AASERT Student Research on In-Situ Toughened Alpha Prime-SiAlON
Abstract
The grant was initiated on May 15,1998 and was completed in August 2001. We have explored the compositions at which in-situ toughened ct-SiAlON can be obtained. This essentially encompasses the entire single a-phase region. It includes both rare-earth ion-added compositions and alkali/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 ci-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 wet chemical technique for etching the highly stable a'-SiAlON, which until now has proved difficult for ceraniographic preparation. We have shown that the mechanical strength of ct-SiAlON can exceed 1 CPa and the strength retention is good at least up to 1350 deg C. We have obtained R-curves for a'SiA1ON ceramics, and show that they can reach a toughness of 11-12 MPa m1t which compares favorably with the state-of-the-art Beta silicon nitride.
Document Details
- Document Type
- Technical Report
- Publication Date
- May 22, 2002
- Accession Number
- ADA404120
Entities
People
- I-wei Chen
Organizations
- University of Pennsylvania