Micro-Raman characterization of plasma nitrided Ti6Al4V-ELI

Titanium nitride surface coatings have been extensively used as wear resistant and biocompatible layers on titanium alloys. Plasma nitriding is a suitable method to obtain these coatings that have to be characterized with phase sensitive techniques, because hardness and wear resistance depend critically on crystallography and stoichiometry. Many of these analytical techniques have very stringent vacuum and sample geometry requirements that frequently do not allow the characterization of surface films ontop of biomedical components (bone or dental implants). Microprobe Raman spectroscopy can be applied without vacuum requirements on samples of variable size and shape. In this work, this technique is used to investigate the TiN layer on a Ti6Al4V-ELI alloy, plasma nitrided at different substrate temperatures, in order to observe the changes in stoichiometry. Changes of the relative intensities of acoustic and optical modes were related to TiN composition, comparing with the results of Nuclear Reaction Analysis, using the 15N(p, αγ)12C reaction induced with 429 keV protons. A linear relationship between the Raman peak area ratio and nitrogen content was observed, that can be used as calibration curve for further Raman measurements of unknown samples.