Microstructure and mechanical properties of hypoeutectic Al–Si composite reinforced with TiCN nanoparticles

Highlights: • High performance hypoeutectic TiCN_p/Al–Si composites were designed. • Large quantities of NPs are distributed along grain boundaries or along the eutectic Si at grain boundaries. • The factors in determining the NP distribution are clarified and analyzed quantitatively. • There is a marked trend of improving mechanical properties with increasing NP additions. In the present work, TiCN_p/Al–11Si composites have been fabricated upon addition of TiCN nanoparticles to the molten alloy, which are dispersed via ultrasonic vibration method. Two distribution types of nanoparticles in the matrix are observed and systematically investigated using SEM and TEM, including intragranular distribution (within the interior of α-Al dendrite) and intergranular distribution (along the grain boundary or the eutectic Si on the grain boundary). During solidification, large quantities of NPs distributed along grain boundaries and then along the eutectic interfaces can form NP layers to physically restrict the growth of primary α-Al and eutectic Si. The refined microstructure and the reinforcing particles with no brittle intermetallics precipitating at the interface can be responsible for the significant improvement in the mechanical properties of the composites. The 2 vol.% TiCN_p/Al–11Si composite exhibits the most excellent performance with its hardness, ultimate tensile strength, yield strength and elongation higher by 45%, 22%, 16% and 108%, respectively, as compared to the matrix alloy.