Microstructural and corrosion evaluation of laser surface nitrided Ti-13Nb-13Zr alloy

The present paper reports on the microstructure, hardness, surface roughness, phases formed and corrosion behaviour of laser nitrided Ti - 13Nb - 13Zr biomedical alloy. Surface melting and nitriding of the alloy were carried out using a Nd: YAG laser in pulsed mode under dilute and pure nitrogen environments. Laser nitriding of the alloy resulted in a hardness of 1600 HV and 650 HK respectively, for pure N-2 and dilute N-2+Ar environments. Cracks were not observed either on the surface or in the vertical cross-section of the samples nitrided in both environments. X-ray diffraction analysis of the sample nitrided in a pure nitrogen environment confirmed the formation of TiN, TiN0.3, alpha and beta phases along with ZrN. Quantitative analysis using electron probe microanalysis (EPMA) showed the enrichment of Zr and Ti in the dendrites. Corrosion resistance of the laser nitrided samples in a simulated body environment (Ringer's solution) was evaluated using the potentiodynamic polarisation method, and was found to be significantly better for the laser nitrided conditions compared with the untreated alloy.