*3.3. Impact Toughness*

Figure 6 illustrates a comparison of impact toughness among different heat treatment methods. The impact toughness of the initial sample measures at 32.19 J/cm2, while the 810AC sample displays a slightly higher value at about 34.69 J/cm2. In general, the impact toughness of the untreated sample and low-temperature treated samples are higher than those of the other samples. Conversely, the impact toughness of the 940WQ, TriAC, and TriWQ samples significantly decreased, measuring at 13.13, 18.75, and 5.31 J/cm2, respectively. It can be inferred that the presence of transformed α phase and acicular α phase will greatly reduce the impact properties of the TA15 titanium alloy.

**Figure 6.** Influence of different heat treatment methods on impact resistance of the TA15 titanium alloy.

## *3.4. Bending Properties*

Figure 7 and Table 3 show that the overall bending properties of TA15 titanium alloys after heat treatment are reduced significantly. The data in Table 3 are calculated by the formula in Li et al. [37]:

$$m\_E = \frac{L\_S^3}{48I} \cdot \left(\frac{\Delta F}{\Delta f}\right) \tag{1}$$

$$R\_{bb} = \frac{F\_{bb}L\_S}{4\mathcal{W}}\tag{2}$$

where *I* = *bh*3/12, *b* is the width of the sample, *h* is the thickness of the sample, *LS* is the distance between the two support points of the sample on the bending test device, and *LS* =100 mm, *Fbb* is the maximum bending stress, and *W* is the section coefficient of the sample (*W* = *bh*2/6).

Based on the analysis presented in Figure 7 and Table 3, it can be observed that the bending strengths of the 810AC and 810WQ samples are approximately 4920.0 MPa and 5572.5 MPa, respectively. Additionally, the bending strengths of the 940WQ, TriAC, and TriWQ samples are approximately 1773.75 MPa, 1267.5 MPa, and 5572.5 MPa, respectively. It is worth noting that the samples subjected to higher heat treatment temperatures (940WQ, TriAC, and TriWQ) exhibit a more significant decline in strength than those subjected to lower heat treatment temperatures (810AC and 810WQ).

**Table 3.** Bending performance test results of different specimens.


**Figure 7.** Effects of different heat treatment methods on bending properties of the TA15 titanium alloy.
