Synergistic Strengthening Mechanisms of Dual-Phase (TiN+AlN) Reinforced Aluminum Matrix Composites Prepared by Laser Powder Bed Fusion.

Dual-phase reinforcing approach provides a novel and efficient strategy for the fabrication of advanced aluminum matrix composites (AMCs). The devisable and desirable performance could be achieved by tuning dual-phase reinforcing system. However, it is still challenging to design a dual-phase reinforcing system with synergistic strengthening effect, especially for the laser powder bed fusion (LPBF) characterized by nonequilibrium metallurgical process. In this work, we designed and fabricated dual-phase (TiN+AlN) particles (20 wt.%) reinforced pure Al by LPBF. The TiN and AlN can form a metastable ternary Ti_1-xAl_xN solid solution in the whole range of composition, which is a promising reinforcing phase for AMCs. We observed novel microstructure in laser-fabricated composites under the action of dual-phase (TiN+AlN) ceramic particles and laser melting process. A gradient layer is formed on the surface of TiN particles. This interfacial structure can act as an anchor for ceramic particles in the Al matrix, which is beneficial to achieve a strong interface bonding and good load transfer. Besides this gradient layer, uniformly dispersed Ti_1-xAl_xN nanoparticles were observed to precipitate, which can effectively hinder dislocation movement and refine grains. Furthermore, the pure Al and TiN/Al, AlN/Al composites were fabricated to compare and reveal the contributions of dual-phase (TiN+AlN) reinforcements. The tensile strength of the (TiN+AlN)/Al composite reach ∼254 MPa, improved by ∼75% and ∼81% compared with those of the TiN/Al and the AlN/Al composites, respectively. This novel microstructure about gradient layer and precipitated nanoparticles contributes to the high strengthening efficiency of the (TiN+AlN)/Al composite.