Hydrogen embrittlement of pseudobinary l1₂-type Ni₃(Alo.₄Mno.6) intermetallic compound

The mechanical properties of the Ll₂-type intermetallic compound Ni₂(Al_0.4,Mn_0.6), which exhibited enough deformability accompanied with the positive temperature dependence of yield stress, were examined from the point of view of its susceptibility to hydrogen embrittlement. Remarkable and moderate increases of elongation and ultimate tensile strength were observed by evacuating and with increasing strain rate, respectively, although the yield stress was almost constant independent of not only testing environment but also strain rate. On the other hand, the cathodically precharged hydrogen showed deteriorated elongations while the baking treatment resulted in restoration of elongation. Fractographic observation revealed the expected correlation between elongation and fracture mode; with increasing elongation the transgranularly fractured region increased. From this result, it is suggested that hydrogen can be removed from the specimen interior by evacuating or baking, and also that hydrogen can be injected from the sample surface by hydrogen charging; that is to say, hydrogen permeation is almost reversible for both processes. It is thus concluded that the present alloy has severe hydrogen embrittlement susceptibility, both from the residual hydrogen in the specimens as well as from that penetrated from the environment.