Free electron laser nitriding of metals: From basis physics to industrial applications

Titanium was laser nitrided by means of free-electron laser irradiation in pure nitrogen atmosphere. The variation of pulse frequency and macropulse duration of the free electron laser resulted in δ-TiN_x coatings with different thickness and different micro- and macroscopic morphologies. The coatings revealed, characteristic values for hardness, roughness and crystallographic texture, which originate from the growth mechanism, the solid-liquid interface energy and the strain. Further investigations showed that the dendritic growth is beginning at the surface and that the alignment of dendrites is normal to the surface. A correlation of the texture with the time structure of the laser pulses was found. Numerical simulations were performed and compared with the experimental results. The simulations can explain the experimental results.