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 TiAlN 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 TiAlN 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.