The role of microstructural stability on compression creep of fully lamellar γ-TiAl alloys

Microstructural instability and embrittlement behaviour of an Al-lean, high-Nb γ-TiAl-based alloy subjected to a long-term thermal exposure in air

“…Increasing evidence has indicated that the retained b phase in highly alloyed TiAl alloys has always been observed as an ordered B2 structure and readily decomposes to an ordered u phase [9,13,23,24,[28][29][30] at room temperature, resulting in the co-existence of the two ordered phases. Segregation of a 2 lamellae is also susceptible to change when subjected to high temperature in air for long periods [31][32][33]. Therefore, a detailed investigation into the changes in microstructure is necessary before these alloys can be used.…”

Thermal stability and precipitation strengthening of fully lamellar Ti-45Al-5Nb-0.2B-0.75C alloy

“…The drop in the α 2 volume fraction during ageing of fully lamellar TiAl alloys is well documented [32][33][34], and it can easily be explained by the fact that a fine lamellar structure with a large α 2 volume fraction is stoichiometrically far from the equilibrium and therefore is not stable during the thermal exposure. The retention of the metastable α 2 before ageing provides a large driving force for its dissolution [32].…”

“…The drop in the α 2 volume fraction during ageing of fully lamellar TiAl alloys is well documented [32][33][34], and it can easily be explained by the fact that a fine lamellar structure with a large α 2 volume fraction is stoichiometrically far from the equilibrium and therefore is not stable during the thermal exposure. The retention of the metastable α 2 before ageing provides a large driving force for its dissolution [32]. The drop in α 2 -phase content is, however, much lower than was reported by Karthikeyan and Mills [32], who reported a decrease of α 2 content in fully lamellar K5 (Ti-46Al-2Cr-3Nb--0.2W) and K5SC (Ti-46Al-2Cr-3Nb-0.2W-0.1C-0.1Si) alloys from 22 and 29 vol.% before exposure to 7.2 and 8 vol.% after exposure at 900…”

“…The retention of the metastable α 2 before ageing provides a large driving force for its dissolution [32]. The drop in α 2 -phase content is, however, much lower than was reported by Karthikeyan and Mills [32], who reported a decrease of α 2 content in fully lamellar K5 (Ti-46Al-2Cr-3Nb--0.2W) and K5SC (Ti-46Al-2Cr-3Nb-0.2W-0.1C-0.1Si) alloys from 22 and 29 vol.% before exposure to 7.2 and 8 vol.% after exposure at 900…”

Reaction procedure of a graphite fiber reinforced Ti-Al composite produced by squeeze casting-in situ reaction

“…However, the major limitation in more widespread usage of TiAl 3 is its low ductility and toughness at room temperature [5]. Recently, many attempts, such as chemical modification [6], microstructure controlling [7], and reinforcement by particulates [8] and continuous fibers [9][10], have been made to overcome these disadvantages.…”