Microstructure evolution, mechanical properties, and strengthening mechanisms of heat-resistant Al-based composite reinforced by a combination of AlN and TiN particles

A novel heat-resistant Al matrix composite was fabricated, reinforced by a combination of nano-AlN and submicron TiN particles, i.e., (5TiN+6.4AlN)/Al composite, using the liquid–solid reaction method, and followed by an extrusion process. According to scanning electron microscopy and transmission electron microscopy results, AlN particles with an average size of 45 nm were mainly distributed along the intergranular grain and partially distributed in the grains, and TiN particles with an average size of 300 nm were uniformly distributed in the Al matrix. The novel composites exhibited excellent tensile strength at both room temperature (RT), especially at high temperature (350 °C, HT), reaching 400 and 195 MPa, respectively. The TiN particles were found to further generate the effect of dispersion strengthening, while the AlN particles were effective in stabilizing the grain boundaries and pinning dislocations at HT. The enhancement of grain boundary stability by the intergranular particles and dislocation pinning by the intragranular particles were the main strengthening mechanisms of the composites at 350 °C. Based on the critical roles of the dispersive reinforcement particles and theoretical calculations at RT, the Orowan strengthening of AlN plays a dominant role at RT. This work may provide new ideas for the development of high-strength heat-resistant Al matrix composites.