Fabrication of Ta-Si-C targets and their utilization for deposition of low friction wear resistant nanocomposite Si-Ta-C-(N) coatings intended for wide temperature range tribological applications

摘要

Powders based on tantalum disilicide and silicon carbide were fabricated by mechanical activation-assisted SHS of reaction mixtures, with SiC concentration varied from 10 to 70%. The single- and double-layer composite targets were produced by hot pressing and further utilized for deposition of Si-Ta-C-(N) coatings by magnetron sputtering. The optimal hot pressing regimes, which allowed the production of dense ceramics with a hierarchical structure at 10 and 30% SiC, were determined. These ceramics were characterized by a relative density of 96-97%, hardness of similar to 19 GPa, and fracture toughness of 63-6.7 MPa x m(1/2). The nanocomposite Si-Ta-C-N coatings consisted of fcc Ta(Si,C,N) solid solution (TaSi2-30%SiC target) and Ta5Si3 compound (TaSi2-10%SiC target) embedded in an amorphous matrix. Depending on the elemental composition, hardness and Young's modulus of the coatings were 16-26 GPa and 155-268 GPa, respectively. The coatings are characterized by high thermal stability and oxidation resistance at temperatures up to 800 degrees C. Tribological tests demonstrated the decrease of the coefficient of friction (CoF) of the coatings with increasing temperature: from 0.38 (25 degrees C) to 0.28 (600 degrees C) and 0.23 (800 degrees C). The low wear rate and CoF of the Si-Ta-C-N coatings at elevated temperatures are explained by the formation of a thin (similar to 100 nm) oxide layer and TaSixOy microfibers on the coating surfaces.