## 3 Results
The increase in the melt-pool temperature or thermal heat led to the inference that the process of doping binary Ti-Al with niobium was \"endothermic\", and this might be an explanation for the absence of surface cracks and surface smoothing with the increase in niobium. The \"endothermic\" nature of the reaction would mean that the process of making Ti-48 Al-xNb was sustained with slow cooling rates when compared to the synthesis of the binary Ti-48 Al. This inference supports the observations by [PERSON] et al. (2019) and [PERSON] et al. (2018) (on cracking). The microstructures of the ternary alloy before heat treatment are reported in Figure 5, with the corresponding chemical composition reported in Table 3. Table 3 shows that three ternary alloys (TA, TB, and TC) were achieved. Table 3 illustrates that niobium content was seen to be decreasing with the increase in rpm. From Table 3, it is seen that the solubility of aluminium in the alloy increased with the decrease in niobium and titanium, respectively. Niobium is regarded as a micro-alloying element with the potential to improve processability and solid solution strengthening of the \(\gamma\)-phase Ti-Al alloys while modifying their deformation mechanism. The microstructures of the alloys are reported in Figure 5.  
Figure 4: As produced coupons of Ti–Al–Nb. SEM micrographs reported in Figure 5 compare the binary alloy to its ternary alloys before heat treatment. Figure 5 indicates that when niobium was added to the Ti48 Al (at. %) alloy, it had a tremendous effect on the resulting microstructure in the as-built state. The binary alloy (BA) microstructure was predominantly \(\alpha_{2}+\gamma\) with thick laths or agglomerated \(\alpha_{2}\) lamellae structures that seemed to form precipitates as indicated on the image. This observation suggests that \(\alpha_{2}\) lamellae structure has a different density and melting temperature than that of the \(\gamma\) rich phases. The bright white fields that are present can be interpreted as aluminium-rich islands, concluding that the binary alloy was heterogeneous. The immediate microstructural transformation with the addition of niobium can be deduced from Figure 5, as seen from the microstructures labelled TA, TB, and TC. It was observed that 6 (at. %) of niobium transformed the previously formed \(\alpha_{2}\) thick laths into a \(\gamma+\alpha_{2}\) microstructure that contained \(\beta\)-precipitate (TC). The 8 (at. %) niobium transformed the previously formed thick laths into lamellae-grained microstructure with some \(\beta\)-precipitate (o) (TB), and finally, the, 10 (at. %) niobium would lead to a full dissolution of the previously formed laths into fine \(\alpha_{2}/\gamma\) lamellar structure, with the observed \(\alpha_{2}\) lamellar structures serving as grain boundaries within which \(\gamma\) phase was contained. Some of the oxides (o) and \(\beta\)-precipitate (o) could still be observed (TA). Chemical analyses conducted on the observed bright white precipitates concluded that this  
Figure 5: Microstructures of the as-built Ti–Al/Nb alloys. \begin{table}
\begin{tabular}{c c c c} \hline
**ID** & **Ti** & **AI** & **Nb** \\ \hline BA & 75.94 (76) & 24.06 (24) & 0.00 \\ TA & 43.93 (44) & 45.93 (46) & 10.15 (10) \\ TB & 33.80 (34) & 58.03 (58) & 8.17 (8) \\ TC & 27.82 (28) & 65.86 (66) & 6.33 (6) \\ \hline \end{tabular} Note that the numbers in brackets are whole numbers of the actual EDS.  
\end{table} 
Table 3: Chemical composition of the alloys. was an alumina (Al\({}_{2}\)O\({}_{3}\)) phase. This oxide phase improves the high-temperature oxidation and creep properties of these alloys. [PERSON] and [PERSON] [14] reported that niobium of up to 10% (at.) can promote the oxidation resistance of the TiAl alloys. The observed microstructural transformation, with the addition of niobium content, can be summarised as follows: thick lamellar \(\rightarrow\)\(\beta\)-precipitates \(\rightarrow\)\(\alpha_{2}+\gamma\) grain formation \(\rightarrow\) fine lamellar structure.