TiC Lattice Research Articles

Spark plasma sintering of TiC with TiAly as sintering aid: Mechanisms and microstructures

TiC features an interesting combination of mechanical properties, high-temperature resistance, and lightness, making it an excellent candidate for several applications in harsh environments. However, its sintering to obtain bulk components is extremely challenging. Herein, we show that titanium aluminide is a promising sintering aid for TiC (5, 10, and 20 vol% were investigated). The aluminide allows the formation of a nearly fully dense component at 1350 °C by spark plasma sintering under 80 MPa. The aluminide forms a grain boundary secondary phase that promotes the Ti diffusion: Ti from TiC can be dissolved within the TiAly at the neck center and precipitate at the neck surface, while C can easily diffuse through the TiC lattice. Higher temperatures cause the extrusion of the aluminide out of the SPS die and its reaction with oxygen impurities. The final microstructure is constituted by nearly pure TiC with isolated alumina pockets at the triple points.

Instability of in situ TiC particles in an Al-12Si alloy

This paper studied the evolution of in situ TiC particles in an Al-12Si alloy and the effect of Si on their stability. The samples were observed with scanning electron microscopy, and the phase analysis was performed by energy dispersive spectroscopy, X-ray diffraction, and transmission electron microscopy. The results demonstrated that Si can directly promote the evolution of TiC. After holding the TiC/Al-12Si alloy (TiC content of 2.75 wt.%) at 800 °C for 5 min, a large amount of TiC reacted with Al to form an Al4C3 phase and the Ti in TiC reacted with Al and Si to form a TiAlSi phase. When the holding time was increased to 20 min, the TiC almost completely disappeared. The morphology of TiC gradually changed from a regular tetra-decahedron to a sphere when Si was not added, and the average size gradually decreased from 1 μm and eventually disappeared completely. Si can diffuse into the TiC lattice to destroy its structure, thus forming a Si-rich disordered layer at the edge of the TiC particles. The values of diffusion resistance of Ti and C atoms in TiC, decrease owing to the destruction of the TiC lattice structure, which accelerates the TiC transformation reaction.

Preparation of TiC/Ti₃SiC₂ Composite by Sintering Mechanical Alloyed Ti-Si-C Powder Mixtures.

The present work aims to evaluate the crystalline phases and microstructure of a TiC-Ti₃SiC₂ ceramic composite, obtained by mechanical alloying of Ti, C and Si powders and subsequent sintering. A mechanical alloying technique in a planetary ball mill for 1, 10, 50, 100 and 200 h using Ti, Si and C powders with molar ratios of 3:1:2 as feedstock in argon (Ar) gas was employed to prepare nano-sized Ti-Si-C powders. TiC crystallite size and lattice strain were evaluated by X-ray diffraction analysis (XRD) and the morphological characteristics and particle size distribution were examined using scanning electron microscope (SEM). After milling, a reduction of the average particle size and crystallinity is observed. Furthermore, after 10 h of milling time, TiC starts to crystallize. The powder mixture obtained after 200 h of milling was compacted and sintered at 1200 °C under controlled atmosphere, for 15 min, 2 h or 4 h with a heating rate of 5 °C/min. Almost full densification of samples sintered for 2 h and 4 h has been achieved, with relative densities close to 98.8±0.2% and TiC and Ti₃SiC₂ as crystalline phases with an average crystallite size of TiC near 0.7 μm. Rietveld refinement indicates that the majority TiC-cubic phase (>85 vol%) presents a unit cell volume of 8.03 nm³ after sintering at 1200 °C. Despite the maintenance of the volume of the hexagonal unit cell of Ti₃SiC₂, (15.05 nm³), the increase of the isothermal sintering time resulted in an increase of the lattice parameter "a", from 0.315 nm to 0.320 nm, and a reduction of the lattice parameter "c" from 1.750 nm to 1.705 nm. The control of the changes in the residual stresses within the TiC matrix and the Ti₃SiC₂ precipitates, which is associated with the deformation in the lattice parameters, must be controlled to achieve high fracture toughness in the composite.

Effect of Zr on undissolved phases and carbide precipitation in Ti microalloyed low-carbon steel

The undissolved phases and carbide precipitation in Ti and Ti–Zr microalloyed low-carbon steels were investigated by scanning electron microscopy, transmission electron microscopy and energy-dispersive X-ray spectrometry. At 1225 °C, the replacement of Ti by Zr formed Zr2CS and (Zr, Ti)N (the Ti/Zr atomic ratio is 0.11) and reduced the consumption of Ti. At 925 °C, it was identified that TiC phases were precipitated at first and Zr was incorporated into the TiC lattice in the subsequent precipitation process, which promoted the precipitation of titanium carbide. The calculation of the interaction coefficient between Ti, C, N and Zr showed that Zr reduced the activity of Ti and C and increased the activity of N in the iron matrix. Therefore, with the addition of Zr, the solubility of Ti was increased, and the consumption of Ti was reduced at high temperature in Ti microalloyed low-carbon steel. The thermodynamic calculation of carbide precipitation transformation showed that the replacement of Ti by Zr increased the nucleation driving force and the nucleation rate of titanium carbide, while the critical core size and the critical nuclear energy were reduced. As the holding time was extended, the Zr/Ti atomic ratio increased and the size of the precipitates also increased. When the Zr/Ti atomic ratio reached a certain level, the size of the precipitates did not increase with further increase in atomic ratio. When the Zr/Ti atomic ratio in (Ti, Zr)C was 0.05–0.17, (Ti, Zr)C was the most stable carbide and the easiest to nucleate at 925 °C. There was more of the (Ti, Zr)C phase than TiC at 925 °C after 50 and 100 s, and the time to complete the coarsening behavior of (Ti, Zr)C was shorter than that of TiC.

Microstructure and mechanical properties of intragranular W-Cu/TiC-ZrC composite prepared by reactive melt infiltration at 1300 °C

Newly intragranular W-Cu/TiC-ZrC composites with nano W dispersoids in TiC matrix have been prepared by reactive melt infiltration at 1300 °C for 1 h in vacuum using molten Zr-Cu binary alloys and a (Ti0.75,W0.25)C solid solution powder as raw materials. The as-synthesized composites consist of major phases of W, Cu, TiC and ZrC. With the decrease of Zr content from 66 to 21 at.% in the Zr-Cu infiltrator, the reaction formed W phase in the composite has changed from micron-sized intergranular grains to nano-sized rounded inclusions in TiCy grains. The crystallographic orientation relationship at W and TiC interfaces are detected as:011¯W//111¯TiC&011W//011TiCand411W//424TiC&011¯W//42¯3¯TiC. Nano-sized lamellar structure with both W and Cu rich is detected to have super-lattice structure based on the TiC lattice. The elastic modulus, flexural strength, fracture toughness of the intragranular W-Cu/TiC-ZrC composite infiltrated with Zr14Cu51 melt are 207.5 GPa, 457 MPa and 10.21 MPa∙m1/2, respectively. The intragranular nano W dispersoids and ribbon like precipitates hinder crack propagation via crack deflection and bridging.

Effect of molybdenum addition on the precipitation of carbides in the austenite matrix of titanium micro-alloyed steels

The present work aims to reveal the effect of Mo on the precipitation behavior of MC-type (M = Ti and Mo) carbides in the austenite matrix of titanium micro-alloyed steel. The precipitation start-time–temperature curve was determined by a double-pass compression test on a Gleeble simulator, and the elemental mass fraction of MC-type carbides was measured by a physical–chemical phase analysis after a single-pass rolling test. The results shows that 0.2 wt% Mo accelerates the precipitation kinetics of MC-type carbides. During the initial stage of precipitation, Mo tends to distribute in the outer region of precipitates by replacing Ti despite of the high solubility of MoC in austenite. The replacement of Ti by Mo in TiC lattice leads to two opposite effects: First, it restrains MC precipitation due to the higher Gibbs free energy of (Ti, Mo)C relative to TiC; Second, it promotes MC precipitation by decreasing the interfacial chemical energy of MC/austenite system. The second effect is more pronounced during the initial stage of precipitation when MC precipitates are relatively small and hence MC precipitation is accelerated by Mo addition. Compared to TiC, (Ti, Mo)C with stronger coarsening resistance suppresses austenite recovery and recrystallization more effectively, which favors maintaining the deformation microstructures at high temperatures.

Pore and microstructure change induced by SiC whiskers and particles in porous TiB2–TiC–Ti3SiC2 composites

TiB2–TiC–Ti3SiC2 porous composites were prepared through a plasma heating reaction using powder mixtures of Ti, B4C SiC whiskers (SiCw) and SiC particles (SiCp). The effects of the SiCw and SiCp content on pore structures, phase constituents, microstructure, and crystal morphology of TiC were studied. The results show that TiC, TiB, Ti3B4 phases are formed within the 5Ti+B4C system. With the addition of SiCw and SiCp, the TiB and Ti3B4 phases are reduced, sometimes even disappeared. Interestingly, the content of TiB2 and TiC increased, resulting in Ti3SiC2 and TiSi2 being formed. The porosity of composites increases notably with the addition of SiCw. However, with the increase of SiCp, the porosity of the composites first decreases, followed by an increase. After adding the specified amount of SiCw/SiCp, the compressive strength of composites are improved significantly. Additionally, the pore size of the composites are decreased significantly with the addition of SiCw/SiCp. During the plasma heating process, some Si atoms will diffuse into the TiC lattice, which in turn made the cubic TiC grains into hexagonal lamellar TiC or Ti3SiC2 grains.

Formation of nanolaminate structures in the Ti-Si-C system: A crystallochemical study

Combustion synthesis of laminate Ti3SiC2 structures from the elements was explored by time-resolved XRD. Crystallochemical modeling and quantum-chemical calculations suggest that the laminate structure of Ti3SiC2 arises due to regular accumulation of difference between the bond lengths of Ti3SiC2 and TiC and population of thus formed vacancies with Si atoms in the TiC lattice.

Incorporation effects of Si in TiCx thin films

Ti-Si-C thin films with varying Si content between 0 to 10at.% were deposited by DC magnetron sputtering from elemental targets. The effects on microstructure and lattice parameters were investigated using x-ray diffraction, x-ray photoelectron spectroscopy, transmission electron microscopy, and first-principles calculations. The results show that the growth of pure TiCx onto Al2O3(0001) substrates at a temperature of 350°C yields (111) epitaxial and understoichiometric films with x ~0.7. For Si contents up to 4at.%, the TiCx epitaxy is retained locally. Si starts to segregate out from the TiCx to column boundaries at concentrations between 1 and 4at.%, and causes a transition from epitaxial to polycrystalline growth above 4at.%. Eventually, the top part of the films form a nanocomposite of crystalline TiC grains surrounded by amorphous SiC and C for Si contents studied up to 10at.%. The results show that Si takes the place of carbon when incorporated in the TiC lattice.

First-principles study of doping and distribution of Si in TiC

In this work, first principles calculations have been performed to study the doping and distribution of Si atoms in TiC lattice. The results confirm that Si atoms prefer to occupy Ti sites and their segregation on the TiC crystal surface may occur. But in the presence of carbon vacancies on the surface, Si atoms tend to be chemically adsorbed around the vacancies rather than occupy the carbon sites. It is also shown that the diffusion of Si may be very difficult in stoichiometric TiC, in particular the diffusion from bulk to surface. However, the carbon vacancies can considerably decrease the energy barrier and enhance the diffusion of Si atoms.

Carbide precipitation in austenite of a Ti–Mo-containing low-carbon steel during stress relaxation

The carbide precipitation behavior in austenite of a 0.04%C–0.10%Ti–0.21% Mo micro-alloyed steel was investigated by the stress relaxation method and transmission electron microscopy. Results showed that the precipitation-time-temperature diagram for carbide precipitation exhibited a typical “C” curve, the nose of which was located at about 925°C. The carbide was identified as a (Ti, Mo)C particle with a NaCl-type crystal structure that contains a certain amount of Mo. As compared with TiC particle in Ti steel, (Ti, Mo)C particle in Ti–Mo steel exhibits a superior coarsening resistance during the coarsening stage. The fraction of Mo in (Ti, Mo)C particle decreases with isothermal holding time or particle growing, indicating that the high level replacement of Ti by Mo in TiC lattice is in a “metastable” state with respect to the equilibrium precipitation of (Ti, Mo)C in austenite.

Formation mechanism of Ti3SiC2 from a TiC lattice: An electron microscopic study

Titanium silicon carbide (Ti3SiC2, TSC) crystals with terraced morphology were prepared by heating a powder mixture consisting of Ti, Ti5Si3 and carbon nanotube (CNT). A sample containing an under-grown TSC crystal was analyzed by the HRTEM, showing various stacking patterns coexisted, including TSC, TiC, twined TiC, other intermediate stacking patterns, etc. A formation mechanism is proposed for the formation of TSC from a TiC lattice. The essential of the formation mechanism contains two steps: atom substitution and atom relocation. Atom substitution includes formation of carbon vacancy and insertion of Si atoms into the TiC lattice, and atom relocation involves position adjustments of C, Si and Ti atoms triggered by the atom substitution. It is illustrated that several atom substitutions and relocations on a starting TSC lattice result in a lattice pattern similar to the lattice observed in the HRTEM images. Lattice spacing values on the HRTEM images were also measured and analyzed, where the reduction of the standard deviation of the lattice spacing along a spatial direction confirmed the crystal growth path from the starting TiC to the product TSC.

Stability of (Ti, M)C (M = Nb, V, Mo and W) carbide in steels using first-principles calculations

The lattice parameters, formation energies and bulk moduli of (Ti, M)C and M(C, Va) with the B1 crystal structure have been investigated using first-principles calculations, where M = Nb, V, Mo and W. The replacement at 0 K of Ti by Mo or W in the TiC lattice is found to be energetically unfavorable with respect to the formation energy. However, it decreases the misfit strain between the carbide and ferrite matrix, a factor which is of critical importance during the early stages of precipitation, thus favoring the substitution of Ti by Mo, as is observed in practice. The effect of Mo in enhancing the coarsening resistance of (Ti, Mo)C precipitates is discussed in terms of its role in the nucleation process, but followed by a more passive contribution during coarsening itself. The role of tungsten has been predicted to have a similar effect to molybdenum on the nucleation and coarsening process. Analysis of precipitates in Ti-, Ti–Mo- and Ti–W-bearing steels shows results consistent with the calculations.

Synthesis of TiC–Al 2O 3 nanocomposite powder from impure Ti chips, Al and carbon black by mechanical alloying

The possibility of providing TiC–Al 2O 3 nanocomposite as a useful composite from low-cost raw materials has been investigated. Impure Ti chips were placed in a high energy ball mill with carbon black and aluminum powder and sampled after different times. XRD analysis showed that TiC has been synthesized after 10 h of milling. It could be observed from the width of XRD patterns’ peaks that the size of produced TiC crystallites is in the order of nanometer. In order to forming of TiC–Al 2O 3 composite, heat treatment was performed in different temperatures. Investigations have revealed that formation temperature of TiC as the dominant phase decreased for the milled specimens during heat treatment, also nanocrystalline TiC–Al 2O 3 composite was formed in this situation. Furthermore milling led to increase of strain and decrease of TiC lattice parameter while during heat treatment nanocrystalline grains grow up and strain decreases.

Synthesis of ultrafine TiC1–X and Ti(CN) powders via planetary milling

Ultrafine TiC1-X and Ti(C,N) powders 100-200 nm in size were synthesised through mechanical alloying for cutting tool applications. Elemental titanium and carbon were processed by a high energy planetary mill in air, argon and nitrogen atmosphere. With variations in the Ti/C ratios, the characteristics of synthesised powders were investigated. Of three atmospheres, argon was effective in synthesising pure TiC1-X powders. However, the presence of oxygen seemed to interfere with carbon and nitrogen diffusion into TiC lattice. Nitrogen exhibited a stronger affinity with titanium than carbon in forming the Ti(C,N) phase. This study shows the parameters used to determine the final compositions of synthesised TiC1-X and Ti(C1-XNX).

Simultaneous Synthesis of Titanium Carbide-Alumina from Woody Materials by Self-Propagating High Temperature Synthesis

In order to prepare simultaneously TiC-Al 2 O 3 , and to suppress formation of carbon defects in TiC prepared from sell-propagating high temperature synthesis (SHS) of woody materials with Ti, the reaction of each woody material with Ti and Al was inyostigated and compared with their reaction with Ti only. The reaction of Japanese cedar (Cryptomeria japonica D. Don) bark, cellulose or lignin as the woody materials, with Ti alone or Al-containing Ti powder was examined under the conditions favorable for the SHS reaction. It was found that TiC-Al 2 O 3 could be saccessfully prepared from the woody materials by means of the SHS reaction. The effectiveness of Al in reducing the amount of carbon defects in the TiC was confirmed by performing the SHS reaction with and without Al. The carbon and oxygen in the woody materials reacted with Ti and Al to yield TiC and α-Al 2 O 3 , respectively. The amount of carbon defects in cellulose-derived TiC decreased with increasing aluminum, whereas lignin-derived TiC hardly changed in that regard. Because added aluminum reacts preferentially with oxygen in the woody material, it is guessed that oxygen which it takes to remove carbon atom from the TiC lattice is used up.

Preferential orientation of titanium carbide films deposited by a filtered cathodic vacuum arc technique

Titanium carbide films with a thickness of approximately 100-nm were deposited on Si(100) substrates by a filtered cathodic vacuum arc technique. The composition and microstructure of the films were assessed by Rutherford backscattering spectroscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and atomic force microscopy. A negative bias voltage ( V S0∼−1000 V) was applied to the substrate during deposition, and the influence of V S on the crystalline orientation of the as-deposited films was investigated. It was found that the crystallites are randomly oriented in the film deposited at V S=0 V. In the bias voltage range of V S=−40∼−500 V, the titanium carbide films exhibited a (111) preferential orientation. When V S was increased to −1000 V, however, the film was (100) preferentially oriented. The compressive internal stress, determined by the radius of curvature technique, in the titanium carbide films exhibited a minimum value at approximately V S =−80∼−120 V. The (111) preferential orientation can be explained by minimization of elastic energy storage in the films; while the (100) preferential orientation in the film deposited at V S =−1000 V is due to the sputter channeling effect, because the (100) direction in the TiC lattice shows the most open channeling direction and therefore the lowest sputtering yield.

Formation of titanium carbonitride phases via the reduction of TiO2 with carbon in the presence of nitrogen

The reduction of rutile (TiO2) with carbon was studied in a range of nitrogen atmospheres. The effect of the reactivity of carbon on the reducibility of TiO2 to titanium carbonitride phase (TiC xNy) was investigated over a range of temperatures between 1173 K and 1773 K. The present study also reports the effect of the presence of ammonia, CO, and hydrogen gases on the reduction reaction equilibrium of TiO2 to carbonitride (TiCN). The compositional dependence of the lattice parameter of TiCN phase on the concentrations of interstitial atoms, C, N, and O is also discussed. The mechanism of TiCN phase formation from TiO2 has been established on the basis of a predominance area diagram in the Ti–C–N–O system derived from the Gibbs free energy data at 1573 K and 1 atm of N2 gas. The derived values of the activation energies for simultaneous reduction-nitridation of TiO2 to TiCN are discussed in the light of interstitial ion diffusion through the B1 (NaCl type) structure. The dependence of TiC lattice parameter on the concentrations of N and O at the interstitial sublattice sites is also established. The apparent values of the activation energies were found to be in the range of 220 kJ to 240 kJ mol−1 for both types of reducing agents: graphite and activated charcoal.

Deposition of titanium carbide films from mixed carbon and titanium plasma streams

Dual source metal plasma immersion ion implantation and deposition was used to deposit TixCy films over a wide range of Ti:C composition. This technique is well adapted for this purpose and allows one to tailor the microstructure and properties of the films. We investigated the variation of the composition, bonding states, and structure as functions of the deposition conditions. Excess carbon and contamination oxygen are incorporated in the TiC lattice interstitially and substitutionally, respectively. The wear mechanism of a stoichiometric TiC film was investigated and compared to that of a diamondlike carbon film. TiC fails by wear and microcrack propagation.

Structure and properties of titanium aluminide with titanium carbide powder: M. Inoue et al. (Tokyo Nishi University, Yamanashi, Japan.) J.Japan Soc. Powder and Powder Metallurgy, vol 42, no 3, 1995, 391–396. (In Japanese.)

Non-stoichiometric titanium carbide layers TiCx (x = 0.26, 0.49 and 0.78) were synthesized by multiple energies ion implantation at the surface of titanium. The carbon concentration profiles obtained from RBS and SIMS measurements are almost flat over the whole implantation depth, in agreement with the simulation calculation. Grazing incidence X-ray diffraction shows the formation of TiC with an NaCl structure in all cases, in spite of the non-stoichiometric composition; nevertheless a small amount of carbon-titanium solid solution is detected on the TiC0.26 sample. The TiC lattice parameter increases with carbon concentration and the carbide layers are formed with small size crystallites. The XPS C1s and Ti2p peaks and the valence band spectrum show that the carbon is fully bonded to the titanium as carbide. Nanoindentation analysis indicates that the carbide layers present an elasto-plastic behaviour with the elastic part increasing with the carbon concentration. The same trend is observed for the hardness and Young's modulus of the TiCx layers.