Ti-35Nb-7Zr-CPP composites were fabricated with mechanical alloy of Ti, Nb, Zr and Nano calcium pyrophosphate (CPP) powders mixture followed by spark plasma sintering (SPS) routes. The effect of CPP ceramic on microstructural evolution and in vitro biocompatibility were investigated. As the addition of CPP (10–30 wt%), ceramic elements spreading towards the matrix, the generated metal-ceramic bioactive phases CaTiO3 are observed well consolidated with β-Ti matrix. With the CPP increasing, Ca and P atoms rapidly migrated to the β-Ti matrix to form granulated Ti5P3, which leads to the increasing porosity (10%–18%) in the composites. The results demonstrated that the favorable cell viability (the cell proliferation rates were higher than 100%) and growth inside the pores of the composites arise from the rough micro-porous surface and the release of bioactive metal-ceramic phase ions into the biological environment. The enhanced bioactivity and microstructural evolution behaviors of the Ti-35Nb-7Zr-CPP composites may provide a strategy for designing and fabricating multifunctional implants.

Effects of Nb Modification and Cooling Rate on the Microstructure in an Ultrahigh Carbon Steel

In this study, two different melting methods were used to investigate effects of Nb modification on microstructure in ultrahigh carbon steel (UHCS). Nb-free and Nb-modified UHCS samples were produced by melting and resolidifying an industrially produced base UHCS with and without addition of Nb powder. Microstructure was characterized using scanning electron microscopy, X-ray diffraction, and electron dispersive spectroscopy. Equilibrium computations of phase fractions and compositions were utilized to help describe microstructural changes caused by the Nb additions. Nb combined with C to form NbC structures before and during austenite solidification, reducing the effective amount of carbon available for the other phases. Cementite network spacing in the Nb-free samples was controlled by the cooling rate during solidification (faster cooling led to a more refined network). Network spacing in the Nb-modified UHCS could be enlarged by NbC structures that formed cooperatively with austenite.

Processing and Characterization of Liquid-Phase Sintered NiTi Woven Structures

Porous NiTi is of interest for bone implants because of its unique combination of biocompatibility (encouraging osseointegration), high strength (to prevent fracture), low stiffness (to reduce stress shielding), and shape memory or superelasticity (to deploy an implant). A promising method for creating NiTi structures with regular open channels is via 3D weaving of NiTi wires. This paper presents a processing method to bond woven NiTi wire structures at contact points between wires to achieve structural integrity: (i) a slurry consisting of a blend of NiTi and Nb powders is deposited on the surface of the NiTi wires after the weaving operation; (ii) the powders are melted to create a eutectic liquid phase which collects at contact points; and (iii) the liquid is solidified and binds the NiTi woven structures. The bonded NiTi wire structures exhibited lower transformation temperatures compared to the as-woven NiTi wires because of Nb diffusion into the NiTi wires. A bonded woven sample was deformed in bending and showed near-complete recovery up to 6% strain and recovered nearly half of the deformation up to 19% strain.

Role of beta-stabilizing elements on the microstructure and mechanical properties evolution of modified PM Ti surfaces designed for biomedical applications

ABSTRACTThis work focuses on the evaluation of modified surfaces on Ti produced by powder metallurgy. These newly designed surface modifications are achieved by deposition and diffusion of a stable aqueous suspension prepared in one case from micro-sized Nb powder (Ti β-stabilizer element) and in another case from Nb plus the addition of ammonium chloride, NH4Cl, (thermo-reactive diffusion process). Different design parameters such as diffusion element (Nb or Mo), state of the Ti substrate (green or sintered) and the treatment process (diffusion or thermo-reactive diffusion) lead to all the surface-modified materials, GreenTi–Nb, SintTi–Nb and Ti–NbNH4Cl, GreenTi–Mo, SintTi–Mo and Ti–MoNH4Cl. The modified Ti surfaces present a gradient in composition and microstructure (β / α+β / α phases) resulting in an improvement in some of their mechanical properties: (1) higher micro-hardness in all the modified materials and (2) lower elastic modulus (more similar to that of the human bone) in those without NH4Cl.Invited keynote papers from EuroPM2017, Milan.

Study for Combined Wire + Powder Laser Metal Deposition of H11 and Niobium

Laser additive manufacturing (LAM) has been proved to be a successful technique to fabricate metallic components for a number of industries; for instance, die & mold, forging and cutting tools, and aerospace. It is, however, facing multitude obstacles due to lack of maturity in terms of process knowledge, design, and qualification. This paper deals with parameters’ study and optimization of combined hot-work tool steel wire (H11) and niobium powder (Nb) deposition by laser. The process is closely analysed and compared with as well as without using Nb powder. Especially, the importance of Nb in order to refine the microstructure is discussed while taking into account the microstructure-property relationships of H11.

Surface modification of TC4 Ti alloy by laser cladding with Ni-Ti-Nb powders

TC4 Ti alloy with the excellent properties can be applied to many fields, but the surface performance such as wear-resisting, fretting wear, contact corrosion etc.can't be met for many special demands. Laser cladding was applied on a TC4 Ti alloy to improve its properties. Mixed Ni,Ti and Nb powders were put onto the TC4 Ti alloy and subsequently treated by laser beam. The experimental results show that the surface hardness and wear resistance are significantly improved. The increase in wear resistance is predicted to be related to the "adaptive" wear mechanism of SMA.The microstructure and composition modifications in the surface layer were carefully investigated by using SEM, EDX and metallographic microscope. Experimental analyses show that the compositions of laser cladding coating are close to shape memory alloy of 44Ni-47Ti-9Nb,and differedt microstructure are rich with different elements. These experimental results are associated with laser processing techniques and alloy composition to some extent.

Mehaničke i strukturne karakteristike slojeva prevlake Nb deponovane u vakuumu

In this paper analyzed was the influence of implementation of inert Ar gas and a mixture of inert plasma Ar / He gases in a vacuum chamber on the deposition of reactive niobium (Nb) powder. The aim of this paper was to deposit coating layers of high density, without oxide content, that will find application in the field of biomedicine. Detailed examination was performed of mechanical properties of microhardness using the HV0.3 method, of tensile bond strength by tensile testing and of the microstructure of the coating layers in the deposited state and after etching. For etching a solution of nitric acid HNO3 and hydrofluoric acid HF in a ratio of 1:1was used. It was found that inert gases, at low pressure prevent the reaction of gases with the metal droplets of molten Nb powder particles during the plasma spray deposition process. The density of the deposited coating in vacuum chamber is higher than that of coatings which are deposited at atmospheric pressure with reactive plasma gases N2 and H2. This is attributed to the elimination of thin oxide and nitride films at the interlamellar Nb contact, substantially increasing the ductility of the coating, eliminating the micro cracks through the deposited layers, which was confirmed by metallographic examination of samples. Tests have shown that VPS - Nb coating layers have mechanical properties and microstructure which completely enable the use of the coating on implants.

Structural and Phase Transformations in Alloys during Spark Plasma Sintering of Ti + 23.5 at % Al + 21 at % Nb Powder Mixtures

We have studied the effect of sintering temperature on the structural and phase transformations of alloys produced by the spark plasma sintering of Ti + 23.5 at % Al + 21 at % Nb powder mixtures at temperatures in the range 1100–1550°C. The sintered alloys have been characterized by X-ray diffraction, scanning electron microscopy, and energy dispersive X-ray spectroscopy (elemental X-ray mapping). The alloys sintered at temperatures of 1100 and 1200°C have been shown to have a nonuniform microstructure. According to electron microscopy results, the alloys consist of grains of the α2 and Nb2Al phases and small precipitates of the O-phase (intermetallic compound Ti2AlNb). In addition, there are particles of unreacted niobium and titanium. The alloys sintered at a temperature of 1300°C have a uniform lamellar structure.

Effect of niobium on microstructure-property relationship in H11 hot-work tool steel via wire- and powder-based laser metal deposition

This paper presents an effect of niobium (Nb) on the microstructure-property relationship in H11 hot-work tool steel. Various amounts of Nb powder were introduced into the molten pool of H11 wire through a novel wire- and powder-based laser metal deposition (WP-LMD) process. With the increase in Nb content up to 3.45 wt.%, the average grain size of H11 decreased from 14.3 µm to 2.83 µm, while the average Vickers microhardness decreased from 706 HV0.2 to 301 HV0.2. The critical amount of Nb was then found to be 1.73 wt.%, which produced a hard (average hardness of 606 HV0.2), and refined (average grain size of 3.01 µm) microstructure of H11. Such kind of microstructures can assure high toughness and high hardness; hence more suitable for hot-working industries such as die and mould, forging and cutting tools.

Features of the microstructure of Ti–Nb alloy obtained via selective laser melting

Ti–Nb alloy with 40 wt % of Nb is obtained from a composite Ti–Nb powder by means of selective laser melting. The Ti–Nb alloy has a two-phase microstructure. The main β-phase of the solid titanium–niobium solution forms grains ranging in size from ~2 to 20 μm. A nonequilibrium α″-phase is found in the forms of lamellar, globular, and packet martensite inside the grains of the β-phase and along their boundaries.

Sliding wear induced subsurface microstructural evolution in nanocrystalline Nb-Ag binary alloys and its impact on tribological performance

Powders of Nb and Ag were first subjected to mechanical alloying to force the formation of supersaturated solid solutions and then compacted to near full density using spark plasma sintering. During the sintering process, Ag precipitated out from the Nb matrix along the Nb grain boundaries, with the size of the precipitates depending on the nominal chemical composition. Pin-on-disk wear tests show that the nanostructured Nb-Ag alloys show good wear resistance. A wear factor of 10−5mm3/(N·m) was observed upon sliding against stainless steel 440C. Ag concentration has a significant effect on the wear rate and wear modes of Nb-Ag alloys. For higher Ag concentration with larger initial Ag precipitate size and lower hardness, severe plastic deformation (SPD) during wear induced the spontaneous formation of alternating Nb and Ag nanolayers. These nanolayered structures remain stable up to the sliding surface, leading to a reduction in the wear rate. In contrast, for lower Ag concentration with smaller Ag precipitate size and higher hardness, SPD can dissolve the Ag precipitates and force the formation of supersaturated solid solutions with equiaxed nanograins below the sliding surface. This results in an increase in the wear rate.

Electrical Conductivity of Cu and Cu-2vol.% Nb Powders and the Effect of Varying Sintering Temperatures on their Mechanical Properties Using Spark Plasma Sintering

The growing demand for relatively inexpensive non-hazardous copper alloys with a good combination of electrical conductivity and high strength has led to increasing researches on Cu-Nb alloys for their excellent predictions over Cu-Be alloys. Cu-2vol.% Nb was produced using spark plasma sintering and the effect of the additive on its electrical conductivity, densification, hardness, corrosion resistance and wear resistance were investigated. It was observed that the additive improved the electrical conductivity of Cu powder from 0.28 to 5.89 S/m within 19–406 ∘C. Relative densities of 97.08% for Cu-2vol.% Nb and 97.33% for pure Cu were obtained at 600 ∘C, while at 650 ∘C, they were 96.08 and 96.82% respectively. The microhardness values were 77 and 72 Hv0.1at 600 ∘C, while at 650 ∘C, they were 83 and 66 Hv0.1 for Cu-2vol.% Nb and pure Cu respectively. The corrosion potential of Cu-2vol.% Nb was noble with a lower anodic current density, suggesting better corrosion resistance at 600 ∘C. Cu-2vol.% Nb showed a better wear resistance at 600 ∘C and an improved electrical conductivity at 650 ∘C.

In-situ formation of NbC in nanocrystalline Cu

We report on an investigation of the in-situ formation of NbC nanoparticles in a Cu nanocrystalline matrix, paying particular attention to the role played by NbC on stabilizing and strengthening the matrix. The material was prepared by milling a Cu-5wt%Nb powder mixture with 1 wt% stearic acid for 36 h, followed by annealing of the milled powder at temperatures ranging from 400 to 1000 °C. Our results show that the NbC nucleates at an approximate temperature of 700 °C and that the associated enthalpy of formation and activation energy of NbC are approximately −0.8 kJ/mol and +312 kJ/mol, respectively. Moreover, the initial size of NbC particles formed at 700 °C was 8 nm, and showed limited coarsening (to 21 nm) even when annealed at 1000 °C for 1 h. With the presence of NbC, dislocation annihilation was impaired and grain boundary mobility was hindered, resulting in a dislocation density as high as 1014 m−2 following annealing at 1000 °C, and a grain size of 96 nm after annealing at 900 °C. The high thermal stability of NbC nanoparticles and the Cu matrix lead to appreciable strengthening of the composite powders as evidenced by a microhardness increase from 2128 MPa for the as-milled powder to 2665 MPa for the powder annealed at 700 °C for 1 h.