The cathodic charging of hydrogen into polycrystalline Ni3Al alloys with B contents from 0.00 to 2.22at% was studied by measurements of the positron lifetime spectra. Hydrogen-filling effects and hydrogen-harmful effects were found in all testing alloys. Hydrogen effects were weak in Ni3Al with 0.52at%B and Ni3Al with 1.37at%B compared with that in B free Ni3Al and Ni3Al with 2.22at%B. This indicated that suitable B atoms segregating to the grain boundary could strengthen the bond cohesion in the grain boundary, as well as counteract hydrogen entering there, and then suppressed both the hydrogen-filling effects and hydrogen-harmful effects in Ni3Al alloys. When B added up to 2.22at%, more defects were induced by boride eutectics forming in the bulk and grain boundary, and the metallic bond cohesion were decreased in those locations. This led to enhancement of both the hydrogen-filling and the hydrogen-harmful effects in Ni3Al with 2.22at%B.

Interaction of Hydrogen and Boron with Defects in Polycrystalline Ni3Al Alloys Investigated by the Positron Annihilation Technique. Deng, W., Xiong, L.Y., Lung, C.W., Wang, S.H., Guo, J.T.: Intermetallics, 1997, 5[4], 265–9