Laser nitriding of iron: influence of the spatial laser intensity distribution

Laser nitriding of metals and alloys has attracted technological interest. Nevertheless, the basic nitriding mechanisms are hardly understood. Hen, a derailed analysis of the nitrogen profiles, laterally and in depth, the sur face profiles and the microhardness is given in their respective dependence on the spatial laser intensity profile. Irradiation with a homogenised las er beam results in a more homogeneous lateral nitrogen distribution and a s mooth surface as compared to irradiation with the inhomogeneous raw beam. F urthermore, the nitrogen saturation concentrations reach over 10 at.% in th e case of the homogenised beam. which is significantly higher than the 3-4 at.% found for the raw beam. On the other hand, the hardness and the harden ing depth are considerably larger for the raw beam treatment, which is expl ained by the high amount of the E-nitride phase formed only in this case. ( C) 1999 Elsevier Science B.V. All rights reserved.