THE EFFECT OF TIN INTERLAYERS ON THE INDENTATION BEHAVIOR OF DIAMOND-LIKE CARBON-FILMS ON ALLOY AND COMPOUND SUBSTRATES

Diamond-like carbon (DLC) films have been deposited onto a polished, C r alloy substrate, with and without the presence of a physical vapor d eposition (PVD) TiN intermediate layer, using a saddle-field, fast-ato m beam source at 40-degrees-C. The process has been utilized to deposi t DLC films ranging in thickness from 0.5 to 2.0 mum. The thicker of t hese films exhibited great difficulty in maintaining adequate adhesion to the Cr alloy substrates, presumably due to the increase in intrins ic (growth) stresses. To investigate the influence of substrate proper ties on the measurement of elastic modulus and hardness, PVD has been used to deposit intermediate layers of TiN, 3.0 mum thick, between the substrates and the DLC films. In addition, a second technique, that o f r.f. electron-beam PVD, has been employed to synthesize DLC onto an uncoated substrate of the tool steel, ASP23. Delicate ultralow-load in dentation measurements have been enabled by the utilization of a comme rcially available nanoindenter to probe the properties of deposited fi lms as a function of indentation load at each Of four loads: 8, 20, 80 and 120 mN. These techniques have demonstrated that the TiN interlaye r possesses both higher elastic modulus and higher hardness compared w ith the DLC coatings, having values of approximately 300 and 20 GPa, r espectively, at an indentation depth of 350 nm. The hardness of the DL C films ranges from 13 to 16 GPa and varies with indentation depth; ha rdness and modulus values begin to approach those of the underlying su bstrate or interlayer with increasing indentation depths. At a constan t load of 20 mN, the 2.0 mum thick DLC coating over the TiN interlayer shows the greatest hardness of the three thicknesses investigated, pe rhaps due to the greater compressive growth stresses normally associat ed with thicker coatings.