Screw-dominated mixed dislocation arrays promote spiral growth in LPCVD TiAlN coatings

TiAlN coatings with self-assembled nanolamellar structures, synthesized via low-pressure chemical vapor deposition (LPCVD), represent a leading material system for high-performance cutting tools. While their layered architecture has been explored extensively, the nature and evolution of associated crystal defects—particularly dislocations—remain insufficiently understood. In this work, dislocation morphologies within 〈111〉-textured columnar TiAlN grains were systematically investigated using multi-scale electron microscopy on cross-sectional and plane-view TEM specimens prepared by focused ion beam (FIB) milling. High-density (∼10¹⁵ m⁻²) dislocation arrays, nearly perpendicular to the lamellae, were consistently observed and exhibited symmetric feather-like contrast in the cross-sectional samples. These long (∼200 nm), straight dislocations were identified as mixed full dislocations with Burgers vectors of b = ½ 〈110〉. Originating from three-fold pyramidal ridges, these dislocations propagate through grains along directions closely aligned with their Burgers vectors, indicating a dominant screw component. This was further validated by spiral features revealed through atomic resolution HAADF imaging. These findings support a dislocation-assisted growth mechanism, in which the screw components act as persistent atomic step sources that facilitate vertical grain growth along three 〈001〉 directions, thereby reinforcing the observed 〈111〉 texture. This dislocation-mediated growth mechanism provides new insights into the defect-microstructure interplay in LPCVD TiAlN coatings and offers guidance for the microstructural design of high-performance CVD coatings.