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Austenitic steel type 316 L is commonly used as material for implants due to its strength and reasonable biocompatibility. To improve its performance in biological applications, different coatings were deposited, usually by PVD methods. The diamond-like carbon (DLC) films are well known for the low friction coefficient, high microhardness and excellent biocompatibility. The inherently large residual stress of DLC films, however, prevents the depositing of thicker films, generating an adhesion problem when these films are deposited onto stainless steel. There were made different attempts to improve the adhesion using intermediate layers of nitrides, carbides or carbo-nitrides, especially for applications in cutting and forming of non-ferrous materials.
The paper presents the results obtained when a compound interface, comprising a multilayered graded structure made of a transitional metal Me, MeN, MeCN and MeC, was deposited between the hydrogenated DLC film and 316L steel substrates. The films were obtained by pulse reactive magnetron sputtering method. The transitional metal was either Ti or Zr. The deposition atmosphere was Ar for metal deposition, Ar+N2 for nitride films deposition, Ar+N2+CH4 for carbo-nitrides deposition, Ar+CH4 for carbides and hydrogenated DLC films deposition. The types of cathodes were used: Ti, Zr and C.
The individual films and the multilayered structure were investigated for their microstructure, morphology, elemental and chemical composition using XRD, AFM, AES, XPS, FTIR and Raman spectroscopy. The films microhardness was determined by using a Vickers intender and a metalographic microscope. The tribological performance of the interface was evaluated using a scratch tester and pin-on-disk tests. The failure mechanism of DLC deposited on austenitic steel substrates was examined using SEM/EDX and TEM microscopy. Experimental results demonstrated an improved adhesion of DLC hard coating on the steel substrates when the multilayered graded structure was present.
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