Influence of Cu on the mechanical and tribological properties of Ti3SiC2

Ti₃SiC₂/Cu composites with different contents of Cu were fabricated by mechanical alloying and spark plasma sintering method. The phase composition and structure of the composites were analyzed by X-ray diffractometry and scanning electron microscopy equipped with energy dispersive spectroscopy. The mechanical and tribological properties of Ti₃SiC₂/Cu composites were tested and analyzed compared with monolithic Ti₃SiC₂ in details. The results show that the Cu leads to the decomposition of Ti₃SiC₂ to produce TiC_x, Ti₅Si₃C_y, Cu₃Si, and TiSi₂C_z. The friction coefficient and wear rate of the composites are lower than that of monolithic Ti₃SiC₂, which is ascribed to the fixing effect of hard TiC_x, Ti₅Si₃C_y, and Cu₃Si to inhibit the abrasive friction and wear. However, at elevated temperatures (ranging from room temperature to 600 °C) the friction and wear of the composites are higher than those at room temperature. Plastic flowing and tribo-oxidation wear accompanied by material transference contribute to the increased friction and wear at elevated temperatures.     

Experimental synthesis and density functional theory investigation of radiation tolerance of Zr3(Al1‐xSix)C2 MAX phases

Synthesis, characterization and density functional theory calculations have been combined to examine the formation of the Zr₃(Al_1–xSi_x)C₂ quaternary MAX phases and the intrinsic defect processes in Zr₃AlC₂ and Zr₃SiC₂. The MAX phase family is extended by demonstrating that Zr₃(Al_1–xSi_x)C₂, and particularly compositions with x≈0.1, can be formed leading here to a yield of 59 wt%. It has been found that Zr₃AlC₂ ‐ and by extension Zr₃(Al_1–xSi_x)C₂ ‐ formation rates benefit from the presence of traces of Si in the reactant mix, presumably through the in situ formation of Zr_ySi_z phase(s) acting as a nucleation substrate for the MAX phase. To investigate the radiation tolerance of Zr₃(Al_1–xSi_x)C₂, we have also considered the intrinsic defect properties of the end‐members. A‐element Frenkel reaction for both Zr₃AlC₂ (1.71 eV) and Zr₃SiC₂ (1.41 eV) phases are the lowest energy defect reactions. For comparison we consider the defect processes in Ti₃AlC₂ and Ti₃SiC₂ phases. It is concluded that Zr₃AlC₂ and Ti₃AlC₂ MAX phases are more radiation tolerant than Zr₃SiC₂ and Ti₃SiC₂, respectively. Their applicability as cladding materials for nuclear fuel is discussed.     

Determination of interdiffusion coefficients of Si and Al in Ti3SiC2–Ti3AlC2 diffusion couple at 1373-1673 K

In the diffusion couple of Ti₃SiC₂ and Ti₃AlC₂, only interdiffusion of Si and Al occurred during diffusion treatment process. Based on the concentration profiles of Si and Al measured by electron probe microanalysis (EPMA), the interdiffusion coefficients of Si and Al at 1373-1673 K in Ti₃SiC₂–Ti₃AlC₂ diffusion couple were determined by both the Boltzmann-Matano (B-M) method and the Saucer-Freise (S-F) method. At the position of Matano plane with the composition of Ti₃Al_0.5Si_0.5C₂, the interdiffusion coefficient could be expressed as D_int (m²/s) = 5.6 × 10⁻⁴⋅exp [−246 ± 14 (kJ/mol)/RT]. Based on the two methods, the calculated interdiffusion coefficients increased with increasing temperature, and the magnitudes of their absolute values were on the order of 10^–13-10^–11 m²/s at 1373-1673 K. At 1373-1573 K, the calculated interdiffusion coefficients decreased monotonously with the increase of Si concentration, that is, x_Si/(x_Al + x_Si). But at 1673 K, the variation trend of interdiffusion coefficients with x_Si/(x_Al + x_Si) was no longer monotonous, probably due to the presence of Ti₅Si₃ phase and voids on Ti₃AlC₂ side.     

Investigation of preparation and properties of Ti3SiC2/Al2O3 multilayered composites

Ti₃SiC₂/Al₂O₃ multilayered composites were prepared by the combination of tape casting and hot pressing sintering. The slurry was produced by adjusting the amounts of each organic material, including triethyl phosphate (TEP) as a dispersion, polyvinyl butyrate (PVB) as a binder, dioctyl phthalate (DOP) as a plasticizer, and anhydrous ethanol as an organic solvent. When TEP content was 3 wt.%, PVB content was 4.5 wt.%, R-value (DOP/PVB) was 1.4, and solid content was 38 wt.%; the cast film with a smooth surface, good flexibility, and uniform thickness was obtained after defoaming, tape casting, and drying. Three samples were prepared, namely, S1–S3. The S1 was monolithic Ti₃SiC₂/Al₂O₃ (mass ratio is 1:1) composites. S2 and S3 were Ti₃SiC₂/Al₂O₃ multilayered composites, which matrix layers were Ti₃SiC₂/Al₂O₃ composites (mass ratio is 1:1) and Al₂O₃, respectively, and their interface layer was Ti₃SiC₂. S1–S3 were also sintered at 1550°C. The bending strength of multilayered materials were lower than that of monolithic material, but the fracture toughness of multilayered materials significantly increased. Due to the introduction of Ti₃SiC₂ interface layer, the friction coefficient and wear rate of Ti₃SiC₂/Al₂O₃ multilayered composites were reduced by 30.7% and 33.8%, respectively, compared with monolithic material.     

Improved mechanical properties of Al2O3 ceramic by in-suit generated Ti3SiC2 and TiC via hot pressing sintering

Al₂O₃ multi-phase composites with different volume fractions of SiC varying from 0 vol% to 30.0 vol% were fabricated by vacuum hot pressing sintering at 1600 °C under the pressure of 30 MPa for 2.0 h. The aim of this work was to investigate the effect of SiC content on the morphology and mechanical properties of the Al₂O₃ multi-phase composite. The results show that the addition of SiC and Ti can produce new strengthening and reinforcing phases include Ti₃SiC₂, TiC, Ti₅Si₃, which would hamper the migration of grain boundaries and promote sintering. The mechanical performances could reach the comprehensive optimal values for 20.0 vol% SiC, delamination and transgranular fracture being the major crack propagation energy dissipation mechanisms.     

Near‐Net‐Shape Fabrication of Ti3SiC2‐based Ceramics by Three‐Dimensional Printing

This paper focuses on the preparation of near‐net‐shaped dense Ti₃SiC₂‐based materials via an indirect three‐dimensional printing (3D printing) and postreactive melt infiltration (RMI) processes. TiC preforms with bimodal pore size distribution were fabricated through 3D printing, followed by the infiltration of Si melt and Al–Si alloy (Al₄₀Si₆₀ and Al₇₀Si₃₀). Dense composites with density of ~4.1 g/cm³ were obtained after the infiltration. No volume shrinkage was obtained after the reactive infiltration with Al–Si alloy. The participation of Al during the infiltration process promoted the formation of Ti₃SiC₂. The as‐fabricated Ti₃SiC₂‐based materials showed enhanced mechanical and electromagnetic interference shielding properties.     

Effect of substituting Al3+ for Ti4+on the microwave dielectric performance of Mg2Ti1-xAl4/3xO4 (0.01 ≤ x ≤ 0.09) ceramics

In this paper, Mg₂Ti_1-xAl_4/3xO₄ ceramics (0.01 ≤ x ≤ 0.09) were synthesized through conventional solid-state ceramic route. The cubic spinel structure, microstructure and microwave properties of Mg₂Ti_1-xAl_4/3xO₄ (x = 0.01, 0.03, 0.05, 0.07, 0.09) ceramics were investigated by X-ray diffraction, Raman spectra, infrared spectra. Rietveld refinements confirm that a spinel structure phase with space group Fd-3m is formed. The variation of the permittivity was concerned with the ionic polarizability, and the value of τ_f was influenced by the bond valence. Both Q × f values and relative density showed an identical trend. Intrinsic properties of Mg₂Ti_1-xAl_4/3xO₄ ceramics were analyzed by infrared spectra and Raman spectra. In addition, the Mg₂Ti_1-xAl_4/3xO₄ ceramic sintered at 1420 °C for 4 h possessed optimal dielectric properties (ε_r = 14.65, Q × f = 182347 GHz, τ_f = −57.7 ppm/°C) when x = 0.09.     

Synthesis and characterization of quarternary Ti3Si(1−x)AlxC2 MAX phase materials

Ti₃Si_(1−x)Al_xC₂ (x=0–1) quarternary MAX phase materials were prepared by spark plasma sintering of TiC, Ti, Si and Al powder mixtures at 1200 °C. Effect of Al addition on lattice parameters, density and hardness were investigated. Impurities are limited to binary phases of TiC and Ti₅Si₃. No multinary compound other than Ti₃Si_(1−x)Al_xC₂ can be detected. TiC exists as impurity in all samples and trace amount of Ti₅Si₃ can be detected in Samples x=0.1–0.6. Oxidation of Al cannot be avoided although all sintering were performed under vacuum and trace amount of Al₂O₃ can be found in all samples with Al addition. Experimental results show that the lattice parameters a and c increase linearly with increasing Al content for x=0–1. The lattice variations are strongly anisotropic and follow Vegard׳s law. Both density and hardness decrease as Al content increases. The linear variation of lattice parameters, d spacings of crystalline faces and density against Al concentration suggest that continuous solid solutions of Ti₃Si_(1−x)Al_xC₂ (x=0–1) may have been formed between Ti₃SiC₂ and Ti₃AlC₂.     

Microstructure and mechanical strength of transient liquid phase bonded Ti3SiC2 joints using Al interlayer

Based on the structure characteristic of Ti₃SiC₂ and the easy formation of Ti₃Si_1−xAl_xC₂ solid solution, a transient liquid phase (TLP) bonding method was used for bonding layered ternary Ti₃SiC₂ ceramic via Al interlayer. Joining was performed at 1100–1500 °C for 120 min under a 5 MPa load in Ar atmosphere. SEM and XRD analyses revealed that Ti₃Si(Al)C₂ solid solution rather than intermetallic compounds formed at the interface. The mechanism of bonding is attributed to aluminum diffusing into the Ti₃SiC₂. The strength of joints was evaluated by three point bending test. The maximum flexural strength reaches a value of 263 ± 16 MPa, which is about 65% of that of Ti₃SiC₂; for the sample prepared under the joining condition of 1500 °C for 120 min under 5 MPa. This flexural strength of the joint is sustained up to 1000 °C.     

Effect of Al dopant on the hydrothermal oxidation behavior of Ti3SiC2 powders

Experimental and thermodynamic studies of the hydrothermal oxidation behavior of Ti₃Si_0.9Al_0.1C₂ powders were performed at 500–700 °C under a hydrostatic pressure of 50 MPa. Titanium, silicon and aluminum were selectively extracted from Ti₃Si_0.9Al_0.1C₂ during hydrothermal oxidation, resulting in the formation of oxides and disordered carbon. A comparative investigation with Ti₃SiC₂ disclosed the evident influence of Al dopant on the hydrothermal oxidation process, i.e. delaying the phase transformation from anatase to rutile, promoting the formation of carbon, the crystallization of silica and decomposition of Ti₃Si_0.9Al_0.1C₂. The corresponding mechanism was discussed.     

Fabrication of TiC coated short carbon fiber reinforced Ti3SiC2 composites: Process,microstructure and mechanical properties

The C_f/Ti₃SiC₂ composites were fabricated through spark plasma sintering (SPS) and hot isostatic pressing (HIP), TiC coated C_f and Ti₃SiC₂ powder were used as starting materials. The improved fracture toughness (K_IC) and Vickers hardness (HV₁) of the TiC coated C_f/Ti₃SiC₂ composite fabricated by SPS were 7.59 MPa·m^1/2 and 7.28 GPa. On this foundation, taking the advantage of better sintering process of HIP, the highest K_IC and HV₁ achieved 8.32 MPa·m^1/2 and 9.24 GPa with fiber content of 10 vol%, which increased by 40% and 65% compared with that of monolithic Ti₃SiC₂. The reasonable control of reactive interface is the main factor for the improved mechanical properties of the composites, the TiC coating effectively protected the fiber structure from interfacial reaction compared with that of the non-coated C_f/Ti₃SiC₂. Meanwhile, the artificially designed and weakly bonded TiC coated C_f can fully exert the toughening mechanisms like fiber pull-out and debonding.     

Fabrication of in-situ Ti-Cx-N1−x phase enhanced porous Si3N4 absorbing composites by gel casting

In view of the lack of a conformal, load-bearing, lightweight, and high-temperature resistant integrated microwave-absorbing composites for applications under extremely complex conditions, this study successfully applies gel casting craft to porous Si₃N₄ microwave-absorbing composites. The high-temperature decomposition reaction of Ti₃SiC₂ powder was utilized to generate uniform Ti-C_x-N_1−x grains in situ and to enhance the mechanical and microwave-absorption properties of porous Ti-C_x-N_1−x/Si₃N₄ composites. The bending strength, fracture toughness, density, maximum reflection loss value, absorption bandwidth and matched thickness in P-band of the composite with 30 wt% Ti₃SiC₂ addition were 164.87 ± 7.56 MPa, 2.61 ± 0.13 MPa·m^1/2, 2.077 g/cm³, 32.42 dB, 1.74 GHz and 4.2 mm, respectively. The fracture toughness and bending strength of the composite were increased by 71.71% and 58.13%, respectively, compared with monolithic porous Si₃N₄. The electromagnetic wave loss mechanisms of the composites are proposed as a combination of conductivity loss, multiple reflections and scattering, interfacial polarization and defect polarization.     

Microstructure and mechanical properties of Ti3SiC2/3Y-TZP composites by spark plasma sintering

Ti₃SiC₂/3Y-TZP (3 mol% Yttria-stabilized tetragonal zirconia polycrystal) composites were fabricated by spark plasma sintering (SPS). The effect of Ti₃SiC₂ content on room-temperature mechanical properties and microstructures of the composites were investigated. The Vickers hardness and bending strength of the composites decreased with the increasing of Ti₃SiC₂ content whereas the fracture toughness increased. The maximum fracture toughness of 9.88 MPa m^1/2 was achieved for the composite with 50 vol.% Ti₃SiC₂. The improvement of the fracture toughness is owing to the crack deflection, crack bridging, the transformation toughening effects.     

Effect of Al2O3 on the microstructure and mechanical properties of Ti3AlC2/Al2O3 in situ composites synthesized by reactive hot pressing

Ti₃AlC₂/Al₂O₃ in situ composites with different Al₂O₃ contents were successfully synthesized from the powder mixture of Ti, TiC, Al and TiO₂ by a reactive hot-pressing method at 1350 °C. The effect of Al₂O₃ on the microstructure and mechanical properties of the composites was investigated in detail. The results indicate that the as-fabricated products mainly consist of Ti₃AlC₂, Al₂O₃ and a small amount of TiC. With increasing the Al₂O₃ content, the flexural strength of Ti₃AlC₂/Al₂O₃ composites increase gradually, the fracture toughness reaches the peak value of 8.21 MPa m^1/2 as the Al₂O₃ content increasing to 9 wt%, the hardness attains the maximum value of 10.16 GPa for 12 wt% Al₂O_3. The strengthening mechanism of the composites was also discussed.     

Preceramic paper-derived Ti3Al(Si)C2-based composites obtained by spark plasma sintering

The paper describes the structure and properties of preceramic paper-derived Ti₃Al(Si)C₂-based composites fabricated by spark plasma sintering. The effect of sintering temperature and pressure on microstructure and mechanical properties of the composites was studied. The microstructure and phase composition were analyzed by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively. It was found that at 1150 °C the sintering of materials with the MAX-phase content above 84 vol% leads to nearly dense composites. The partial decomposition of the Ti₃Al(Si)C₂ phase becomes stronger with the temperature increase from 1150 to 1350 °C. In this case, composite materials with more than 20 vol% of TiC were obtained. The paper-derived Ti₃Al(Si)C₂-based composites with the flexural strength > 900 MPa and fracture toughness of >5 MPa m^1/2 were sintered at 1150 °C. The high values of flexural strength were attributed to fine microstructure and strengthening effect by secondary TiC and Al₂O₃ phases. The flexural strength and fracture toughness decrease with increase of the sintering temperature that is caused by phase composition and porosity of the composites. The hardness of composites increases from ~9.7 GPa (at 1150 °C) to ~11.2 GPa (at 1350 °C) due to higher content of TiC and Al₂O₃ phases.     

Mechanical properties and microstructure of Al2O3-SiCw ceramic tool material toughened by Si3N4 particles

Al₂O₃-SiC_w toughened ceramic tools play vital role in high-speed machining of nickel-based superalloys due to their superior mechanical properties. Herein, owing to synergistic toughening mechanism, α-Si₃N₄ particles are employed as reinforcement phase into Al₂O₃-SiC_w ceramic composite to optimize mechanical properties of Al₂O₃-SiC_w ceramic tools. Moreover, the influence of Si₃N₄ content and sintering parameters on microstructure and mechanical properties of Al₂O₃-20 vol%SiC_w ceramic tool material is systematically investigated. Results reveal that appropriate amount of Si₃N₄ particles is required to effectively increase the density of Al₂O₃-SiC_w ceramic composites. The presence of Si₃N₄ particles leads to formation of novel β-sialon phase during hot-press sintering, which effectively enhances fracture toughness and flexural strength of Al₂O₃-SiC_w ceramic composites. It is observed that grain size of newly formed β-sialon phase is extremely sensitive to hot-pressing sintering conditions. The degree of chemical transformation of α-Si₃N₄ into Si_6-zAl_zO_zN_8-z (β-sialon) and z-value of Si_6-zAl_zO_zN_8-z are significantly influenced by sintering temperature. Overall, Al₂O₃-20 vol%SiC_w-15 vol%Si₃N₄ ceramic tool material, with 1.5 vol%Y₂O₃-0.5 vol%La₂O₃-0.5 vol%CeO₂ (YLC) sintering additive, rendered optimal mechanical properties after sintering at 1600 °C under 32 MPa for 30 min. Improved mechanical performance can be ascribed to synergistic toughening and strengthening influence of whiskers and particles.     

Phase Evolution of Ti3SiC2 Annealing in Vacuum at Elevated Temperatures

The thermal decomposition of Ti₃SiC₂ in vacuum furnace up to 1500°C has been investigated. The results show that the mild decomposition of Ti₃SiC₂ commences at 1300°C and the higher the holding temperature, the larger the volatilization of Si atoms. The Ti₃SiC₂ decomposition occurs simultaneously on the surface and in the bulk. Four phases coexist at 1400°C and 1450°C and the Ti₅Si₃C_x phase appears in the bulk and/or surface. Diffusion distance, rate, and volatilization of Si contribute to the porous structure and the presence of Ti₅Si₃C_x. The evolution of furnace pressure reflects the decomposition kinetics of Ti₃SiC₂.     

Microstructure and properties of Al2O3-TiC-Ti3SiC2 composites fabricated by spark plasma sintering

Abstract

Abstract

Highly densified Al₂O₃-TiC-Ti₃SiC₂ composites were fabricated by spark plasma sintering technique and subsequently characterised. From fracture surface observation, it is found that Al₂O₃ is 0·2-0·4?μm, TiC is 1-1·5?μm and Ti₃SiC₂ is 1·5-5?μm in grain size. With the increase in Ti₃SiC₂ volume contents, Vickers hardness of the composites decreases because of the low hardness of monolithic Ti₃SiC₂. The fracture toughness rises remarkably when the contents of Ti₃SiC₂ increase, which is attributed to the pullout and microplastic deformation of Ti₃SiC₂ grains. At the same time, the flexural strength of the composites shows a considerable improvement as well. The electrical conductivity rises significantly as the Ti₃SiC₂ contents increase because of the formation of Ti₃SiC₂ network and the increase in conductive phase contents.     

Effect of Ti5Si3 on wear properties of Ti3Si(Al)C2

Near-fully dense Ti₃Si(Al)C₂/Ti₅Si₃ composites were synthesized by in situ hot pressing/solid–liquid reaction process under a pressure of 30 MPa in a flowing Ar atmosphere at 1580 °C for 60 min. Compared to monolithic Ti₃Si(Al)C₂, Ti₃Si(Al)C₂/Ti₅Si₃ composites exhibit higher hardness and improved wear resistance, but a slight loss in flexural strength (about 26% lower than Ti₃Si(Al)C₂ matrix). In addition, Ti₃Si(Al)C₂/Ti₅Si₃ composites maintain a high fracture toughness (K_IC = 5.69–6.79 MPa m^1/2). The Ti₃Si(Al)C₂/30 vol.%Ti₅Si₃ composite shows the highest Vickers hardness (68% higher than that of Ti₃Si(Al)C₂) and best wear resistance (the wear resistance increases by 2 orders of magnitude). The improved properties are mainly ascribed to the contribution of hard Ti₅Si₃ particles, and the strength degradation is mainly due to the lower Young's modulus and strength of Ti₅Si₃.     

High strengthening effects and excellent wear resistance of Ti3Al(Si)C2 solid solutions

The Ti₃Al_1.2−xSi_xC₂ (x = 0, 0.2, 0.4) powders were synthesized from Ti, Al, Si, and TiC powders, and nearly pure Ti₃Al_1.2−xSi_xC₂ bulks were fabricated by the means of two-time hot-pressing method. Significant strengthening effect in bulks was found after the addition of 0.2 Si and 0.4 Si to form Ti₃Al(Si)C₂ solid solutions. The flexural strengths of Ti₃AlSi_0.2C₂ and Ti₃Al_0.8Si_0.4C₂ were 485 and 554 MPa, 14% and 30% larger than the strength of Ti₃AlC₂, respectively. The Vickers hardness of these compounds were separately, 6.95 and 7.57 GPa, representing the enhancements of 37% and 49% over those of Ti₃AlC₂. The tribological behavior was studied by dry-sliding method with a S45C steel at the sliding speed of 30 m/s and the normal load of 20-80 N. The results showed that after incorporating different contents of Si, the friction coefficient was between 0.22 and 0.30, correspondingly lower wear rate was 3.19-2.61 × 10⁻⁶ mm³/Nm. These excellent tribological performances were attributed to the presence of continuous self-generated oxidized films during tribological examination. Finally, the phase compositions and microhardness of the oxidized films were analyzed and characterized.