Intergranular penetration and embrittlement of solid nickel through bismuth vapour condensation at 700 degrees C

Grain boundary penetration of liquid bismuth in polycrystalline nickel is i nvestigated at 700 degreesC. The contact between the two metals is ensured by bismuth transport through vapour phase. The formation of a nanometre-thi ck Bi-rich layer on external surfaces of solid nickel is revealed by glow d ischarge optical spectroscopy. This layer is the consequence of Bi vapour c ondensation on nickel substrate at 700 degreesC. The liquid Bi/solid Ni con tact leads to grain boundary penetration of liquid bismuth in the form of a film of nanometric thickness as revealed by Auger electron spectroscopy. T he presence of these intergranular films causes strong room temperature bri ttleness of nickel, as shown by tensile and bending tests. The comparison w ith results due to the direct contact between solid nickel and bulk liquid bismuth-rich alloy indicates that in both cases intergranular penetration r ate and embrittlement are of the same magnitude. Based on these results, a concept of a new device for liquid metal embrittlement (LME) tests is outli ned. (C) 2001 Elsevier Science B.V All rights reserved.