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, AlN, TiO_xN_y and SiN_x. 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.