3.3.1. Tensile Properties

The tensile sample was fabricated using the optimized process parameters (RD ≥ 99%) and tensile properties of 90W-7Ni-3Fe were investigated. Figure 14 depicts the tensile stress–strain curve of SLM-built 97W-7Ni-3Fe. The ultimate tensile strength (UTS) was 1121 MPa when there was no significant yield platform. The tensile fracture surface was characterized (Figure 15) and analyzed in order to illustrate the tensile fracture mode. In general, for WHA, there exist four kinds of fracture modes: matrix failure, W cleavage, a W–W inter granular fracture, and W-matrix interfacial separation [35]. The coexistence of these four fracture modes is common in tungsten alloys, and the tensile properties of the WHA are determined by the proportion of four fracture modes. From Figure 15a, the W–W inter granular fracture and W-matrix interfacial separation can be found; few (and shallow) dimples and W cleavage are shown in Figure 15b. Therefore, the 90W-7Ni-3Fe tensile samples fabricated by SLM in this work have the characteristic of brittle fracture. Table 4 lists and compares the tensile properties of the 90W-7Ni-3Fe samples in this study and previous studies. The 90W-7Ni-3Fe fabricated in this work presented a higher tensile strength but a similarly poor elongation. Therefore, in order to obtain the comprehensive mechanical properties, and realize the balance between tensile strength and elongation, subsequent heat treatments might be required. Appropriate heat treatments for these SLM-built WHA samples will be investigated in our future work. In addition, the mechanical behavior of samples could be affected by the building direction in SLM [36]. Thus, the relationship between 90W-7Ni-3Fe mechanical properties and building direction will also be discussed in our future work.

**Figure 14.** The tensile properties of 90W-7Ni-3Fe fabricated by SLM.

**Figure 15.** Tensile fracture morphology of 90W-7Ni-3Fe fabricated by SLM. (**a**) Low magnification; (**b**) high magnification of zone A (**a**).

**Table 4.** Comparison of the tensile properties of 90W-7Ni-3Fe between this work and the published results.

