単繊維B/Al複合体の引張強度に及ぼすα-AIB₁₂相の影響

抄録

Laminated B/Al films and mono-filament B/Al composites were prepared by ion plating aluminium onto boron films and boron fibers respectively. The formation of the α-AlB₁₂ phase at the boron-aluminium interface and its influence on the tensile strength of the mono-filament B/Al composite were investigated quantitatively. It was found that the α-AlB₁₂ phases were formed continuously on the boron films and the boron fibers and also partially in aluminium matrice in the determining process of boron-diffusion rate into α-AlB₁₂. The activation energy of the formation of the α-AlB₁₂ phase was 130 kJ/mol. Thermal exposure decreased the tensile strength of the mono-filament B/Al composites due to the formation of the α-AlB₁₂ phases at the interface. Relation between the tensile strength of the mono -filament B/Al composite and the thicknness of the α-AlB₁₂phase was represented by a Griffith's equation.
The α-AlB₁₂ phase is brittle and fractures under small strains, forming notches. The formed notch hastens fracture of the boron fiber, resulting in loss of the tensile strength of the mono-filament B/Al composite. The dependence of the tensile strength of the mono-filament B/Al composite on heat treatment conditions can be expressed by the following equation.
σ_c= 8.3 × 10⁷{exp(-16000/ T )× t } ^-1/4 (Pa)
where σ_c is the tensile strength of the mono-filament B/Al composite and T and t are heat treatment temperature and time respectively.