THE INFLUENCE OF BINDERS ON INTERFACIAL FAILURE IN SAPPHIRE FIBER-REINFORCED NIAL COMPOSITES

The influence of organic binders on fiber/matrix bonding during the po wder metallurgy fabrication of sapphire fiber-reinforced NiAl matrix c omposites (sapphire/NiAl) was investigated. One composite panel was fa bricated using a poly(methyl methacrylate) (PMMA) fiber binder and a t eflon matrix powder binder; another panel was fabricated by binderless powder metallurgy consolidation. The effect of the binders on fiber/m atrix bonding was evaluated by fiber push-out testing from room temper ature to 900 degrees C. Examination of mating fiber and matrix-trough fracture surfaces by scanning electron microscopy (SEM) and Auger elec tron spectroscopy (AES) revealed differences in interfacial morphology and chemistry, depending on the use of binders in fabrication. The pr imary difference between the two composites was the much higher concen tration of carbon at the fiber/matrix interface in sapphire/NiAl fabri cated with binders. This carbon residue from binder burnout prevented clean contact between the sapphire fiber and NiAl matrix surfaces, res ulting in a weak, thermomechanically clamped fiber/matrix interface, i n contrast to the stronger, less temperature dependent, interfacial bo nding observed without binders.