Ti Si Research Articles

Effect of pull-down rate and power on electromagnetic separation of hypereutectic Ti–Si alloy under vacuum

Effect of pull-down rate and power on electromagnetic separation of hypereutectic Ti–Si alloy under vacuum

The microstructures and properties of diamond reinforced Cu–Ni–Si–Ti alloys

In this work, Cu–Ti–Ni–Si- diamond (Di) composites were successfully prepared by casting method based on Ti–Si–C system. The microstructures and properties of the prepared Cu-3.57Ni-1.8Ti-0.85Si-1Di composites were investigated. It is found that, besides core-shell Di@TiC particles formed by Ti-Di reaction, the Ni16Ti6Si7 phase will be formed prior to other Ni–Si phases during both casting and aging treatment processes. The morphologies of the aging precipitated Ni16Ti6Si7 depend on the concentration of Ni, Ti and Si solutes in the Cu matrix. If the concentration of the Ni, Ti and Si solutes is low, the needle-like Ni16Ti6Si7 with a large aspect ratio will be precipitated. On the contrary, when sufficient Ni, Ti and Si are dissolved in the Cu matrix, the Ni16Ti6Si7 will be changed from a needle-like phase to a spherical phase. The hot rolling can promote the solid solution of the dendritic Ni16Ti6Si7 formed during casting, and make the Ni16Ti6Si7 easier to precipitate in a spherical shape. As a result, the Cu–Ni–Ti–Si-Di composites will have excellent comprehensive properties after rolling, solution and aging treatment. The tensile strength of the Cu-3.57Ni-1.8Ti-0.85Si-1Di can get to 702.2 MPa with the elongation of 3.5% and the hardness of 291.1HV. At the same time, the conductivity is kept at 40%IACS.

Mechanical, structural and oxidation behavior of ultra high-temperature ceramic Ti–B–Si hard composite

The synthesis of Ultra-High Temperature Ceramic (UHTC), Titanium Diboride–Si composite TiB2–Si (Ti–B–Si) composite was carried out by Self-propagating high-temperature synthesis SHS). The structural, mechanical, oxidation behavior is studied. A very dense Ti–B–Si composite with very fine grain structure (1–3 μm), high hardness (∼29 GPa) & (648.8 GPa) modulus and good oxidation resistance up to 900 °C was synthesised by SHS process.

“Even Romanians Come Research Us Now”. On Positionality in Southeast European Studies, between ti si naš and Nested Orientalisms

“Even Romanians Come Research Us Now”. On Positionality in Southeast European Studies, between ti si naš and Nested Orientalisms

Low-temperature reactive spark plasma sintering of dense SiC-Ti3SiC2 ceramics

SiC-based ceramics are of great interest for various advanced applications. However, its fabrication requires high-temperature treatment at ∼2000 – 2100 °С. In this study, we developed an approach based on low-temperature reactive spark plasma sintering to produce dense SiC-based ceramics with superior mechanical properties. It was found that an SPS temperature of 1600 °C and introduction of 10 – 15 wt% of mechanically activated non-oxide Ti–Si–C additive is required to manufacture ceramics with a theoretical density of higher than 90%. Nonetheless, employing 5 – 15 wt% of the additive mixture and an SPS temperature of 1700 °C, the maximum density of ∼ 98% was achieved. The controlled formation and decomposition of the in-situ Ti3SiC2 MAX phase enables the fabrication of the engineering ceramics with enhanced compressive strength (550 MPa), elastic modulus (485 GPa), and microhardness (32 GPa), which are comparable to the best-reported SiC ceramics. The study has a significant potential for practical application in the production of advanced SiC-based ceramics for various purposes and could be used for further understanding and development of the high-temperature sintering methods.

Multilevel microstructure control of cast Al–7.0Si–4.0Cu alloy with high strength–toughness synergy via micro-alloying combined with manipulation by in-situ nano-ceramics

Incident Ti–Si poisoning when applying traditional agents of microstructure manipulation in Al–Si alloys is always adverse to realize multilevel microstructure control. This work combined the manipulation by physically formed in-situ nano-ceramics from Fe79.58B11.26Si9.26 amorphous alloy and the micro-alloying to comprehensively improve the microstructure configuration of Al–7.0Si–4.0Cu alloy. It was suggested that micro-alloying of Mg and Sb prominently refined α-Al dendrites and eutectic silicon. Micro-alloying with Mg increased the nucleating temperature of α-Al, meanwhile Mg atoms can hinder the growth of α-Al and eutectic silicon. Sb atoms can also be adsorbed to the growth interfaces of eutectic silicon hindering the growth process. On this basis, trace Fe79.58B11.26Si9.26 amorphous alloy brought further optimization on α-Al dendrites and eutectic silicon, especially Al2Cu and Mg2Si, realizing the multilevel microstructure control. In-situ Fe2B and Fe3Si nano-ceramics were confirmed to have low lattice misfits with α-Al and silicon, serving as efficient nucleation sites and growth retardants. After combined micro-alloying and manipulation, the mean sizes of α-Al and eutectic silicon were significantly refined by 72.7% and 79.9%, respectively, meanwhile, the ultimate tensile strength (UTS) and plastic strain (δ) were improved to 480 MPa and 9.4%, corresponding to 30.1% and 77.4% improvement, respectively. This work provides new mentality to realize multilevel microstructure control and improvement of strength–toughness synergy in Al–Si alloys.

Behavior of Eutectic Ti–Si–Zr Titanium Alloys in Different Friction Conditions

Behavior of Eutectic Ti–Si–Zr Titanium Alloys in Different Friction Conditions

Directional Solidification of Al–Si–Ti Irregular Ternary Eutectic Alloy and Thermophysical Properties

Directional Solidification of Al–Si–Ti Irregular Ternary Eutectic Alloy and Thermophysical Properties

Synthesis and Study of Si–Ti Mixed Oxides Modified with Dibenzo-18-Crown-6 Complexes with Metal Cations

Synthesis and Study of Si–Ti Mixed Oxides Modified with Dibenzo-18-Crown-6 Complexes with Metal Cations

Phase Continuity, Brittle to Ductile Transition Temperature, and Creep Behavior of a Eutectic Mo–20Si–52.8Ti Alloy

Mo–Si–Ti alloys, like eutectic Mo–20Si–52.8Ti (at%), have previously been intensely investigated, owing to their excellent oxidation and creep resistance. To better understand high‐temperature mechanical behavior, a holistic assessment of microstructural features is necessary. Correspondingly, 3D‐focused ion beam tomography is carried out in Mo–20Si–52.8Ti. The results indicate a severely interconnected network of Mo solid solution (MoSS) and intermetallic (Ti,Mo)5Si3. Both phases retain similar network connectivity, lamellar sizes, etc. The brittle to ductile transition temperature (BDTT) is then determined through a series of bending tests and interpreted using the microstructural information. The BDTT is found to be ≈1100–1150 °C, different from Mo–9Si–8B with a continuous MoSS network. The BDTT is an immediate consequence of the continuous network of both MoSS and (Ti,Mo)5Si3. The MoSS network is instrumental in crack trapping and bridging, indicating that the present phase distribution maximized the mechanical performance over (Ti,Mo)5Si3. Having determined the network microstructure and BDTT, tensile creep behavior is evaluated and compared to previously published compressive creep results. The results show consistency in terms of strain rate, stress exponent, and microstructural features indicating a reliably good creep resistance for the network microstructure of Mo–20Si–52.8Ti regardless of loading direction.

The improved SiC joints prepared by pressureless braze joining using Ti–Si interlayer with metallic infiltration

In this study, braze joining of SiC ceramics using a Ti–Si as the interlayer was first obtained at 1500 °C under pressureless condition in a conventional graphite heater furnace, and the shear strength of the resulted SiC joint was only 2.7 ± 1.2 MPa. Results showed that the joining condition could be improved by adding metallic infiltration of Fe, Co, and Ni to Ti–Si interlayer and the shear strength was significantly increased to 73.7 ± 11.7 MPa under the same processing conditions employed in this study. The joining mechanism was then proposed based on thermodynamics calculation, elements mapping as well as the microstructural analysis. In a graphite vapor environment, decomposition of the interlayer (Ti3SiC2) was readily promoted as compared to tungsten or molybdenum vapor environment. The decomposed products (Si) would easily dissolve into the liquid phase of Fe, Co, and Ni. Therefore, the infiltration of the above metallic elements would promote the decomposition of the Ti3SiC2 phase by decreasing the partial pressure of Si. However, the pores, which was produced by the graphite environment as well as the infiltration of the above metallic elements, provided a route for the diffusion of Fe, Co, and Ni elements. Results of this study showed that a robust SiC joint could be obtained by the decomposition of the interlayer first and then the densification of the interlayer under the same process with the metallic infiltration.

Thermodynamic modelling of the V–Ti–B system

Thermodynamic modelling is an effective approach to accelerate the development of novel materials such as V-based alloys. In the present work, the results of thermodynamic modelling of the ternary system V–Ti–B using the “CALculation of PHAse Diagrams” (CALPHAD) method are presented. The thermodynamic descriptions of the binary systems V–Ti, V–B, and Ti–B are based on available publications whereas thermodynamic parameters for the ternary system stem from the iterative approximation to the experimental investigations, which further serve for verifying the calculated phase diagram. Thus, eight different alloys in the compositional range of 10–40 at.% Ti and B were analyzed aiming at identifying the evolving phases. A set of thermodynamic parameters is proposed. The calculated isothermal phase diagram at 1673 K exhibits a high degree of agreement with the literature and experimental observations. In our further work, the thermodynamic data generated in this study will be useful to develop the quaternary V–Ti–Si–B system.

The Effect of Fe Addition in the RM(Nb)IC Alloy Nb-30Ti-10Si-2Al-5Cr-3Fe-5Sn-2Hf (at.%) on Its Microstructure, Complex Concentrated and High Entropy Phases, Pest Oxidation, Strength and Contamination with Oxygen, and a Comparison with Other RM(Nb)ICs, Refractory Complex Concentrated Alloys (RCCAs) and Refractory High Entropy Alloys (RHEAs).

In this work, the RM(Nb)IC alloy Nb–30Ti–10Si–5Cr–5Sn–3Fe–2Al–2Hf (NV2) was studied in the as-cast and heat-treated conditions; its isothermal oxidation at 700, 800 and 900 °C and its room temperature hardness and specific strength were compared with other Sn-containing RM(Nb)ICs—in particular, the alloy Nb–24Ti–18Si–5Cr–5Fe–5Sn (NV5)—and with RCCAs and RHEAs. The addition of Fe (a) stabilised Nbss; A15–Nb3X (X = Al, Si and Sn) and Nb3Si; metastable Nb3Si-m’ and Nb5Si3 silicides; (b) supported the formation of eutectic Nbss + Nb5Si3; (c) suppressed pest oxidation at all three temperatures and (d) stabilised a Cr- and Fe-rich phase instead of a C14–Nb(Cr,Fe)2 Laves phase. Complex concentrated (or compositionally complex) and/or high entropy phases co-existed with “conventional” phases in all conditions and after oxidation at 800 °C. In NV2, the macrosegregation of Si decreased but liquation occurred at T >1200 °C. A solid solution free of Si and rich in Cr and Ti was stable after the heat treatments. The relationships between solutes in the various phases, between solutes and alloy parameters and between alloy hardness or specific strength and the alloy parameters were established (parameters δ, Δχ and VEC). The oxidation of NV2 at 700 °C was better than the other Sn-containing RM(Nb)ICs with/without Fe addition, even better than RM(Nb)IC alloys with lower vol.% Nbss. At 800 °C, the mass change of NV2 was slightly higher than that of NV5, and at 900 °C, both alloys showed scale spallation. At 800 °C, both alloys formed a more or less continuous layer of A15–Nb3X below the oxide scale, but in NV5, this compound was Sn-rich and severely oxidised. At 800 °C, in the diffusion zone (DZ) and the bulk of NV2, Nbss was more severely contaminated with oxygen than Nb5Si3, and the contamination of A15–Nb3X was in-between these phases. The contamination of all three phases was more severe in the DZ. The contamination of all three phases in the bulk of NV5 was more severe compared with NV2. The specific strength of NV2 was comparable with that of RCCAs and RHEAs, and its oxidation at all three temperatures was significantly better than RHEAs and RCCAs.

The influence of V addition on the structure, mechanical properties, and oxidation behaviour of TiAlSiN coatings deposited by DC magnetron sputtering

The influence of V content on the morphology, structure, hardness (H) and reduced Young's modulus (E), adhesion, and oxidation resistance of TiAlSiN coatings is investigated. The coatings were produced by DC reactive magnetron sputtering, with increasing V contents from 0, 4.8 and 11.0 at.%. All coatings exhibit a fcc type structure. The coating with 4.8 at.% of V shows the highest values of H and E, whereas the values are similar for the reference coating and the coating with 11.0 at.% of V. The coatings adhere well to the substrates and show a dense and compact columnar growth extending from the adhesive interlayer to the top surface of the coatings. The dynamic thermal gravimetric oxidation curves reveal that V additions decreases the onset point of oxidation significantly and degrades the oxidation resistance of the coatings. A dual oxide layer is formed on the top surface of the reference coating: an outer porous Ti–Al–O rich layer with plate-like features on the top, which classified to TiO2 (rutile and anatase) and Al2O3 phases, and an inner Ti–Si–O rich layer with Al depletion that identified as mixture of amorphous Si–O and Ti–Si–O protective oxides. The diffusion of V to the top surface governs the oxidation process of the V-containing coatings, i.e. increasing V concentration leads to disrupt the formation of the protective continuous oxide layers easily.

Oxidation behavior of Ti-Nb-Mo-Al-Six refractory high entropy alloy at 1000℃

The oxidation behavior of TiNbMo0.5Al0.225Six (x = 0.1, 0.25, 0.4, 0.55) refractory high entropy alloys in air at 1000 ℃ was investigated. These novel alloys have a BCCss / (Nb, Ti)5Si3 eutectic structure in the as-cast state. Oxidation resistance results reveal that the mass gain shifts from a mass loss (Si0.1) to a parabolic law (Si0.25, Si0.4, Si0.55). An appropriate increase in Si content favors a lower oxidation rate. The β-(Nb, Ti)5Si3 was studied to have excellent oxidation resistance, while the region where γ-(Nb, Ti)5Si3 existed is the main site of porosity generation. The suitable Si content promotes the appearance of a Mo-rich layer, thus preventing the oxide evaporation. Data availabilityThe data that support the findings of this study are available from the corresponding author, specifically Professor Liang Wang of the Harbin Institute of Technology (email: wliang1227@hit.edu.cn) upon reasonable request.

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.

Structural Characterization of Titanium-Silica Oxide Using Synchrotron Radiation X-ray Absorption Spectroscopy.

In this study, titania–silica oxides (TixSiy oxides) were successfully prepared via the sol–gel technique. The Ti and Si precursors were titanium (IV), isopropoxide (TTIP), and tetraethylorthosilicate (TEOS), respectively. In this work, the effects of pH and the Ti/Si atomic ratio of titanium–silicon binary oxide (TixSiy) on the structural characteristics of TixSiy oxide are reported. 29Si solid-state NMR and FTIR were used to validate the chemical structure of TixSiy oxide. The structural characteristics of TixSiy oxide were investigated using X-ray diffraction, XRF, Fe-SEM, diffraction particle size analysis, and nitrogen adsorption measurements. By applying X-ray absorption spectroscopy (XAS) obtained from synchrotron light sources, the qualitative characterization of the Ti–O–Si and Ti–O–Ti bonds in Ti–Si oxides was proposed. Some Si atoms in the SiO2 network were replaced by Ti atoms, suggesting that Si–O–Ti bonds were formed as a result of the synthesis accomplished using the sol–gel technique described in this article. Upon increasing the pH to alkaline conditions (pH 9.0 and 10.0), the nanoparticles acquired a more spherical shape, and their size distribution became more uniform, resulting in an acceptable nanostructure. TixSiy oxide nanoparticles were largely spherical in shape, and agglomeration was minimized. However, the Ti50Si50 oxide particles at pH 10.0 become nano-sized and agglomerated. The presence of a significant pre-edge feature in the spectra of Ti50Si50 oxide samples implied that a higher fraction of Ti atoms occupied tetrahedral symmetry locations, as predicted in samples where Ti directly substituted Si. The proportion of Ti atoms in a tetrahedral environment agreed with the value of 1.83 given for the Ti–O bond distance in TixSiy oxides produced at pH 9.0 using extended X-ray absorption fine structure (EXAFS) analysis. Photocatalysis was improved by adding 3% wt TiO2, SiO2, and TixSiy oxide to the PLA film matrix. TiO2 was more effective than Ti50Si50 pH 9.0, Ti50Si50 pH 10.0, Ti50Si50 pH 8.0, and SiO2 in degrading methylene blue (MB). The most effective method to degrade MB was TiO2 > Ti70Si30 > Ti50Si50 > Ti40Si60 > SiO2. Under these conditions, PLA/Ti70Si30 improved the effectiveness of the photocatalytic activity of PLA.

Stable nitride precipitation in additively manufactured nickel superalloys

With negligible quantities of nitrogen, wrought and welded solid solution strengthened nickel superalloys usually contain carbides and topologically close-packed phases, such as Laves phase. However, appreciable nitrogen levels on the order of 0.1 % mass fraction drove the precipitation of a range of unanticipated nitride phases in additively manufactured Inconel 625 in the as-deposited and post process hot isostatically pressed conditions. Different nitride phases were observed with small changes in alloy chemistry. Cubic metal nitrides (MN), tetragonal Z-phase (CrNbN), and diamond-cubic metal η-nitrides (M 6 N) were found within the γ matrix of Inconel 625 containing relatively low Fe (1 %), low Ti (0.02 %), and high Si (0.39 %) mass fractions. Conversely, these phases were replaced by only MN nitrides in a similar Inconel 625 alloy with elevated mass fractions of Ti (0.21 %) and Fe (4 %). These various phases, however, were not fully predicted using state-of-the-art computational thermodynamic tools and databases, indicating a sparsity of data for nickel superalloys. Even after hot isostatic pressing, many nitrides persisted and only experienced slight changes in composition and lattice parameters in both materials. The stability of these nitride phases presents a potential pathway for achieving enhanced high temperature and creep properties within this and similar alloy systems. • Significant nitrogen contents are measured in Inconel 625 powder. • Only nitrides (MN, Z-phase, η-nitride) are observed in two as-deposited Inconel 625 alloys. • Minor alloying elements influence the type of nitride that forms. • Most nitrides persisted after post-process hot isostatic pressing.

Effect of Ti–Si–Fe alloys on microstructure and properties of nitride/oxynitride bonded SiC ceramics sintered under CO/N2 atmosphere

Ti–Si–Fe alloys extracted from high-titanium blast furnace slag were utilized to replace part of the silicon powders, and then nitride/oxynitride bonded SiC ceramics were prepared by reactive sintering in graphite bed. Ti–Si–Fe alloys could react with CO/N2 at a low temperature (1200 °C), and the addition of Ti–Si–Fe alloys could reduce the nitriding temperature of Si. Density functional theory calculations suggested that Ti–Si–Fe alloys enhanced reaction activity via weakening the strength of CO and NN bonds. The regional equilibrium phase diagrams of Si–C–N–O and Ti–Si–C–N–O under CO/N2 atmosphere were calculated by thermodynamics. The change of whiskers morphology was observed by scanning electron microscope. Furthermore, the bulk density, the cold modulus of rupture, and the cold compressive strength improved with Ti–Si–Fe alloys content. The results showed that the addition of Ti–Si–Fe alloys not only significantly promoted nitriding of Si and formation of Si3N4 whiskers, but also improved the mechanical properties of the samples.

Interface reactions of magnetron sputtered Si-based dual layer coating systems as oxidation protection for Mo-Si-Ti alloys

Mo-Si-Ti alloys show an improved oxidation behaviour at temperatures above 1000 °C compared to Mo-Si-B alloys by forming a SiO2-TiO2 oxide layer but at intermediate temperatures around 800 °C the major alloying element Mo still often leads to a catastrophic oxidation. Hence, Mo-Si-Ti alloys to be used at high temperature need a protective coating. In this study two coating systems were applied on the Mo-12.5Si-8.5B-27.5Ti-2Fe (at.%) and the Mo-21Si-34Ti-0.5B alloy. The coefficient of thermal expansion of the alloys was analysed to be about 7.8 × 10−6 °C−1 at 1200 °C. The two coating systems consisted of a graded Mo-Si interlayer but differently sputtered Si top layers. The coating systems were investigated with respect to their deposition parameters, oxidation protection and interface reactions with the alloys. The coatings could protect the alloys successfully at 800 °C for 100 h. At 1200 °C both coating systems evolved a thermally grown oxide SiO2 forming a dense layer which can protect the alloys. At the interface between coating system and alloy an interdiffusion zone of mostly (Mo,Ti)5Si3 grew with increasing testing time.