**5. Conclusions**

save the source of energy. The three-dimensional morphologies of the lasermicromachined surface with various input energy measured by AFM were shown in

with laser input energy. When the input energy is lower, the effect of laser processing parameters on the morphology of DF2 is not distinct, as shown in **Figure 17a**. With the increase of input energy, there are large amount of micro-pits distributed on the micromachined surface (**Figure 17b**) which could efficiently improve the load-carrying capacity and permit ease of release for mold made by DF2 [14]. Also, for the surface material removal, the main mechanism of the laser-

processed surface relies on evaporation, melting, and its subsequent re-

solidification. When the input energy of laser processing is lower, the influence of laser micromachining in this stage will mainly depend on the substrate melting. If the input energy of laser-processed surface of substrate is higher than that shown in **Figure 17b**, the 3D topography of the processed surface will vary accordingly. The relevant results are shown in **Figure 17c**. It shows that the micro-pits distributed on the processed surface as shown in **Figure 17b** are mostly melted and the morphology of the processed surface becomes relatively smooth. The effect of laser micromachining in this period is the synergetic action of the melting and little vaporizing of the substrate. With the input energy becoming higher, the morphology of laser processing will lie on the metal melting and medium vaporizing as shown in **Figure 17d**. It could be found that the surface is covered by melted metal with smoother texture and the property of substrate is changed to some extent because there are more laser energy inputs into the substrate. With the further increase of the input energy into the substrate, the surface of DF2 steel will be melted and vaporized seriously as shown in **Figure 17e**. It can be seen that there are

*Cross-section microstructures of laser-micromachined specimen (a) A-Harden layer, B-Fine grained zone, C-Heat affected zone, (b) B-Fine grained zone, C-Heat affected zone, (c) C-Heat affected zone, D-Substrate.*

**Figure 17** shows that the morphology of laser-micromachined surface is changed

**Figure 17**.

*Engineering Steels and High Entropy-Alloys*

**Figure 18.**

**96**


*Engineering Steels and High Entropy-Alloys*

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