Effect of the filament discharge current on the microstructure and performance of plasma-enhanced magnetron sputtered TiN coatings

Abstract

Titanium nitride (TiN) coatings were synthesized by plasma-enhanced magnetron sputtering (PEMS) on 316L austenitic stainless steel and YG8 cemented carbide substrates. The plasma enhancement process involved the use of hot filaments as additional sources of electrons for the magnetron discharge. The structural, morphology, crystallinity, thickness, abrasion resistance and adhesion of the TiN coatings, as well as the nanohardness and Young's modulus were investigated at different filament discharge currents. The results showed that with increasing discharge current, the deposition rate of the coating decreased, the structural morphology of the TiN coatings became finer and denser and the columnar grain size decreased. The critical load for failure in scratch adhesion tests of the coatings on stainless steel and YG8 substrates were over 22 N and 141 N, respectively. The nanohardness and Young's modulus both improved significantly from 8 GPa and 200 GPa to 38 GPa and 500 GPa, respectively, after the discharge current increased from 6 A up to 12 A. The adhesion and the abrasion resistance of the coating on cemented carbide increased, and those on stainless steel decreased, with increasing filament discharge current. It was found that matching the Young's modulus of the coating to that of the substrate was important to improve the adhesion and abrasion resistance of the coating. The results demonstrate that TiN coatings can be prepared by PEMS at appropriate filament discharge currents, resulting in coatings with uniform thickness, dense structure and high hardness, abrasion resistance and adhesion.