The tensile fracture behaviour of the aligned Al-Al₃Ni and Al-CuAl₂ eutectics at various temperatures

Abstract

The tensile behaviour of single crystals of the unidirectionally-solidifled Al-Al₃Ni fibrous and Al-CuAl₂ lamellar eutectics has been investigated at ambient and elevated temperatures. Fractured specimens have been studied directly by scanning electron microscopy, and longitudinal sections through each fracture surface by optical microscopy. At low temperatures, fracture of the Al-Al₃Ni eutectic is caused by the brittle failure of Al₃Ni fibres. At intermediate temperatures broken fibres may be present without causing composite fracture, whilst at high temperatures fibre pull-out occurs. The properties of the Al-CuAl₂ eutectic are controlled by the brittle CuAl₂ phase, except when the temperature is such that both phases are plastic. During fracture at high temperature the Al-CuAl₂ eutectic undergoes micromorphological degradation in the vicinity of the fracture surface.