Abstract
β–Si3N4 whisker preforms are directly formed from amorphous Si3N4 (obtained by imido process) with addition of yttrium oxide by baking under specially controlled conditions. Their volume fraction is only 13%, but their flexural strength is more than 10 MPa. In-situ formed β–Si3N4 whisker preform is used for the reinforcement of 6061 and 7075 aluminum alloys by vertical squeeze casting. Even for a whisker volume fraction of 13%, the in-situ preforms have no cracks nor deformation. On the other hand, the filtration β–Si3N4 whisker preforms with a volume fraction of 25% have some cracks or deformation. Therefore in-situ formed β–Si3N4 whisker preforms are suitable for squeeze casting. Aluminum alloy composites have high flexural strength from room temperature to 573 K. Also the rotary bending fatigue tests show that fatigue properties of 6061 and 7075 aluminum alloy are much improved by reinforcement of β–Si3N4 whiskers. The SEM observation of fracture surface, revealed that β–Si3N4 whiskers has good compatibility with 6061 and 7075 aluminum alloys.
