αPhase in Plasma Nitrided Titanium Alloys: Preferred Orientation and Composition

Abstract

Conventional (wide angle) and advanced (microdiffractometry) X-ray diffraction techniques have been used to characterise plasma nitrided specimens of commercial α+β titanium alloys (Ti-4Al-2Mn, Ti-5Al-2Fe, Ti-6Al-4V) in order to study the α phase (interstitial solid solution of nitrogen in hcp titanium). The results show that the (J. phase crystals, when in direct contact with the δand/or 8 titanium nitrides that form the compound layer, present a preferred orientation with the {Oll} lattice planes orthogonal to the direction of nitrogen diffusion. At greater depths, however, this preferred orientation becomes less marked, and in the diffusion layer disappears completely. By measuring the variations in {Oll} and {002} interplanar spacing it has been possible to correlate the nitrogen content of the α phase with distance from the specimen surface.