Nb-Si Alloys Research Articles

Synergistic effect of Zr and Ti on microstructure and properties for Nb[sbnd]Si based in-situ composites

To reduce the adverse effects of highly active titanium elements in NbSi alloy, a series of high content of Zr and Zr for Ti substitution in NbSi based alloys are studied. The results show that the addition of Zr changes the solidification path from hypoeutectic to eutectic. The fracture toughness significantly enhances in 24Ti-xZr (x = 0, 4, 8, 16) alloys, owing to the increase of Nbss phases and microstructure refinement in the matrix. Moreover, the room-temperature compression properties increase in 24Ti-xZr alloys, resulting in the effect of significant solution strengthen. In 24Ti16Zr alloys, three-types of Nbss/Nb5Si3 eutectic are found, resulting in large supercooling degree and rapid cooling condition. The maximum KQ value and compressive strength are 12.47 MPa·m1/2 and 1800 MPa respectively in 24Ti16Zr alloys. The KQ values in Nb-16Si-(24-x)Ti-xZr (x = 4, 8, 16, 24) alloys enhance with element Zr increases to 16 at.% and then decline slightly, suggesting that appropriate substitution of Zr for Ti is effective for promotion of toughness. It's owing to the formation of complex Nbss/(Nb, X)5Si3 eutectic. The high-temperature compressive strength is also prepared (1200 °C), element Zr can provide a signally work hardening by making a strong cooperative deformation of Nbss and γNb5Si3 phases, and the highest true stress values are found in 8Ti16Zr alloys.

Simultaneous improving high temperature oxidation resistance and room temperature toughness of Nb[sbnd]Si based alloy via appropriate Ta content addition strategy

NbSi based alloys are expected to become the application materials for high pressure turbine blades of aircraft engines. This paper investigates the impact of Ta addition on room temperature fracture toughness and isothermal oxidation behavior at 1250 °C of four NbSi based alloys with compositions of Nb-16Si-20Ti-8Zr-4Hf-1.5Al-xTa (x = 0, 1, 2, and 4 at.%) fabricated through vacuum non-consumable arc-melting. The results show that the room temperature fracture toughness and 1250 °C oxidation resistance of the alloys increase first and then decrease with the addition of Ta element. The room temperature fracture toughness of 1Ta alloy is the best, reaching 17.1 MPa·m1/2. Adding a moderate amount of Ta (1 at.%) significantly enhances the alloy's oxidation resistance, but an excessive Ta content diminishes this enhancement. This research has obtained a Nb-16Si-20Ti-8Zr-4Hf-1.5Al-1Ta alloy with high room temperature fracture toughness and excellent high temperature oxidation resistance simultaneously, which provide an ideal path for designing NbSi alloys with superior comprehensive properties.

Mechanism of solute hardening and dislocation debris-mediated ductilization in Nb-Si alloy

Niobium (Nb) is sensitive to even minute quantities of silicon (Si) solutes, which are known to induce pronounced hardening. However, the underlying mechanism for hardening remains elusive since the effect of Si solutes on dislocation behavior is unclear. Here, using tensile testing, in-situ microscopy and nanomechanical testing, the behavior of dislocations in dilute Nb-Si alloys, containing from 0 at.% to 0.8 at.% Si, is investigated. We show that the hardness, strength and strain hardening rate increase from two to four times, while the uniform elongation in tension only reduces 50 % as the Si content increases. Dislocations evolve from complex entangled patterns in Nb to parallel long-straight screw dislocation-dominated structures in Nb-Si alloys. In-situ indentation reveals that the origins of the marked hardening in Nb-Si alloy are the reduction of dislocation mobility and cross-slip propensity. Large densities of dislocation debris-superjogs and loops introduced throughout the sample during warm rolling and annealing are found to provide active internal dislocation sources, which explain the minimal ductility loss seen in these Nb-Si alloys. These findings can help guide the alloy design of high-performance refractory materials for extreme temperature applications.

Investigation of microstructure evolution and mechanical properties of cold crucible directional solidification Nb-Si alloy

In this work, the microstructure and properties of Nb-16Si-24Zr alloy directionally solidified by electromagnetic cold crucible under different process parameters were investigated. As the pulling rate increases, the size of both primary Nbss and eutectic Nbss decreases, resulting in a straighter primary dendrite γ-Nb5Si3 and a fishbone like Nbss/γ-Nb5Si3 coupling structure of secondary eutectic. As the power supply increases, the size of the nascent Nbss and γ-Nb5Si3 increases, and the coupling growth trend of Nbss and Nb5Si3 weakens. As the pulling rate and power supply increase, the toughness shows a trend of first increasing and then decreasing, while the room temperature compressive strength gradually increases.

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 microstructure and high-temperature oxidation resistance of Si-rich Mo-Si-B coatings prepared by ultrasonic vibration assisted laser cladding

Si-rich Mo-Si-B powders (Mo-62Si-5B at%) were deposited on Nb-Si based alloy by laser cladding assisted with ultrasonic vibration. The obtained coatings mainly consist of MoSi2 and (Mo, X)5Si3 (X = Nb and Ti). With the introduction of ultrasonic vibration during laser cladding, the lath-shaped MoSi2 phase transforms into cellular gradually. Meanwhile, the discrepancy on the microstructure of the top region and the bottom region is eliminated gradually, indicating that the cavitation and acoustic streaming of ultrasonic vibration not only refines the microstructure, but also homogenizes the element and phase distribution in the coatings. High-temperature oxidation experiment at 1250 ℃ were conducted to assess the oxidation resistance of the coatings. Compared with Nb-Si alloy, the coated specimens have much lower oxidation weight increase. Furthermore, with the assistance of ultrasonic vibration, the oxidation resistance of the coating is enhanced further. The oxide scales on the coatings consist of two layers: an upper amorphous aluminoborosilica with TiO2 particles dispersed and a lower crystalline SiO2 layer. With the introduction of ultrasonic vibration, the microstructure of the coatings is refined, resulting in more phase and grain boundaries in the coatings. Therefore, the diffusion of the elements to the surface is accelerated and the protective oxide scale can be formed quickly.

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.

Atomic structure of intermetallic compound Nb5Si3 by new cluster transformation analysis method

The structure of Nb5Si3 at the atomic level is fundamental for identifying its complicated structure in atomic simulations and for further understanding the phase selection behaviors during the solidification of Nb-Si alloys. In this study, the structure of Nb5Si3 was investigated using deep-learning molecular dynamic simulations. The ideal βNb5Si3 is characterized by Nb-centered Voronoi polyhedrons (VPs) <0,0,12,3>, <0,0,12,2>, and Si-centered VPs <0,2,8,2>, <0,2,8,0>. Most initial VPs are distorted at high temperatures due to intense thermal perturbation. A new cluster transformation analysis (CTA) method was proposed to evaluate the stability of ideal VPs against perturbation and predict the possible transformations of the initial VPs in atomic simulations. Most transformations of the initial VPs in βNb5Si3 originate from distortions at the edges of the Nb-centered VPs and the faces/vertices of the Si-centered VPs. The distorted VPs in βNb5Si3 at high temperatures are dominated by <0,1,10,4>, <0,1,10,5>, <0,2,8,1> and <1,2,5,3> VPs, which are predicted as the primary transformations by the CTA.

Multi-component Alloying Effects on the Stability and Mechanical Properties of Nb and Nb–Si Alloys: A First-Principles Study

Multi-component Alloying Effects on the Stability and Mechanical Properties of Nb and Nb–Si Alloys: A First-Principles Study

Anisotropy of mechanical properties in directionally solidified Nb-Si alloys at room temperature compression

The room-temperature compressive strength and deformation mechanisms in directional solidified Nb-Si alloy with different orientations were studied. The Electron Backscattered Diffraction (EBSD) experiment further explained that the orientation relationship between the Nbss phase and the α-Nb5Si3 phase is [001] Nbss // [001] α-Nb5Si3, (110) Nbss // (110) α-Nb5Si3, and the corresponding relationship between the material crystal structure and macroscopic spatial coordinates was established. The anisotropy of mechanical properties and failure mode in the alloys are attributed to the phase structures which are the long rod-like morphology of the α-Nb5Si3 phase growing along [001] and the spatial asymmetry of a single (110) Nbss // (110) α-Nb5Si3 phase interface. The Tsai-Hill criterion was applied to explain the anisotropy of the compressive strength of alloy at an angle to the direction of the heat flow. In addition, phase boundary separation was considered to be an important reason for the higher plasticity exhibited by the [100] compression orientation.

Synchronous enhancement of hot deformation capacity and properties of Nb-24Ti-16Si-2Al alloy by composite alloying of Fe and V

To improve the thermal deformation ability of Nb-Si alloy whilst increasing the comprehension properties, the synergistic effects of Fe and V on microstructural evolution and properties of Nb-24Ti-16Si-2Al alloys are investigated. Results show that with the co-addition of Fe and V, the formation of (Nb, X)3Si is suppressed and a new silicide Nb4FeSi is obtained. The constituent phases of the alloys transform from Nbss + β-(Nb, X)5Si3 + (Nb, X)3Si to Nbss + β-(Nb, X)5Si3 + Nb4FeSi. Element Fe is primarily enriched in Nb4FeSi phase, while V is mainly dissolved in Nbss and Nb4FeSi phases. The room temperature fracture toughness is significantly enhanced by the co-addition of Fe and V, in which the KQ value of 2Fe-5V alloy reaches 12.87 MPa m1/2, improved by 96.2% compared with the initial alloy. Hot deformation behavior is sensitive to composition and temperature, and an excellent hot deformation ability is exhibited as close to the melting point of Nb4FeSi (1348 °C). After hot deformation, the composition homogenization is achieved and the Nbss/β-(Nb, X)5Si3 eutectics have evolved into a continuous Nbss matrix with dispersed β-(Nb, X)5Si3 particles. The Fe enrichment region will become the source of the splitting of (Nb, X)5Si3 during hot deformation, resulting in the fragmentation and refinement of the coarse silicides.

Orientation dependence of microcosmic plasticity and toughness in Nb-Si alloys

The nano-hardness and elastic modulus on (001), (100), and (110) planes of Nbss and α-Nb5Si3 phase in Nb-Si alloys were investigated by nanoindentation. Electron backscatter diffraction (EBSD) and scanning electron microscopy (SEM) were performed to research the surface orientation and morphology of the enhancing deformation fields around the indents. The orientation dependence of microcosmic fracture toughness in Nb-Si alloys was predicted by the nano-hardness and elastic modulus of the individual phase. A simple phase boundary crystallographic model of (110) Nbss // (110) α-Nb5Si3 between Nbss and α-Nb5Si3 phases was established by EBSD analysis. The Easy-slip model was adopted to explain nanoindentation-induced deformation mechanisms of Nbss, which point to the activation of slip plane in the maximum Schmidt factor.

Microstructure and mechanical properties of Nb–Si alloy with addition of Mn

The effect of Mn element on the microstructure and mechanical properties of Nb–Si based alloys is studied, and the investigated alloys compositions are Nb–16Si–22Ti–xMn (x = 0, 2, 4, 8 at.%). Solubility of Mn in Nbss phase is higher than that in silicide. This dissolution of Mn in Nbss phase and silicide causes solid solution strengthening. Tiss phase and Mn2Ti phase eutectic structure precipitates between dendrites of 8Mn alloy, which affect room-temperature fracture toughness and compressive strength adversely. After heat treatment, Tiss phase and Mn2Ti eutectic structure almost disappears in Mn-contained alloys (Nb, Ti)3Si phase decomposes and transforms to Nbss phase and α-(Nb, Ti)5Si3 phase. The fracture toughness of heat treated 8Mn alloy has been improved greatly due to Mn solution strengthening in Nbss phase.

Rapid Eutectic Growth Kinetics of Undercooled Nb-Si Alloys at Electrostatic Levitation State

The rapid eutectic growth kinetics of undercooled Nb-Si alloys was investigated by using electrostatic levitation (ESL) technique combined with triggering method. For eutectic Nb-17.3 at.% Si alloy, the rapidly solidified microstructure was characterized by (Nb) dendrites and (Nb)+Nb3Si eutectics, which was different from the master alloy composed of complete eutectic structures. The transition of primary phase from the faceted Nb3Si phase to non-faceted (Nb) phase and the formation of complete eutectic microstructure were observed within hypereutectic Nb-18.7 at.% Si alloy with the increase of undercooling. Three distinct solidification paths leading to different microstructures and constituent phases were revealed by controlling the melt undercooling. Furthermore, the phase selection mechanism was clarified from the perspective of nucleation kinetics. Based on the experimental and analytical results, the coupled zone of (Nb)+Nb3Si eutectic was qualitatively predicted. The final microstructures solidified at different undercoolings were all composed of the (Nb) phase and Nb3Si phase, whose crystaline structures were both confirmed by transmission electron microscopy analysis. Besides, it was found that the volume fractions of (Nb) and Nb3Si phases could be undercooling control adjusted by. According to the nano-indentation and Vickers micro-indentation tests, the mechanical properties varied significantly with solidification paths. Compared with the master alloy, the hardness of hypereutectic Nb-18.7 at.% Si alloy at 157 and 473 K undercoolings was decreased by 42.7 % and 9.9 %, while the fracture toughness was enhanced remarkably by 593.1 % and 144.8 %, respectively. This may provide a desirable approach for designing Nb-Si alloys with improved performances.

Strengthening and toughening effect of laser melting deposited Nb–16Si–20Ti–3Al with nano-ZrC additions

The phase composition, microstructure, and properties of Laser Melting Deposited (LMD) Nb–16Si–20Ti–3Al alloys with different nano-ZrC (0, 2.5, 5.0, 10.0 wt%) addition were detailed investigated in this study. Results showed that the LMDed Nb–16Si–20Ti–3Al alloy was composed Nb-based solid solution (Nbss) and Nb3Si. The addition of nano-ZrC promoted the decomposition of the Nb3Si phase and the eutectic transformation from Nb3Si to (Nbss+γ-Nb5Si3) eutectic structure. With the content of nano-ZrC increased from 2.5 wt% to 5.0 wt%, the (Nbss+γ-Nb5Si3) eutectic structure was significantly refined. Nb-rich TiC phase precipitated at the grain boundaries of (Nbss+γ-Nb5Si3) eutectic structure by the titanium in the alloy reacted with nano-ZrC additions. With the content of nano-ZrC increased to 10.0 wt%, coarse and irregular primary γ-Nb5Si3 phase and dendritic TiC were observed in the Nb–Si alloy. The fracture toughness was improved from 5.1 MPa m½ to 17.1 MPa m½ by adding an optimized amount of nano-ZrC (5.0 wt%) due to the refinement of (Nbss+γ-Nb5Si3) eutectic structure and dispersion distributed nano-ZrC in the alloys. The Nb–16Si–20Ti–3Al alloy with 5.0 wt% nano-ZrC addition has the maximum compressive strength of 1836 MPa and a compressive strain of 12.6%. The crack deflection seems an important toughening mechanism for Nb–16Si–20Ti–3Al alloys containing nano-ZrC. The fracture mode of each Nb–16Si–20Ti–3Al alloys with (0, 2.5, 5.0, 10.0 wt%) addition exhibited a brittle quasi cleavage fracture.

Interfacial microstructure and shear performance of TiAl to Nb–Si alloy diffusion bonded with pure Ti interlayer

Diffusion bonding of high niobium β-γ TiAl (HNBG) to Nb–Si alloy was carried out using Ti foil as interlayer. The interfacial microstructural evolution, growth kinetics and mechanical properties of HNBG/Ti/Nb–Si joint were investigated in detail. The microstructure observations indicate that the interfacial microstructure of the joint was composed of β-(Nb, Ti)5Si3, (Nb,Ti)ss//α-Ti, β-Ti//α2//β/B2 from zone I to zone IV. The β-Ti phase and α-Ti phase in zone II obey the orientation relationship, {110}β || {0002}α and <111>β|| <11–20>α. The γ phase in HNBG alloy and β/B2 phase in zone IV obey the orientation relationship, {111}γ || {110}β/B2 and <110>γ || <111>β/B2. The growth activation energies of β-(Nb, Ti)5Si3 and β/B2 phases were 166 kJ/mol and 507 kJ/mol respectively. The content of β phase in zone II and the average grain size of α2 phase in zone III increased with bonding temperature or bonding time. The shear test results showed that the ultimate shear strength was 385 MPa at 1000 °C-10 min-10 MPa. Fracture mainly occurred beween the interface of zone III and IV, and between the interface of zone IV and HNBG alloy. The fracture mode was mainly characterized by brittleness rupture along the phase boundaries of α2 and β/B2, β/B2 and HNBG alloy with slight amount of cleavage fracture in zone IV.

Orientation Dependence of Microcosmic Plasticity and Toughness in Nb-Si Alloys

Orientation Dependence of Microcosmic Plasticity and Toughness in Nb-Si Alloys

Multi-Component Alloying Effects on the Stability and Mechanical Properties of Nb and Nb-Si Alloys: A First-Principles Study

Multi-Component Alloying Effects on the Stability and Mechanical Properties of Nb and Nb-Si Alloys: A First-Principles Study

Anisotropy of Mechanical Properties in Directionally Solidified Nb-Si Alloys at Room Temperature Compression

Anisotropy of Mechanical Properties in Directionally Solidified Nb-Si Alloys at Room Temperature Compression

Microstructure and Mechanical Properties of Nb-Si Alloy with Addition of Mn

Microstructure and Mechanical Properties of Nb-Si Alloy with Addition of Mn