| Titanium alloy has been widely used in aeronautics area for its unique high specific strength and good corrosion resistance. But, because of high chemical activation in high temperature, low thermal conductivity and low elastic modulus of titanium alloy, the problem of adhesion and high surface temperature will occur when cutting titanium alloy by tools, which will aggravate the wear and result in the failure of tools. In order to improve the cutting properties of tools, surface modification of cemented carbide was conducted.In this study, these six TiSiCN、TiSiCON、TiCrSiCN、TiCrSiCON、CrSiCN and CrSiCON coatings were deposited by plasma enhanced magnetron sputtering (PEMS) technique. The morphology, microstructure and mechanical properties of these six coatings were studied by using X-ray Diffraction (XRD), Scanning Electron Microscope (SEM), X-ray Photoelectron Spectroscopy (XPS), Vickers hardness test, load-depth-sensing indentation, scratch test and friction-wear test. And the effect of oxygen element on the structure and mechanical properties were studied. Results showed that, growth pattern of as-deposited films was columnar crystal, and addition of oxygen element increased the defects of coatings, which reduced the integrity of columnar crystals and density of coatings. The crystal structures of as-deposited film were mainly (111) and (200) lattice plane of fcc Ti(C)N-type (or Cr(C)N-type) structure. Si element was existed mainly as amorphous phase in coatings. Oxygen-containing TiSiCON coating showed obvious diffraction peak of TiO2 phase. The intensity of diffraction peak of CrSiCN was the lowwest for the effect of complex crystal structure of Cr-C.Addition of oxygen element would lead to the decrease of the hardness (H), elasticity and indentation toughness of Ti(Cr)SiC(O)N coatings. Indentation toughness of TiSiCON coatings was the worst of three oxygen-containing coatings. The wear mode of as-deposited Ti(Cr)SiC(O)N coatings against Al2O3 was mainly abrasive wear. Wear abrasion resistance of TiSiCN coating was better than TiSiCON coating. But for TiCr-based and Cr-based coatings, the friction coefficient and wear rate of TiCrSiCON and CrSiCON coatings was obviously lower than TiCrSiCN and CrSiCN coatings, respectively, which means that addition of oxygen element improved the wear abrasion property of TiCrSiCN and CrSiCN coatings.After heat treatment in air under 700℃ for 2 h, homogeneous and thick oxide layer was formed on TiSiCN coating while the oxide layer of CrSiCN coating was much thinner, oxidation resistance of TiCrSiCN coating formed thinnest oxide layer. For CrSiCON coating, oxide occurred after heat treatment under 500℃ in vacuum and 700 "C in air. After heat treatment under 500℃in 4×10-3Pa vacuum and 700℃ in air, hardness of non-oxygen coatings decreased obviously, while oxygen-containing coatings nearly did not decrease. These two heat treatment methods increased the adhesion property of Ti-based TiSiCN coatings, but decreased that of TiCr-based and Cr-based coatings. The wear mode against titanium alloy of TiCrSiCN and CrSiCN coatings after 500 ℃ heat treatment and TiSiCN coating after 700 ℃ heat treatment transferred into abrasive wear, which reduced the adhesion of titanium alloy obviously.The hardness and elastic modulus of DLC coating and TiSiCN/DLC coating were lower than these six Ti(Cr)SiC(O)N coatings, but the elasticity was better than those six coatings. The friction coefficient of DLC coating and TiSiCN/DLC coating against Ti6A14V titanium alloy was lower than 0.1, which exhibited excellent friction and wear properties. |
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