Preparation of Al₂O₃-Ni cermet composites by aqueous gelcasting

Abstract

The main objective of producing ceramic-metal composites is to improve the fracture toughness of the brittle ceramic matrix. Classical methods of powder metallurgy (such as isostatic or uniaxial pressing) are not capable of fabricating complex-shape elements. For this reason, colloidal processes have been applied recently in manufacturing of ceramic matrix composites. In the present work, Al₂O₃-3 vol.% Ni composites were prepared by aqueous gelcasting process and sintering in reducing atmosphere. The commercially available monomers 2-hydroxyethyl acrylate and N,N‘-methylenebisacrylamide as cross-linking agents were used. The activator was N,N,N‘,N‘,-tetramethylenediamine (TEMED) and ammonium persul-fate was added as an initiator of the polymerization process. Composite slurries were obtained from alumina powders (grain size 0.21 #956;m) and 3% (in respect to the total solid volume) of two nickel powders of different grain size (~10 and ~0.4 #956;m). The paper describes the rheological properties of the obtained composite slurries. The properties of green and sintered elements have also been presented. It was found that the presence of nickel particles had a significant influence on the slurry polymerization process. The green and sintered relative density was in every case higher than 57 and 97%, respectively.