Nb Si Research Articles

Variation in morphology and crystallographic orientation of directionally solidified Nb–Si based alloys at high withdrawal rates

Nb–Si based alloys are directionally solidified at the withdrawal rates of 100, 500 and 1000 μm/s respectively. At the withdrawal rate of 100 μm/s, the eutectic presents well-coupled lamellar structure. Besides, NbSS and γ-(Nb, X)5Si3 phases are well oriented along [111]Nb and [0001]γ crystallographic orientations respectively and the crystallographic orientation relationship of <111>Nb//<0001>γ, {110}Nb//{101‾0}γ is obeyed. When the withdrawal rate reaches to 500 μm/s, the eutectic begins to transform into irregular fibrous structure and no crystallographic orientation relationship can be detected, and it is caused by the variation in growth direction of NbSS phases from [111]Nb to [100]Nb.

Vacuum Induction Furnace Melting Technology for High-Temperature Composite Material Based on Nb–Si System

FGUP VIAM has developed technology for melting high-temperature composite material based on the Nb–Si system by vacuum induction melting in a ceramic crucible based on yttrium oxide operating at a melting temperature of more than 2000°C and chemically resistant during melting a highly active composite. This technology makes it possible to prepare billets for directional crystallization of the required geometric dimensions, ensuring a homogeneous chemical composition close to that calculated, and a low impurity content, in particular oxygen.

Structure and High-Temperature Mechanical Properties of High-Carbon Niobium-Based Alloys

Abstract—The structure and the mechanical properties of Nb80C20 and Nb40Mo40C20 alloys have been studied at temperatures 20–1500°C. The mechanical properties of the Nb80C20 alloy from room temperature to 1300°C are shown to be slightly lower than those of complex Nb–Si alloys. The short-time and 100-h strengths of the Nb40Mo40C20 alloy at 1500°C are higher than those of Nb–Si alloys. The Nb40Mo40C20 alloys have a low fracture toughness.

Prediction of good glass forming ability in amorphous soft magnetic alloys by thermocalc simulation with experimental validation

Alloys in a (Fe70Ni30)80(B–Si–Nb)20 system, with good glass forming ability (GFA), were identified using Thermocalc software to simulate liquidus temperatures (T's) and solidification ranges (areas between the liquidus and solidus in a binary phase diagram,a line at fixed T). A region with excellent GFA was identified at 14–18% B and 0–7% Si with the balance Nb, showing minima in liquidus and solidification range. A region with a solidification range minimum, but no corresponding liquidus minimum was identified at 3–8% B and 5–10% Si but had lower GFA. A shallow liquidus minimum, with no minimum in solidification range, at 3–5% B and 1–3% Si had the lowest GFA and did not produce amorphous material. Measured GFA was ranked using parameters Trg, ΔTxg, and γm, defined herein. Only the reduced glass transition temperature, Trg, was predictive for the alloys. Differential Scanning Calorimetry (DSC) data showed liquidus T's to agree. Curie temperatures, Tc's were observed to increase with B/Nb ratio. Simulations of liquidus and solidification range for alloys with 18 and 15% glass formers do not show regions with minima in both, indicating good GFA is not expected.

Orientation Relationships and Lattice Misfit between a Nb Matrix and γ-Silicide in a Nb–Si Composite

Orientation relationships {110}Nb||{100}γ and 〈111〉Nb||〈001〉γ between the crystal lattices of the Nb solid solution and particles of γ-silicide Nb5Si3 were determined by transmission electron microscopy. The following two types of matching planes were found: {110}Nb||{100}γ and {111}Nb||{001}γ. The former planes form steps at an angle of 120°. The correctness of the calculated orientation relationships was confirmed and these relationships were compared with experimental electron diffraction patterns using methods of mathematical modeling, which enable one to obtain superimposed electron diffraction patterns of several phases and tilt the model crystal. An interface model in two sections was constructed. The morphology of the interface between the particle and the matrix was explained in terms of structural features. The lattice misfit between the matrix and γ-silicide was calculated.

Vacuum brazing of the ultrathin-walled structure using particulate-reinforced composite filler metal: Microstructural evolution and mechanical properties

A novel Inconel 718 particulate reinforced composite filler metal was used to fabricate the Ni-based superalloy ultrathin-walled structure by vacuum brazing. The brazing process was carried out at various temperatures (1423 K, 1443 K, 1463 K). Moreover, the effects of brazing temperature and the particulate content on wettability, solidification behaviour, typical microstructural evolution and the mechanical properties of the brazed ultrathin-walled structure were investigated in detail. The results indicate that increasing reinforced particulate would result in a worse wettability and higher liquidus temperature of the composite filler metal, which is attributed to the inevitable diffusion phenomenon. The microstructure in the brazed region is mainly composed of γ-Ni solid solution, Ni5Si2, Cr3Ni5Si2, G-phase and Ni–Si–Nb intermetallic compound. The elevated brazing temperature would cause a significant decrease in the mechanical properties of the ultrathin-walled structure. With the addition of the reinforced particulate, the mechanical properties increase obviously and the response effect of the particulate is better at higher brazing temperature. Meanwhile, the area of the Ni-based solid solution and the dispersion degree of the eutectic phase in the brazing fillet increase as the increase of the particulate content. However, the solute loss phenomenon induced by adding excessive reinforced particulate would decrease the mechanical properties. The result reveals that the tensile strength increases by 70 MPa, 103 MPa and 100 MPa, while the elongation increases by 0.8%, 5.4% and 6.8% at various brazing temperatures, comparing with the ultrathin-walled structure using the initial filler metal.

Study of Interfacial Bonding in Composite Materials Based on NbSi Eutetic Reinforced with Single-Crystal α-Al2O3 Fibers with a W Coating

Abstract—The relationship between the Nb–Si–Ti matrix and single-crystal α-Al2O3 fibers with a W barrier coating at the interphase matrix–coating–fiber boundaries is studied. It is established that at 1300°C the bending strength of the composite material reinforced with fibers with a coating is 2 times higher than that of the matrix and is 1.3 times higher than the strength of the composite material reinforced with fibers without a coating.

Re-Melting Nb–Si-Based Ultrahigh-Temperature Alloys in Ceramic Mold Shells

In furnaces with different heating elements, Nb–Si based ultrahigh-temperature alloy rods were re-melted in pure yttria mold shells and zirconia face-coat mold shells at 1850 °C for 30 min. The results evidenced that in the furnace with a tungsten heating element, the microstructure of the re-melted alloy became coarser, and the composition varied depending on the type of mold shell. Although the interface reaction layer between the re-melted alloy and the zirconia face-coat mold shell was much thicker, the deformability of the mold shell and the sand burning phenomenon of the alloy inside it were improved and ameliorated, respectively. However, after being re-melted in the furnace with a graphite heating element, the misrun phenomenon occurred in both specimens. Both re-melted alloys inside the mold shells were divided by a gap into an internal and an external part, with totally different microstructures and compositions. No reaction layer emerged at the interface between the re-melted alloy and the mold shells. Instead, infiltration zones arose in the mold shells adjacent to the interface.

Формування структури литих біосумісних стопів системи Ti–Nb–Si

Формування структури литих біосумісних стопів системи Ti–Nb–Si

Ti-Zr-Si-Nb Nanocrystalline Alloys and Metallic Glasses: Assessment on the Structural Development, Thermal Stability, Corrosion and Mechanical Properties.

The development of novel Ti-based amorphous or β-phase nanostructured metallic materials could have significant benefits for implant applications, due to improved corrosion and mechanical characteristics (lower Young’s modulus, better wear performance, improved fracture toughness) in comparison to the standardized α+β titanium alloys. Moreover, the devitrification phenomenon, occurring during heating, could contribute to lower input power during additive manufacturing technologies. Ti-based alloy ribbons were obtained by melt-spinning, considering the ultra-fast cooling rates this method can provide. The titanium alloys contain in various proportions Zr, Nb, and Si (Ti60Zr10Si15Nb15, Ti64Zr10Si15Nb11, Ti56Zr10Si15Nb19) in various proportions. These elements were chosen due to their reported biological safety, as in the case of Zr and Nb, and the metallic glass-forming ability and biocompatibility of Si. The morphology and chemical composition were analyzed by scanning electron microscopy and energy-dispersive X-ray spectroscopy, while the structural features (crystallinity, phase attribution after devitrification (after heat treatment)) were assessed by X-ray diffraction. Some of the mechanical properties (hardness, Young’s modulus) were assessed by instrumented indentation. The thermal stability and crystallization temperatures were measured by differential thermal analysis. High-intensity exothermal peaks were observed during heating of melt-spun ribbons. The corrosion behavior was assessed by electrocorrosion tests. The results show the potential of these alloys to be used as materials for biomedical applications.

On the Microstructure and Isothermal Oxidation of Silica and Alumina Scale Forming Si-23Fe-15Cr-15Ti-1Nb and Si-25Nb-5Al-5Cr-5Ti (at.%) Silicide Alloys.

An Nb-silicide based alloy will require some kind of coating system. Alumina and/or SiO2 forming alloys that are chemically compatible with the substrate could be components of such systems. In this work, the microstructures, and isothermal oxidation at 800 °C and 1200 °C of the alloys (at.%) Si-23Fe-15Cr-15Ti-1Nb (OHC1) and Si-25Nb-5Al-5Cr-5Ti (OHC5) were studied. The cast microstructures consisted of the (TM)6Si5, FeSi2Ti and (Fe,Cr)Si (OHC1), and the (Nb,Ti)(Si,Al)2, (Nb,Cr,Ti)6Si5, (Cr,Ti,Nb)(Si,Al)2 (Si)ss and (Al)ss (OHC5) phases. The same compounds were present in OHC1 at 1200 °C and the (Nb,Ti)(Si,Al)2 and (Nb,Cr,Ti)6Si5 in OHC5 at 1400 °C. In OHC1 the (TM)6Si5 was the primary phase, and the FeSi and FeSi2Ti formed a binary eutectic. In OHC5 the (Nb,Ti)(Si,Al)2 was the primary phase. At 800 °C both alloys did not pest. The scale of OHC1 was composed of SiO2, TiO2 and (Cr,Fe)2O3. The OHC5 formed a very thin and adherent scale composed of Al2O3, SiO2 and (Ti(1−x−y),Crx,Nby)O2. The scale on (Cr,Ti,Nb)(Si,Al)2 had an outer layer of SiO2 and Al2O3 and an inner layer of Al2O3. The scale on the (Nb,Cr,Ti)6Si5 was thin, and consisted of (Ti(1−x−y),Crx,Nby)O2 and SiO2 and some Al2O3 near the edges. In (Nb,Ti)(Si,Al)2 the critical Al concentration for the formation of Al2O3 scale was 3 at.%. For Al < 3 at.% there was internal oxidation. At 1200 °C the scale of OHC1 was composed of a SiO2 inner layer and outer layers of Cr2O3 and TiO2, and there was internal oxidation. It is most likely that a eutectic reaction had occurred in the scale. The scale of OHC5 was α-Al2O3. Both alloys exhibited good correlations with alumina forming Nb-Ti-Si-Al-Hf alloys and with non-pesting and oxidation resistant B containing Nb-silicide based alloys in maps of the parameters δ, Δχ and VEC.

Mechanical Activation and Thermal Treatment of Low-Energy Nb-2Si Powder Blend. The Experiment. II. Mathematical Model

The paper proposes a mathematical model of thermal explosion in mechanically activated Nb–2Si powder blend. A study of the dynamics of mechanical activation synthesis of the Nb–Si system shows that preliminary activation of the initial powder components intensifies the formation of NbSi2 phase. Thermokinetic and thermophysical constants are obtained for the mechanochemical synthesis using the experimental data and the inverse problem method.

Friction wear property of laser surface processed Ni-based amorphous alloy coatings

A Ni–Fe–B–Si–Nb amorphous alloy was deposited on a steel substrate surface via a laser cladding process, and a laser cladding plus laser remelting process. The wear behavior of the laser processed samples and the bulk metallic glass (BMG) sample with the same nominal composition were tested using a pin-on-disc type testing machine. The nano-mechanical properties of the samples were measured with a nano-characterization system. The friction wear tests showed that deep grooves and wear debris were formed on the worn surface of the laser cladded coating, while only shallow grooves for the laser remelted coatings. The friction coefficients of laser remelted coatings and BMG were lower than the laser cladded coating. The wear mass losses of the laser remelted coating were less than the BMG when the laser remelting scanning speed was higher than 6 mm/min. The nano-hardness and elastic modulus of the remelted coating is higher than that of the laser cladded coating. Also, they increase with the increasing laser scanning speed with 1227.9 HV and 277.4 GPa when the remelting scanning speed is 8 m/min. Based on the nano-indentation and friction wear tests results, it was found that the friction wear properties of the laser cladded coating, laser remelted coatings and BMG related well to the ratio of H3/E2. A higher value of H3/E2 can lead to a better wear resistance property.

Microstructures and properties of Nb–Si-based alloys with B addition

The Nb–16Si–18Ti–xB (at%, similarly hereinafter, x = 0, 1, 2, 3) alloys were prepared by arc melting in a water-cooled copper crucible. The influences of B addition on their microstructures and properties were based on the data of X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), and electronic universal material testing machine. It is found that the addition of B promotes the formation of α-Nb5Si3 phase and suppresses the formation of Nb3Si phase. B addition also tends Nb–16Si–18Ti alloy to form the hypereutectic structures. The content of silicide phases shows a trend of firstly decreasing and then increasing in Nb–16Si–18Ti–xB (x = 0, 1, 2, 3) alloys. The size of Nb solid solution (Nbss) phase increases in Nb–16Si–18Ti–xB (x = 0, 1, 2, 3) alloys after heat treatment at 1523 K for 10 h. The room temperature compression strength of Nb–16Si–18Ti alloy increases firstly and then decreases with B addition. The high-temperature compression strength of Nb–16Si–18Ti alloy decreases firstly and then increases with B addition. It is found that the volume and size of silicide phases have a synergistic effect on the compression strength of Nb–Ti–Si-based alloys.

Fabrication of the Nb–16Si Alloy Powder for Additive Technologies by Mechanical Alloying and Spheroidization in Electric-Arc Discharge Thermal Plasma

The development of new, more refractory heat-resistant materials for gas-turbine engines is one of most important problems of modern materials science. This is associated with the fact that nickel superalloys currently used for this purpose have a lower melting point of ~1400°C, which limits their own maximal working temperature by a range of 1100–1150°C. The Ni alloys can be replaced by natural composites, in which refractory metals are a matrix, while their silicides are intermetallic hardeners. Only three “refractory metal–silicon” binary systems manifest stability to the Me5Si3 silicide, notably, Nb5Si3, Re5Si3, and W5Si3. From the viewpoint of a combination of a high melting point and a low density, the Nb5Si3 compound is optimal among other silicides. The use of alloys of the Nb–Si system in additive manufacturing machines is of considerable interest. This work presents the results of experimental investigations into the treatment of the Nb–16 at % Si powder fabricated using mechanical alloying of elemental Nb and Si powders in the thermal plasma flux. The Nb–16Si alloy powder is fabricated by the mechanical alloying of powders of pure elements in a Fritsch Pulverisette 4 planetary mill. The powder spheroidization is performed in a plasma installation based on a discharge vortex-stabilized electric-arc thermal plasma generator. Based on the results of experimental investigations, the principal possibility to perform the plasma spheroidization of particles of the Nb–16Si alloy prepared by mechanical alloying is shown. It is shown that the surface of spheroidized particles is rough and reflects the cast material structure. Three phase components Nb5Si3, Nb3Si, and Nbss having different optical contrast are revealed in microslices, which is confirmed by X-ray phase analysis.

Distribution of Substitutional Alloying Elements and Interstitial Impurities in In Situ Multicomponent Composites Based on the Nb–Si System

The distribution of substitution alloying elements in the structure of hexagonal silicide Nb5Si3 of the γ-modification, which serves as a reinforcing phase of the composite, and in the Nb solid solution matrix of a high-temperature natural composite based on Nb–Si is studied. Studies were carried out on samples in a cast state and after homogenizing thermal treatment. A structural model of the γ-modification of silicide Nb5Si3 is constructed. On the basis of the crystal-chemical analysis of the structure of hexagonal silicide, possible causes of phase instability of the composite after thermal treatment are revealed.

Calculated Location of Carbon and Boron Atoms in the Crystal Structures of α- and γ-Nb5Si3

Atomistic computer simulation is used to calculate the Gibbs energy at 300 K in the α and γ modifications of Nb5Si3, which are reinforcing phases in in situ composite materials based on the Nb–Si system. The calculations are carried out for boron and carbon atoms at interstitial sites. The calculated change in the Gibbs energy ΔG300 K and crystal chemistry analysis are used to conclude about the referred localization and solubility of boron and carbon atoms in the structures of the α and γ modifications of Nb5Si3.

Tendency Towards Strain Ageing of Sheet Steel EH36 150 mm Thick for Marine Applications

The effect of strain ageing parameters on the impact strength of low-carbon microalloyed C–Mn–Si–Nb–V–Ni–Cu-steel on the example of rolled product 150 mm thick after normalizing and additional heat treatment is demonstrated. The change in steel critical impact strength with the degree of prior cold deformation and with additional heating to 250°C is studied. Tendency towards strain ageing at 1/8 and 1/4 of sheet steel thickness after heat treatment is studied.

Diffusion Paths for Interstitial Impurities in Different Polymorphic Modifications of Niobium Silicide Nb5Si3

Structural models of the α, β, and γ modifications of Nb5Si3 silicides, which are used as a reinforcing phase in composites obtained in situ based on the Nb‒Si system, have been constructed by computer simulation methods. A geometric analysis of unit cells is performed using the H-poisk program to estimate the voids existing in the structures. The results of measuring the number of voids and their sizes are reported. A conclusion about possible diffusion paths of interstitial boron, carbon, nitrogen and oxygen atoms is drawn based on the calculation results, and the solubility of these impurities in the structure of each Nb5Si3 modification is estimated.

Mechanical properties, bonding characteristics, and oxidation behaviors of Nb–Si–N coatings

Nb–Si–N coatings with Si contents of 0–30 at% were fabricated through reactive direct current magnetron cosputtering. The processing parameters were various sputtering powers, substrate holder rotation speeds, and nitrogen flow ratio (N2/(N2 + Ar)). Three phase regions, namely face-centered cubic (f.c.c.) NaCl structure, X-ray amorphous, and nanocrystalline phases, were identified and related to the chemical compositions of the coatings. Low-Si-content (0–13 at%) and middle-N-content (39–45 at%) Nb–Si–N coatings exhibited an f.c.c. structure, high-Si-content (17–30 at%) and high-N-content (45–53 at%) Nb–Si–N coatings exhibited an X-ray amorphous structure, and low-Si-content (6 at%) and low-N-content (26–30 at%) Nb–Si–N coatings exhibited a nanocrystalline structure. Examining the bonding characteristics of the Nb–Si–N coatings by using X-ray photoelectron spectroscopy indicated that NbN tended to form preferentially and was followed by Si3N4, which is consistent with the laws of thermodynamics. The correlations between the mechanical properties, residual stresses, and structures of the Nb–Si–N coatings were investigated using nanoindentation, a curvature method, and X-ray diffraction. The oxidation behaviors of the Nb–Si–N coatings annealed in air at 400–600 °C were also examined.