Toughening magnetron sputtered TiB2 coatings by Ni addition

Abstract

TiB2 coatings, despite their high hardness, suffer from brittleness. To improve their toughness without significantly sacrificing the hardness, we have added small quantities of Ni into the TiB2 coatings by magnetron co-sputtering from TiB2 and Ni targets, and examined their effect on the microstructure, hardness, and toughness. Over the Ni content of 0–12.6at.%, hexagonal TiB2 was the only crystalline phase. HRTEM examination revealed a cemented nanostructure, in which <10nm TiB2 grains were cemented by the 1–2nm Ni-rich binder, in the coating with 10.8at.% Ni. The nanoindentation hardness varied in the range of 28–44GPa. Improved toughness was confirmed by nanoscratch tests, Vickers indentation, and normalized plastic depth. The results indicate that addition of ductile metals to form the cemented boride nanostructure could noticeably toughen the TiB2 coatings while retain their high hardness.