(Ti,Al)O2 Whiskers Grown during Glow Discharge Nitriding of Ti-6Al-7Nb Alloy

Abstract

Plasma nitriding of titanium alloys is capable of effective surface hardening at temperatures significantly lower than gas nitriding, but at a cost of much stronger surface roughening. Especially interesting are treatments performed at the lower end of the temperature window used in such cases, as they are least damaging to highly polished parts. Therefore identifying the most characteristic defects is of high importance. The present work was aimed at identifying the nature of pin-point bumps formed at the glow discharged plasma nitrided Ti-6Al-7Nb alloy using plan-view scanning and cross-section transmission electron microscopy methods. It helped to establish that these main surface defects developed at the treated surface are (Ti,Al)O2 nano-whiskers of diameter from 20 nm to 40 nm, and length up to several hundreds of nanometers. The performed investigation confirmed that the surface imperfection introduced by plasma nitriding at the specified range should be of minor consequences to the mechanical properties of the treated material.

Corrosion Behavior of Nitrided Layer of Ti6Al4V Titanium Alloy by Hollow Cathodic Plasma Source Nitriding

“…The surface microstructure of hollow cathodic nitriding samples at 500 • C is similar to the result of conventional plasma nitriding at 850 and 900 • C studied by Czyrska-Filemonowicz et al [48]. Furthermore, short-time nitriding assisted by hollow cathodes avoids surface defects of plasma nitriding (e.g., nano-whiskers of Ti and Al oxides [49]). The interface between the layers was obvious.…”

“…Czyrska-Filemonowicz et al [48]. Furthermore, short-time nitriding assisted by hollow cathodes avoids surface defects of plasma nitriding (e.g., nano-whiskers of Ti and Al oxides [49]). The interface between the layers was obvious.…”