Structural characterization and mechanical properties of a titanium nitride-based nanolayer prepared by nitrogen ion implantation on a titanium alloy

Abstract

A functionalized surface nanolayer less than 200 nm in thickness was prepared by nitrogen ion implantation at fluences of 2·1017, 4·1017, and 6·1017 cm-2 and at an accelerating voltage of 90 kV on the Ti6Al4V alloy. The evolution of the surface mechanical properties and the structural mechanism of the hardening were investigated. X-ray diffraction showed a great number of Ti+N interstitial nitrogen atoms and finely dispersed TiN precipitates in the modified surface nanolayer. The functionalized surface nanolayer on the sample with applied fluence of 2·1017 cm-2 had a predominant amount of Ti+N of about 45 wt% with minority TiN compound up to 20 wt%. The TiN content increased dramatically with increasing fluence of the implanted nitrogen. Nanoindentation investigations found that the indentation hardness improved up to 408% and that the reduced elastic modulus was increased up to 140%. The main hardening mechanism varied with the nitrogen concentration. Nitrogen ion implantation at low fluence of 2·1017 cm-2led to a functionalized surface nanolayer in which the hardening was mainly caused by the microstrain due to the large amount of interstitially located nitrogen. Applied fluences of 4·1017 and 6·1017 cm-2 increased the content of TiN compounds, which became the predominant hardening mechanism.