Tensile properties of directionally solidified Al-Al₃Ni composites with off-eutectic compositions

Abstract

Ingots (1/8 in. diameter) of Al-Al₃Ni with off-eutectic compositions were directionally solidified at two growth rates. At 1 cm h⁻¹ fibres exhibited a blade-like morphology, and at 11 cm h⁻¹, a rod-like morphology. Speciments were mechanically evaluated in tension. The composite modulus at stresses above the yield strength of the aluminium matrix obeyed the rule of mixtures, assuming ideal plastic behaviour of the matrix. An extrapolation of these data for composites with rod fibres gave a value of 146 GN m⁻² for the modulus of Al₃Ni. Tensile strength of composites with rod-like fibres followed the rule of mixtures, whereas those with non-uniform blade fibres showed a lower strength. In composites with blade-like fibres the extrapolated aluminium matrix strength was 86.3 MN m⁻², a high value attributed to dispersion hardening, and that of the fibres was 2.69 GN m⁻². Composites with blade-like fibres failed at lower strains than did those with more uniform rod-like fibres.