Effects of gaseous hydrogen and water vapor pressure on environmental embrittlement of Ni < inf> 3 Al

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Tensile ductilities of undoped and boron-doped Ni3Al have been determined under H2 and H2O pressures in the range of 10-3 ∼ 103 Pa. In agreement with other studies, boron-doped Ni3Al was found to be insensitive to water vapor, while undoped Ni3Al is severely embrittled by water vapor at pressures greater than about 10-3 Pa. This observation is consistent with previous conclusions that the ductilizing effect of boron additions in Ni3Al is at least partly due to its remedial effect on embrittlement by environmental water vapor. For undoped Ni3Al in H2 and H2O, and for boron-doped Ni3Al in H2, ductilities increased as the pressure of the embrittling gas was decreased. In each case, however, a critical gas pressure was observed, below which no further improvement in tensile ductility was observed. The limiting ductility of each alloy at very low pressures (i.e., under ultrahigh vacuum) is taken to represent the intrinsic ductility of the alloy. Comparison of intrinsic ductilities for boron-doped and undoped Ni3Al indicates that boron additions also exert an intrinsically ductilizing effect, independent of the remedial effect associated with embrittlement by environmental water vapor. © 1997 Elsevier Science Limited.

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