3.3.2. Microhardness

Microhardness along the building direction of the sample was measured under the selected process parameter combinations. Figure 16a shows the microhardness distribution of the samples obtained under different volumetric energy densities at five points. The microhardness of the 90W-7Ni-3Fe samples fabricated by SLM presented an apparent fluctuation at every VED. This phenomenon might be ascribed to the inhomogeneous microstructure in the 90W-7Ni-3Fe samples (Figure 12). The average microhardness values of the 90W-7Ni-3Fe samples under different VEDs are shown in Figure 16b. The average microhardness was 406.83HV0.3 when the VED was 253.97 J/mm3, and the average microhardness increased to 467.46HV0.3 when the VED was 777.78 J/mm3. The average microhardness slightly increased with the increase of VED. This result could be explained by the nearly full density of the sample and the fine grains mentioned above. Compared to the result shown in Figure 17b, pores and irregular defects can be found in Figure 17a, which lead to a slight decrease of the average microhardness.

**Figure 16.** Microhardness under different VEDs. (**a**) Microhardness of each point; (**b**) average microhardness.

**Figure 17.** Vertical morphology of the 90W-7Ni-3Fe under different VEDs. (**a**) 253.97 J/mm3; (**b**) 518.52 J/mm3.
