## 3 Results
### Twinning in Annealed Conditions  
3.2.1. Condition 1: Annealing Twinning in the Binary Samples  
[PERSON] et al. proposed that Nb, when added to the \(\gamma\)-TiAl alloy, will lead to twinning in the annealing condition. To ascertain this proposal, the microstructures of the alloys post-annealing and the corresponding XRD graphs are reported in Figures 10-15, respectively, for Condition 1 (1200 \({}^{\circ}\)C) and Condition 2 (1400 \({}^{\circ}\)C). Figure 10 presents the effects of heat treatment on twinning in the binary alloy. The peaks were assigned using these reference codes: TiAl\({}_{3}\) (00-026-0038), TiAl (00-005-0678), Ti\({}_{3}\)Al (00-052-0859), Al\({}_{2}\)O\({}_{3}\) (00-004-0877), TiO\({}_{2}\) (00-015-0875), Cubic Pm-3m (04-016-6790), hexagonal (P63/mmc), Orthorhombic (04-017-6137), and TiAlNbO\({}_{2}\) (01-088-1981).  
Figure 10 shows explicitly that not only does heat treatment promote homogenisation in this alloy, but it also dissolves the unstable \(\alpha_{2}\) phase, leading to a stable pure \(\gamma\) phase alloy. No twinning was observed for the alloy after heat treatment at 1400 \({}^{\circ}\)C. Perfect twins of the \(\alpha_{2}\) phase are observed after heat treatment at 1200 \({}^{\circ}\)C at 20 positions of 40.255\({}^{\circ}\) and 40.754\({}^{\circ}\). An intense peak (20 of 26.442\({}^{\circ}\)) was observed post-heat treatment at 1200 \({}^{\circ}\)C that corresponds to the titanium oxide (TiO\({}_{2}\)) phase, which is absent in the as-built and samples that were heat treated at 1400 \({}^{\circ}\)C. The as-built sample and the sample that was heat treated to 1400 \({}^{\circ}\)C have an oxide layer present at the 20 peak position of 39.677\({}^{\circ}\) that corresponds to the Al\({}_{2}\)O\({}_{3}\) phase. Overall, this XRD spectrum concludes that the as-built alloy was a dual phase alloy (\(\alpha_{2}+\gamma\)), where \(\alpha_{2}\) phase was the figure print of the alloy, and after heat treatment the aluminium-rich phase (\(\alpha_{2}\)) was dissolved, leading to the alloy where \(\gamma\) phase was the figure print, as seen from Figure 11, which reports the SEM images of the alloys post-heat treatment.  
Figure 9: Twinning in the Ti–Al/Nb alloys.  
Figure 11 presents the near lamellar and fully lamellar microstructures of the binary alloy post-heat treatment at 1200 \({}^{\circ}\)C and 1400 \({}^{\circ}\)C, respectively. These SEM images validate that the binary alloy post-heat treatment at 1400 \({}^{\circ}\)C was dual phase (\(\alpha_{2}+\gamma\)) in \(\gamma\) with dislocation pile-up present in the \(\alpha_{2}\) while the \(\gamma\) just experienced dislocation motion. No twinning was observed in this alloy. Primary and secondary dislocation planes and a few dislocation pile-ups were observed in the sample heat-treated to 1200 \({}^{\circ}\)C. The dark phase is typically \(\gamma\), while the bright phase is typically indexed \(\alpha_{2}\) in Ti-Al research. It can simply be concluded that, indeed, twinning was present in the \(\alpha_{2}\) phase in this alloy as per the XRD data. Twinning in the ternary alloys is studied next in Conditions 2 and 3 for 1200 \({}^{\circ}\)C and 1400 \({}^{\circ}\)C, respectively.  
Figure 11: SEM microstructure of the heat treated: 1200 (**left**) and 1400 (**right**) samples.  
Figure 10: Anneal twinning in the binary alloy.