Phase equilibria among α (hcp), β (bcc) and γ (L10) phases in Ti–Al base ternary alloys

Precipitation Behavior of ωo Phase in Ti-37.5Al-12.5Nb Alloy

“…Commonly, the observed ω o phase in high Nb-TiAl alloys can form from the "ω-collapse" in β o phase [6], i.e., the {111} β o layers "collapse" and the "-A-B-A-B-A-B-A-" stacking sequence in β o phase transforms into "-A-B/A-B-A/B-A-". There are four equivalent {111} β o layers so that four possible ω o variants can form in one β o grain.…”

“…Repeating this mechanism every two basal planes of the hexagonal matrix leads to the crystal structure change, thus, the stacking faults can act as the nucleus of the γ phase [25,26]. Moreover, it has also been reported that γ phase precipitated in this alloy after annealing at 700 • C for 26 days [6]. However, the γ phase observed in [6] consists of γ grains precipitated directly from the matrix and not thin γ laths transformed from the α 2 phase.…”

“…Recently, Stark et al showed that the amount of ω o phase increased with the content of Nb in high Nb-TiAl alloy [4,5]. Meanwhile, Nb is a β phase stabilizer that extends the β phase field and facilitates the ordered ω (ω o ) phase transitions in the β o phase in high Nb-TiAl alloys [6][7][8][9]. Numerous studies have reported the ω o phase transformations in high Nb-TiAl alloys, indicating that the ω o phase is stable at 700-900 • C [10,11].…”

“…Numerous studies have reported the ω o phase transformations in high Nb-TiAl alloys, indicating that the ω o phase is stable at 700-900 • C [10,11]. However, these studies have mainly focused on the transition process between the β o and ω o phases [6][7][8][9][10][11][12][13] or the α 2 to β o phase [14][15][16]. Recently, some reports concentrated on the precipitation of the ω o phase in α 2 laths during aging and studied the relationship between the α 2 and ω o phases [10,[17][18][19][20].…”

The temperature effect of hot isostatic pressing of γ-TiAl based alloy castings on phase composition and structure

“…Особенностью γсплавов является высокая чув ствительность их свойств даже к небольшим из менениям концентраций легирующих элемен тов, а также к параметрам технологического процесса, в частности к режиму термо обработки [7][8][9]. Дру гой проблемой является неоднородность струк туры (например, изза ликвационных явлений), что может приводить к недопустимому разбро су по служебным характеристикам.…”