Microstructure of SiC_w reinforced Al–12Ti composites prepared by powder metallurgical technique

Abstract

Silicon carbide whisker reinforced Al–12Ti composites were fabricated by a powder metallurgical technique, and the microstructures were characterised by the means of X-ray diffraction, SEM, TEM, and energy dispersion X-ray analysis. It has been shown that secondary phase particles, Al₃ Ti, form in situ during hot pressing after premechanically ball milling, and a small amount of α-Ti is left because the in situ reaction between α-Ti and Al is not complete. High density dislocations including dislocation lines and dislocation loops exist in the coarse Al₃ Ti grains, while, hardly any dislocations can be found using TEM in the very fine (∼150 nm) Al₃ Ti grains. In addition, nanometer equiaxed γ-Al₂O₃ and stick shaped Al₄ C₃ dispersoids form in the Al matrix as a result of the addition of a processing control agent. There is no fixed orientation relationships between γ-Al₂O₃ , Al₄ C₃ , and the Al matrix. Dislocations in the Al matrix are too sparse to be found even in the zones around SiC whiskers. Silicon carbide whiskers uniformly scatter in the Al matrix, and no reaction products are formed. A few microzones with nanosized (∼20 nm) Al grains exist in the Al matrix, and an amorphous phase is usually found in the zones adjacent to SiC whiskers. The formation mechanism of the amorphous phase is discussed.