Laser pulse structure dependent texture of FEL synthesized TiNx coatings

Titanium was laser nitrided by means of free electron laser ( FEL) irradiation in pure nitrogen atmosphere. The variation of macropulse frequency and duration of the FEL micropulse trains resulted in the formation of delta-TiNx coatings with different thicknesses 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 begins at the surface and the alignment of the dendrites is normal to the surface. A correlation of the texture with the time structure of the laser pulses was found. Combined numerical simulations of temperature evolution and nitrogen diffusion were performed and the results were compared with the experimental findings. The simulations can explain the experimental results to a great extent.