Ti3SiC2 Grains Research Articles

Effects of TiC, Si, and Al on Combustion Synthesis of Ti3SiC2/TiC/Ti5Si3 Composites.

The fabrication of Ti3SiC2 from TiC-containing reactant compacts was investigated by combustion synthesis in the mode of self-propagating high-temperature synthesis (SHS). The initial sample composition was formulated based on (3 - x)Ti + ySi + (2 - x)C + xTiC + zAl, with stoichiometric parameters of x from 0 to 0.7, y = 1.0 and 1.2, and z = 0 and 0.1. For all samples studied, combustion was sufficiently exothermic to sustain the reaction in the SHS manner. Due to the dilution effect of TiC, combustion wave velocity and reaction temperature substantially decreased with TiC content. When compared with the TiC-free sample, the TiC-containing sample facilitated the formation of Ti3SiC2 and the TiC content of x = 0.5 produced the highest yield. Excess Si (y = 1.2) to compensate for the evaporation loss of Si during combustion and the addition of Al (z = 0.1) to promote the phase conversion were effective in improving the evolution of Ti3SiC2. All final products were composed of Ti3SiC2, TiC, and Ti5Si3. For the TiC-containing samples of x = 0.5, the weight fraction of Ti3SiC2 increased from 67 wt.% in the sample without extra Si and Al to 72 wt.% in the Si-rich sample of y = 1.2 and further up to 85 wt.% in the Si-rich/Al-added sample of y = 1.2 and z = 0.1. As-synthesized Ti3SiC2 grains were in a thin plate-like shape with a thickness of 0.5-1.0 μm and length of about 10 μm. Ti3SiC2 platelets were closely stacked into a layered structure.

Oxidation behavior of Ti3SiC2 powder synthesized by using biochar, Si and Ti

Biochar was proposed as a novel carbon source for synthesizing Ti3SiC2 powder with high purity by a simple pressureless sintering at 1673 K, and Ti3SiC2 grains exhibited the typical nanolayered structure. The oxidation behavior of Ti3SiC2 powder showed the parabolic law during isothermal oxidation from 1273 K to 1473 K. Dense and continuous oxidation layer consisting of mixed TiO2 and SiO2 was formed rapidly on the surface of Ti3SiC2 particles as a diffusion barrier, which effectively retarded the inward diffusion of oxygen, conferring good oxidation resistance of the powder.

Effect of texture and grain size on the compressive creep of Ti3SiC2 MAX phase ceramics

The sintering and simultaneous texturing of Ti3SiC2 MAX phase ceramics have been reported. The degree of orientation of Ti3SiC2 grains were quantified with X-ray diffraction for the bulk crystallographic texture and electron back scattered diffraction for local and morphological texture. Analysis revealed that the basal plane of Ti3SiC2 was aligned perpendicular to the direction of applied external force during sintering. The textured MAX phase was subjected to high temperature annealing to induce grain growth which resulted in a duplex microstructure. The ceramics with fine (∼1 µm) and duplex (500 µm wide elongated grains in a matrix of equiaxed 1 µm grains) microstructure were subjected to compressive creep tests at high temperature (1000–1300 °C) in different directions with respect the orientation of the crystals in the bulk Ti3SiC2. The creep resistance was highest for fine grained Ti3SiC2 with basal planes aligned perpendicular to the direction of applied stress, whereas the ceramics with duplex microstructure and basal plane aligned parallel to the direction of applied stress suffered the highest creep deformation. A probable mechanism for the creep response of the different grades of Ti3SiC2 has been proposed.

In-situ formation of Ti3SiC2 interphase in SiCf/SiC composites by molten salt synthesis

Titanium silicon carbide (Ti3SiC2) film was synthesized by molten salt synthesis route of titanium and silicon powder based on polymer-derived SiC fibre substrate. The pre-deposited pyrolytic carbon (PyC) coating on the fibre was utilized as the template and a reactant for Ti3SiC2 film. The morphology, microstructure and composition of the film product were characterized. Two Ti3SiC2 layers form the whole film, where the Ti3SiC2 grains have different features. The synthesis mechanism has been discussed from the thickness of PyC and the batching ratio of mixed powder respectively. Finally, the obtained Ti3SiC2 film was utilized as interphase to prepare the SiC fibre reinforced SiC matrix composites (SiCf/Ti3SiC2/SiC composites). The flexural strength (σF) and fracture toughness (KIC) of the SiCf/Ti3SiC2/SiC composite is 460 ± 20 MPa and 16.8 ± 2.4 MPa∙m1/2 respectively.

Effect of Texture and Grain Size on the Compressive Creep of Ti <sub>3</sub>SiC <sub>2</sub> MAX Phase Ceramics

The sintering and simultaneous texturing of Ti3SiC2 MAX phase ceramics have been reported. The degree of orientation of Ti3SiC2 grains were quantified with X-ray diffraction for the bulk crystallographic texture and electron back scattered diffraction for local and morphological texture. Analysis revealed that the basal plane of Ti3SiC2 was aligned perpendicular to the direction of applied external force during sintering. The textured MAX phase was subjected to high temperature annealing to induce grain growth which resulted in a duplex microstructure. The ceramics with fine (~1 µm) and duplex (500 µm wide elongated grains in a matrix of equiaxed 1 µm grains) microstructure were subjected to compressive creep tests at high temperature (1000-1300 °C) in different directions with respect the orientation of the crystals in the bulk Ti3SiC2. The creep resistance was highest for fine grained Ti3SiC2 with basal planes aligned perpendicular to the direction of applied stress, whereas the ceramics with duplex microstructure and basal plane aligned parallel to the direction of applied stress suffered the highest creep deformation. A probable mechanism for the creep response of the different grades of Ti3SiC2 has been proposed.

Synthesis, microstructure, and mechanical properties of TiC‐SiC‐Ti3SiC2 composites prepared by in situ reactive hot pressing

AbstractIn this work, TiC‐SiC‐Ti3SiC2 composites were synthesized by in situ reactive hot pressing using β‐SiC, graphite, and TiH2 powders as initial materials. Microstructure and mechanical properties of as‐prepared dense composites were systematically investigated. It was found that by increasing the initial SiC content the final SiC content in the composites increased in contrast to the decrease in TiC and Ti3SiC2 contents. In the dense composites, TiC and Ti3SiC2 grains exhibited transgranular fracture, whereas SiC particles showed intergranular fracture. The composite containing 77 vol.% TiC, 4 vol.% SiC, and 19 vol.% Ti3SiC2 had the highest flexural strength of 706.6 MPa. The composite consisting of 44 vol.% TiC, 49 vol.% SiC, and 7 vol.% Ti3SiC2 exhibited the highest Vickers hardness of 22.3 GPa and the highest fracture toughness of 6.0 MPa·m1/2.

Joining of high thermal-expansion mismatched C-SiC composite and stainless steel by an Ag + Ti + Mo mixed powder filler

Abstract High thermal-expansion mismatched C-SiC composite and 304 stainless steel have been bonded by a 72Ag + 18Ti + 10Mo (at%) mixed powder filler. At the bonding temperature (1020 °C), the filler was in semi-solid state, i.e. solid-liquid mixed state of Mo particles, TiAg grains and Ag(Ti) liquid. Microstructural analysis indicated that the high activity and viscosity of the semi-solid filler help to obtain a large-thickness homogeneous joining layer (∼416 mm), in which Mo particles were clad by (Ti,Mo) solid solution and uniformly dispersed in Ag matrix together with the TiAg grains. The large thickness joining layer mainly composed of low coefficient of thermal expansion (CTE) Mo particles and ductile Ag matrix can effectively reduce the high residual stresses of the joint caused by the thermal-expansion mismatch between the dissimilar materials. Additionally, interfaces between the base materials and the joining layer were well bonded without continuous layered brittle compounds. The interfacial reaction products at C-SiC side were TiC, Ti5Si3 and Ti3SiC2 grains in Ag matrix. At 304 interface, Ti2Ni + Ti(Fe,Ni) compounds grew in columnar and gathered nearby. The characteristics of the joining layer and the bonding interfaces contribute to the high joint strength. The average shear strength of the joint at room temperature was 156 MPa.

Joining of Cf/SiC composite and stainless steel via Ag+Ti filler in-situ alloying

The microstructure and formation mechanism of the Cf/SiC composite and stainless steel joints brazed with Ag+Ti filler were investigated. The effects of Ti content (10%˜40%, at %), bonding temperature (990˜1080 °C) and holding time (15˜60 min) on microstructure and mechanical properties of the joints were discussed. The results indicated that a large-thickness interlayer was formed after bonding, in which in-situ formed TiAg particulates and residual Ti particles were dispersed in Ag matrix. Compared with the common composite interlayers, the interlayer formed via Ag+Ti in-situ alloying had more and finer reinforcing phases without reducing the activity of the filler material. The ductile Ag matrix contributed to accommodate the large strain mismatch by elastic deformation. The interfaces between the adjoining materials and the interlayer were well-bonded without any cracks. At Cf/SiC side interface, TiC, Ti5Si3 and Ti3SiC2 grains were generated from SiC matrix and carbon fibers were exposed. A meshing interface was formed, which was beneficial to arrest and deflect cracks and improve the shear strength of the joints. Kirkendall voids were observed at 304 side interface. Especially they were formed in the joints prepared using high Ti content filler materials (Ag+30%˜40%Ti, at %) or bonded at relatively low joining temperature (990 °C). When the content of Ti was fixed, the joint shear strength increased firstly and then decreased with the bonding temperature. Different Ti contents corresponded to different peak bonding temperatures. The holding time had a similar effect on the joint strength as bonding temperature. The maximum joint shear strength at room temperature was 141 MPa obtained at 1020 °C for 30 min with Ag+30 at %Ti composite filler.

The Influence of Synthesis Temperature on the Phase Composition and Structure of Ternary Compounds Produced from TiH2–Si–C Powder Mixtures

The paper examines the formation of phases and structure in ternary compounds produced by thermal synthesis from the TiH2–Si–C powder mixture. The alloys were thermally synthesized in vacuum at 1150, 1300, and 1400°C. According to X-ray diffraction and structural analysis, titanium carbide is the major phase in the alloy synthesized at 1150°C. The alloy also contains a Ti5Si3 silicide phase and an insignificant amount of free carbon. When synthesis temperature increases to 1300°C, the titanium carbide content decreases and a Ti5Si4 silicide phase and ternary Ti3SiC2 compound show up in the alloy. When synthesis temperature increases further to 1400°C, the alloy mainly consists of laminar ternary Ti3SiC2 grains and an insignificant amount of titanium carbide and Ti5Si4 intermetallide. An increase in the synthesis temperature from 1150 to 1400°C leads to a significant growth of grains representing the main alloy components.

Microstructure and mechanical properties of hot pressed Ti3SiC2/Al2O3

In this work, Ti3SiC2/Al2O3 composites with various volume contents of Ti3SiC2 were fabricated under different orthogonal processes by vacuum hot pressing sintering. optimized comprehensive mechanical properties and relative density (＞97%) were obtained (the microhardness, flexural strength and fracture toughness reached the values of 16.25 GPa, 536.31 MPa and 9.3 MPa m1/2, respectively.) when the Al2O3 (60.0 vol %) and Ti3SiC2 (40.0 vol %) were sintered at 1500 °C for 0.5 h at 30 MPa, which basically correspond to the best level of after orthogonal calculation. The orientational growth behavior of Ti3SiC2 was further confirmed by EBSD, and temperature was found to play a prominent role in the growth of Ti3SiC2 to some extents, fewer columnar Ti3SiC2 grains were observed at lower temperature and weak decomposition of Ti3SiC2 was observed at 1500 °C. Meanwhile, high volume Ti3SiC2 was beneficial to the improvement of mechanical properties for the intrinsical layered structure.

Improved shear strength of SiC-coated 3D C/SiC composite joints with a tailored Ti-Si-C interlayer

SiC-coated 3D C/SiC composites were successfully joined using SPS technology with a Ti-Si-C interlayer. The interface morphologies, phase composition, and mechanical properties of the joints were investigated in detail. By adjusting the joining temperature, the interlayer transitioned, in situ, from Ti-Si-C compounds to Ti3SiC2 grains without decomposition. Because of the plastic deformation behavior of Ti3SiC2 grains, the ability of the interlayer to inhibit crack propagation increased. For joints with different interlayer thickness, the distribution of thermal residual stress was calculated using finite element analysis, and the distribution was associated with the evolution of interlayer morphologies, which was eventually used to establish fracture models. Optimized bonding was achieved without erosion of carbon fibers and also without interfacial defects. Finally, a reliable joint with shear strength of 51 ± 3.0 MPa was obtained by precisely controlling the interlayer reaction and optimizing thermal residual stress.

Spherical nanoindentation, modeling and transmission electron microscopy evidence for ripplocations in Ti3SiC2

Herein we present experimental and modeling evidence for a new deformation micromechanism operating in layered solids termed a ripplocation. Select Ti3SiC2 grains were cyclically indented – either parallel or normal to the basal planes - with spherical tips with radii, R of 21 μm and 100 μm. When the load vs. displacement curves were converted to indentation stress vs. a/R curves, where a is the contact radius, fully and spontaneously reversible hysteresis loops were recorded. The energy dissipated per unit volume per cycle, Wd, was found to be a function of basal plane orientation; Wd was smaller when the basal planes were loaded edge on. Transmission electron microscope images of areas under the indentations revealed the existence of defects that previous work confirmed have a strain component along the c-axis and for which no g·b condition was found that resulted in their disappearance. These defects thus cannot be basal dislocations; their characteristics, however, are consistent with bulk ripplocations, BRs. It is the to-and-from movement of these BRs – and not basal dislocations as previously assumed - that is believed to be responsible for the fully and spontaneously reversible loops in Ti3SiC2 and possibly in most other layered solids. Consistent with the need of the basal planes to expand upon the introduction of BRs, the initial friction stress needed to move them was found to be almost three times lower when the basal planes were loaded edge-on. Molecular dynamics simulations on graphite at 10 K faithfully reproduce many features observed below the indenter in this, and previous, work on Ti3SiC2. The existence of BRs will require a revisiting and reassessment of our understanding of how layered solids - from geologic formations to 2D solids – deform.

High temperature properties of the monolithic CVD β-SiC materials joined with a pre-sintered MAX phase Ti3SiC2 interlayer via solid-state diffusion bonding

Monolithic high purity CVD β-SiC materials were successfully joined with a pre-sintered Ti3SiC2 foil via solid-state diffusion bonding. The initial bending strength of the joints (∼ 220MPa) did not deteriorate at 1000°C in vacuum, and the joints retained ∼ 68% of their initial strength at 1200°C. Damage accumulation in the interlayer and some plastic deformation of the large Ti3SiC2 grains were found after testing. The activation energy of the creep deformation in the temperature range of 1000 – 1200°C in vacuum was ∼521kJmol−1. During the creep, the linkage of a significant number of microcracks to form a major crack was observed in the interlayer. The Ti3SiC2 interlayer did not decompose up to 1300°C in vacuum. A mild and well-localized decomposition of Ti3SiC2 to TiCx was found on the top surface of the interlayer after the bending test at 1400°C in vacuum, while the inner part remained intact.

The tribological properties of Ti3SiC2/Cu/Al/SiC composite at elevated temperatures

Dense Ti3SiC2/Cu/Al/SiC composites (TCASc) were successfully produced by powder metallurgy/spark plasma sintering (SPS). The composition and microstructure of the composites were analyzed by X-ray diffractometry and scanning electron microscopy equipped with energy dispersive spectroscopy. The tribological properties of the TCASc sliding against Si3N4 ball at temperatures ranging from room temperature (RT) to 800°C were investigated in comparison with those of Ti3SiC2 (TSC). The tribology tests were conducted on dry sliding tribometer by ball-on-disk configuration. The wear mechanisms were discussed in detail. The results show that the main phases of the composite include TSC, AlCu, SiC, and Al2O3. The incorporation of Al could inhibit the decomposition of TSC. The hardness and flexural strength of the composite are slightly lower than those of TSC. The tribological properties of TCASc and TSC are intensively dependent on temperature. The tribological properties of TCASc are better than those of TSC at room and medium temperatures (wear rate, WR, of TSC at RT and 200°C: (8.63±0.37)×10−4 and (2.15±0.18)×10−3 of TCASc (5.31±0.55)×10−4 and (1.12±0.02)×10−3mm3/N·m, respectively), while the wear properties of TCASc are not better than that of TSC at 400–800°C (WR at 600°C, for example, for TSC: (9.7±1.4)×10−5 and TCASc (2.27±0.15)×10−4mm3/N·m, respectively). Abrasive wear dominates the wear mechanisms at RT and 200°C for TCASc. The incorporated phases of AlCu, SiC, and Al2O3 reinforce the bonding of TSC grains and nail the surrounding soft TSC matrix under the cyclic stress. At high temperature, dynamic-equilibrium tribo-oxides layers show the lubricating and wear-reduction effects contributing to the decreasing friction and wear for both TSC and TCASc. The adhesive wear resulting from the plastic flow is one of the reasons of the higher WR of TCASc than that of TSC.

High-temperature hydrogenation behaviour of bulk titanium silicon carbide

Thermal stability of Ti3SiC2 was investigated at 1200–1400°C in hydrogen atmosphere for 3 hours. The hydrogenation mechanism was clarified by a combination of X-ray diffraction, scanning electron microscope, Raman spectroscopy and first principles calculation. At 1200°C, a dense and uniform TiSi2 layer formed on the sample surface, which originated from both the preferable lose of silicon from the Ti3SiC2 substrate and the dissociation of Ti3SiC2. As temperature increased to 1300°C, TiSi2 layer began to scale off and presented laminated Ti3SiC2 grains beneath this layer, which indicated preferential hydrogenation occurred along the basal planes. This phenomenon was ascribed to the fact that the introduction of H interstitial atom weakened the combination between titanium and silicon interface layer, which was confirmed by first principles calculations. In addition, the formation of TiSi2 owing to the dissociation of Ti3SiC2 caused the volume expansion after hydrogenation, resulting in that majority of TiSi2 layer spelled off at 1400°C.

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.

Characterisation of graphene nanoplatelets reinforced hot pressed Ti3SiC2 ceramic

Ti3SiC2 based ceramic reinforced by 5 wt-% graphene nanoplatelets (GNPs) was prepared by hot pressing at 1550°C for 1 h under a uniaxial pressure load of 30 MPa. The effects of GNPs on the strengthening and toughening of the hot pressed Ti3SiC2 based ceramic were investigated. Comparing with t monolithic Ti3SiC2 ceramic, the flexural strength and facture toughness of the Ti3SiC2–GNP ceramic were significantly improved. The flexural strength and fracture toughness increased from 451.9 to 800.6 MPa, and from 6.23 to 9.67 MPa m1/2 respectively. The mechanism for these mechanical property improvements was attributed to the layered fracture of Ti3SiC2 grains, refined crystalline strengthening and GNP strengthening.

Self-propagating high-temperature synthesis in the Ti-Si-C system: Features of product patterning

Nanolaminate Ti3SiC2-based material is prepared by self-propagating high-temperature synthesis (SHS) from elements, and the processes of its phase and structure formation is investigated. The Ti3SiC2 content in combustion products grows with an increase in the lifetime of the melt. The stratification observed at the level of the crystal structure results in the pronounced nanolaminate structure of Ti3SiC2 grains. The formation of the Ti3SiC2 phase occurs behind the combustion front with the interaction of stoichiometric TiC with the melt based on Ti-Si. Quantum-chemical calculations show that the formation of Ti-Si bonds is energetically preferable to Ti-C bond formation. A comparison of TiC and Ti3SiC2 crystal structures allow the assumption to be made that the laminate shape of Ti3SiC2 crystals is caused by the accumulation of structure discrepancies and hence by a lack of conjugation between the crystals.

Nucleation and growth of Ti3SiC2 on SiC by interfacial reaction

In this study, we investigated the nucleation and growth of TE3SiC2 by an interfacial reaction between a SiC substrate and a Ti/Al bilayered film at various temperatures. The specimens were prepared by depositing Ti/Al on a 4H-SiC substrate and subsequently annealing the substrate in a vacuum. The interfacial structures were analyzed by X-ray diffraction analysis and transmission electron microscopy. Ti3SiC2 nucleated even when annealed at a low temperature of 973 K. The Ti3SiC2 grains formed at 973 K were isolated and nonepitaxial with respect to the SiC substrate. By increasing the annealing temperature to 1273 K, the Ti3SiC2 grains became epitaxial with the SiC substrate, spreading preferentially on it, and coalesced with each other, forming a layer without grain boundaries.

Tribochemistry of Ti3SiC2/Si3N4 tribopair in ethanol

Tribological chemistry of Ti3SiC2/Si3N4 tribopair in two low-viscosity fluids (water and ethanol) was investigated. The chemical compositions of worn surfaces and friction media were determined by X-ray photoelectron spectroscope and Fourier transform infrared spectroscopy. Results show that the friction and wear of Ti3SiC2/Si3N4 tribopair in water was moderate while that in ethanol was low. Mechanical wear characterized by pullout of Ti3SiC2 grains was responsible for high coefficient of friction and wear rate. In ethanol, tribochemical products, i.e., colloid silicic acid from Ti3SiC2 and silicon alkoxide and amines from Si3N4 dissolved in the friction liquid and were responsible for low coefficient of friction and wear rates.