FIBROUS MONOLITHIC CERAMICS .4. MECHANICAL-PROPERTIES AND OXIDATION BEHAVIOR OF THE ALUMINA NICKEL SYSTEM

Fibrous monolithic ceramics were fabricated in the alumina/nickel syst em. The microstructure consists of high-aspect-ratio polycrystalline c ells of alumina separated by thin cell boundaries of nickel. The nicke l content in the material is 3 to 8 vol%. The fibrous monolith with un iaxially aligned cells fails noncatastrophically in flexure. Bridging ligaments of nickel, crack deflection along cell boundaries, and crack branching in the axial direction are observed in flexure bars and not ched beams. Strength values range from 246 to 375 MPa. Indentations ca use controlled damage on the surface but do not introduce strength-deg rading flaws. The alumina/nickel fibrous monoliths also show potential for use at high temperatures in oxidizing environments. Noncatastroph ic fracture behavior is observed at room temperature after 10 h at 120 0-degrees-C in air. The Ni cell boundary network is oxidized to a dept h of 50 to 100 mum by this heat treatment. The NiO oxidation product i n the cell boundaries reacts partly with alumina from the cells to for m NiAl2O4, which would provide better protection.