Microstructure and properties of TiAlSiN ultra-hard coatings prepared by plasma immersion ion implantation and deposition with TiAlSi alloy cathodes

TiAlSiN coatings with different Si contents (1.84-4.81 at.%) were prepared on WC-Co substrates by plasma immersion ion implantation and deposition using different TiAlSi cathodes. (Ti, Al)N (200), (220) and (311) diffraction peaks could be found in X-ray diffraction (XRD) patterns of the as-deposited coatings and a preferred orientation (Ti, Al)N (200) was obvious for all samples. X-ray photoelectron spectroscopy (XPS) results showed the existence of TiN, MN, TiOxNy and SiNx. High resolution transmission electron microscopy (HRTEM) images exhibited that the microstructure of TiAlSiN coating was gradually changed from poly-nanocrystalline to (200) preferred oriented (Ti, Al)N embedded in an amorphous matrix. Nanoindentation results revealed that all the coatings exhibited high hardness, where the maximum value reached 45.3 GPa at a silicon content of 3.43 at.%. Scratch tests were performed on these samples, and the highest critical load (L-C4) of the coatings reached 158.4 N, indicating that good adhesive strength was obtained by this deposition method.