The recovery behaviour of deformed Ni-Cr-Co superalloys, the effect of boron on vacancy-like defects of Ni_3Al alloy, the interaction between hydrogen and defects in polycrystall Ni_3Al alloy have been studied by positron annihilation technique and transmission electron microscopy. Two recovery stages of annealing are found in deformed Ni-Cr-Co superalloy. The first recovery stage is due to vacancy moving, the second stage is attributed to dislocation motion and recrystallization. The beginning recrystallization temperature of Ni-Cr-Co superalloy is about 500 ℃. Under the same reduction, the less the Co Content in the alloy is, the more the defects are. In the recovery process, the dislocation in lower Co content alloy recover faster than of in higher Co content alloy. The apparent activation energy of recrystallization of the alloy increases with Co content. The openning space of the grain boundary is larger than that of the dislocation and vacancy in polycrystall Ni_3Al Alloy. When boron atoms are added to single crystal and polycrystall Ni_3Al alloy, some of them are solid solutioned in the crystal lattice of Ni_3Al in a manner of occupying interstitial sites, and the others are resided in vacancy like defects. The content of boron in the Ni_3Al alloy reaching 1.37at% may be a saturation point for filling to defects. Further increasing the content of boron can produce more defects. In polycrystall Ni_3Al alloy, boron atoms tend to segregate strongly to grain boundaries. When boron content reaching 1.37at%, the boundaries are filled by boron atoms, the strengthening effect by grain boundary is largest. If boron addition is too high, there are boride eutectie pricipitating in grains and at grain boundaries, the larger open-space defects appear, and the grain boundaries become weak. With the increasing of hydrogen in polycrystall Ni_3Al alloy with different boron content, its behaviour can be concluded to two obvious stages: the first stage is the effect of hydrogen atoms filling in the vacancy-like defects, the second stage is hydrogen producing defects. The ability to trap positrons of the defects which have been filled with boron atoms become feeble. Boron atoms segreting to grain boundaries can inhibit hydrogen atoms gathering to the grain boundaries. Suitable boron atoms obviously increase the cohesion of grain boundaries, resist the crack propagration and enhance the anti-hydrogen ability of polycrystall Ni_3Al alloy.
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