Synergistic thermo-mechanical-driven microstructural evolution in AlTiN coatings and their friction–wear mechanisms against Si3N4 counterparts

Abstract

Cemented-carbide tools endure extreme thermo-mechanical coupling during cutting; clarifying the microstructural evolution and wear mechanisms of coatings under such synergistic conditions is key to developing high-performance coated tools. Focusing on arc-deposited AlTiN coatings, this study captures the complete microstructural trajectory during argon heat treatment and subsequent deformation, and elucidates—from a coupled thermo-mechanical perspective—the intrinsic physical mechanisms underlying the enhanced wear resistance conferred by argon heat treatment. Thermally induced spinodal decomposition enriched the AlTiN coating with w-AlN, converting the structure from single-phase FCC to FCC + HCP. Concurrently, columnar grains refined into a fine-grained matrix, and microcracks propagated through the w-AlN domains. As the annealing temperature rises, cracks at the indentation periphery widen and proliferate, whereas those within the stressed zone narrow and disappear. Annealing softened the coating by forming w-AlN, which improved elasticity, yet introduced microcracks that lowered crack resistance. After 1100 °C annealing, the wear rate fell to 1.75 × 10⁻¹⁵ m³·N⁻¹·m⁻¹—only 17 % of the as-deposited value. Microcracks cushioned compressive shear, while w-AlN promptly fragmented, oxidized, and formed protective debris that halted further wear.