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A plasma nitriding of titanium alloys is very efficient method of their surface hardness and wear resistance improvement without compromising a core strength of the treated elements. The surface roughening increasing with the temperature of this treatment is a major obstacle on the way toward production of the fine quality products. Confronting of the roughness measurements performed at different scales range with complementary plan-view surface observations (OM, SEM/SE, FIB/SE, AFM) and cross-section (TEM) ones, focused on description of the surface defects, allowed the mechanism of their development to be explained. Namely, the TiN layer produced at lower temperatures (∼620°C) grows predominantly with a flat front, roughly reproducing the substrate morphology, while at intermediate and higher temperatures (680°C - 830°C) it is a subjected of severe self-spalling of the upper part of this layer. It …