## 3 Results
### Twinning in Annealed Conditions
#### 3.2.2 Condition 2: Heat Treatment at 1200 \({}^{\circ}\)C  
Figure 12 reports the microstructures of the ternary alloys after heat treatment at 1200 \({}^{\circ}\)C and furnace cooling in an argon environment.  
The microstructures are identified as near gamma for the alloy containing 6% Nb (TC), nearly lamellar/gamma for the alloy containing 8% Nb (TB), and fully lamellar for the alloy containing 10% Nb (TA). The Al\({}_{2}\)O\({}_{3}\) particles, indicated by a circle (O) on the microstructure, are present in all the ternary alloys except for the alloy that contained 10% Nb (TA), which serves as an indication that the latter alloy was oxidation resistant. There exists no perfect \(\gamma\) anneal twinning in the 10% Nb alloy (TA), and the \(\gamma\) phase lamellar highlighted experienced no dislocation pile-up, but dislocation rupture terminated and continued to form \(\alpha_{2}\) phase lamellar structures. Dislocation pile-ups are experienced by the \(\alpha_{2}\) phase in this alloy. Similarly, an alloy containing 8% Nb, even though it did not experience any dislocation motion, cannot be said to have twinning present. No twinning or dislocations are expected for the near gamma alloy (TC). The XRD plots of these alloys are reported in Figure 13.  
The XRD spectrum shows no signs of anneal twinning. There are three peaks in the 20 region of 76-79.8\({}^{\circ}\), which correspond to the \(\gamma\) phase. A shift towards the low 20 values,  
Figure 14: Twinning in the annealing condition is only possible at 1400 \({}^{\circ}\)C.  
Figure 13: XRD plots of TiAl–Nb after heat treatment at 1200, lower (**a**) and higher (**b**) 2\(\Theta\) values.  
Figure 15: Twinning in an annealing condition (HT 1400 \({}^{\circ}\)C).  
from 65 to 66\({}^{\circ}\) in the TB and TC alloys to 63 to 65\({}^{\circ}\) in the alloy that contained 10% Nb (TA), can be observed. Normally, the shift in the crystal's structure can be an indication of atomic rearrangement. These two peaks correspond to the \(\gamma\) phase peak. A cubic (Pm-3m) Ti-Al-Nb phase is a major peak for the TB alloy only and a second most intense peak for the TA and TC alloys, which happened to have \(\alpha_{2}\) as their major peak. Both TC and TB alloys have a TiO\({}_{2}\) phase that is absent in the TA alloy. Likewise, the \(\gamma\)/Al\({}_{2}\)O\({}_{3}\) phase is absent in the TA alloy and present in the TA and TB alloys. These two phases, TiO\({}_{2}\) and \(\gamma\)/Al\({}_{2}\)O\({}_{3}\), seem to decrease in intensity with the addition of Nb to a point of diminishing in the TA alloy that has a higher Nb content. The observation of the oxide phase in the TB and TC alloys is supported by the SEM images of the alloys, which are presented in Figure 12. Additionally, the observation that the TC alloy was near gamma is corroborated by the XRD data, as this alloy is missing the \(\gamma\) peak (20 of 38\({}^{\circ}\)) as one of the intense peaks. Unfortunately, these alloys are missing the anticipated anneal twins, leading to the conclusion that 1200 \({}^{\circ}\)C did not promote twinning in the Ti-Al-Nb alloy system. Further investigation on anneal twinning is discussed next in Condition 3.