Nitride and carbide preforms for infiltration process

Purpose: Infiltration of molten metals into porous ceramic preforms is the only technique suitable for the fabrication of high volume fraction of ceramic materials in MMCs. The most popular material for porous preforms is Al2O3 because of its low cost. Infiltration process generates thermal stresses in the Al2O3 preforms. The thermal shock resistance of Al2O3 is lower than for Si3N4 or Al2O3/TiC+TiN materials. The aim of this study is to obtain the nitride and carbide base preforms material for the infiltration process of molten aluminium alloys. Design/methodology/approach: The method of obtaining the silicon nitride and oxide-carbonitride porous preform for the infiltration process is the free sintering process. Some of selected properties of this material are presented. The preforms were produced by the mixing of ceramic powders with organic binders, followed by forming, drying and firing. Ceramic preforms of 65% porosity were produced. Microscopic investigations revealed good joints between the ceramic particles. Findings: The material consist of the base component (90 wt.% of α-Si3N4, 5 wt.% of Al2O3, 5 wt.% of Y2O3), which were mixed with 40 wt.% of polyethylene glycol 6000 (mixed in Turbula) porosity is 25.7 %. The higher value of porosity 66.6% was obtained for material with 20 wt.% tylose. The grain size of Si3N4 and method of the mixtures preparing (mixing with or without milling) have the significant influence on compacts’ porosity. For 68 wt.% Al2O3, 2 wt.% ZrO2 and 30 wt.% Ti(C,N) with addition of glycol 6000, the value of porosity is 67%. α-Si3N4 material produced shows strong bonding with aluminium and AlSi11 aluminium alloy. Practical implications: Pressureless infiltration of molten metals into ceramics is the most cost-effective approach to liquid-metal processing of MMCs. Metal matrix composites are applied widely in aircraft production technologies and defence technology. Originality/value: Compared to widely used alumina performs, those made from non-oxide ceramics demonstrate better physicochemical compatibility with aluminium alloys. New kinds of porous materials were obtained.