## 3 Results and Discussions  
### Composition and Microstructure  
The XRD analysis results of the treated samples at different bording temperatures are shown in Figure 5. In all processing temperatures, the dominant diffraction peaks were assigned to the TiB\({}_{2}\) phase and showed relatively higher intensity than those of the TiB phase. It resulted that the surface of the base sample formed a thick and dense layer of TiB\({}_{2}\). Similar results have been reported in previous studies [14]. TiB\({}_{2}\) was the dominant phase for the samples treated at all bording temperatures. At lower bording temperatures, a very thin boride layer composed of TiB\({}_{2}\) and TiB was formed on the Ti surface. However, borided layer composition changes with increasing bording temperature; [PERSON] et al. [26] noted that under the same XRD analysis conditions, the thickness of the TiB\({}_{2}\) layer increased with the processing temperature increasing. In addition, the TiB phase became undetectable. Here, a similar trend can be observed. Figure 4: Experimental apparatus of wear and fricative testing. Figure 3: The specific variables of Equation (1). Figure 6 shows the Gibbs free energy (\(\Delta rG\)) profile of the boring reaction in the temperature range from 300 to 2000 \({}^{\circ}\)C (see Equations (2)-(4) below), as calculated using the NIST-JANAF thermochemical numeric data [27]; the values corresponding to specific temperatures are listed in Table 1.  
\[\text{Ti}+2\text{B}\rightarrow\text{TiB}_{2} \tag{2}\]  
\[\text{Ti}+\text{B}\rightarrow\text{TiB} \tag{3}\]  
\[\text{Ti}+\text{TiB}_{2}\rightarrow\text{2 TiB} \tag{4}\]  
As is well-known, the reaction can only occur when the \(\Delta rG\) is less than zero, and the smaller the \(\Delta rG\), the easier the reaction occurs [28]. From Figure 6, the Gibbs free energy values of the boring reactions were negative, which indicates that the boriides' relative energy was lower than that of titanium and boron in the energy level distribution, and the boriides could be formed with sufficient activation energy. Under the same conditions,  
Figure 5: XRD patterns of the surface of specimens with different boring temperatures. Figure 6: Gibbs free energy of B–Ti compounds with different boring temperatures. when the value of free energy was larger, namely less negative, the reaction proceeded with more difficulty. Due to the lower Gibbs free energy required to form TiB\({}_{2}\) compared to TiB, TiB\({}_{2}\) was preferentially produced at the same boriding temperature with sufficient Ti and B elements. As shown in Table 3, at higher temperatures, a lower Gibbs free energy for both TiB and TiB\({}_{2}\) formation was required, and hence, they formed more easily. Therefore, for the same products, higher boron contents are expected for samples borided at higher temperatures. From the perspective of material analysis, it is necessary to calculate the thermodynamic parameters. Thermodynamic calculations were performed on pure titanium, and the simulation results showed the types of borides that may be generated during the boriding of pure titanium in this study. During the boriding process, boron atoms diffuse from the molten salt into the titanium lattice from the surface to the substrate and react with titanium. With increasing boriding time, the number of boron atoms on the surface is higher than that in the bulk of the sample. Hence, most of the reactions between boron atoms and Ti occur on the surface. In this case, the reaction shown in Equation (2) was more likely to occur than those shown in Equations (3) and (4), resulting in TiB\({}_{2}\), rather than TiB, being formed on the outermost surface of the Ti sample. This is consistent with the preferential formation of TiB\({}_{2}\) detected by XRD at 1150 \({}^{\circ}\)C. Beneath the continuous TiB\({}_{2}\) layer, boron content was relatively low. At this condition, boron content dominates the boriding reaction.