Unveiling kink band formation mechanism in MAX phases

Plastic deformation in hexagonal MAX phases with atomistically layered structures is facilitated by the formation of kink bands when compressed parallel to the layers, such as along the basal planes. However, understanding of the kink banding process remains limited and often contradictory, hindering advances in controlling this unique mode of plastic deformation. Here, using molecular dynamics simulations of the Ti3SiC2 MAX phase with a highly accurate spectral neighbor analysis potential, we discover that pyramidal dislocation loops act as carriers of incipient plasticity under load parallel to the layers. These loops cause the elastic bending of the layers, allowing shear stress to resolve into basal planes. Consequently, basal edge dislocations nucleate through interlayer sliding, leading to further rotation of basal planes and the formation of high-angle kink boundary pairs. This discovery provides critical insights into the mechanisms behind kink band formation in elastically isotropic MAX phases, challenging previous assumptions of elastic buckling or ripplocations as the primary causes. MAX phase ceramics are known to plastically deform via kink banding, but the precise mechanism is challenging to explore experimentally. Here, molecular dynamic simulations with an accurate spectral neighbor analysis potential reveal pyramidal dislocation loops act as carriers for plasticity, causing elastic bending of atomic layers.