*3.2. Microhardness*

The average microhardness of TA15 alloys with various heat treatments is presented in Figure 5. It is evident that the microhardness of the untreated sample is the lowest, measuring at 310.5 HV. All heat treatment methods result in an improvement of microhardness in TA15 titanium alloys. However, there is no significant increase in microhardness observed with 810AC and 810WQ, which measured at 365.9 HV and 338.2 HV, respectively. The 940WQ sample exhibited a more extensive decomposition of metastable β phase than the 810WQ sample, resulting in an increased microhardness [19]. The TriAC sample, with the largest volume fraction of α phase, has the highest microhardness at about 601.3 HV.

Furthermore, the TriAC and TriWQ samples underwent triple heat treatment processes, which fully decomposed the β phase and led to even higher microhardness [36].

**Figure 4.** EDS mapping and elemental content analysis of TA15 microstructure.

**Figure 5.** Effect of different heat treatment methods on microhardness of the TA15 titanium alloy.
