Nb Si Research Articles

Microstructural and phase evolution in Nb–Si intermetallic thin films deposited using the pulsed laser ablation technique

Microstructural and phase evolution in Nb–Si intermetallic thin films deposited using the pulsed laser ablation technique

Investigation of scale formation and degeneration of silicide coating on Nb–Si based alloy in the temperature range from 1250 °C to 1560 °C

Nb silicide coatings modified with active elements have good oxidation resistance, but there is a lack of systematic research on their oxidation behavior at high temperatures above 1250 °C. The aim of this work is to investigate the oxidation behavior of an Al–Y modified silicide coating on Nb–Si based alloy in the temperature range from 1250 °C to 1560 °C. After oxidation at 1250 °C, the scale displays a typical layered structure consisting mainly of a TiO2 outer layer, an amorphous SiO2 matrix layer embedded with TiO2 and ZrSiO4, and an inner layer consisting of SiO2 and Cr2O3. Above 1350 °C, the evaporation reaction of Cr2O3 into CrO3 (g) is significantly accelerated and Cr2O3 disappeared gradually with temperature or time. The TiO2 layers covering on the scales formed at 1250–1500 °C grow along the crystallographic orientation of [100]. The micropores formed on the surface of TiO2 should be attributed to the further oxidation of Cr2O3 into volatile oxide CrO3 (g). The scales exhibit a similar structure consisting mainly of a SiO2 glass matrix embedded with ZrSiO4 and a surface TiO2 layer until 1500 °C. Above the eutectic temperature of SiO2–TiO2 system, the scale is mainly composed of a matrix layer of SiO2–TiO2 eutectic embedded with block TiO2 particles, and a thin SiO2 interface layer at 1560 °C. The degeneration path of the (Nb,X)Si2 coating is (Nb,X)Si2 → (Ti,Nb)5Si4 → γ-(Nb,X)5Si3.

Formation of near core-shell-like structure and dual-phase nanoprecipitation behavior in Nb–Si–Ti based alloys

Dual-phase metal materials can usually take into account the advantages of both phases, but the heterogeneity of dual-phase properties will cause flow instability. Therefore, it is difficult to further improve the microstructure and properties of Nb–Si–Ti based alloys containing ductile Nbss and hard silicides through hot working. Here, we propose a method for interface modification by precipitating an intermediate phase and forming a core-shell-like structure with silicides. A novel near core-shell structure (β-Nb5Si3/Nb4FeSi) is obtained in Nb–Si–Ti based alloy by deep cryogenic quenching and annealing. The precipitation of Nb4FeSi is closely related to stacking faults, where high-density stacking faults can develop into the nanotwins during annealing at 1200 °C. In addition, two types of nanoprecipitation behaviors are observed in the Nbss and β-Nb5Si3. The nanoscale plate-like δ-Nb11Si4 is precipitated along the [100]Nbss and [010]Nbss in the Nbss matrix, while the precipitation of granular Nb4FeSi from β-Nb5Si3 satisfies (1‾10)β//(01‾0)Nb4FeSi. In addition to the twinning induced plasticity of Nb4FeSi (shell), a phase transformation from β-Nb5Si3 to α-Nb5Si3 and Nbss that occurs within the core-shell structure is beneficial for the hot forming of the alloy.

Enhancement of comprehensive properties of Nb–Si based in-situ composites by Ho rare earth doping

Enhancement of comprehensive properties of Nb–Si based in-situ composites by Ho rare earth doping

Synergistic effects of trace silicon, calcium and cerium on the microstructure and properties of a novel Cu–Cr–Nb–Si–Ca–Ce alloy

In this paper, a novel Cu-0.60Cr-0.20Nb-0.05Si-0.02Ca-0.02Ce (CCNSCC, wt.%) alloy is designed. By comparing the differences in the properties and microstructure with the Cu-0.60Cr-0.20Nb (CCN, wt.%) alloy under the same process, the effects of trace Si, Ca, and Ce elements on the CCNSCC alloy are disclosed. After undergoing cold rolling by 80% and aging at 450 °C for 60 min, the CCNSCC alloy exhibits a tensile strength of 524 MPa and a softening temperature of 600 °C. These values represent an increase of 104 MPa and 90 °C respectively compared with the CCN alloy. After a multi-stage combined thermo-mechanical treatment including preaging at 400 °C for 30 min, the tensile strength and electrical conductivity of the CCNSCC alloy reach 618 MPa and 75.2%IACS respectively. Microstructure analysis shows the existence of rod-like and polygonal Cr8Nb3Si particles, as well as globular, ellipsoidal, and crescent-shaped (Ca,Ce)Cu5 particles. During the process of aging, the precipitation of the Cr phase occurs at the phase boundaries of Cr8Nb3Si particles. Additionally, significant quantities of fine Cr particles at the nanoscale surround the Cr8Nb3Si particles, exerting a beneficial influence on the strength and electrical conductivity of the CCNSCC alloy. Besides, the CCNSCC alloy has finer Cr particle size and lower volume fraction of recrystallized grains after aging in comparison to the CCN alloy. This indicates that the addition of trace Si, Ca, and Ce elements significantly inhibits the growth of Cr particles and occurrence of recrystallization. Plenty of dislocations are observed in different states of the CCNSCC alloy, and their interaction with the Cr precipitates is the primary factor contributing to the excellent mechanical properties of the CCNSCC alloy. The findings of this study provide valuable insights for improving the properties and microstructure of Cu–Cr–Nb alloys.

Influence of pre-heating on TIG-welding thermal cycle of high-temperature titanium alloy of TI‒AL‒ZR‒SN‒MO‒NB‒SI system

Influence of pre-heating on TIG-welding thermal cycle of high-temperature titanium alloy of TI‒AL‒ZR‒SN‒MO‒NB‒SI system

Powder production, FAST processing and properties of a Nb-silicide based alloy for high temperature aerospace applications

A Nb-silicide based alloy with nominal composition Nb–18Ti–22Si–6Mo-1.5Cr–2Sn-1Hf (at. %), designed for high temperature aerospace applications, was produced via a powder metallurgy (PM) route. The raw elements were arc melted, crushed, and milled to powder, then consolidated using Field Assisted Sintering Technology (FAST). The compressive creep of the alloy was evaluated using electro-thermal mechanical testing (ETMT). The study demonstrated the production of larger 60 mm diameter samples, with potential for further scale up. The microstructure of the FAST alloy, which is comprised of bcc Nbss and tetragonal αNb5Si3 was more homogenous compared with the cast alloy, with some interstitial contamination that occurred during powder production. The FAST alloy had lower density than state of the art Ni-based superalloys and refractory metal complex concentrated alloys (RCCAs) and high entropy alloys (RHEAs), and its yield strength and specific yield strength was higher than those of the latter metallic Ultra high temperature materials (UHTMs) and comparable to those of Nb-silicide based alloys with B addition. The stress exponent n in compressive creep was in the range 1.7–2.6, similar to that of binary Nb–10Si and Nb–16Si alloys and its creep rate at 1200 °C and 100 MPa was similar to that of the MASC alloy (Nb–25Ti–16Si-8Hf-2Al–2Cr (at.%)). Like the latter, the creep of the FAST alloy did not meet the creep goal.

Solute-solute interactions in dilute Nb-X-O alloys from first principles

Recent efforts to develop Refractory Multi-Principal Element Alloys (RMPEAs) for high temperature applications have led to a renewed interest in elucidating fundamental properties of refractory metals. These metals can dissolve high concentrations of interstitial oxygen to the detriment of their mechanical properties and oxidation resistance. Strategies are therefore sought to control the oxygen solubility of refractory alloys. Even in simple dilute refractory alloys, the underlying mechanisms driving binding energies between substitutional solutes and oxygen is not fully understood. We have used first principles calculations of Nb-X-O alloys to examine the interactions between interstitial oxygen and dilute substitutional solutes X = Al, Si, Sc, Ti, V, Cr, Y, Zr, Mo, Ru, Hf, Ta, W, and Re in BCC Nb. Electronegativity differences drive charge transfer between the Nb matrix and both the substitutional and interstitial solutes. This transfer of charge results in strong electrostatic interactions at short distances that play a key role in determining X-O binding energies. The solute misfit volume, which leads to local straining of the surrounding BCC Nb lattice, is also found to have a strong effect on the X-O binding energies. Finally, we identify a repulsive interaction, of significance for a subset of X-O pairs, that arises from a closed-shell hybridization between localized orbitals on solutes.

Diffusion bonding behaviour of Nb–Si and TiAl alloys by spark plasma sintering

Nb–Si alloy and high niobium β-γ TiAl alloy(HNBG) was joined by diffusion bonding ranging from 1000 to 1100 °C at 10 MPa for 20 min by spark plasma sintering. The phase sequence from HNBG to Nb–Si side was HNBG||β/B2+α2-Ti3Al||δ-(Nb, Ti)3Al+σ-(Nb, Ti)2Al + Ti rich γ-(Nb, Ti)5Si3||Nb–Si in the joint. The sound joints without any pores were obtained with the bonding temperature above 1050 °C. The nano-indentation test results showed that Ti rich γ-(Nb, Ti)5Si3 and σ-(Nb, Ti)2Al phases had relatively high hardness and elastic modulus in the diffusion zones II. The highest shear strength of 269 MPa was achieved at 1050 °C. Fracture mainly occurred along the interface of the diffusion zones due to low interfacial adhesion induced by lower bonding temperature. As the bonding temperature was higher, the cracks propagated mainly from in the interface to through the phases due to the increase of interfacial adhesion. The joining mechanism of HNBG/Nb–Si joint was analysed through diagram.

The process and mechanical properties of Nb–Si–Mo–Ti alloy prepared by spark plasma sintering

In recent years, spark plasma sintering (SPS) has emerged as a widespread method to produce high-quality intermetallic-based materials. This paper prepared the Nb–16Si–10Mo alloy and Nb–16Si–10Mo–10Ti alloy using SPS at 1400 °C, 1450 °C, and 1500 °C at a pressure of 30 MPa and a time of 15 min. The influence of temperature on the microstructure and mechanical properties of the two alloys at room temperature was investigated. The corresponding results showed that the relative density of the two alloys exceeded 99.4 %. Besides, adding Ti decreased the relative density and made the microstructure evolve from Nbss + Nb3Si + Nb5Si3 phases to Nbss + Nb5Si3+Tiss phases, and the fracture type varied from brittle fracture to the coexistence of brittle fracture and ductile fracture. As the temperature increased, the flexural strength and the fracture toughness decreased, and the maximum hardness and compressive strength existed at 1450 °C. Furthermore, the appropriate sintering temperature was 1450 °C for a connected mechanical property and microstructure. The flexural strength, fracture toughness, hardness, and compressive strength of Nb–16Si–10Mo alloy and Nb–16Si–10Mo–10Ti alloy sintered at 1450 °C were 462.6 MPa and 565.3 MPa, 6.76 MPa m1/2 and 8.81 MPa m1/2, 757.6 HV and 626.5 HV, 2359 MPa and 2143 MPa, respectively.

Strength-ductility synergy of element Ru for Nb–Si based in-situ composites

Nb–Si based alloys are regarded as the most potential material to substitute the Nickel-based superalloys. The influence of Ru on comprehensive properties of Nb–16Si–24Ti alloys is researched in our paper. The results show that the Nbss phases are coarsened as the doping of Ru. Element Ru mainly dissolves in Nbss and its distribution is heterogeneous in different regions of Nbss phases. In 2Ru alloys, two-types of Nbss/Nb5Si3 eutectic are found due to the large supercooling degree and rapid cooling condition. The coarsened Nbss and complex Nbss/γ(Nb, X)5Si3 eutectic can make a positive impact of fracture toughness, and the maximum KQ value is 8.88 MPa m1/2 in 0.5Ru alloys. Element Ru also plays a great role of solution strengthening, and the maximum value of room compressive strength is 2012 MPa. The thermal compression tests are also prepared, the hot deformation ability signally improves, suggesting that more Ru atoms dissolve into Nbss phases and inhibit the softening of Nbss in HT condition.

Optimization of Zr and Mo element on room-temperature fracture toughness and the integrity of oxide film

In this paper, Zr and Mo elements are introduced into the Nb–Si based alloy to improve the room-temperature fracture toughness and oxidation resistance at high-temperature environment. Nb–16Si–24Ti-xZr-yMo (x = 4, 8; y = 3, 6) alloys were prepared by arc melting and their room-temperature fracture toughness and oxidation resistance at 1250 °C is investigated. Results show that the addition of Zr and Mo element promotes the formation of lamellar Nbss-(Nb, X)5Si3 eutectic structure, which is beneficial to the fracture toughness. The room-temperature fracture toughness increases with the content of alloying element. The KQ value of Nb–16Si–24Ti–8Zr–6Mo alloy reaches 14.88 MPa ·m1/2, which is 72% higher than that of the Nb–16Si–24Ti original alloy. The oxidation resistance decreases due to the presence of more Nbss phase and the holes left by Mo oxide. However, the generation of ZrO2 and the volatilization of Mo oxide relieve the internal stress of oxide film and improve the integrity and adhesion of the oxide layer.

Physicochemical and Service Properties of Nb–Si–Al–Fe–Ti Alloys

Physicochemical and Service Properties of Nb–Si–Al–Fe–Ti Alloys

Phase transformation and dislocation behavior dependence on cooling rate in novel refractory high entropy alloy

A newly named “NbSi-containing refractory high-entropy alloy (RHEA)” is proposed using the Nb–Si based alloy insight. Light-weight TiNbMo0.5Al0.225Six RHEAs were designed (6–6.67 g/cm3), then we studied the dependence of cooling rates on the phase transformation, and the deformation mechanism at the room, high temperatures. Two portions of phase transitions were observed, β-(Nb, Ti)5Si3 to γ-(Nb, Ti)5Si3, and BCC solid solution (BCCss) to γ’-(Nb, Ti)5Si3 precipitates. Elemental diffusion drives the splitting of the grain boundary grooving into sub-boundary, accompanied by phase transformation that occurs. An appropriate Si content favors an excellent strength-plasticity synergy, resulting in 1763.58 MPa compressive strength and 23.65% compressive strain at room temperature (RT), also exhibiting superior yield strength of 1444.82 MPa and relevant strain of 17.48% at elevated temperature (800 °C). The high-temperature dislocation behavior of quenched alloy, evolves from cross-slip (as-cast alloy) to climb-slip coupled deformation mechanism, which plays a crucial role in homogeneous plastic deformation. Therefore, the current work having designed novel alloys sheds new light on designing nanoprecipitates and diversifying dislocation modes.

Creep damage mechanism of 20Cr32Ni1Nb steel at high temperatures

In the petrochemical industry, the centrifugally cast austenitic 20Cr32Ni1Nb stainless steel used in steam reformer furnace's hot outlet manifold experiences creep failure and microstructural degradation, impacting its structural integrity. Understanding the causes of these issues is crucial for addressing the associated challenges. This study examines the creep deformation behaviour, damage mechanisms, and microstructural evolution of 20Cr32Ni1Nb steel under stresses of 22–50 MPa at temperatures of 1163 K (890 °C) and 1223 K (950 °C). Analysis of creep and creep strain rate curves revealed the presence of both primary and tertiary creep stages, with the power law relationship governing the stress-dependent minimum creep rate and rupture life. The variance of creep damage tolerance factor was also analysed, with results showing that in high-stress regimes, loss of section and necking along with cavity growth may initiate tertiary creep, while in low-stress regimes, microstructural degradation, specifically G-phase formation, may initiate tertiary creep. As the duration of creep exposure increases, microstructures were observed to degrade, with the growth and coarseness of NbC and M23C6 carbides. The structure of the space group for the Ni–Nb–Si enriched G-phase in 20Cr32Ni1Nb steel was found to be Fm3‾m, with a lattice parameter of about 1.14 nm.

Microstructure and fracture behaviours of Nb–16Si ultra-high temperature alloy fabricated by laser directed energy deposition

Microstructure and fracture behaviours of Nb–16Si ultra-high temperature alloy fabricated by laser directed energy deposition

Revisiting band structures in 118Xe nucleus via in-beam γ-ray spectroscopy* *The authors are grateful for the pelletron and support staff of IUAC, New Delhi. We would also like to acknowledge the contribution of the INGA collaboration, which is partially funded by the Department of Science and Technology (DST, GoI; project no. IR/S2/PF-03/2003-I) and University Grants Commission (UGC). This work was

The neutron deficient Xe nuclei with A 120 are predicted to have strong octupole correlation at low spins. In the present study, an attempt was made to improve upon the level scheme and also to examine the signatures of octupole correlation in Xe via high spin γ-ray spectroscopy. High spin states in Xe have been populated via the Nb(Si, p2n)Xe fusion-evaporation reaction at a beam energy of 115 MeV provided by the 15 UD pelletron accelerator facility at IUAC, New Delhi. In the experiment, seven new γ-transitions have been found and placed appropriately in the level scheme. A theoretical study using the triaxial projected shell model (TPSM) approach suggests that the first bandcrossing is due to the alignment of two neutrons, and a parallel band tracking the yrast configuration is the γ-band built on the two-quasiparticle state. Enhanced E1 transition rates measured between opposite parity bands involving νh and ν d orbitals having Δj = Δl = 3 indicate the presence of octupole correlation in this nucleus.

Microstructure evolution, growth kinetics and formation mechanisms of silicon-rich NbSi2 coatings on Nb substrate

A Si-rich NbSi2 coating was prepared on Nb substrate by hot dip silicon plating process, which mainly consists of Nb5Si3 interfacial layer, NbSi2 intermediate layer and silicon-rich NbSi2 outer layer. The Si-rich NbSi2 coating has flat surface and dense structure, and the surface roughness is only 0.218–0.548 μm. Raising the deposition temperature can also significantly increase the growth rate of the Si-rich NbSi2 coating. The hot-dip silicon plating process has an extremely low reaction activation energy (249.99 kJ mol−1), which indicates that there are a large number of activated molecules during hot dip silicon plating. The silicon atoms in the molten bath deposited on the Nb surface and maintained a high chemical potential gradient continuously. Therefore, the solid diffusion reaction of Nb–Si was continuous, and the Nb5Si3 phase was generated and consumed continuously, and transformed into NbSi2 phase, which led to a higher growth rate of coating (1.7 × 10−13 to 4.3 × 10−13 m2 s).

Experimental investigation and thermodynamic modeling of Cu–Nb–Si system

AbstractThe phase equilibria of the Cu—Nb—Si system were investigated via a combination of key equilibrated alloys, thermodynamic modeling and first-principles calculations. Sixteen ternary alloys were prepared to determine the isothermal sections at 600 and 700 °C, by means of X-ray diffraction (XRD) and scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM−EDS). The three- and two-phase regions were determined. The existence of ternary compound τ1 (Cu4Nb5Si4) was confirmed. The solubilities of Cu in the NbSi2 and Nb5Si3 phases were measured. Based on the experimental equilibria data from the literature and the present work, a thermodynamic description of the Cu—Nb—Si system was carried out by using the calculation of phase diagrams (CALPHAD) method supported by first-principles calculations. The substitutional model and sublattice model were employed to describe the solution phases and intermediate phases, respectively. A set of self-consistent thermodynamic parameters of the Cu—Nb—Si system were conclusively obtained. Most of the reliable experimental data were reproduced by the present thermodynamic modeling.

A videographic and numerical study of nonisothermal oscillation process for electrostatically levitated liquid Nb–Si alloy

The heat transfer and oscillation dynamics of the liquid Nb-17.3 at.% Si eutectic alloy at high temperatures of approximately 2200 K were explored with electrostatic levitation (ESL) technique. Different second-order oscillation modes of levitated alloy droplets were successfully induced by both excited oscillation with smaller amplitude and spontaneous oscillation with larger amplitude. Importantly, an oscillation mode transition from second to third order was observed as the alloy droplet size increased to 3.96 mm. Meanwhile, a mathematical model coupling heat transfer and droplet oscillation was developed to simulate this nonisothermal oscillation process. The entire thermal history was numerically predicted and proved consistent with experimental measurements. The shape evolution dynamics of second- and third-order oscillations together with the corresponding liquid flow patterns inside alloy droplet was revealed in detail, which helped to clarify the mutual influence mechanism between heat transfer and droplet oscillation.