Microstructure, bonding state and phase formation behavior of carbon-doped TiZrN coating by laser carburization

The phase formation behavior of carbon-doped TiZrN upon the variation of thermal energy was investigated in terms of microstructure and bonding state. The laser output was changed by 10% in the range of 20% to 70% after covering the carbon paste on the TiZrN coating. Degradation occurred on the coating surface by the laser ablation of 60% and 70% output. Phase analysis and the Rietveld refinement for the coating, which did not exhibit degradation, indicated that the phase fraction of the graphite inside the coating increased as the thermal energy increased. The lattice constant of TiZrN was 0.431 nm initially, but it gradually increased to 0.449 nm at the output of 50%. FIB, Cs-TEM, and TEM-EDS analyzed the formation of (Ti, Zr)C phase and the variation of lattice constant via cross-sectional microstructure and showed the increase in carbon content and carbon-substituted (Ti, Zr)C phase formed along with the existing (Ti, Zr)N phase. XPS analysis for the bonding of the doped carbon indicated that the substitution ratio of the doped carbon was approximately 4.4% at the output of 20%, and the substitution rate increased with increasing thermal energy resulting in 19.6% at the output of 50%. The ZrC phase mostly existed at the output of 20% for the substitutional carbon, and the proportion of the TiC phase increased with the increase in thermal energy, resulting in more than 50%. The formation energy of ZrC phase was lower than that of TiC phase, and the formation energy of TiC was satisfied with the increase in thermal energy. The hardness increased to 38.3 GPa at the output of 50% as the ratio of TiC phase was increased, which was approximately 20% higher than that of the TiZrN.