Fraunhofer Project Center for Coatings in Manufacturing PCCM

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  • Publication
    Grain size effect of pre- and post-coating treated cemented carbides on PVD films' adhesion and mechanical properties
    ( 2013)
    Bouzakis, K.-D.
    ;
    Michailidis, N.
    ;
    Skordaris, G.
    ;
    Tsouknidas, A.
    ;
    Makrimallakis, S.
    ;
    Bouzakis, E.
    The grain size of coated cemented carbide tools may significantly affect the tool life by influencing either the coating adhesion to the substrate or the coating growth during deposition. In the present study three variously grained cemented carbides were coated with two different PVD films. Various pre- and post-treatments were applied, while their effect on the films' mechanical properties and adhesion was assessed by nanoindentations and inclined impact tests. The coatings deposited on ultra-fine-grained substrates exhibited the highest mechanical properties overall. The research revealed elevated adhesive properties for the fine-grained substrate compared to the normal and ultra-fine-grained one. The film adhesion of normal and fine-grained substrate can be further enhanced through micro-blasting. Post-treatments of the coatings were beneficial in all substrate cases, as brushing of the film surface removed droplets while at the same time inducing surface residual s tresses at the coating resulting in a hardness increase.
  • Publication
    Nano-impact test on PVD-coatings with graded mechanical properties for assessing their brittleness
    ( 2013)
    Bouzakis, K.-D.
    ;
    Skordaris, G.
    ;
    Gerardis, S.
    ;
    Bouzakis, E.
    In the described investigations, nano-impact tests were conducted on PVD films with graded mechanical properties. The properties gradation was induced by micro-blasting at different pressures for constant duration. Micro-blasting improves the film mechanical properties due to the induced residual compressive stresses into the coating structure. The film mechanical properties as well as the ratio of the film yield to rupture stress (SY/SM) grow up to a certain micro-blasting pressure. The augmentation of S Y/SM ratio increases simultaneously the film brittleness. For analyzing the effect of the SY/SMratio on the film brittleness, a multi-layer 3D-FEM model simulating the nano-impact test was developed employing the LS-DYNA software package. The FEM calculated results converge sufficiently with the attained experimental ones. Based on these results, the film's failure initiation and evolution can be predicted depending on the SY/SMratio of the individual film layers.