No abstract

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.

Ti 3 SiC 2 /Al 2 O 3 composites have attracted attention due to their excellent mechanical and electromagnetic properties, but the high temperatures (≥ 1400 ℃) required for the densification of aluminum oxide (Al 2 O 3 ) leads to the decomposition of Ti 3 SiC 2 . To address this issue, Ti 3 (Si x Al 1−x )C 2 /Al 2 O 3 (x represents the Si content) composites were synthesized for the first time via hot-pressing (HP) sintering and current-assisted sintering (CAS) of mixed Ti 3 AlC 2 and silicon monoxide (SiO) powders at 1300 and 1200 ℃, respectively. Both approaches produced composites with x values greater than 0.9, indicating that the compositions of the prepared composites were similar to those of Ti 3 SiC 2 /Al 2 O 3 composites. The synthetic mechanism involved substitution and continuous interdiffusion of Al and Si atoms. The composite prepared by CAS at 1200 ℃ was compacted, whereas the composite prepared by HP had a low density. The low-temperature densification mechanism is attributed to the combined effects of amorphous SiO, liquid Al, and the high heating rates for CAS. The flexural strength and hardness of the composite prepared by CAS were also comparable to those of compacted Ti 3 SiC 2 /Al 2 O 3 composites.

Y2O3 and CeO2 were chosen as additives to investigate the effect of different additives on the microstructure, composition of phases and mechanical properties of Si3N4/SiC ceramics using pressureless sintering. Si3N4/SiC ceramic without additives had a high density, while after adding Y2O3 and CeO2, the density and flexural strength of Si3N4/SiC ceramics were significantly decreased due to the increase of porosity. The main phase compositions of samples were β-Si3N4 and SiC. Moreover, the liquid phases Y-Si-O-N and Ce-Si-O-N were observed after adding Y2O3 and CeO2 respectively. It also indicated that for Si3N4/SiC composite ceramics, the high aspect ratio β-Si3N4 overlapped with each other and closely bonded with glass phase could improve flexure strength effectively. Besides, the SiC crystal grains mainly existed in grain boundary, which could inhibit the secondary recrystallization to avoid that the decrease of flexural strength caused by the overgrowth of β-Si3N4 grains.