In-Situ Toughened alpha-SiALON
Abstract
The grant was initiated on November 15, 1997. We have explored the compositions at which in-situ toughened alpha'-SiAlON can be obtained. This essentially encompasses the entire single a'-phase region. It includes both rare-earth ion-added composition and alkali-earth ion-added compositions. We have made a systematic effort to obtain kinetic data on phase transformation at different compositions, since this knowledge is critically important for the precise control of nucleation and growth which dictate the microstructure. We have developed methods for controlling microstructure in alpha'-SiAlON prepared from commercial a-Si3N4 powders. These materials have faster transformation rate and the microstructure control must rely on nucleation treatment of external seeding. We have developed the method to grow and harvest seed crystals, of a controlled composition, size and morphology, which can be used to nucleate a'-SiAlON grains in the ceramic to allow tailored grain growth. We have developed a theory for grain growth, based on the recent observations of the morphology of isolated grains from the oxynitride liquid. This model successfully predicted the novel shape transition observed experimentally. We have developed a theory to describe the chemical potential of anisotropic grains under equilibrium and non-equilibrium conditions. This model is applicable for both silicon nitride and silicon carbide. We have developed a wet chemical technique for etching the highly stable alpha'-SiAlON, which until now has proved difficult for ceramographic preparation. We have shown that the mechanical strength of alpha'-SiAlON can exceed 1 GPa and the strength retention is good at least up to 1 350 deg C.
Document Details
- Document Type
- Technical Report
- Publication Date
- Jul 01, 2001
- Accession Number
- ADA393842
Entities
People
- I. W. Chen
Organizations
- University of Pennsylvania