Abstract
The dissolution and reprecipitation behaviors of ωo phase during isothermal annealing and ensuing re-aging at 700–800°C are investigated on an as-cast high Nb containing TiAl alloy with nominal composition of Ti–45Al–8.5Nb–0.2W–0.2B–0.02Y (at.%). The microstructural characterization revealed that numerous micron-sized ωo particles exist within the ordered βo phase in the as-cast alloy. These ωo particles have high thermal stability when annealing at 800°C and 850°C for 100h. Increasing the temperature to 900°C, the ωo particles began to decompose into βo phase with a low transformation rate. Further increasing temperature causes accelerated dissolution kinetics of ωo phase. Ensuing re-aging at 700°C and subsequent quenching lead to the reprecipitation of nano-sized ωo particles accompanied by extremely fine γ plates. When the aging temperature increases to 800°C, the micron-sized ωo particles precipitate from βo phase accompanied by coarsened γ plates. Possible mechanism of the reprecipitation behavior of ωo phase is discussed.
Published Version
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