Microstructure Design And Properties Of A-C Based Films By Magnetron Sputtering

Amorphous carbon (a-C) films are one of the most promising thin-film materials in tribological and biomedical applications, due to their low friction coefficient, high hardness, excellent wear resistance and good biocompatibility. However, hard a-C films have significant intrinsic stress, which can cause adhesive failure, limiting their utilization in surface protections. In this present work, element doping, functional grading and multilayer structuring are used in the design of a-C based films. Meanwhile, the internal mechanisms between the microstructure and mechanical properties of the films are discussed and investigated.Ti-contained a-C gradient composite film with a thickness1.5μm is deposited on medical Ti6A14V alloy substrate using a closed field unbalanced magnetron sputtering with bias-graded voltage through-20V to-150V. the graded bias does not have much impact on the TiC formation in case of bias-graded Ti-contained a-C layer, but it leads to low internal stress and sp3contents of the bias-graded film. Compared with the constant-bias film deposited at-150V, the bias-graded film has the approximate hardness (19GPa) but higher toughness and adhesion strength. At a normal load of10N, the bias-graded composite film shows a low friction coefficient of0.08and wear rate of2.89×10-16m3N-1m-1in ambient air. While in Hanks’ solution, the film has the same low friction coefficient but lower wear rate of4.63×10-17m3N-1m-1. This is attributed to the Hanks’solution which provides the pronounced lubrication effect.An a-C/a-C:Ti multilayer film with a bilayer period of40nm is deposited on medical Ti6A14V alloy using a closed field unbalanced magnetron sputtering. Nanoindentation tests show that the hardness of the multilayer film reach25GPa with good toughness. Due to the presence of nanocrystallines TiC and plenty of interfaces, the hardness and adhesion strength of the nanomultilayer are significantly improved. In humid air without lubrication, the a-C/a-C:Ti nanomultilayer film have a low friction coefficient of0.080and wear rate of1.95×10-16m3N-1m-1at a load of10N. While in Hanks’ solution, the film exhibit lower friction coefficient of0.074and wear rate of4.25×10-17m3N-1m-1.For further study of the a-C based multilayer film, thick a-C/a-C:Ti multilayer films with bilayer periods of12-70nm are deposited on Ti6A14V alloy substrate by means of closed field unbalance magnetron sputtering. The thicknesses of all the films are about3μm and they exhibit excellent ability to complying with the substrate deformation and high load-bearing capacity. The mechanical properties of the a-C/a-C: Ti multilayer films are tailored with the decrease of bilayer period. The multilayer film with a bilayer period of12nm show the highest adhesion strength, hardness (26.2GPa) and elastic modulus (231.5GPa), also have the lowest average friction coefficient (0.093) and wear rate of8.06×10-17m3N-1m-1.