Abstract: Hydrogen-induced cracking (HIC) of two-phase alloy of Ni3Al+NiAl was in situ investigated using a WOL (wedge opening-loading) constant deflection specimen in an optical microscopy and using a notched tensile specimen in scanning electron microscopy (SEM). Results showed that the threshold stress intensity of HIC was KIH=15.7 MPa·m1/2, and (da/dt)II=0.019 mm/h. For the uncharged specimen, microcrack initiated and propagated preferentially within the NiAl phase, resulting in cleavage fracture, but for the precharged specimen with hydrogen concentration of 24.7×10-4%, hydrogen-induced crack initiated and propagated preferentially along the Ni3Al/NiAl interfaces, resulting in interphase fracture.

Key words: Ni3Al+NiAl, HIC, In situ extending, SEM