E驅≈3S Journal of the European Ceramic Society 21(2001)1027-1035 www.elsevier.com/locate/jeurc Colloidal processing of Al2O3-based composites reinforced with tiN and TiC particulates, whiskers and nanoparticles Eric laar a, Mats carlsson b,*, BenoitⅤiⅤie Mats Johnsson Mats Nygren b, Lennart Bergstrom Institute for Surface Chemistry, PO Box 5607, S-114 86 Stockholm, Swe dEpartment of Inorganic Chemistry, Stockholm University, S-1069/ Stockholm, Sweden Received 29 June 2000; received in revised form 13 October 2000: accepted 21 October 2000 o. A colloidal processing route has been developed for the preparation of dense and homogeneous Al2O3-TiN/TiC composites.The ispersion and rheological properties of mixtures of TiN or TiC particulates and Al,O3 particles were investigated using electro- kinetics and steady-shear rheology. We found that well-dispersed aqueous suspensions with low viscosity could be prepared by adding a poly(acrylic acid) dispersant and controlling ph in the alkaline range. This processing scheme was also suitable for pre paration of whisker and nanoparticle composite suspensions. The alumina-based composite suspensions with a secondary-phase concentration of 25 vol. were freeze-granulated and hot-pressed, and the resulting bodies were fully densified with well-dispersed secondary phases. Homogeneous Al2O-TiN nanoparticle composites could only be prepared with additions of up to 5 vol% nanoparticles; higher additions resulted in agglomeration and subsequent grain growth of the nanoparticles. C 2001 Elsevier Science Ltd. All rights rese Keywords: Al2Or-TiC: Al2Oy-TiN; Composites; Microstructure-final: Suspensions; TiC: TIN 1. ntroduction with homogeneous microstructure. Based on thorough powder characterization and on the results of dispersion Mechanical properties of ceramic materials are experiments, we have developed an optimized proces- strongly dependent on their microstructure. The frac- sing scheme and assessed its applicability to systems ture toughness, for instance, can be improved sub- containing TiN and TiC with a wide range of morphol- stantially by ade dding a secondary reinforcing phase to ogies. Thus, the preparation of composites containing the matrix. It has been shown that the addition of a tin micronsized TiN and TiC particles, nanosized Tin par- or TiC phase to an alumina matrix increases hardness, ticles, and TiC and Ti(C, N)whiskers has been investi fracture toughness and thermal shock resistance at gated. The results will be applied in a forthcoming temperatures up to 800oC. In order to optimize the investigation of the mechanical properties(e.g. thermal properties, the reinforcing particulate phase must be shock resistance)of Al_ O -TiN/TiC compacts. Experi- well dispersed in the matrix. Mixing, deagglomeration mentally, our study has included mainly electrokinetic and dispersion of the reinforcing components are com- and rheological characterization of aqueous composite monly performed in a liquid medium, preferably water. suspensions and microstructure evaluation of sintered Additions of dispersing agents and/ or manipulation of bodies by means of scanning electron microscopy the solution properties, e.g. the pH value, are frequently used to optimize the suspension properties In this work, we have attempted to develop an aqu- 2. Experiment eous colloidal processing route for preparating well-dis- persed powder mixtures in the AlO3-TiN/TiC systems, 2.1. Powder characterization which upon densification would yield dense compacts The manufacturer specifications of the starting pow ders are given in Table 1. For simplification we will refer to the nano-and micronsized titanium nitride powders 0955-2219/01/S. see front matter C 2001 Elsevier Science Ltd. All rights reserved. PII:S0955-2219(00)00302-2
              
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