Now showing 1 - 4 of 4
  • 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.
  • 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
    Effect of tool diameter and cutting edge entry impact duration on coated tool wear in milling of various kinematics
    ( 2012)
    Bouzakis, K.-D.
    ;
    Katirtzoglou, G.
    ;
    Bouzakis, E.
    ;
    Makrimallakis, S.
    ;
    Maliaris, G.
    The die and mold industry registers nowadays a significant growth due to current developments among others in the sectors of energy and aerospace. The manufacturing procedure of dies and molds primarily includes milling operations, which are commonly linked to complicated chip geometry and contact conditions between tool and workpiece. Therefore, the optimisation of the cutting conditions and the description of the tool wear is a great challenge for production engineers. In the described experiments, cement-coated carbide inserts fixed on milling cutters with various diameters were applied in down and up milling for monitoring the wear behaviour at various cutting edge entry conditions. The corresponding developed strain rates cause different film-substrate deformations and resulting loads. These phenomena were investigated with the aid of a new impact tester with adjustable impact force characteristics. The effective tool life up to a certain flank wear land width vers us the cutting edge entry duration was explained and analytically described.
  • Publication
    Determination of PVD coating mechanical properties by nanoindentations and impact tests at ambient and elevated temperatures
    ( 2012)
    Bouzakis, K.-D.
    ;
    Pappa, M.
    ;
    Gerardis, S.
    ;
    Skordaris, G.
    The performance of physical vapour deposition (PVD) films depends on the operational mechanical and thermal loads of coated tools or components. To withstand these loads, sufficient film strength properties, at ambient and elevated temperatures are required. The present paper deals with the mechanical properties and the impact resistance of cemented carbides and high speed steel specimens, coated with various films, at temperatures up to 400 °C. Nanoindentations were conducted by a nanoindentation device, enabling measurements at room and elevated temperatures in an inert gas atmosphere. The obtained results were evaluated using appropriate FEM algorithms for determining the film stress-strain curves, at the temperatures of the conducted nanoindentations. The lesuits reveal a nonlinear temperature dependence of the coating properties. Moreover, perpendicular impact tests on the coated specimens were carried out up to 400°C, for investigating the film impact behaviour. T he developed impressions were recorded by scanning electron microscopy and white light confocal measurements. The attained results demonstrate a non-linear dependence of the film fatigue properties versus temperature, whereas a significant impact resistance improvement at approximately 150°C develops. Finally, a convergence between the yield and the fatigue endurance stress versus the temperature was revealed.