Gelcasting of carbide ceramics(<Feature>SiAlons and Non-oxides)
In this article, the aqueous gelcasting of carbide ceramics (SiC, TiC, B_4C) was studied systematically. For SiC with the addition of AI_2O_3 and Y_2O_3 as sintering additives, tetramethylammonium hydroxide (TMAH) is used as the dispersant for making slurry with high solids lading and low viscosity. N,N-dimethyl acrylamide (DMAA) and N,N'-methylenebisacrylamide (MBAM) are applied as organic monomers and cross-linker respectively. Ammonium persulfate (APS) acts as initiator for the polymerization of acrylamide monomers. Gelcasted SiC samples are pressureless sintered at 2000℃ with the relative density higher than 97%. The gelcasting of TiC/Ni system are studied with PEI as the dispersant. An azocompound, 2,2'-azobis[2-(imidazolin-2-yl) propane]dihydrochloride(AZIP・2HCl) is selected as the initiator. The green samples with the relative density as high as 57.5% can be densified at 1530℃ in vacuum. The linear shrinkage, relative density, apparent porosity, flexural strength, Young's modulus and Rockwell hardness(HRA) are (15.96 ± 0.65)%, (93.3 ± 0.7)%, (1.03 ± 0.16)%, (1062.77 ± 49.81) MPa, (323.93 ± 4.00)GPa and (84.74 ±0.63)% respectively. PEI is also an effective dispersant for B_4C powder in aqueous media. With the addition of PEI, the solids loading of B_4C slurry higher than 50 vol% can be obtained. The pressureless sintering of B_4C with 10 mass% TiC as sintering additives is performed at 2250℃ for 30 min in Ar atmosphere. The relative density of B_4C sintered samples is around 96.2%. Results showed that gelcasing is an effective processing technique for preparing carbides with complex shape and satisfied properties.