Hardness and elastic modulus of ion-nitrided titanium obtained by nanoindentation

Hardness and elastic modulus profiles of commercial titanium submitted to glow discharge at different N2/H2 atmospheres and temperatures were measured by nanoindentation. The nitriding atmosphere was changed from pure nitrogen to the richest hydrogen with substrate temperatures ranging from 600 to 900 °C. The TiN, Ti2N, TiO and TiO2 phases were identified by X-ray diffraction. Roughness effects on surface were observed at different working conditions. The tip penetration depths in nanoindentation tests were corrected by the contact stiffness curves at shallow tip penetrations to avoid errors induced by initial surface contact on the rough surface. The highest hardness of about 30 GPa was obtained for samples treated at 900 °C in presence of high hydrogen content. Elastic modulus profiles reveal a stiffer region near the surface, increasing from 140 GPa for the untreated sample to approximately 450 GPa after nitriding