Gelcasting of carbide ceramics

Abstract

In this article, the aqueous gelcasting of carbide ceramics (SiC, TiC, B4C) was studied systematically. For SiC with the addition of Al 2O3 and Y2O3 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°C 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 2HCI) is selected as the initiator. The green samples with the relative density as high as 57.5% can be densified at 1530°C 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 B4C powder in aqueous media. With the addition of PEI, the solids loading of B4C slurry higher than 50 vol% can be obtained. The pressureless sintering of B4C with 10 mass% TiC as sintering additives is performed at 2250°C for 30 min in Ar atmosphere. The relative density of B4C sintered samples is around 96.2%. Results showed that gelcasing is an effective processing technique for preparing carbides with complex shape and satisfied properties. ©2008 The Ceramic Society of Japan. All rights reserved.