Protective Coating by Surface Nitridation of Boron Filaments

Abstract

A protective coating is obtained by nitriding the boron filament surface. The existence of a boron nitride coating is shown by chemical analysis, optical microscopy, and electron microprobe analysis. The protective nature of the coating is illustrated metal lographically by using several composite fabrication techniques with pure aluminum and 2024 aluminum alloy as matrices. The interaction of aluminum with nitrided and as-received boron fila ments at 600, 700, and 800°C is studied using a simple experimental set-up. The boron nitride coating serves as an effective diffusion barrier in molten aluminum up to 10 min. at 800°C. Tensile tests on nitrided filaments show no degradation of mechanical properties due to the nitridation process. The results demonstrate the potential usefulness of the process to the development of improved boron- aluminum composites. The prevention of deleterious interactions between matrix and reinforcement should result in higher com posite strengths.