Numerous hydrogen energy systems have been studied and developed as an alternative to fossil fuels for carbon neutrality. In many metal materials used for hydrogen storage, such as carbon steel, stainless steel and aluminum alloys, hydrogen embrittlement occurs due to the presence of hydrogen in the material. Hard coating materials (e.g., TiN, TiC, and BN) are widely used for hydrogen permeation barrier coatings and amorphous carbon is spotlighted as a hydrogen permeation barrier coating because of its high mechanical properties, chemical inertness, and low aggressiveness against materials.
We studied amorphization and surface roughness of carbon-doped TiZrN coatings in terms of lattice distortion and bonding state for the hydrogen permeation barrier coating. The carbon-doped TiZrN coatings were prepared by applying carbon paste on the TiZrN coating and adjusting the laser output. The crystal structure analysis show that the TiZrN (111) peak shifts to lower angles due to carbon doping, and the lattice constant, calculated by Rietveld refinement, increased from 3.612 Å to 3.964 Å, confirming expansion lattice distortion. XPS analysis and Raman analysis were conducted to identify the bonding state of the doped carbon, and the sp²/sp³ ratio and I_G/I_D ratio decreased by 26% and 59%, respectively. This indicates that amorphous carbon is formed due to high thermal energy and internal stress by the expansion lattice distortion. The number of columnar grains in the coating decreases and disordered structure by amorphization is observed by TEM as the laser output increases, and the SAED pattern changes from a distinct dot pattern to a diffused ring pattern. The variation of surface roughness with the generation of amorphous carbon in the carbon-doped TiZrN coating was measured using AFM, and the R_a value decreased from 12.913 nm to 7.127 nm after carburization. The diffusion mechanism of amorphous carbon with hydrogen permeability will be discussed.