THE EFFECT OF PRE-DEFORMATION ON MOISTURE-INDUCED EMBRITTLEMENT OF NI3AL ALLOYS

The effect of pre-deformation on moisture-induced embrittlement of Ni3 Al alloys (doped with boron) is investigated by tensile test and SEM f ractography. The pre-deformation is done in environmental conditions w here entry of hydrogen is inhibited, and re-deformation is done in air at room temperature. As the predeformation increases, tensile elongat ion of the Ni3Al alloy increases. As the pre-deformation temperature d ecreases from 473 to 77 K, tensile elongation of the Ni3Al alloy incre ases. As annealing temperature preceded by the pre-deformation decreas es, tensile elongation of the Ni3Al alloy increases. Corresponding to this increase of tensile elongation, the fracture mode of re-deformed Ni3Al alloy changes from intergranular to transgranular fracture. It i s suggested that reduction of the moisture-induced embrittlement by th e pre-deformation is due to scavenging (trapping) of hydrogen atoms to dislocations (or vacancies), or, to an increase of soluble hydrogen i n lattices. Consequently, hydrogen reaching grain boundaries can be re duced to a level below a critical content causing intergranular fractu re, resulting in a suppression effect of the moisture-induced embrittl ement of the Ni3Al alloys. (C) 1997 Elsevier Science Limited.