Ordered α2 to ωo phase transformations in high Nb-containing TiAl alloys

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

“…Thus, both ORs calculated from the transformation matrices are the same as the results obtained by edge-to-edge matching calculation in Ti-45Al-9Nb alloy [10]. According to the results, the selection of OR between the α 2 and ω o phases is essentially based on which ω o variant has good lattice matching with α 2 phase.…”

“…Second, Bystrzanowski et al observed that the applied stress could enhance the ω o precipitation and suggested that the ω o precipitation was directly transformed from the α 2 phase [20]. Furthermore, Song et al observed the direct α 2 to ω o phase transformation in Ti-45Al-9Nb alloy after aging at 900 • C [10]. Although these studies discussed the transformation process and orientation relationships (ORs) between the ω o and α 2 phases, few reports focused on the nucleation sites of the ω o phase and the preferential ORs between the ω o and α 2 phases.…”

“…According to the results, the selection of OR between the α 2 and ω o phases is essentially based on which ω o variant has good lattice matching with α 2 phase. It was reported that the misfit between the α 2 and ω o phases had a minimum value if ORI was formed [10]. Thus, it is believed that only one ω o variant nucleated at the α 2 boundary.…”

“…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]. 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].…”

“…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].…”