Nitridation of Ti–6Al–4V powder in thermal plasma conditions and sintering of obtained TiN powder

• Published in: Surface & coatings technology 2006-10, Vol.201 (5), p.1988-1994
• Main Authors: Marchand, Cécile, Maître, Alexandre, Grimaud, Alain, Denoirjean, Alain, Lefort, Pierre
• Format: Article
• Language: English
• Subjects: Applied sciences; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Heat treatment; Hot pressing; Materials science; Metals. Metallurgy; Other topics in materials science; Physics; Plasma spraying; Production techniques; Sintering; Surface treatment; Thermochemical treatment and diffusion treatment; Titanium alloy; Titanium nitride
• ISSN: 0257-8972; 1879-3347
• DOI: 10.1016/j.surfcoat.2006.04.041

This study is devoted to plasma nitridation of a Ti–6Al–4V powder, and sintering of reaction products so-obtained. Ti–6Al–4V spherical particles (22–45 μm) were injected in a plasma jet using N 2 as plasma gas and collected in two spots: in a cold area located far from the torch and in a hot area submitted to the plasma thermal effect. After plasma nitridation, particles of substoichiometric titanium nitride (TiN 1− x ) with no nitrogen gradient were obtained. The reduction of nitrogen concentration in plasma gas improved the massic output of gathered powders. These powders were not exclusively composed by TiN 1− x , since titanium alloy often remained, and a secondary phase β-Ti containing vanadium and aluminium was always present inside the grains. The nitridation rate depended on the collected area. Titanium oxide (rutile) was detected in powders collected in the hot area. Titanium nitride powders in which no rutile was detected were hot pressed up to 1450 °C under flowing nitrogen. In this case, the densification rate did not overload 83% of theoretical value. This fact can be explained by the nitridation of both TiN 1− x and titanium intermetallic phases during the heat treatment. In the case of inert atmosphere (argon), there was only the densification phenomenon which gave a density close to the theoretical value. This work has to be developed on the one hand to improve powder synthesis and its natural sintering, and on the other hand to approach hot pressing sintering mechanism.