Physical aspects of laser nitriding of yttria stabilized t-zirconia

This manuscript describes the surface nitriding of yttria (Y2O3) stabilized tetragonal zirconia (t-ZrO2) by using the pulsed Nd-YAG laser irradiation in the nitrogen atmosphere. The results show modification of the crystallographic structure between the original tetragonal zirconia and the treated one. Nitrogen atoms enter in zirconia substituting oxygen atoms in the network. X-ray diffraction and Raman spectra show an efficient transformation of the t-ZrO2 at the surface that exhibit typical yellow-gold color of ZrN with high hardness and wear resistance. The X-ray diffraction results evidenced the new diffraction lines [c-ZrN(2 0 0)] that appear on the nitrided sample with alteration and shift in peaks as well as change in d-spacing or lattice parameter, whereas the Raman spectra revealed the two characteristics band related to acoustic part of low frequency in the 150-260 cm−1 region and optical part at high frequency in the 450-750 cm−1 region. Nitriding is accompanied by the formation of a few micron thick gradient layer of ZrN structure on the top via dissociative process: 2ZrO2 + N2 = 2ZrN + 2O2 and a partial transformation of t-ZrO2 into cubic zirconia (c-ZrO2) beneath deep in the bulk due to nitrogen concentration gradient. Some new features on the physical characteristics such as hardness and roughness of the cut sections of t-ZrO2 in the N2 and O2 atmosphere are discussed.