Issue 42

A. Strafella et alii, Frattura ed Integrità Strutturale, 42 (2017) 352-365; DOI: 10.3221/IGF-ESIS.42.36 363 a) b) c) d) Figure 14 : SEM micrographs: a) fracture surface at low magnification; b) portion of surface showing a dominant ductile fracture mode; c) portion of surface showing both transgranular and ductile fraction; d) deformation bands: elongated dimples on fracture surface. a) b) Figure 15: SEM micrographs after Pb creep: fracture surface a) before and b) after chemical polishing. The comparison between the specimen tested in air and in lead revealed a different fracture mode: mixed cup- cone/transgranular for creep test in air, while intergranular for creep test in lead. This difference is ascribable to the effect of lead embrittlement: the transition from mixed fracture mode, ductile/transgranular, which takes place in air, to fully brittle/intergranular mode, in lead, is consistent with the definition of LME (stated in paragraph 3.2) and with the creep phenomena in liquid metal, as described in other scientific works. According to Hough and Rolls (1971)[12], phenomena associated with creep rupture in liquid metal can include: