Ti–N phases formed by reactive ion plating

Abstract

Thin Ti–N films were prepared by reactive triode ion plating. The nitrogen content was varied from 17 to 50 at. % nitrogen. Two series of experiments corresponding to differing values of deposition rate and cathode current density were carried out. The nitrogen depth profiles were analyzed using the nuclear resonance broadening (NRB) technique. The performance of the coatings was evaluated in cutting tests. The films corresponding to a high deposition rate showed columnar growth morphology and consisted of metastable α-titanium and cubic titanium nitride. Dense and noncolumnar films approaching the structures predicted on the basis of the bulk phase diagram could be produced with a lower deposition rate and higher current density. The best cutting performance was obtained with substoichiometric films containing about 36 to 42 at. % N and consisting of a Ti+Ti2N structure. The lifetimes corresponding to critical crater wear in turning increased ninefold after coating with substoichiometric Ti+Ti2N film, while a threefold increase was observed after coating with stoichiometric TiN. Annealing at temperatures ranging from about 765 to 1175 K did not result in any major phase transformations, except at 40 at. % N, where transformation from α-Ti to δ-TiN was observed at 1175 K. The annealing did not greatly affect the cutting performance, which in some cases even decreased slightly after the heat treatment.