Laser nitriding of iron with laser pulses from femtosecond to nanosecond pulse duration

Pulsed-laser nitriding is an attractive method to improve metal surface properties, such as hardness, wear, and corrosion resistance, with the advantage of simple experimental setup, rapid treatment, and precise process control. Here, the dependence of the laser nitriding process on the laser pulse duration was investigated over five orders of magnitude in a series of experiments employing pulsed lasers ranging from nanosecond excimer laser pulses (55 ns) and Nd-doped yttrium aluminum garnet (Nd:YAG) laser pulses (8 ns), to ultrashort Ti:sapphire laser pulses (150 fs). The results revealed that for all laser pulse durations and different wavelengths a large nitriding effect was observed. The excimer laser shows the highest nitriding efficiency. The basic processes for the femtosecond pulsed laser are not well understood but seem to result at least partly from processes within the plasma, whereas nanosecond nitriding is based mainly on processes within the liquid/solid surface. (C) 2002 American Institute of Physics.