Influence Of Micro-alloying And Compounding On The Properties Of Nanocrystalline Ti₅Si₃ Film

Titanium alloy has a wide range of application in the aerospace, petrochemical and medical industries due to its favorable properties, such as low density, high strength-to-weight ratio, superior biocompatibility, etc. However, certain inherent shortcomings have limited its use in many applications. Surface modification can effectively improve surface properties of titanium alloy. In view of some disadvantages of surface modification techniques, it is necessary to conduct comprehensive and thorough research into the improvement of surface modification technique, the choice of coating material system, as well as the design of microstructure of coating.Nanocrystalline Ti₅Si₃ and Ti₅Si₃C_0.8 films were deposited onto Ti-6Al-4V alloy substrate by double cathode glow discharge technique using Ti₅₀Si₅₀ and Ti_45.5Si_45.5C₉ as target, respectively. The SEM micrographs showed that two kinds of nanocrystlline films were well adherent,uniform and dense without cracks and pinholes. Unlike a residual tensile stress existed in nanocrystalline Ti₅Si₃ film, C micro-alloying resulted in the formation of a compressive stress in nanocrystaaline Ti₅Si₃C_0.8 film , and C atoms were dissolved in the Ti₅Si₃ lattice, which didn't alter the crystalline structure of Ti₅Si₃. The microstructure of nanocrystalline Ti₅Si₃C_0.8 film, like nanocrystalline Ti₅Si₃ film, exhibited cauliflower-like cluster. The electrochemical corrosion results indicated that C micro-alloying promoted the formation of SiO₂ in the passive film, reduced the donor density in the anodic oxide film, increased the thickness of space-charge layer, which endowed nanocrystalline Ti₅Si₃C_0.8 film with more outstanding corrosion resistance.To investigate the influence of compounding on the properties of nanocrystalline Ti₅Si₃ film, a TiC reinforced Ti₅Si₃ matrix composite film (TiC/Ti₅Si₃) was prepared. XPS result revealed that, in nanocrystalline TiC/Ti₅Si₃ film, some C dissolved in the Ti₅Si₃ lattice as interstitial atoms, and the rest combined with Ti atoms to form TiC which were distributed between Ti₅Si₃ cauliflower-like clusters. The hardness, elastic modulus, fracture toughness and bonding strength with the substrate of nanocrystalline TiC/Ti₅Si₃ film were obviously higher than those of nanocrystalline Ti₅Si₃ film on account of the combining effects of C micro-alloying and TiC compounding. The results of electrochemical tests showed that the incorporation of TiC increased the donor density and diffusion coefficient of oxygen vacancy in the anodic oxide film,decreased the corrosion resistance of nanocrystalline TiC/Ti₅Si₃ film to a certain extent, but the pitting resistance was remarkably increased. The wear experiment results indicated that nanocrystalline TiC/Ti₅Si₃ film exhibited excellent wear resistance with the lowest specific wear rate; on the contrary, nanocrystalline Ti₅Si₃ film cracked and peeled off prematurely, and coating fragments resulted in abrasive wear, which severely worsened the wear resistance of nanocrystalline Ti₅Si₃ film.