**3.4 Phase transformation**

**Figure 4** shows XRD patterns of the as-SLM, UNSM-25C and UNSM-800C samples. The change in diffraction peaks and phase transformation were confirmed by the relative intensity and the formation of a new peak after UNSM at 800°C. It was found that the intensity of all alpha phase peaks reduced except for (002) phase after UNSM at both 25 and 800°C. The intensity of alpha (101) phase increased for UNSM-800C sample and reduced for UNSM-25C sample. For as-SLM and UNSM-25C samples, the microstructure exhibited a full α/α`-phase, where α phase resulted from decomposition of α` during the SLM. For UNSM-800C sample, a precipitation of beta (110) phase was detected leading to a microstructure consisting of α and β phases as the temperature was higher than that of Ms. (575°C) [33]. Further, a broadening in full width at half maximum (FWHM) of the α peaks took place after UNSM, which led to the increase in dislocation density [27]. It is also obvious that

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**Table 3.**

*Calculated FWHM results based on XRD pattern.*

**3.5 Tribology**

**Figure 4.**

*Tribology of Ti-6Al-4V Alloy Manufactured by Additive Manufacturing*

*XRD patterns of the as-SLM, UNSM-25C and UNSM-800C samples.*

the UNSM increased the relative intensity of α (101) phase of the UNSM-800C sample as shown in **Figure 4**. Hence, it can be concluded that the UNSM resulted in grain size refinement. As a result, the FWHM values of the α (100) peak for the samples were listed in **Table 3**. It can be seen that FWHM of the as-SLM sample was broadened after UNSM at 25 °C. Furthermore, the FWHM of the UNSM-800C sample was found to be wider than that of the UNSM-25C sample, which signified that the refined grain after UNSM at 25°C was further refined after UNSM at 800°C. In general, it is well documented that the reduction in relative intensity of the peaks is responsible for the grain size refinement, which means that the UNSM refined the coarse grains into nano-grains, and also strain induced lattice distortion [34].

**Figure 5** shows the friction coefficient as a function of sliding cycles of the samples. It can be seen that all the samples came into contact with bearing steel (SAE 52100) underwent a running-in and steady-state frictional behavior. As shown in **Figure 5**, the friction coefficient of the as-SLM sample was found to be approximately 0.36 at the beginning of the friction test and increased continuously up to 0.52 for about 2000 cycles, which is considered as a running-in period. Then the friction coefficient continued being stable with a friction coefficient of 0.58 till the end of the test. **Figure 5** also shows the friction coefficient of the UNSM-25C sample. It was found that the friction coefficient demonstrated a similar friction behavior to the as-SLM sample, but the UNSM was able to reduce the friction coefficient in both the running-in and steady-state periods, where the friction coefficient was approximately 0.38 and 0.43, respectively. Overall, the friction behavior of the as-SLM sample was very highly fluctuated, which is associated with the initial rough surface. The frictional behavior of the UNSM-25C sample was relatively lower fluctuated, where the reduced surface roughness after UNSM is responsible for it. In addition,

**Samples FWHM SD** As-SLM 0.46347 0.00738 UNSM-25C 0.59442 0.00628 UNSM-800C 0.77026 0.01093

*DOI: http://dx.doi.org/10.5772/intechopen.93836*

*Tribology of Ti-6Al-4V Alloy Manufactured by Additive Manufacturing DOI: http://dx.doi.org/10.5772/intechopen.93836*

**Figure 4.** *XRD patterns of the as-SLM, UNSM-25C and UNSM-800C samples.*

the UNSM increased the relative intensity of α (101) phase of the UNSM-800C sample as shown in **Figure 4**. Hence, it can be concluded that the UNSM resulted in grain size refinement. As a result, the FWHM values of the α (100) peak for the samples were listed in **Table 3**. It can be seen that FWHM of the as-SLM sample was broadened after UNSM at 25 °C. Furthermore, the FWHM of the UNSM-800C sample was found to be wider than that of the UNSM-25C sample, which signified that the refined grain after UNSM at 25°C was further refined after UNSM at 800°C. In general, it is well documented that the reduction in relative intensity of the peaks is responsible for the grain size refinement, which means that the UNSM refined the coarse grains into nano-grains, and also strain induced lattice distortion [34].
