Decomposition Of Ti3AlC2 Research Articles

Microstructure and mechanical properties of high-entropy diboride-based ceramic assisted by Ti3AlC2 additive

Ti3AlC2 was used as the additive to fabricate a novel (Zr0·2Ta0·2Nb0.2Hf0.2Mo0.2)B2-based (HEBTAC) ceramic using spark plasma sintering at 1900 °C. The as-prepared HEBTAC ceramic sample consists of (Ti, Zr, Hf, Ta, Nb, Mo)B2, multiscale (Zr, Hf, Ta, Nb, Mo)C, and Al2O3 phases, which are produced by the decomposition of Ti3AlC2 and subsequent exchange reaction & solid solution reactions during the sintering process. The relative density, hardness, fracture toughness, and flexural strength of the HEBTAC ceramic sample are 99.43 %, 27.92 ± 1.87 GPa, 5.84 ± 0.14 MPa m1/2, and 629 ± 8.7 MPa, respectively, which are even better than the same class of high-entropy diboride ceramics previously published. Solid-solution strengthening, dislocation strengthening and nano-HEC strengthening existed in the ceramic sample contribute to its excellent mechanical properties. The in situ formed Al2O3 and (Zr, Hf, Ta, Nb, Mo)C effectively enhances the toughness of the HEBTAC ceramic sample through the synergistic effect of intrinsic and extrinsic toughening. This study presents a new approach for reactive sintering densification of high-entropy diborides with both high strength and high toughness.

Damage mechanisms of Ti3AlC2 ceramics in pulsed laser processing

The damage mechanisms of Ti3AlC2 ceramics during laser processing in air and water were studied using the pulsed laser. The focused high-energy laser induced the melting of surface of Ti3AlC2 ceramics, causing the decomposition of Ti3AlC2 into TiC and Al with Al rapidly evaporating. During the laser processing in the air, oxygen diffused inward to form a solid solution of TiCxOy, and the rapidly heating and cooling of resolidified layer generated high thermal tensile stresses to result in a large amount of microcracks. When processing in the water, the thermal stresses were greatly weakened, and the outward diffusion of Al steam resulted in the voids on the sample surface. Additionally, it is determined that after treating in the air and water, the residual flexural strengths of Ti3AlC2 ceramics could retain the high values of 292 MPa and 484 MPa, and the Weibull moduli were kept at 7.2 and 16.0, respectively, exhibiting the excellent damage tolerance and high reliability.

Oxidation behavior of high Cr white iron composites reinforced with TiC and nonstoichiometric TiCx in air at 600 °C

High Cr white irons (HCWIs) are often used as high-temperature components exposed to the temperatures exceeding 500 °C. Improving oxidation resistance of HCWI components is necessary for engineering applications. In the present study, oxidation behaviors of high Cr white iron (HCWI) and its composites reinforced with 1–2 μm nonstoichiometric TiCx resulting from the decomposition of Ti3AlC2 (in situ TiCx/HCWI), and 2–4 μm irregular-shape of TiC (TiC/HCWI) at 600 °C for 96 h in air were investigated. Results showed that the two composites exhibited better oxidation resistance than the pure HCWI material. The oxidation test revealed a weight loss for the unreinforced HCWI but a weight gain for the composites. Among these materials, the in situ TiCx/HCWI composite has the best oxidation resistance due to its dense and fine microstructure. Oxidative thermodynamics and oxidation mechanism were discussed. This work suggests that in situ formed TiCx is an effective reinforcement to improve the oxidation resistance of HCWIs.

Tribological properties of self-healing NiCrAlY/Cr3C2-Ti3AlC2 coating at high temperatures

Ti3AlC2 is a layered-structure material with both ceramic and metallic properties and is often used as a solid lubricant. To improve the lubrication and wear resistance of engine components in a wide temperature range, especially at high temperatures, a series of Ti3AlC2 enhanced NiCrAlY/Cr3C2 self-lubricating coatings were prepared on TC4 titanium alloy substrates by atmospheric plasma spraying. The tribological properties of the coatings from room temperature to 800 °C were evaluated through a pin-on-disk wear test. The wear mechanism of the coating was analyzed by SEM, XRD and a three-dimensional optical profiler. The results show that the coating with 20 wt% Ti3AlC2 has the lowest friction coefficient (0.341) and lowest wear rate (2.73 × 10−5 mm3 N−1 m−1) among all the samples at 800 °C. The worn surface of the 20 wt% Ti3AlC2 sample was examined after the test. TiO2 particles, together with Al2O3, resulting from the decomposition of Ti3AlC2 in the coating, aggregated on the surface. Compared with the sample without added Ti3AlC2, the high-temperature decomposition products of Ti3AlC2 contributed to the reduction in the friction coefficient and wear rate of the coating. These particles also play a role in filling the worn area on the coating, which endows it with a self-healing ability.

Carbon reduction of Ti3AlC2 phase for TiC nanosheet production

ABSTRACT In this study, we investigated the formation of TiC nanosheets from carbon black and Ti3AlC2 mixtures in NaCl-KCl eutectic salt. The effects of raw material ratio, molten salt ratio, and heating temperature on TiC formation were studied in detail. Results show that carbon black may enhance the decomposition of amounts of Ti3AlC2 at 1,100°C by heat treatment without salt addition, while molten salt plays key roles in the total decomposition of Ti3AlC2 and the formation of TiC nanosheets at 1,000°C. Higher heating temperature and excess carbon black benefits the synthesis of high content TiC. The as-synthesized TiC nanosheets are approximately 15 nm thick and 80–220 nm long. We propose a possible reaction mechanism that governs TiC formation in molten salts and explain the observations based on kinetic considerations.

Sintering and Mechanical Properties of (SiC + TiCx)p/Fe Composites Synthesized from Ti3AlC2, SiC, and Fe Powders.

Ceramic-particle-reinforced iron matrix composites (CPR-IMCs) have been used in many fields due to their excellent performance. In this study, using the fast resistance-sintering technology developed by our team, iron matrix composites (IMCs) reinforced by both SiC and TiCx particles were fabricated via the addition of SiC and Ti3AlC2 particles, and the resulting relative densities of the sintering products were up to 98%. The XRD and EDS analyses confirmed the in situ formation of the TiCx from the decomposition of Ti3AlC2 during sintering. A significant hybrid reinforcing effect was discovered in the (SiC + TiCx)p/Fe composites, where the experimental strength and hardness of the (SiC + TiCx)p/Fe composites were higher than the composites of monolithic SiCp/Fe and (TiCx)p/Fe. While, under the condition of constant particle content, the elongation of the samples reinforced using TiCx was the best, those reinforced by SiC was the lowest, and those reinforced by (SiC + TiCx) fell in between, which means the plastic response of (SiC + TiCx)p/Fe composites obeyed the rule of mixture. The successful preparation of IMCs based on the hybrid reinforcement mechanism provides an idea for the optimization of IMCs.

Comparison of high Cr white iron composites reinforced with directly added TiC and in situ formed TiCx

Two kinds of high Cr white iron (HCWI) composites reinforced with directly added TiC (TiC/HCWI) and in situ formed TiCx (TiCx/HCWI) have been successfully synthesized by powder metallurgy method. The directly added TiC grains are irregular in shape with a mean size of about 2−4 μm, but the in situ formed TiCx grains from the decomposition of Ti3AlC2 are spherical and about 1–2 μm in size. The microstructure, mechanical properties and wear resistance of the two composites were compared. The in situ TiCx/HXCWI composite possesses finer microstructures and superior mechanical and wear resistant properties than TiC/HCWI composite. The phase composition and microstructure were characterized with X-ray diffraction analysis, scanning electron microscopy and transmission electron microscopy.

Effect of Ti3AlC2 Content on Electrical Friction and Wear Behaviors of Cu–Ti3AlC2 Composites

The effect of Ti3AlC2 content on electrical friction and wear behaviors of Cu–Ti3AlC2 composites is investigated. Composites with different volume ratios of Ti3AlC2 are prepared by the hot-pressing method, and experiments are performed on a block-on-ring sliding electrical wear tester. The results demonstrate that with increasing Ti3AlC2 content, the contact voltage drops of the Cu–Ti3AlC2 composites increase, the friction coefficient decreases, and the wear rate initially decreases and then increases. A lubricating film forms on the worn surface during the process of electrical sliding wear, which improves the wear resistance of the material. Raman spectroscopy and X-ray photoelectron spectroscopy spectra of the worn surface show that the lubricating film comprises Ti3AlC2, CuO, TiO2 and Al2O3, where the TiO2 and Al2O3 result from decomposition of Ti3AlC2.

Microstructural characterization and abrasive wear resistance of a high chromium white iron composite reinforced with in situ formed TiCx

Abstract A high chromium white iron (HCWI) composite reinforced with in situ formed 17.2 wt.% TiCx has been prepared. The in situ formed TiCx grains resulting from the decomposition of Ti3AlC2 are round and small. The presence of small TiCx grains effectively inhibited the rapid growth of M7C3 (M: Fe, Cr and other strong carbide formers) carbides, refining the microstructure of composite. High resolution TEM micrographs show that interfaces of TiCx/M7C3 and TiCx/matrix are clean, suggesting the formation of strong bonding interfaces in the composite. The wear behavior of the composite and the unreinforced HCWI material as a function of the normal load in the range of 78–123 N was investigated using dry sliding pin-on-disc wear testing against a YG8 disk under ambient conditions. The wear resistance of HCWI and TiCx/HCWI decreased with increasing load. However, the wear resistance of the TiCx/HCWI composite was over six times that of the unreinforced HCWI material even at the highest load of 123 N. The improved wear resistance of the composite should be ascribed to contributions from both the presence of smaller TiCx grains reinforcing the matrix and the refinement of the M7C3 structure. Scanning electron microscopy was used to characterize the microstructures of materials before and after wear testing.

Physical, mechanical, and ablation properties of Cu–Ti3AlC2 composites with various Ti3AlC2 contents

ABSTRACTThe effects of Ti3AlC2 content on the physical, mechanical, and arc ablation resistance properties of a fabricated Cu–Ti3AlC2 composite are investigated in detail. Composite samples containing 10, 15, 20, 25, 30, and 35 vol.-% Ti3AlC2 are sintered at 800°C without decomposition of Ti3AlC2. It is demonstrated that with increasing Ti3AlC2 content, the relative density, electrical conductivity, and flexural strength of Cu–Ti3AlC2 decrease but the Brinell hardness first increases and then decreases. After eroded by an electric arc, Cu–Ti3AlC2 oxidises to CuO, TiO2, and Al2O3. Meanwhile, field emission-SEM observations reveal that the dimensions of protrusions and the percentage of TiO2 increase with increasing Ti3AlC2 content. Remarkably, the electric arc mainly occurs at the Ti3AlC2 particles, and the Cu matrix remains well protected.

Effect of TiC Content on the Microstructure and Mechanical Properties of Ti<sub>3</sub>AlC<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> <i>In Situ</i> Composites Synthesized by Hot Pressing

The Ti3AlC2/Al2O3 in situ composites were successfully synthesized from the system of Ti-TiC-Al-TiO2 by reactive hot pressing at 1350 °C. The effect of TiC content on the phase composition, microstructure and mechanical properties were investigated in detail. The results indicate that the fabricated products possess the highest purity as the TiC contents reduce to 90 % of its theoretical content. This deviation is mainly attributed to the decomposition of Ti3AlC2 and vaporization of Al at high temperatures. The effect of TiC content on the fracture toughness, flexural strength, Vickers hardness of Ti3AlC2/Al2O3 composites was also discussed in detail.

Preparation, Microstructure, and Mechanical Properties of TiB2 Using Ti3AlC2 as a Sintering Aid

Titanium diboride (TiB2) was successfully hot‐pressed at 1500°C using titanium aluminum carbide (Ti3AlC2) as a sintering aid. The mechanisms for the improved sinterability of TiB2 by the addition of Ti3AlC2 involve, first, the Al coming from the decomposition of Ti3AlC2 can eliminate the oxide layer on the surface of TiB2; second, the TiCx (also from the decomposition of Ti3AlC2) has a positive influence on the densification of TiB2 due to its plasticity at high temperatures. TEM observations reveal that the interface between TiB2 and TiCx is coherent and strong, free of amorphous layers and oxide phases. An optimized composition of TiB2‐10 wt% Ti3AlC2 was obtained with the unique combination of mechanical properties, including the elastic modulus of 567 GPa, the fracture toughness of 4.8 MPa·m1/2, the flexural strength of 711 MPa, and the hardness of 25 GPa.

In Situ High‐Temperature Diffraction Study of the Thermal Dissociation of Ti3AlC2 in Vacuum

In this paper, the effect of high‐temperature vacuum annealing on the dynamic phase stability and phase transition of Ti3AlC2 at up to 1550°C was studied using in situ neutron diffraction. The decomposition of Ti3AlC2 into TiCx at an elevated temperature was observed to occur through the continuous sublimation of Al and Ti species in a dynamic environment of high vacuum. The rate of decomposition decreased with increasing temperature, resulting in negative apparent activation energy (i.e., −71.9 kJ/mol). Depth profiling of vacuum‐annealed Ti3AlC2 by grazing‐synchrotron radiation diffraction has revealed a graded composition of TiCx at the near‐surface.