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The interface fatigue strength of coated tools with nano-crystalline diamond (NCD) coatings affects their milling performance. Depending on the developed cutting loads and temperatures, the repetitive impacts on the tool deteriorate progressively the coating-substrate interface strength, thus influencing the effective NCD film adhesion. Aiming at a comprehensive investigation of this effect, NCD coated cemented carbide inserts with improved or insufficient adhesion were manufactured. Hereupon, a parameter characterizing the coatings' interface adhesion strength, the shear failure stress (SFLS) was estimated by inclined impact tests and FEM calculations at ambient and elevated temperatures. This metric is significantly affected, among others, by the compressive residual stresses developed in the NCD film during cooling after its deposition and the coating operational temperature. A correlation between the determined SFLS at the investigated adhesion levels and the FEM calculated maximum shear stress in the coating interface during milling AA 7075T6 contributed to the explanation of the wear evolution on the employed NCD coated tools. Prime novelty statement The submitted paper aims at investigating the effect of the interface fatigue strength of NCD coated hardmetal inserts on their cutting performance in milling. The fatigue strength of the NCD coating-substrate interface is a dominant mechanical property for the NCD coated tool life. In the submitted work, NCD coated cemented carbide inserts with different adhesion qualities were manufactured. The interface fatigue strength at temperatures up to 400 °C was quantified using a critical shear failure stress (SFLS). This was attained by conducting appropriate FEM supported evaluation of the inclined impact test results at ambient and elevated temperatures. A correlation between the determined SFLS at various adhesion levels and the FEM calculated maximum shear stress in the film interface during milling AA 7075T6 contributed to the explanation of the wear evolution on the employed NCD coated tools. This is a new and original contribution to the field of testing NCD coatings and their effective application in cutting. The submitted paper is not being considered for publication elsewhere.

The determination of the temperature dependent interface fatigue strength of Nano-Crystalline Diamond (NCD) coatings facilitates a thorough understanding of the NCD coated cutting tools wear mechanisms. In the present paper, the fatigue strength of the interface region between a NCD film and its hardmetal substrate was investigated by inclined impact tests at various temperatures. Depending upon the impact load and the applied temperature, after a certain number of impacts, damages in the film-substrate interface develop, resulting in coating detachment and lifting. These effects were attributed among others to the release of highly compressive residual stresses in the NCD coating structure. The attained inclined impact testâs results contributed to the explanation of the wear-evolution of NCD-coated tools with diverse film-substrate adhesion qualities. The related milling experiments using as work material AA 7075 T6 verified the dominant effect of the film adhesion on the NCD coated tool life.