A Study Of Surface And Interfacial Properties For Chromium-based Hard-and-multilayered Films

On the basis of Cr-based hard films in combination with architecture design ofcomposite and multilayered gradient films, three different Cr-based hard films wereprepared by mid-frequency magnetron sputtering technology, including Cr/CrxOymultilayered films, Cr modulation multilayered DLC films and Cr-gradually dopedmultilayered DLC films. The influence of process parameters, the thickness ofmodulation period and different doping modes on the microstructures andcomposition of surface and interface and mechanical properties were investigated.Explore the formation mechanism of surface defect and the mechanism of theinterface performance. The following results were obtained:(1) The structures of Cr/CrxOymultilayered films were Cr/CrxOy/Cr/CrxOy. Therestill existed with some randomly distributed and several microns scale irregulardroplets and craters on the film surface, which had a great influence on themechanical properties of films. The arcing in the reactive sputtering process resultedin surface defects on the films deposited. Results from orthogonal testing and varianceanalysis showed:(i) the target current was the most significant factor influencing theformation of defect density, and the subsequent significant factors in descending orderwere the pressures and the substrate bias voltages; and (ii) the optimal parametercombination for obtaining high-quality Cr/CrxOymultilayered films with low surfacedefect density, and high microhardness and critical load was: Itargetat16A, P(Ar+O2)at0.31Pa, Vbiasat values in the range of-240~-120V.(2) The Cr modulation multilayered DLC films consisted of Cr layer and DLClayer alternately, and the modulation ratio of Cr and C layer was about1/3. Theinterface structures and mechanical properties of the multilayer films were highlycorrelated with the thickness of modulation period. With the decrease of themodulation period, the contents of sp2-C and metal carbide in the films were increased.The hardness and elastic modulus presented same change trend: the optimummechanical performance with hardness of21.25GPa, elastic modulus of110GPa andcritical load of70.5N was achieved for the Cr modulation multilayered DLC films with the modulation period was400nm. Fracture toughnesses of three samples wereall very high, and with the decrease of the modulation period, fracture toughnessincreased gradually.(3) The Cr-gradually doped multilayered DLC films were composed ofCr-interlayer and Cr-gradually doped DLC top layer, which contained step-likegradient and linear gradient doped DLC films. The interface composition, structureand mechanical properties of the multilayer films showed a significant dependence onthe different doping modes. The contents of sp2-C and metal carbide in the lineargradient doped DLC films were larger, while the contents of Cr dispersed the Cmatrix in the step-like gradient doped DLC films were more. Hardness, elasticmodulus and critical load of linear gradient were higher than step-like gradient, butthe fracture toughness of step-like gradient was bigger than the linear gradient.(4) The influence of different interface structures and compositions of threetypical Cr-transitions on internal stress and adhesion strength was investigated.Interface property depended on the synergy among various factors affecting theperformance. The internal stress of linear gradient was the least; the adhesion strengthof linear gradient was the best. Even though the fracture toughness of linear gradientwas worse than modulation period, the interface property of DLC films was finallythe best, according to the synergistic effect of interface.