*3.1. Microstructure Observation*

Figure 2 displays the X-ray diffraction patterns of TA15 titanium alloys subject to various heat treatments. All samples exhibit α phase, while some also exhibit β phase. However, after TriAC or TriWQ treatment, only α phase is detected. Figure 3 illustrates the microstructures of TA15 titanium alloys under different heat treatment methods. Combined with XRD diffraction results and SEM images, it is evident that the initial sample comprises primary equiaxed α phase and β grain microstructures (Figure 3a). However, the microstructures present various morphologies after different heat treatments. Figure 3b–d demonstrate that the microstructures comprise secondary α phase and transformed β phase after 810AC, 810WQ, and 940WQ treatments, respectively. Figure 3e,f indicate that the main microstructure after TriAC and TriWQ treatments is acicular α phase, with the α phase being slenderer after TriWQ treatment than after TriAC treatment.

To better illustrate the variation in elemental content between the α and β phases, we conducted an EDS scanning analysis of the initial sample's microstructure, as presented in Figure 4. The TA15 alloy consists predominantly of Ti, Al, and V. The EDS mapping results indicate that the α phase is primarily composed of Ti and Al elements, whereas the β phase contains more Mo and O. Additionally, V is found to be evenly distributed across the entire surface.

**Figure 2.** X-ray diffraction patterns of the TA15 Titanium Alloy under different heat treatment conditions.

**Figure 3.** SEM images of the TA15 Titanium Alloy under different heat treatment methods: (**a**) None, (**b**) 810AC, (**c**) 810WQ, (**d**) 940WQ, (**e**) TriAC, (**f**) TriWQ.
