Grain Boundary Energetics in Non-Oxide Ceramics.
Abstract
Research on 'Grain Boundary Energetics in Non-Oxide Ceramics' has been conducted at CWRU since 1975 and has concentrated on two specific areas--the beta to alpha transformation in polycrystalline SiC, and the nature of grain boundary phases in hot-pressed Si3N4 containing various densification aids. The beta to alpha transformation in polycrystalline SiC is unusual in that it appears to occur in two stages. The first involves the growth of composite plates consisting of alpha-SiC plates sandwiched between recrystallized envelopes of beta SiC. This stage ends when the original polycrystalline beta matrix is consumed. The second and more sluggish stages involves the thickening of the alpha plates within their beta envelopes and requires repeated piecewise nucleation of alpha at the beta to alpha interface. High resolution TEM has been used to show that the commercial MgO-doped hot-pressed Si3N4 apparently contains a continuous grain boundary phase that is responsible for the poor high-temperature performance. Grain boundary microstructures have been characterized in polycrystalline Si3N4 containing Y2C3, ZrO2, and BeSiN2; the latter additive appears to be the most promising, since a continuous grain boundary film is not present. (Author)
Document Details
- Document Type
- Technical Report
- Publication Date
- Feb 28, 1978
- Accession Number
- ADA054179
Entities
People
- A. H. Heuer
- T. E. Mitchell
Organizations
- Case Western Reserve University