Strain rate effect on moisture and hydrogen-induced environmental embrittlement of Ni < inf> 3 Al with and without boron

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At slow strain rates, boron-free Ni3Al was embrittled in both moist Ar and mixture of Ar + 5% H2. In contrast to this, boron-doped Ni3Al was not embrittled in moist Ar, but susceptible to embrittlement in mixture of Ar + 5% H2. These results indicate that while the addition of boron virtually eliminates embrittlement of Ni3Al due to water vapor, it does not eliminate embrittlement due to gaseous hydrogen. This different behavior of the boron-doped Ni3Al tends to suggest that the beneficial role of boron segregation in suppressing moisture-induced embrittlement may be associated with its effect on the interaction between water vapor and the intergranular crack surface, rather than on hydrogen transport along grain boundaries. The environmental component of the embrittlement was greatly diminished at higher strain rates. The increased tensile ductilities of boron-doped Ni3Al as compared to those of boron-free Ni3Al at the higher strain rates then can be interpreted to be due to an intrinsically beneficial boron effect. This suggests that the role of boron in ductilizing Ni3Al is at least two-fold: (1) it acts partly to limit the embrittling effects of water vapor, and (2) it strengthens the boundaries sufficiently to eliminate intergranular failure, but the latter effect seems to be large. © 1995.

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Scripta Metallurgica et Materiala