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Within this work, the thermal stress build-up of chemically vapor deposited TiCN/α-Al 2 O 3 bilayer coatings was controlled by tuning the coefficient of thermal expansion (CTE) of the substrate material. This was implemented through a Co content variation from 6 to 15 wt.% in WC-Co substrates, which exhibit higher CTEs with increasing Co contents and thereby approach the CTE values of TiCN and α-Al 2 O 3. High temperature X-ray diffraction was employed to determine thermal expansion of an α-Al 2 O 3 powder. Crystallographic texture of the α-Al 2 O 3 coating layer was evaluated by electron backscatter diffraction and taken into consideration in order to assign the appropriate in-plane CTE. This consideration indicated a lower CTE mismatch of α-Al 2 O 3 with WC-Co, compared to TiCN with WC-Co. X-ray diffraction was further utilized for the determination of residual stress in TiCN and α-Al 2 O 3 , demonstrating a decrease in both layers for Co contents below 12.5 wt.%. Decreasing stress signaled the formation of thermal crack networks confirmed by scanning electron microscopy surface images. Lower residual stresses were determined in TiCN compared to α-Al 2 O 3 layers of bilayer coatings, contradicting finite element simulations of thermo-elastic stress, that were carried out to illustrate the stress relaxation effects caused by thermal cracks. Monolayer TiCN coatings were annealed at 1000 °C, to replicate stress relaxation taking place during α-Al 2 O 3 deposition, exhibiting a similar residual stress state to TiCN base layers of bilayer coatings. Thermal crack formation was found to be the dominating stress relaxation mechanism in α-Al 2 O 3 , while TiCN undergoes further relaxation through secondary mechanisms. • Temperature-dependent coefficients of thermal expansion (CTEs) of TiCN and α-Al 2 O 3 • Stress build-up in TiCN and α-Al 2 O 3 layers through increasing CTE mismatch • Thermal crack formation signaled by the decrease of residual stress • Finite element simulations of thermo-elastic stress in TiCN/α-Al 2 O 3 coatings [ABSTRACT FROM AUTHOR]

TiCN coatings were grown by chemical vapor deposition (CVD) on WC-Co substrates with different Co contents, in order to control thermal stress. The driving force for the development of thermal stress is attributed to the difference between room and deposition temperature (ΔT ≈ −780 °C), and the mismatch of the coefficient of thermal expansion (CTE) between substrate and coating. Co contents of 6, 7.5, 10, 12.5, and 15 wt% were utilized to adjust the CTE of the substrate, and therefore tune the stress in TiCN coatings. Dilatometry of the substrates and high temperature X-ray diffraction of a powdered TiCN coating indicate a decreasing CTE-mismatch for increasing substrate Co contents. In consequence, residual stress in TiCN determined by X-ray diffraction increases up to 662 ± 8 MPa with decreasing Co contents down to 10 wt%. For Co contents below 10 wt%, the residual stress decreases. The formation of thermal crack networks in TiCN, analyzed by scanning electron microscopy, coincides with 10 wt% Co. Stress relaxation in TiCN coatings through the formation of thermal cracks becomes evident. A finite element simulation utilized for the calculation of residual stress distributions reveals shielding effects, which occur with the introduction of thermal cracks. Discrepancies between experimental and simulated thermo-elastic stresses imply the presence of secondary relaxation sources. High temperature residual stresses in TiCN, determined up to 1000 °C (i.e. above deposition temperature), suggest additional thermal crack formation for substrate Co contents of 6 wt%. • Coefficients of thermal expansion (CTEs) of CVD TiCN and WC-Co substrates • CTE mismatch tuning of TiCN and WC-Co through adjustment of Co content • Elimination of thermal crack networks in TiCN for 12.5 and 15 wt% Co • Illustration of crack shielding effects by finite element simulations • High temperature residual stress of TiCN coatings grown on WC-Co substrates [ABSTRACT FROM AUTHOR]