Ti Si System Research Articles

Spark plasma sintered TiB2-SiC UHTC derived from B4C and stoichiometric intermetallic phases from Ti-Si system

Previously conducted studies determined that the reactive sintering of B4C and stoichiometric additions of TiSi2 or Ti5Si3 intermetallics created a dense TiB2-SiC double-phase system that could be classified as ultra-high temperature ceramics (UHTC). In this work, a spark plasma sintering (SPS) technique was used to improve the sintering process and thus further reduce the obtaining temperature and improve the final microstructure and mechanical properties of the proposed, double-phase TiB2-SiC UHTC systems. To evaluate the effects of the experiment, a comprehensive study of phase composition, microstructure and mechanical properties was added. As a result, minimal sintering temperatures were further reduced from 1420 - 1650 ºC to a range of 1200–1400 ºC. Among the prepared composites those sintered at 1400 ºC achieved the best properties. The prepared composites maintained high hardness (up to 24.85 GPa), high tensile strength (up to 309 GPa), relatively high fracture toughness (up to 4.80 MPa∙m1/2) and relatively low density, all of which characterized TiB2-SiC UHTC systems.

Thermodynamic reassessments of the Ti–Si–C/Ti–Si–N systems and thermodynamic calculations of CVD TiSiCN hard-coating based on the Ti–Si–C–N quaternary system

The Ti–Si–C and Ti–Si–N systems were thermodynamically reassessed by using the CALculation of PHAse Diagram (CALPHAD) approach. A more suitable Gibbs energies expression of Ti3SiC2 was obtained to fit better with heat capacity data in the Ti–Si–C system. The thermodynamic parameters of the Ti–Si–N system were adjusted based on the revised Ti–Si system. A self-consistent thermodynamic database of the quaternary Ti–Si–C–N system was established. The calculated thermodynamic data and phase diagrams agree well with the experimental data. The CVD (Chemical Vapor Deposition) process for TiSiCN coatings was simulated using the newly evaluated thermodynamic parameters of the Ti–Si–C–N system. A good agreement between the predicted coating composition and the experimental ones was achieved, verifying the reliability of the thermodynamic database obtained in the present work.

Ceramic Matrix Composites Obtained by the Reactive Sintering of Boron Carbide with Intermetallic Compounds from the Ti-Si System

In this study, we investigated the effect of adding two different intermetallics, Ti5Si3 and TiSi2, for the preparation of TiB2-SiC-B4C composites. As part of the research, stoichiometric composites consisting only of two phases TiB2 and SiC were obtained. The TiB2-SiC-B4C composites were prepared via pressureless sintering. The presence of the phases in the sintered composites was confirmed using X-ray diffraction and scanning electron microscopy. The SEM-EDS examination revealed that the TiB2 and SiC phases were formed during the composite process synthesis and were distributed homogeneously in the B4C matrix. The obtained results allowed us to usually exceed 2000 °C and the use of specialized equipment for firing, that is, vacuum or protective atmosphere furnaces as well as control and measurement equipment. Such an approach generates high costs that are decisive for the economics of the technological processes. In the case of our compositions, it is possible to lower the temperature to 1650 °C. The TiB2-SiC-B4C composites were classified as UHTCs.

Wenjiite, Ti10(Si,P,☐)7, and kangjinlaite, Ti11(Si,P)10, new minerals in the ternary Ti-P-Si system from the Luobusa ophiolite, Tibet, China

Abstract The new minerals wenjiite, Ti10(Si,P,☐)7 (IMA2019-107c) and kangjinlaite, Ti11(Si,P)10 (IMA2019-112b) occur with badengzhuite, zhiqinite, and a K-bearing dmisteinbergite-like mineral in a spheroid 20 μm across enclosed in corundum from the Cr-11 podiform chromitite orebody near the Kangjinla, Luobusa ophiolite, Tibet, China. In addition, wenjiite occurs with deltalumite, jingsuiite, osbornitekhambaraevite, and the K-bearing dmisteinbergite-like mineral in a lamellar intergrowth 100 μm long, also enclosed in corundum from the same locality. The new minerals were characterized by energy-dispersive spectroscopy and three-dimensional electron diffraction, which enabled us to obtain an ab initio structure solution and dynamical refinement from grains a few micrometers across hosted in a FIB lamella. Four analyses of wenjiite from the spheroid gave in wt% Si 21.67, P 6.24, Ti 66.39, V 1.37, Cr 2.20, Mn 0.97, and Fe 1.17 (normalized to 100), which corresponds to (Ti0.93Cr0.03Mn0.01Fe0.01V0.02)10 (Si0.79P0.21)6.51 on the basis of 10 cations excluding Si and P. The simplified formula is Ti10(Si,P)6.5, or more generally Ti10SixPy, where x > y and 6 ≤ (x + y) ≤ 7, i.e., Ti10(Si,P,☐)7. Wenjiite has hexagonal symmetry, space group: P63/mcm (no. 193), with a = 7.30(10) Å, c = 5.09(10) Å, V = 235(6) Å3, Z = 1, and is isostructural with xifengite, mavlyanovite, synthetic Ti5Si3, and synthetic Ti5P3.15. Four analyses of kangjinlaite gave in wt% Si 25.56, P 9.68, Ti 62.35, V 0.21, Cr 0.83, Mn 0.42, and Fe 0.95 (normalized to 100), which corresponds to (Ti10.65V0.03Cr0.13Mn0.06Fe0.14)Σ11.01(Si7.43P2.55)Σ9.99. The simplified formula is Ti11(Si,P)10. Kangjinlaite is tetragonal, with space group: I4/mmm (no. 139), a = 9.4(2) Å, c = 13.5(3) Å, V = 1210(50) Å3, Z = 4, and is isostructural with synthetic compounds of the Ho11Ge10 type, being the most compact of these phases. Despite there now being over 70 compounds containing 38 elements isostructural with Ho11Ge10, synthesis of an analog of kangjinlaite has not been previously reported in either the Ti-P or Ti-Si binary systems or in a multicomponent system. The previously deduced crystallization sequence with decreasing temperature of the four minerals in the spheroid is wenjiite → kangjinlaite → zhiqinite + badengzhuite. This sequence is consistent with relationships reported in 9 binary systems containing intermetallic compounds of Ge and Sn isostructural with Mn5Si3 and Ho11Ge10. In eight of these systems the Mn5Si3 analog melts congruently, whereas the Ho11Ge10 analog never does. Instead, the Ho11Ge10 analog melts peritectically, generally to an Mn5Si3 analog and less commonly to compounds with 5:4 stoichiometry. Final crystallization of the spheroid to zhiqinite + badengzhuite is expected to be well below the temperature of 1500 °C for the congruent melting of zhiqinite in the Ti-Si system, i.e., in the range of ~1100–1300 °C.

Synthesis Features, Structure, and Properties of Promising High-Temperature Ceramics in the Hf–Ta–B–Ti–Si System

Synthesis Features, Structure, and Properties of Promising High-Temperature Ceramics in the Hf–Ta–B–Ti–Si System

Evolutionary search for new compounds in the Ti–Si system

In this work, the results of the evolutionary variable-composition search for binary compounds in the Ti–Si system are presented. The evolutionary algorithm did not find any new stable structures of silicides at 0 K and 0GPa. On the other hand, many low-energy metastable and unstable structures are predicted. The 33 predicted and 10 known from literature but previously unstudied structures of compounds with low formation energies with respect to the ground-state line are analyzed. The mechanical properties, electronic band structures, densities of states, and temperature dependencies of thermodynamic stability of 17 dynamically stable previously unstudied structures are calculated.

Synthesis of titanium carbosilicides in Ti–Si and Ti–Si–Cu systems under mechanical alloying of elemental powders in liquid hydrocarbon

The paper studies synthesis of titanium carbosilicides in Ti–Si and Ti–Si–Cu systems under mechanical alloying of elemental powders of Ti, Si and Cu in a liquid hydrocarbon and subsequent annealing at 900 and 1300 ​°C. It has been shown that mechanical alloying of Ti–Si system facilitates the formation of Ti5Si3Cx carbosilicide as well as Ti(C,H) carbohydride which further transforms into TiC under annealing. The MAX phase Ti3SiC2 is formed in a small amount only after annealing. In addition to Ti5Si3Cx and TiC, a phase in amount of ~40 ​vol% is formed in the Ti–Si–Cu system after annealing, with the structure of Fd3¯m type and a lattice parameter of 11.12-11.13 ​Å, being an oxide or oxycarbide of the Ti–Cu–Fe system.

Investigating boron and phosphorus removal from silicon by Si-Ti and Si-Ti-Fe alloying systems

B and P content of purified Si through alloying refining by Ti was investigated. 65–75% P removal and 39–80% B removal were obtained by the addition of 5–20 wt% Ti to silicon. The reduction of impurities was recognized to be attributable to the formation of Ti5P3.16 and TiB2. The iron addition (up to 20 wt%) to the Si-Ti system increased B removal from 63 to 83% and 74 to 92% in the presence of 10 wt% and 15 wt% Ti, respectively. Nevertheless, iron addition did not make any noticeable improvement in P removal. Phosphorus removal in the Fe containing samples may be ascribed by the formation of the TiFeP phase. Overall, the best impurity removal was obtained for the sample containing 15 wt% Ti + 20 wt% Fe that showed 75% P and 92% B reduction in the purified Si. The directional solidification of a sample containing 20 wt% Ti slightly improved the removal rates compared to its corresponding furnace cooled sample. Also, it resulted in the enhancement of (220) plane of silicon in the solidified alloy. At last, boron removal as a result of TiB2 formation was studied from the thermodynamic point of view.

Phase equilibria of (Gd, Er) –Ti–Si systems at high temperatures

ABSTRACTInteractions of rare earth elements with Ti–Si system at high temperatures are of academic interests for the development of refractory lightweight structural materials. As part of the fundamental research of multicomponent Ti–Si-based alloys, solid phase equilibria of the Gd–Ti–Si ternary system at 1073 K and Er–Ti–Si ternary system at 1273 K were investigated through analysis of X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS). Two isothermal sections of the phase diagram and solid solubility of each equilibrium phase have been determined. The ternary compounds i.e. ErTiSi, GdTiSi, Er2Ti3Si4 and Gd1.9Ti3Si4 have been confirmed in the present condition. Binary compound ErSi1-x has not been observed. Ti3Si was confirmed to be nonexistent at both 1073 K and 1273 K. There is no intermetallic compound present in both Gd–Ti and Er–Ti binary systems.

The Effects of Fe and Si Elements on Structural, Mechanical, and Electronic Properties of an Fe–Si–Ti System by First‐Principles Calculations

Herein, first‐principles calculations with density functional theory are used to investigate the structural, mechanical, and electronic properties of Fe–Si–Ti alloys, aiming to study the effects of Si and Fe in titanium alloys. The calculated lattice parameters are in good agreement with previous data. Alloying with Si/Fe can produce more brittle/ductile materials, due to the weaker/stronger metallic bonds. Furthermore, the effect of alloying with Si and Fe on the anisotropic properties is negligible. The increasing range of Debye temperatures by alloying with Si is greater than that by alloying with Fe. The capacity of Si to enhance the interatomic bonding force is greater than that of Fe due to the stronger covalent bonds. Similarly, the charge density reflects that the capacity of Si to enhance the interatomic bonding force is better than that of Fe for titanium alloys. In addition, the metallic conductivity of these alloys is verified, with there being no gaps at the Fermi level. The localization of electrons in the SiTi alloy is observed to be relatively strong around the Fermi level. In addition, the amplitude of the top of the valence band and the bottom of the conduction band is smooth, showing great effective mass.

The influence of lattice vibrations and electronic free energy on phase stability of titanium silicides and Si solubility in hcp titanium: A DFT study

In this paper, we evaluated the influence of vibrational and electronic free energy on the thermodynamic phase stability of the Ti5Si3, Ti3Si, Ti6Si3, and other silicides in the binary Ti-Si system and the solubility of Si in α-Ti within the density functional theory and harmonic approximation. We showed, that vibrational and electronic free energy thermodynamically stabilize the Ti3Si silicide and destabilize the Ti6Si3 silicide with respect to the Ti5Si3 and α-Ti. According to our calculations, the transition from equilibrium of Si solid solution with the Ti5Si3 silicide to the equilibrium of Si solid solution with the Ti3Si silicide should be at ∼ 900 K. The account of both the vibrational and electronic free energy increase the calculated solubility limit of Si in α-Ti and make it closer to the experimental one.

Influence of C addition on solid-state reaction of Ti-Si-C system

The effect of C addition on synthesis behavior, microstructure, reaction mechanism and high-temperature oxidation resistance of Ti-Si system was investigated. The Ti5Si3Cx-TiC composite was synthesized by introducing the C into Ti-Si system and using mechanically activated self-propagating high-temperature synthesis (MASHS). The addition of 1 mol C into 5Ti+3Si reduced activation energy of reaction from 207.5 kJ/mol to 189 kJ/mol. The reaction in the Ti-Si-C system was initiated by the formation of TiC and followed by synthesis of an interstitial solid solution of Ti5Si3Cx, while reaction in Ti-Si was activated by solid-state diffusion of Si into Ti. The ignition temperature of the reaction was reduced from 1000 °C to 900 °C when the combustion temperature slightly increased as a result of the C addition into the system. The wave velocity of the reaction was also declined from 55 mm/s to 48 mm/s. The microstructural observations show that dissolution of the C in Ti5Si3 crystal structure restricted microcracks formation through coarse grains. Moreover, the oxidation resistance of titanium silicide was improved by the formation of the interstitial solid solution.

Effects of Alloying Elements on the Formation of Core-Shell-Structured Reinforcing Particles during Heating of Al-Ti Powder Compacts.

To prepare core-shell-structured Ti@compound particle (Ti@compoundp) reinforced Al matrix composite via powder thixoforming, the effects of alloying elements, such as Si, Cu, Mg, and Zn, on the reaction between Ti powders and Al melt, and the microstructure of the resulting reinforcements were investigated during heating of powder compacts at 993 K (720 °C). Simultaneously, the situations of the reinforcing particles in the corresponding semisolid compacts were also studied. Both thermodynamic analysis and experiment results all indicate that Si participated in the reaction and promoted the formation of Al–Ti–Si ternary compounds, while Cu, Mg, and Zn did not take part in the reaction and facilitated Al3Ti phase to form to different degrees. The first-formed Al–Ti–Si ternary compound was τ1 phase, and then it gradually transformed into (Al,Si)3Ti phase. The proportion and existing time of τ1 phase all increased as the Si content increased. In contrast, Mg had the largest, Cu had the least, and Si and Zn had an equivalent middle effect on accelerating the reaction. The thicker the reaction shell was, the larger the stress generated in the shell was, and thus the looser the shell microstructure was. The stress generated in (Al,Si)3Ti phase was larger than that in τ1 phase, but smaller than that in Al3Ti phase. So, the shells in the Al–Ti–Si system were more compact than those in the other systems, and Si element was beneficial to obtain thick and compact compound shells. Most of the above results were consistent to those in the semisolid state ones except the product phase constituents in the Al–Ti–Mg system and the reaction rate in the Al–Ti–Zn system. More importantly, the desirable core-shell structured Ti@compoundp was only achieved in the semisolid Al–Ti–Si system.

Experimental Study on the Shock Consolidation of Ti+Si Powders

The research on the explosive compaction of reactive powders is a hot issue. In this work, unreacted Ti-Si block with high compactness has been successfully fabricated under explosive-driven compaction process. The precursors of Ti-Si powder with different stoichiometric ratios undergo pre-compaction shaping by hydraulic press and then shock loading treatment by using low-detonation-velocity explosives of varying loading conditions. The results show that the chemical reaction between Ti and Si powders are partly initiated even under low detonation pressures, indicating extremely low reaction threshold in the Ti-Si system. Meanwhile, optimal experimental conditions are displayed as the initial pressing compactness degree of 61%, and shock pressure of 11GPa. A compactness of 97% is achieved in the synthesized Ti-Si block with the lowest reactivity.

The influence of high-energy ball milling on the heterogeneous reaction kinetics in the Ti-Si system

The high-temperature (1300–1600 K) kinetics for the Ti-Si reactive system were investigated using electro-thermal analysis. The influence of short-term (1–3 min) high-energy ball milling (HEBM) of Ti+0.6Si heterogeneous powder mixtures on the kinetic parameters was also studied. It was shown that HEBM leads to a significant decrease of the apparent activation energy (Ea) of the solid-state reaction between silicon and titanium. For the non-milled mixture, Ea is 339 ± 63 kJ/mol, while after 3 min of HEBM it drops more than twice to 148 ± 12 kJ/mol. The reaction initiation temperature also decreases with an increase of HEBM time: from 1467 ± 62 K for the pristine mixture to 1110 ± 42 K after 3 min of mechanical treatment. The conclusion was made that a decrease of crystalline size and an increase of the crystal lattice defect concentration, which in combination enhance the grain boundary diffusion, can be responsible for the high reactivity of the mechanically activated mixtures.

Phase equilibria in the Nb–Ti side of the Nb–Si–Ti system at 1200 °C and its oxidation behavior

Abstract Nb–Si based composites are one of the most promising superalloy for the next generation turbine airfoil materials. Alloying Ti can efficiently improve their poor oxidation resistance. In this work, five equilibrium alloys were used to determine the unclear but underlying phase equilibria in the Nb–Ti rich region of the Nb–Si–Ti system at 1200 °C. Convincing evidences on three-phase equilibria of bcc(Nb,Si,Ti) + αNb(Ti) 5 Si 3 + (Nb,Ti) 3 Si, αNb(Ti) 5 Si 3 + (Nb,Ti) 3 Si + Ti(Nb) 5 Si 3 and αNb(Ti) 5 Si 3 + (Nb,Ti) 3 Si + Ti(Nb) 5 Si 3 at 1200 °C were obtained. The important tie-triangle of bcc(Nb,Si,Ti) + αNb(Ti) 5 Si 3 + (Nb,Ti) 3 Si turns out to be much narrower than the previous calculation. An optimized thermodynamic description validated in the Nb–Ti rich (≤37.5 at.% Si) region between 1000 and 1500 °C of the Nb–Si–Ti system was subsequently acquired based on calculation of phase diagram (Calphad) method. Furthermore, the oxidation kinetics of three equilibrated alloys with increasing Ti content (5–30 at.%) were evaluated at 1050 °C. The one with bcc(Nb,Ti,Si) + (Nb,Ti) 3 Si equilibrium performed the lowest oxidation rate, which might due to the formation of compact TiO 2 film and the absent of fine eutectic structure bcc(Nb,Si,Ti) + αNb(Ti) 5 Si 3 . These knowledge is contributive to understanding the Ti effect on oxidation resistance of Nb–Si based alloys along with the variation of phase constitutions and microstructures.

Thermodynamic reassessment of the Ni–Si–Ti system using a four-sublattice model for ordered/disordered fcc phases supported by first-principles calculations

A thermodynamic reassessment of the ternary Ni–Si–Ti system was performed by means of CALPHAD (CALculation of PHAse Diagram) method. The fcc_A1/Ni3Si-L12 disordered/ordered transition was described using a four-sublattice model. The enthalpies of formation of the ternary compounds τ1, τ2, and τ4 and end-members of the Ti5Si3 and Ni3Ti phases at 0 K in the Ni–Si–Ti ternary system were computed via first-principles calculations to supply necessary thermodynamic data for the CALPHAD modeling. In the Ni–Si–Ti ternary system, it was clarified that the ordered Ni3Si-L12 phase is formed from the liquid phase with the addition of Ti. An optimal set of thermodynamic parameters for the Ni–Si–Ti system was obtained by taking into consideration of the experimental data from the literature and theoretic values from the present first-principles calculations. Comparisons between the calculated and measured phase diagrams indicated that almost all the reliable experimental information was satisfactorily accounted for by the present modeling.

Assessment of the Ti-Rich Corner of the Ti-Si Phase Diagram: The Recent Dispute About the Eutectoid Reaction

The thermodynamic optimization of Ti-Si-X systems requires that their respective binary systems are constantly updated. The Ti-Si system has been experimentally investigated since the 1950s and these critical experimental data can be employed to calculate the Ti-Si phase diagram using thermodynamic modeling. The most recent assessment of the Ti-Si system was performed in 1998, showing the presence of stoichiometric Ti3Si as phase. In the light of the dispute over the stability of Ti3Si phase in the eutectoid reaction of the Ti-Si and Ti-X-Si systems, the present work assessed the Ti-rich corner of the stable (featuring Ti3Si phase) and metastable (featuring Ti5Si3 phase) Ti-Si phase diagrams. The phase boundaries, the values of the error of the least-square method of the optimization procedure and the relative standard deviation of the calculated variables of the assessed diagrams; and previous investigations were discussed in order to inspire further experimental work on the eutectoid reaction of the Ti-Si phase diagram.

Thermodynamic investigation on phase formation in the Al–Si rich region of Al–Si–Ti system

The thermodynamic condition for phase formation in the Al–Si–Ti system is crucial for understanding the reason behind deteriorations of grain refinement and castability of Al–Si–Ti alloys. Seven Al–Si–Ti alloys annealed between 550 and 650°C were used to clarify the inconsistencies of phase equilibria in the Al–Si rich region. The existences of τ1 (Zr3Al4Si5-type tetragonal), τ2 (ZrSi2-type orthogonal) and the three-phase equilibrium of τ1+α-Al+Si were confirmed. Combined with a critical review of literature data, a CALPHAD-type thermodynamic description was developed for the phase equilibria in the Al–Si rich region of the Al–Si–Ti system between 550 and 900°C. Meanwhile, edge-to-edge matching analysis according to the crystal structures of τ1 and τ2 shows that their nucleation efficacies for α-Al are both weaker than that of Ti(Al,Si)3. From the calculated phase equilibrium of L+τ2+Ti(Al,Si)3 at 727°C and the local equilibrium principle, τ2 would form on the surface of TiAl3 particle and deteriorate its grain refinement efficiency for α-Al. From the calculated liquidus projection, Ti(Al,Si)3 is the primary phase within 0–10.3wt.% Si and 0.08–0.30wt.% Ti. To avoid the formation of τ1 and τ2 for retaining good grain refinement efficiency and castability, a Ti/Si threshold was determined by thermodynamic calculations.

Effect of precursor fraction on silicide nanopowder growth under thermal plasma conditions: A computational study

Computational study is carried out to clarify the growth mechanisms and the effects of the silicon fraction in precursor on the fabricated nanopowders for metal–silicon binary systems (Co–Si, Mo–Si, and Ti–Si systems) under a thermal plasma condition, using a model that can simulate the collective and simultaneous combined processes of binary homogeneous nucleation, binary heterogeneous co-condensation, and coagulation among nanoparticles with different compositions as well as solidification temperature depression. Those three systems that have different ratios of the materials' saturation pressures show different growth behaviors and mature states of the nanopowders. Furthermore, parametric studies indicate that the majority of the fabricated nanoparticles have the silicon content identical to the initial precursor's silicon fraction. Because the solidification temperature depends on the silicon content in the material, the yield and size of the nanopowder are also affected indirectly by the precursor's silicon fraction.