Nb-rich Phase Research Articles

Development of a new β Ti alloy with low modulus and favorable plasticity for implant material

One of the most important development directions of the Ti and its alloys is the applications in medical field. Development of new Ti alloys with low elastic modulus and/or favorable biocompatibility plays an important role for promoting its application in medical field. In this work, a new β Ti alloy (Ti–31Nb–6Zr–5Mo, wt.%) was designed for implant material using d-electron alloy design method. Microstructure and tensile properties of the designed alloy after hot rolling (HR) and solution followed by aging treatments (SA) were investigated. Results show that the designed alloy is composed of single β phase. However, microstructural analysis shows that the β phase in the designed alloy separates into Nb-rich and Nb-poor phase regions. The Nb-rich regions in HR specimen are typical elongated fiber texture, but are equiaxed particles with several micrometers in SA specimen. Tensile results show that the designed alloy has low Young's modulus of 44GPa for HR specimen and 48GPa for SA specimen which are very close to the extreme of Young's modulus of bulk titanium alloys. At the same time, the designed alloy has favorable plasticity in term of elongation of 26.7% for HR specimen and 20.6% for SA specimen, and appropriate tensile strength over 700MPa. In short, the designed alloy has low elastic modulus close to that of bone and favorable plasticity and strength which can be a potential candidate for hard tissue replacements.

High temperature and high pressure oxidation behavior of Zr-2.5Nb pressure tube material – Effect of β phase composition and surface machining

Pressure tube material, Zr-2.5Nb, of pressurized heavy water reactors was given selective heat-treatments. The objective was to generate microstructures with different compositions of the second phase β namely, Νb depleted βZr phase and Nb rich βNb phase. The material with βZr was then subjected to surface machining. The presence of phases after different heat-treatments was confirmed by X-ray diffraction and the resultant microstructures were characterized by transmission electron microscopy and electron back scattered diffraction. The Nb content in the β phase after heat-treatments and residual stresses before and after surface machining were measured using X-ray diffraction. Oxidation was carried out in steam at 400 °C and 10 MPa up to 30 days and the oxides were characterized by Raman spectroscopy. It is shown that the presence of Nb rich βNb in the microstructure and faster diffusion of Nb into β phase brought about by surface machining resulted in an enhanced oxidation resistance.

The effects of Mn and Nb on the microstructure and mechanical properties of Alloy 152 welds

Abstract This study was to investigate the synergetic effects of Mn and Nb on the microstructure and mechanical properties of Ni-based welds. The dissimilar weldments of Alloy 690 and SUS 304 L were welded with a manual shielding metal arc welding (SMAW) process. The weld metals were made of a core wire of Alloy 52 coated with fluxes of various Mn and Nb additions. The results showed that an increase in Mn could induce finer grains and smaller Nb-rich phases in the welds, while the dendrites and Mn-oxides became larger. For the welds with 3.99 wt.% Mn and 1.82 wt.% Nb, Nb-rich precipitates and Mn-oxides became smaller, and dendrites grew denser concurrently. The elongation of the welds at room temperature increased with the addition of Mn, but, by contrast, their hardness decreased. High contents of Mn and Nb could improve the notch strength and ductility at 300 °C, while they had little effects on the tensile stress at room temperature. Ductile ridges were the dominant fracture feature of the welds with an addition of Mn. For the welds with 3.99 wt.% Mn and 1.82 wt.% Nb, ridges dotted with small and deep dimples became prevalent.

Superelasticity of NiTi–Nb metallurgical bonding via nanoindentation observation

Sandwich architecture with cross-shape periodic cellular cores is synthesized via eutectic reaction between NiTi and Nb powder, such forming metallurgical bonding between NiTi wires near eutectic reaction temperature. Superelasticity is investigated systematically via nanoindentation tests. The Ti-rich phase is weaker in superelastic recovery comparing with that of Nb-rich phase, lamellar and rod-like NiTi–Nb eutectic. Inconsistent Nb element distribution in the interface of eutectic area and NiTi wire enhances the martensitic transformation.

Investigations on Structure–Property Relationships of Inconel 718 and AISI 430 Dissimilar Weldments

In this research work, an attempt has been made to weld nickel-based superalloy, Inconel 718 and ferritic stainless steel, AISI 430, using a gas tungsten arc welding process employing ER2553 and ERNiCrMo-4 fillers. Microstructure studies revealed the formation of an unmixed zone and the presence of tiny Nb-rich phases in the heat-affected zone (HAZ) of Inconel 718; also, grain coarsening was observed at the HAZ of AISI 430. Tensile studies corroborated that the failures occurred at the parent metal of AISI 430 in all the experimental trials. Bend test results revealed that no cracks occurred in either of the weldments reporting for ductility and soundness of the weld joints. This work also articulates the detailed structure–property relationships of these dissimilar weldments using the combined techniques of optical and scanning electron microscopy. The outcomes of the present study will be helpful to the aerospace and nuclear sectors.

Microstructure, phase transformation and mechanical property of Nb-doped Ni–Mn–Ga alloys

This study investigated the microstructure, phase transformation and mechanical property of (Ni49.8Mn28.5Ga21.7)100-xNbx (x = 1, 3, 6, 9) alloys. The Nb1 alloy exhibited a single austenite phase at room temperature. With increasing Nb content for Nb3, Nb6 and Nb9, the alloy changed to a dual phase consisting of austenitic matrix and Nb-rich second phase with a hexagonal structure, and the amount of the second phase increased with the increase of Nb content. The martensitic transformation temperature and Curie temperature were changed and the transformation enthalpy was gradually reduced with increasing Nb content. The change of martensitic transformation temperature and Curie temperature was related to the introduction of Nb in the Ni–Mn–Ga structure that decreased valence electron concentration (e/a), increased unit cell volume and reduced magnetic exchange of the alloys. The decrease of transformation enthalpy was mainly attributed to the formation and increase of the Nb-rich second phase that reduced volume fraction of the matrix taking part in phase transformation. All the alloys presented a similar compression behavior with progressively fracturing characters (occurrence of several stress drops before complete fracturing). The fracture strength was slightly enhanced with increasing Nb content from Nb0 to Nb9, but the ductility has no apparent improvement.

Microstructure, transformation behavior and mechanical properties of a (Ti50Ni38Cu12)93Nb7 alloy

A (Ti50Ni38Cu12)93Nb7 alloy is fabricated by arc melting, forging and drawing. The microstructure, transformation behavior and mechanical properties were investigated by means of scanning electron microscope (SEM), differential scanning calorimeter (DSC), dynamic mechanical analyzer (DMA) and tensile test machine. SEM observation showed that the as cast alloy is composed of TiNiCu and Nb-rich phases. After drawing, the alloy showed single step transformations during heating and cooling within the whole annealing temperature range from 400°C to 800°C. With the increase of the annealing temperature, both the transformation temperatures and the damping capacity increased first and then decreased. The ultimate strength of the alloy after annealing at 400°C is over 1500MPa and the maximum elongation of the alloy after annealing at 800°C is more than 20%.

Phase equilibrium between bcc solid solution matrix and B2 aluminides in Nb-based alloy

ABSTRACTB2 aluminides have a role of Al reservoir for Al2O3 surface and it is expected to increase oxidation resistance of (Nb,Mo)-bccss substrate. For the accumulation of the basic information to design the alloy composed of B2 coating on bccss matrix, bccss - B2 two-phase field was investigated in the Nb-Mo-Ni-Pd-Al system at 1273 K. It is found that Pd-rich B2-(Ni,Pd)Al phase is in equilibrium with Nb-rich bccss phase, while without Pd, the composition range of bccss coexisting with B2-NiAl phase is limited to be low Nb.

Effects of sintering process on microstructure and microwave dielectric properties of Ba(Co1/3Nb2/3)O3 ceramics

Ba(Co1/3Nb2/3)O3 (BCN) ceramics were prepared using a conventional solid-state route. Effects of sintering on microstructure and microwave dielectric properties of Ba(Co1/3Nb2/3)O3 ceramics were systematically investigated. Appropriate sintering temperature could restrain the evaporation of CoO and the formation of Nb-rich phase. The dielectric constants and temperature coefficients of resonant frequency changed slightly with the variation in sintering temperatures. The high Q × f value with prolonged sintering time was related to the improvement of 1: 2 ordered arrangement in the B site, rather than the compactness of ceramics. Excellent microwave dielectric properties (e r =32.6, Q × f =86857 GHz, τ f =−14 ppm/°C) were obtained in the Ba(Co1/3Nb2/3)O3 ceramics sintered at 1380°C for 12 h.

Precipitation of Nanosized MX at Coherent Cu-Rich Phases in Super304H Austenitic Steel

The present investigation of transmission electron microscopy reports the precipitation of nanosized and cubical-shaped incoherent Nb-rich MX at the coherent Cu-rich phases in the austenitic matrix of the Super304H steel. In addition, the nanosized Nb-rich MX phases were often observed to precipitate on dislocations during creep. It is concluded that the dense incoherent Nb-rich MX and coherent Cu-rich precipitates with a nanosized diameter contribute excellent creep resistance in the steel.

De-vitrification of nanoscale phase-separated amorphous thin films in the immiscible copper–niobium system

Copper and niobium are mutually immiscible in the solid state and exhibit a large positive enthalpy of mixing in the liquid state. Using vapour quenching via magnetron co-sputter deposition, far-from equilibrium amorphous Cu–Nb films have been deposited which exhibit a nanoscale phase separation. Annealing these amorphous films at low temperatures (~200 °C) initiates crystallization via the nucleation and growth of primary nanocrystals of a face-centred cubic Cu-rich phase separated by the amorphous matrix. Interestingly, subsequent annealing at a higher temperature (>300 °C) leads to the polymorphic nucleation and growth of large spherulitic grains of a body-centred cubic Nb-rich phase within the retained amorphous matrix of the partially crystallized film. This sequential two-stage crystallization process has been investigated in detail by combining transmission electron microscopy [TEM] (including high-resolution TEM) and atom probe tomography studies. These results provide new insights into the crystallization behaviour of such unusual far-from equilibrium phase-separated metallic glasses in immiscible systems.

Effect of the Linear Electromagnetic Stirring on Microstructure and Properties of Cu-10%Nb Alloys

Cu-10%Nb alloys were solidified with or without electromagnetic stirring. The effect of electromagnetic stirring (EMS) on the distribution of Nb particles in solidified Cu-10%Nb ingots and the performance of its deformed wires were studied. The 300A/16Hz EMS has refined the microstructure of Cu-10%Nb alloy, with smaller phase size and larger amount, and is benefit to the homogenous distribution of Nb-rich phases. The fitted lognormal distribution of Nb phase size in case without or with EMS is compared, and the EMS case has the higher frequency percentage in the range of smaller size for both the solidified ingot and the deformed wire. Cu-10%Nb wires in EMS case have a less value of electrical conductivity and a considerably higher ultimate tensile strength compared with that without EMS.

Microstructural characteristics of a cast IN718 superalloy bonded by isothermal solidification

Isothermal solidification is a key feature of transient liquid phase bonding which prevents the formation of deleterious intermetallic phases in the joint centerline and results in bonds with improved mechanical performance. This paper discusses the metallurgical characteristics and mechanical properties of an as-cast IN718 superalloy bonded by diffusion-induced isothermal solidification of Ni-7Cr-4.5Si-3.2B-3Fe (wt%) filler metal. After transient liquid phase bonding of as-cast IN718 at 1000 °C for 60 min, a bond exhibiting a solid solution microstructure with joint efficiency of 72% in terms of shear strength was obtained. The joining process was effectively able to prevent the formation of hard and brittle nickel and chromium borides, which typically lead to critical problems in brazing. The formation of Nb-rich Laves phase, which is well known as a major issue in the fusion welding of IN718, was not observed. The bonding time, which governs the extent of isothermal solidification, was a critical parameter for controlling the mechanical properties of the joints in terms of shear strength and hardness distribution across the bond.

Dissimilar pulsed Nd:YAG laser welding of pure niobium to Ti–6Al–4V

Dissimilar butt welding of pure niobium plate to the titanium alloy Ti–6Al–4V sheet using a pulsed Nd:YAG laser is performed. Effects of laser pulse energy, duration and repetition rates on the melt profile on both sides of the weld line were investigated. Considering the thermo-physical properties of the two base metals, variation of the weld profiles on different sides of the weld line is discussed. Through optimization of the process parameters a sound weld with full penetration along the dissimilar interface was obtained. However, islands of Ti rich and Nb rich phases were identified in the weld metal. Tensile strength of the welded joints matched that of the weaker base metal i.e. niobium and the specimens broke outside the fusion line.

Microstructure and Hardness Properties Investigation of Ti and Nb Added FeNiAlCuCrTi x Nb y High Entropy Alloys

Properties of pure metals can be enhanced by alloying with other metallic or non-metallic elements according to the need. However, as multiple alloying elements in an alloy may lead to the formation of many intermetallic compounds with complex microstructures and poor mechanical properties, new types of metallic alloys called high entropy alloys with at least five elements with equimolar ratios were developed. In this study, FeNiAlCuCrTi x Nb y (x, y = 0, 0.5, 1.0, 1.5) alloys have been prepared using Ar arc melting technique. Microstructural studies using scanning electron microscope and XRD showed that Ti addition promoted secondary BCC2 phase whereas, Nb acted as FCC stabilizer. Samples with combined Nb and Ti addition showed FCC1 and FCC2 structure with Nb-rich FCC2 dendritic phase as dominant phase. Though, individual Nb and Ti additions have resulted in increased hardness, combined additions have resulted in highest hardness of 797 HV under 1 kg load.

Aspectos metalúrgicos de revestimentos dissimilares com a superliga à base de níquel inconel 625

Prolongar a vida útil e aumentar a confiabilidade de equipamentos e tubulações de plantas de produção e processamento de petróleo é uma busca constante no setor de petróleo e gás. Tais aspectos dependem essencialmente do uso de ligas resistentes à corrosão. Neste contexto, a soldagem de revestimento com superligas à base de níquel tem sido uma alternativa interessante, pois confere aos equipamentos uma alta resistência à corrosão com um custo inferior, se comparado à fabricação de componentes ou tubulações maciças com superligas. Assim, o objetivo do presente trabalho foi investigar o comportamento metalúrgico de revestimento de superliga à base de níquel do tipo Inconel 625 depositados pelo processo TIG com alimentação de arame frio. As soldagens foram realizadas em uma bancada robotizada, empregando uma fonte eletrônica de soldagem com sistema de aquisição de dados para o monitoramento dos sinais de corrente e tensão. A caracterização microestrutural foi realizada através das técnicas de microscopia eletrônica de varredura (MEV) e transmissão (MET), espectroscopia de energia dispersiva de raios-X (EDS). Os resultados mostraram que a microestrutura do metal de solda foi constituída por uma matriz γ com fases secundárias ricas em Nb. Foi encontrada a formação de precipitados complexos de carbonetos/nitretos de Ti e Nb.

Uranium-niobium-rich alteration products after “písekite”, an intimate mixture of Y,REE,Nb,Ta,Ti-oxide minerals from the Obrázek I pegmatite, Písek, Czech Republic

An improperly described association, further called pisekite aggregate, of fine-grained, mostly metamict U, Th-enriched Y, REE, Nb, Ta, Ti-oxide minerals from Obrazek I pegmatite, Pisek, forms an intimate mixture of polycrase-(Y), samarskite-(Y) and fergusonite-(Y). It underwent a low-temperature hydrothermal alteration the products of which are depleted in Y and REE>U and significantly enriched in Si, As and P. Two distinct assemblages of secondary phases were recognized to be associated with pisekite aggregate, namely (i) that developed within the central parts of the aggregate and (ii) pocket assemblage in albite adjacent to it. Both assemblages are dominated by Fe-rich smectite. Pisekite aggregate is intensively replaced by U, Nb, Ti, Fe, As, P-rich phases of variable chemical composition: phase A (Nb>Ti>Fe>U>As) from the first assemblage, as well as phases B (U similar to Nb>Ti>As>P>Fe) and C (U>Nb>As>Fe>Ti) from the second assemblage. Associated pharmacosiderite and kahlerite/metakahlerite as well as Fe-rich smectite indicate a low temperature of the alteration processes (less than 150-200 degrees C). Whereas the pisekite aggregate was the likely source of U, Nb and Ti, arsenopyrite of the host pegmatite yielded As with Fe. The textural features show that the Fe-rich smectite replacement by the U, Nb-rich phases A, B and C took place on a micrometer scale, and these highly heterogeneous U, Nb-rich phases likely represent a mixture of nanoscale, possibly amorphous hydrated oxides, phosphates-arsenates as well as silicates of U, Fe and Ca.

Influence of isochronal annealing on the microstructure and magnetic properties of Cu-free HITPERM Fe40.5Co40.5Nb7B12 alloy

Systematic study of the effect of isochronal annealing on the structure and magnetic properties of Cu-free HITPERM alloy (Fe40.5Co40.5Nb7B12) is described herein. Mössbauer spectroscopy (MS) and anomalous x-ray diffraction (XRD) measurement at Fe K-edge (7.112 keV) jointly provide clear evidence for the presence of atomically ordered α′-FeCo (B2 structure) phase as a nanocrystalline ferromagnetic phase. Being a short range order probe, Mössbauer spectroscopy also confirms the development of an additional non-magnetic Nb-rich phase in the nanocrystalline specimens (annealed above 723 K) with simultaneous lowering of the volume fraction of ferromagnetic phases. The fraction of Fe atoms in the non-magnetic phase is ∼15% upon annealing at 773 K for 1 h, which increases gradually and reaches to as high as ∼19% after annealing at 923 K. This phase was not detected by XRD and transmission electron microscopy (TEM) measurements, which may be attributed to tiny crystallite size and/or high degree of disorder. In the second stage of crystallization, i.e., above 923 K, the alloy becomes fully crystalline and a stable, hard magnetic fcc-(FeCo)23B6 type phase was observed as a main boride phase along with soft magnetic α′-FeCo phase and Nb rich non-magnetic phase. Thermo magnetic measurement evidenced re-crystallization process as a considerable decrease in magnetization at the second transformation stage. Simultaneous lowering of the volume fraction of magnetic phases with the formation of non-magnetic phase provides convincing origin for the decrease in magnetization at the second crystallization stage.

The precipitation strengthening behavior of Cu-rich phase in Nb contained advanced Fe–Cr–Ni type austenitic heat resistant steel for USC power plant application

Copper has been used as a strengthening element in newly developed Fe–Cr–Ni type austenitic heat resistant steel for inducing Cu-rich phase precipitation to meet high temperature strength requirement for 600°C Ultra Super-Critical (USC) coal fired power plants for many years. However, the precipitation behavior and strengthening mechanism of Cu-rich phase in these advanced austenitic heat resistant steels is still unclear. In order to understand the precipitation strengthening behavior of Cu-rich phase and to promote high strength austenitic heat resistant steel development, 18 Cr9 NiCuNb steel which is a Cu-added Nb contained advanced Fe–Cr–Ni type austenitic heat resistant steel has been selected for this study to be aged at 650°C till to 10,000h. Micro-hardness and room temperature tensile test were conducted after long-time aging. SEM, TEM, HRTEM and three dimensional atom probe (3DAP) technology accompanying with thermodynamic calculation have been used to investigate the Cu-rich phase precipitation behavior during 650°C aging. The experimental results showed that Cu atoms can quickly concentrate in clusters at very early precipitation stage to form the fine nano-size Cu-rich “segregation areas” within less than 1h at 650°C. With increasing aging time at 650°C Cu atoms continuously concentrate to Cu-rich segregation areas (clusters) and simultaneously other kinds of atoms such as Fe, Cr and Ni diffuse away from Cu-rich segregation areas to austenitic matrix, and finally to complete the transformation from Cu-rich segregation areas to Cu-rich phase. However, there is only Cu atoms concentration but not crystallographic transformation from early stage of Cu-rich clusters forming to the final Cu-rich phase formation. Even the Cu atom becomes the main composed element after 500h aging at 650°C the Cu-rich phase still keeps coherent relationship with austenitic matrix. According the experimental results in this study, Cu-rich phase precipitation sequence which starts from the Cu atom segregation followed by the Cu diffusing from matrix to segregation areas and Fe, Cr and Ni atoms diffuse out from Cu-rich areas to matrix without crystallographic transformation is proposed. The Cu-rich phase is the most dispersed phase and contributes the most important strengthening effect among all precipitated phases (M23C6, MX and Cu-rich phase). It has been found that Cu-rich phase is very stable and still keeps in nano-size even for 10,000h aging at 650°C. The unique precipitation strengthening of Cu-rich phase in combination with nano-size Nb-rich MX phase and grain-boundary M23C6 carbide contributes excellent strengthening effect to 18 Cr9 NiCuNb austenitic heat resistant steel.

Effect of niobium on microstructure and magnetic properties of bulk anisotropic NdFeB/α-Fe nanocomposites

Bulk anisotropic NdFeB/α-Fe nano-composites were obtained directly from alloys of Nd11Dy0.5Fe82.4−xNbxB6.1 (x=0,0.5,1.0,1.5). High resolution transmission electron microscopy images showed the existence of Nb-rich amorphous grain boundary phase in the alloys with Nb doped. Field emission scanning electron microscope morphologies and X-ray diffraction patterns revealed the grain size and grain alignment of hot pressed and hot deformed nanocomposites. It was found that Nb could refine the grain size and grain texture in hot worked ribbons. Vibrating sample magnetometer results showed that the magnetic properties of the anisotropic nanocomposites were improved with increased Nb doping. The remanence, coercivity and maximum energy product of the bulk anisotropic Nd11Dy0.5Fe80.4Nb2B6.1 nanocomposites were 1.04T, 563kA/m and 146kJ/m3, respectively.