Crystallization of MgAl2O4 and its effect on strengthening-toughening behavior in TiAlN/MgAl2O4 nanomultilayers

TiAlN/MgAl2O4 nanomultilayers with different MgAl2O4 layer thickness (lMgAl2O4) were fabricated. Studies show that under the template effect of TiAlN layers driven by interfacial energy minimization, amorphous MgAl2O4 crystallized and grew epitaxially with TiAlN layers, forming high-quality layered structure and coherent interface at low lMgAl2O4 (≤0.7 nm) and achieving maximum hardness of ∼46.0 GPa at lMgAl2O4 = 0.7 nm. Nevertheless, the hardness enhancement was obviously weakened by the partial amorphization of MgAl2O4 layer at larger lMgAl2O4. Additionally, the formation of layered-structure in the TiAlN/MgAl2O4 nanomultilayers remarkably improved the fracture toughness by deflecting and blunting cracks through layer interface.