# Development of a CALPHAD Thermodynamic Database for Pu-U-Fe-Ga Alloys
## 3 Literature Review
### The Iron-Gallium Phase Diagram  
The Fe-Ga system was largely investigated by [65, 66, 67, 68, 69, 70, 71, 72] with various techniques including thermal analysis, dilatometry, XRD, light microscope and Mossbauer spectroscopy to cover the full composition range of the system and elucidate phase relations, especially the complex ordering of the iron-rich BCC (including D0\({}_{3}\)) phases. The liquidus and solidus curves were measured by [65], who deduced the general shape of the phase diagram, but did not take into account the above-mentioned ordering on the iron rich side. Elemental gallium melts at 30 \({}^{\circ}\)C and does not exhibit any solubility of iron within its structure. Two Ga-rich phases were found to form peritectically; FeGa\({}_{3}\) phase decomposes at 824 \({}^{\circ}\)C into the monoclinic Fe\({}_{3}\)Ga\({}_{4}\) and liquid phases with a composition of 81.5 and 85 at. % Ga, according to [72] and [65] respectively. The second peritectic reaction occurs at 906 \({}^{\circ}\)C [L + \(\alpha\)(B2) \(\leftrightarrow\) Fe\({}_{3}\)Ga\({}_{4}\)]. Both phases were found to have a small composition ranges by [65], which was confirmed by [67] for the Fe\({}_{3}\)Ga\({}_{4}\) phase, but not the FeGa\({}_{3}\)[67; 72]. Additionally, [PERSON] et al. [66; 67] identified the Fe\({}_{6}\)Ga\({}_{5}\) phase, which was not considered by [65], that forms via a peritectoid reaction [\(\alpha^{\prime}+\) Fe\({}_{3}\)Ga\({}_{4}\leftrightarrow\beta\)-Fe\({}_{6}\)Ga\({}_{5}\)] at 800 \({}^{\circ}\)C and exists in its \(\alpha\)-Fe\({}_{6}\)Ga\({}_{5}\) polymorphic form below 778 \({}^{\circ}\)C. The Fe\({}_{3}\)Ga phase is found to be stable until 600 \({}^{\circ}\)C with a composition varying from 25-29 at. % Ga according to [65; 71]. [PERSON] et al. identified this phase as having two different polymorphs; the \(\alpha\)-Fe\({}_{3}\)Ga which exhibits a composition range between 26.1 and 29.5 at. % Ga until 605 and 619 \({}^{\circ}\)C respectively, above these temperatures the \(\beta\)-Fe\({}_{3}\)Ga phase is stable, with a slightly narrower composition range and transforms at 681 \({}^{\circ}\)C and 82.5 at. % Fe into the \(\alpha^{\prime}\) (B2') phase. Gallium solubility in BCC iron extends to a maximum composition of 47.5 at. % gallium and is accompanied by various ordered structures, including the \(\alpha^{\prime}\) (B2) CsCl-type phase with composition range from 31.5 at. % Ga up to the aforementioned maximum. The existence of this phase was verified by [68] and [71] via quenching from the liquid. [PERSON] et al. [66] found that the \(\alpha^{\prime}\) (B2) phase crystallizes directly from the melt at 1037 \({}^{\circ}\)C and 35.5 at. % Ga, and the phase is stable down to 950 \({}^{\circ}\)C, below which the \(\alpha^{\prime\prime}\) (B2') exists until 650 \({}^{\circ}\)C where it undergoes a eutectoid decomposition to \(\alpha^{\prime\prime}\) (D0\({}_{3}\)) and \(\alpha\)-Fe (A2) and is coupled to the magnetic transition temperature of \(\alpha\)-Fe. [PERSON] et al. [66; 67] also identified an ordered phase \(\alpha^{\prime\prime}\) that is involved in a eutectoid reaction: [\(\alpha^{\prime\prime\prime}\leftrightarrow\alpha\)-Fe + \(\alpha\)-Fe\({}_{3}\)Ga]. The authors however were skeptical of the \(\alpha^{\prime\prime}\) phase being an equilibrium structure, since most of their samples in this phase region also contained traces of \(\beta\)-Fe\({}_{3}\)Ga and even found some samples containing two-phases: \(\alpha\)-Fe + \(\beta\)-Fe\({}_{3}\)Ga, making the latter structure the probable equilibrium phase. [PERSON] et al. [66; 67] indicated that the phase field between 21-26 at. % Ga and 580-680 \({}^{\circ}\)C is a likely metastable domain as reactions proceed extremely slowly and with difficulty in reproducing the data. Finally, there is limited solubility of gallium in \(\gamma\)-Fe (FCC), with a characteristic \(\gamma\)-loop in which the maximum solubility is 2.8 at. % Ga at 1140 \({}^{\circ}\)C.