## 3 Results and Discussion  
### Microstructural Characterization  
The microstructures of the designed P/M alloys are presented in Figure 2a,b. Due to the furnace cooling after the sintering process, Widmansattein, in which the dark \(\alpha\) and light \(\beta\) phases were generated in a layered pattern in all P/M alloys and pores, were also  
Figure 1: Bo and Md stability phase map showing the positions of the designed alloys [26]. observed. In the case of the inside of TMF 34 I/M, \(\alpha+\beta\) lamellar Widmanstatten structures were observed and the \(\alpha\) phases precipitated within the equiaxed \(\beta\) grain inside of the TMF 54 I/M. In the case of the I/M alloy, the lamellar Widmanstatten microstructure with a \(\alpha+\beta\) was observed in TMF 34 I/M, and in the case of TMF 54 I/M, the \(\alpha\)-phase precipitated inside equiaxed \(\beta\) grain had different structures (Figure 2c,d). In the case of the Widmanstatten structure, cracks are first generated at the boundary of colony or grain boundary \(\alpha\)-phase and it is reported that cracks are propagated in this way and its tensile ductility is low [30]. In the equiaxed structure, cracks occur mainly at the interface of \(\alpha/\beta\), resulting in high strain. Therefore, it is expected that TMF 54 I/M with the equiaxed structure represents higher strain than TMF 34 I/M with the \(\alpha+\beta\) lamellar Widmanstatten. Figure 3 shows an observation of the Inverse pole figure (IPF) map for analyzing the Widmanstatten observed in the P/M alloys. The thickness of the Widmanstatten \(\alpha\)-lath of TMF 34 P/M was measured to be 12.289 \(\upmu\)m and the thickness of the Widmanstatten \(\alpha\)-lath of TMF 54 P/M was measured to be 10.547 \(\upmu\)m. It can be seen that as the Mo content increases, the thickness of the Widmanstatten \(\alpha\)-lath becomes thinner. Mo is one of the \(\beta\)-stabilizer elements and the temperature in the \(\beta\) transformation point decreases. In this study, when furnace cooling is performed after the sintering process at 1250 \({}^{\circ}\)C, the exposure time to the \(\beta\) transformation temperature increases according to the increase in the Mo content. Therefore, the fraction rate of the \(\beta\) phase increases, and accordingly, it is determined that the thickness of the Widmanstatten \(\alpha\)-lath decreased as the time of exposure to the \(\alpha\) phase decreased. In the practical observation of the EBSD phase map of the TMF 34 and TMF54 alloys, it was confirmed that the fraction rate of the \(\alpha\) phase decreased from 56% to 50.4% and the fraction of the \(\beta\) phase increased from 44% to 49.6% (Figure 4). Figure 2: Optical micrographs of (**a**) TMF 34P/M, (**b**) TMF 54 P/M, (**c**) TMF 34 I/M, and (**d**) TMF 54 I/M. Figure 4: EBSD analysis of phase map of (**a**) TMF 34 P/M and (**b**) TMF 54 P/M. Figure 3: Inverse pole figure (IPF) maps of (**a**) TMF 34 P/M and (**b**) TMF 54 P/M. Figure 5 shows the pore analysis table observed in the P/M alloys. Small pores below 10 \(\upmu\)m are mainly due to the 'Kirkendal' effect in powder metallurgy and are caused by atomic mutual diffusion during a solid-phase sintering process [31]. While pores with sizes of 40 \(\upmu\)m or more were not observed in TMF 34 P/M, pores with sizes of 40 \(\upmu\)m to 45 \(\upmu\)m were observed in TMF 54 P/M. As a result of analyzing the pore distribution, the pore fraction rate increased by about 1.4% from 2.1% to 3.5% as the content of Mo increased. This is due to the low-diffusion coefficient of Mo and the diffusion rate of Mo in Ti particles is slower than that of Ti itself. Therefore, the addition of Mo interferes with the sintering reaction and is sensitive to the formation of Kirkendall pores [31; 32]. Thus, the pore fraction rate of the TMF 54P/M alloy was measured to be 1.4% higher because the Mo content of TMF 54P/M was increased more than that of TMF 34P/M. In addition, it is known that the low diffusivity of Mo interferes with the movement of the particle boundary and affects grain refinement [33].