Study of the Use Beta-Alumina as a Weak Interface in Alumina Fiber Composites

摘要

Results are presented from a three-year study aimed at identifying and developingsuitable inter-phase materials for oxide-oxide composites that are stable in high temperature oxidizing environments, yet sufficiently weak to allow debonding as required for toughening. Most of the effort was devoted to two systems: LaP04 (monazite) and beta-aluminas. Monazite satisfied all of the requirements for an interphase in alumina-alumina composites (and most likely many other ceramic matrix-fiber combinations). It has a high melting point (2074 deg C); it is stable with alumina at high temperature in both oxidizing and slightly reducing environments and it forms a sufficiently weak bond with alumina. Beta-alumina materials, which possess weak mica-like planes in their crystal structures, are phase compatible with alumina, and their debonding characteristics are adequate. However, their use and fabrication temperatures are limited by morphological instability of the fiber/matrix interface (grain growth of the beta-alumina platelets into the fibers).