Tribological and mechanical properties of hardness-modulated TiAlSiN multilayer coatings fabricated by plasma immersion ion implantation and deposition

TiAlSiN monolayer coatings with different hardness and hardness-modulated TiAlSiN multilayer coatings with varied modulation periods were obtained on WC-Co substrates by plasma immersion ion implantation and deposition using TiAlSi cathodes. (Ti, Al)N (111), (200), (220), (311) and (222) diffraction peaks could be found in X-ray diffraction (XRD) patterns of the as-deposited coatings and a preferred orientation (Ti, Al)N (200) peak was obvious for all samples. Energy dispersive X-ray spectrometry (EDS) results showed that the TiAlSiN monolayer coating prepared at a high N₂ pressure obtained a large Si content. The nano-indentation tests revealed that the hardness of the TiAlSiN monolayer coating could be varied from 33.71 to 41.43 GPa when the N₂ pressure during the deposition process was changed from 0.08 to 0.2 Pa, which proved that hardness-modulated TiAlSiN multilayers could be obtained by varying the working pressure. Meanwhile, the hardness (32.25–37.56 GPa) of the modulated multilayers lied between those of the TiAlSiN monolayers. Scratch tests exhibited that the TiAlSiN monolayer coating prepared at 0.2 Pa N₂ pressure peeled obviously at the L_C1 value of 20.8 N, while that of the multilayer coating occurred at 144.4 N. Tribological tests showed that the wear rate of the hardness-modulated TiAlSiN multilayer coating could be reduced to 1/8 of that of the monolayer coating.