Crack arrest in nanoceramic multilayers via precipitation-controlled sublayer design

Improving the fracture toughness of transition metal nitride thin films while maintaining their functional properties remains a critical challenge in materials science. The intrinsic brittleness of these ceramics demands innovative approaches to reduce crack-driving forces through microstructurally induced shielding mechanisms. Here, we present a novel crack arrest mechanism achieved through a precisely designed multilayer architecture with sequentially tailored grain boundary precipitation. The multilayer consists of alternating periods of ∼250 nm thick Al0.8Cr0.2N and ∼50 nm thick nanocomposite Al0.675Cr0.075Si0.25N sublayers, deposited by cathodic arc deposition and subsequently heat-treated at 1050 °C for 5 min. Atom probe tomography and transmission electron microscopy confirmed precipitation within the Al0.8Cr0.2N sublayers and the absence of precipitates in the Al0.675Cr0.075Si0.25N sublayers. In situ microcantilever bending tests revealed a stable crack arrest within the heat-treated multilayer. Crack arrest was further supported by an analytical approach correlating the increasing cantilever compliance with the crack growth. The crack stabilization mechanism is attributed to the alternation between transgranular fracture in precipitate-toughened sublayers and intergranular fracture in precipitate-free sublayers. Our findings demonstrate that crack propagation in otherwise brittle ceramic thin films can be stabilized through a precipitation-controlled sublayer design, offering a promising pathway for enhancing the fracture resistance without compromising functional properties.