The role of plastic deformation in liquid metal embrittlement

AbstractTensile and four-point bend tests on specimens of polycrystalline copper – 8 wt% aluminum coated with mercury have shown that plastic deformation is a necessary precursor to intergranular fracture. The existence of long cracks associated with unfailed notches indicates that a period of stable crack growth precedes failure. X-ray line broadening and microhardness measurements indicate considerable plastic deformation in the region of the fracture path and an effective surface energy of 109 ergs/cm2 is estimated. It is suggested that there is no critical applied stress criterion for this type of fracture, but that decohesion is due to the creation of a localized condition of instability at the crack tip from the creation of dislocation pile-ups against the grain boundary just ahead of the crack and the weakening of cohesive bonds in this area by the penetration of liquid metal atoms into it. Resume Des essais de traction et de flexion entre 4 points sur du cuivre polycristallin contenant 8% poids d'...