Sl. Semiatin et Pr. Smith, MICROSTRUCTURAL EVOLUTION DURING ROLLING OF TI-22AL-23NB SHEET, Materials science & engineering. A, Structural materials: properties, microstructure and processing, 202(1-2), 1995, pp. 26-35
The evolution of microstructure during hot pack rolling of the orthorh
ombic titanium aluminide alloy Ti-22Al-23Nb was investigated. The star
ting material was a prior hot-rolled sheet with an elongated ordered b
eta (B2) grain structure whose grain boundaries were decorated with or
thorhombic (O) phase. Two different types of rolling schedule were uti
lized, one consisting of rolling below the beta (B2) transus alone and
the other comprising supertransus preheating (in order to dissolve th
e second phase) followed by rolling through the transus under decreasi
ng temperature conditions. For both schedules, the rolled structure co
nsisted of elongated beta (B2) grains and a fine dispersion of second-
phase (O) particles. The absence of recrystallization of the B2 grains
, particularly for sequences involving supertransus preheating, was ex
plained by measurement of the precipitation kinetics for the second ph
ase. These measurements indicated very rapid grain boundary precipitat
ion, even close to the transus, an effect that leads to the pinning of
the beta (B2) grain boundaries.