Surface Hardening of Titanium Alloys: Chemical Characterisation of the Nitrided Layers

The investigations were made on alloys OT-4 (Ti-3Al-1. 5 Mn), IMI318 (Ti-6Al-4V) and IMI550 (Ti-4Al-4Mo-2Sn-0. 5Si) of the alpha-beta type. The pressure was fixed at 10 torr and the temperature was made to vary between 800 and 1,000 degree C. A gaseous mixture was chosen, composed of 60 nitrogen and 40 hydrogen vol% and times of 4, 8 and 16 hours were selected for treatment with an ionic discharge. Diffractometric analysis was used for identification of the type of phases present on the hardened surface. It was found that the alloying elements modify the morphology of the surface layer.