Study of the Quenched Defects in TiAl Alloy by Positron Annihilation

Abstract

The recovery behavior of quenched‐in defects in TiAl alloys was studied by positron annihilation lifetime measurements. The results indicate that there is a certain number of grain boundaries in fully annealed TiAl samples, and after being quenched, the samples contain quite a lot of secondary defects such as vacancy clusters besides a large amount of mono‐vacancies. The vacancy clusters aggregate further in the temperature range from 300 to 600 °C due to the impurity atoms.

Configuration and the recovery of defects in TiAl intermetallic compounds studied by positron annihilation

“…The first component, s 1 , of three samples approximates the reported lifetime of 150 AE 5 ps in perfect lattice [6,13,14], and represents the annihilation in bulk alloys. The second component, s 2 , of the three alloys was much larger than the lifetime of 230 ps for annihilation in a single-vacancy [6], indicating positrons trapped by some grain boundaries [15] or both boundaries and vacancies. It was estimated through X-ray diffraction that fully annealed samples appeared as uniform g-phase polycrystals before irradiation.…”

“…However, above 800 K, s 2 and I 2 remained at about 350 ps and 10%, respectively, which is much higher compared to lifetime for annihilation in grain boundaries [15]. It can be inferred that some microvoids were formed during annealing process by migration and congregation of vacancies, and they are difficult to be eliminated.…”