Strengthening and Modification of Ti(Al / Pt)N Film on the Surface of Low Modulus Ti6Al4V

To solve the problem of film failure caused by the large difference in the hardness and modulus between hard films and soft substrates, and improve the adaptability of hard films on Ti6Al4V (TC4) titanium alloy substrates, doped titanium nitride (TiN) ceramic films are used to strengthen the surface of low modulus Ti6Al4V alloys. Ti(Al / Pt)N films, including intrinsic TiN, TiAlN, and TiAl(Pt)N films, were prepared on the surface of a Ti6Al4V alloy by the hot-wire plasma-enhanced magnetron sputtering technique. The microstructure, composition, phase structure, internal stress, nanohardness and modulus, and wear resistance of the Ti(Al / Pt)N films were characterized by scanning electron microscopy, X-ray diffraction, nano-indentation, Rockwell hardness testing, and friction and wear testing. The results showed that Al doping refined the columnar structure of TiN films, and made the cross-section morphology of columns much more compact. In addition, Al doping increased the critical fracture stress within the film, which reduced the film toughness. Doping with a small amount of metallic Pt enhanced the film toughness, and the fractured section of TiAl(Pt)N exhibited the ductile tearing mode. The diffraction patterns of the intrinsic TiN and TiAlN films showed a TiN (111) orientation. Al atoms replaced the Ti atoms in the TiN lattices and formed a substitutional solid solution of TiN, which widened and weakened the TiN (111) peak. During metallic Pt doping of the TiAlN film, the preferred film orientation changed to the low surface energy (200) of TiN, and the film stress decreased. Al doping increased the distortion of the TiN lattice. The internal stress increased from -13 MPa of intrinsic TiN to -115 MPa of TiAlN, which caused the deterioration of the film-to-substrate adhesion. In other words, film spalling occurred in the Rockwell indentation along with friction and wear. Owing to the excellent deformation ability of the metallic Pt element, the addition of Pt to TiAlN helped release the residual stress and enhanced the film toughness; therefore, the internal stress of the film due to Pt doping decreased to -66 MPa. In the Rockwell indentation experiment, the Ti(Al / Pt)N film was well bonded to the substrate, and only a few annular cracks were observed. In the friction and wear experiments, the wear loss of the TiAlN film was the largest because of the film peeled off, and the wear marks of the TiAl(Pt)N and intrinsic TiN films were very shallow. In short, the TiN films had high hardness and modulus, and were relatively brittle. Because the of the low internal stress of the TiN film, it did not peel off in the indentation detection test, and only edge cracks were observed. The Al-doped TiN film had refined columns, a distorted lattice, and high internal stress. The film peeled off from the TC4 substrate in the Rockwell indentation test. The TiAl(Pt)N film co-doped with Al and Pt showed refined columns, reduced lattice distortion, different orientations, and relatively low internal stress. Cracks appeared at the edge of the indentation, and the film was well bonded to the substrate. The coordination between the Ti(Al / Pt)N film and titanium alloy substrate demonstrated their strong adaptability and good mechanical properties. The Al and Pt co-doped TiN films on the surface of the Ti6Al4V alloy have potential applications in improving the coordinated deformation between hard films and soft substrates.