Fig. 1. (a) Experimental platform and schematic diagram of laser-excited ammonia assisted nitriding; (b) Nitriding process diagram of 38CrMoAl steel; (c) XRD pattern of 38CrMoAl steel surface after different power of laser-excited ammonia assisted nitriding

Fig. 2. Surface morphology of 38CrMoAl steel. (a) SEM topography of nitrided 38CrMoAl steels with laser excitation of ammonia at different laser powers; (b) The average size of nitride particles on 38CrMoAl steel surface varies with laser power; (c) Variation of 38CrMoAl steel surface roughness with laser power

Fig. 3. Surface elemental distribution characterization of nitrided 38CrMoAl steels. (a) EDS profile of a nitrided 38CrMoAl steel with laser excitation of ammonia at 200 W; (c) EDS spectra of a nitrided 38CrMoAl steel with laser excitation of ammonia at 200 W; (b) Comparison of N and Fe atomic ratios of nitrided 38CrMoAl steels with laser excitation of ammonia at different laser powers

Fig. 4. Cross-section morphology and elemental distribution characterization of 38CrMoAl steels. (a) Cross-section metallography of nitrided 38CrMoAl steels with laser excitation of ammonia at different powers; (b) Enlarged section of 38CrMoAl steel after 200 W laser assisted nitriding; (c)EPMA characterization of cross section of 38CrMoAl steels, the red line indicates the line scanning of depth-dependent N distribution; (d) N element count characterized by EPMA of nitrided 38CrMoAl steels at different laser power plotted as a function of depth

Fig. 5. Hardness test analysis of 38CrMoAl steels. (a) Diagram of Vickers microhardness tester; (b) Surface hardness of nitrided 38CrMoAl steels with laser excitation of ammonia at different laser power; (c) Schematic illustration of the distribution of test points for sectional hardness test; (d) Cross-section hardness of 38CrMoAl steel after laser nitriding with different power