Functionally graded Ti(C,N) coatings and their production on titanium using solid-state carburization associated with induction heat treatment

On the titanium surface functionally graded layers in the form of carbonitride TiC0.45–0.72N0.28–0.47 coatings were obtained by solid-state carburization associated with induction thermochemical (ITC) treatment at temperatures from 1050–1100 to 1300–1400 °C and exposure time within 8 min. A homogeneous porous structure of coatings with the thickness of 2.9–5.9 μm was formed in the low (1050–1100 °C) and medium (1250–1300 °C) temperature ranges. The average nanograin size varied from 63–68 to 100–121 nm and the size of the holes (pores) ranged from 45–58 to 64–84 nm. The hardness of coatings varied from 20.8 to 49.7 GPa and elasticity modulus – from 235 to 525 GPa. However, a high hardness value H = 47.6 ± 12.9 GPa, a low elasticity modulus E = 290 ± 73 GPa combined with microhardness H0.49 = 12.0 ± 0.9 GPa and calculated plasticity index H/E = 0.16 and brittle fracture resistance H3/E2 = 1.28 GPa were provided by ITC treatment of titanium at a temperature T = 1250–1300 °C and exposure duration t = 4 min. High hardness at various indentation loads of the carbonitride TiC0.58N0.42 coating was also explained by the formation of an underlying modified layer with an α′-Ti structure.