Influence of α-Al2O3 texture on residual stress, cooling cracks and hardness in CVD α-Al2O3/Ti(C,N) coatings on cemented carbide

CVD α-Al 2 O 3 coatings on cemented carbides are widely used in steel turning, where cutting tool performance is strongly dependent on the crystallographic texture of the α-Al 2 O 3 layer. Residual stress, cooling-crack density, and hardness are key factors influencing coating integrity during machining. Although texture has been reported to affect these properties, trends remain inconsistent in the literature. In this work, three CVD α-Al 2 O 3 /Ti(C,N) coatings with identical architecture, substrate, and processing route, but distinct α-Al 2 O 3 textures: i. c-plane 0001 , ii. r-plane 01 1 ¯ 2 , and iii. a-plane 11 2 ¯ 0 were investigated to isolate the role of texture under controlled conditions. The 0001 coating exhibited the highest tensile residual stress and the lowest crack density, while the 01 1 ¯ 2 and 11 2 ¯ 0 coatings showed lower stresses and denser crack network. This behaviour is consistent with a texture-dependent thermal expansion mismatch, complemented by orientation-dependent stress accommodation during cooling. The 01 1 ¯ 2 and 11 2 ¯ 0 textures, with a greater in-plane contribution of the c-axis, develop higher intrinsic thermal stress and thus promote more extensive crack formation for stress relaxation compared to 0001 texture. Nanohardness values were comparable across the three textures. The results demonstrate that α-Al 2 O 3 texture has a clear influence on residual stress and cracking, but a limited effect on hardness. These findings provide a more consistent basis for interpreting texture–property relationships and suggest that the performance of 0001 -textured coatings in steel turning is primarily associated with reduced crack density and their response under directional loading, rather than with differences in hardness.