Depth profiling characterization of the nitride layers on gas nitrided commercially pure titanium

The thermochemical gas nitriding of the commercially pure titanium was conducted in a pure nitrogen atmosphere under the pressure of 2.5 × 10⁵ and 4 × 10⁵ Pa at the temperature ranging between 800 and 1323 K for 8 and 36 hours. The surface microstructures, chemical composition and hardness of the nitrided specimens were characterized using the scanning electron microscopy (SEM), Glow discharge optical emission spectroscopy (GDOES), X-ray diffraction (XRD), electron backscatter diffraction (EBSD), X-ray photoelectron spectroscopy (XPS), and Vickers micro hardness tester. The nitrided layers, comprising TiN, Ti₂N and TiN_0.3 phases, as well as a solid solution of nitrogen in the titanium so called diffusion zone were formed during the gas nitriding process. The thickness of the nitrided layers and diffusion zone varied with the processing temperature and pressure. Furthermore, oxygen and carbon impurities were detected in the outermost titanium nitride layer. The influence of the processing temperature and pressure on the chemical and phase composition, microstructure development, lattice parameters, texture evolution, hardness and chemical state of the main elements in the nitrided layers have been discussed.