Liquid metal embrittlement of aluminium single crystals by gallium

Abstract

Liquid gallium is known to cause liquid metal embrittlement (LME) of stressed polycrystalline aluminium, but reports of its effects on single crystal aluminium are contradictory. We have therefore carried out tensile tests at room tempeniture on orientated single crystals wetted with gallium over part of their surface. Liquid metal embrittlement was observed after plastic extensions of 15–35% and the specimens failed by the slow propagation of a cleavage-type crack at a velocity controlled by the extension rate of the test. Crack growth rates varied from 0.02 to 5 mm s⁻¹ as the extension rates increased from 0.05 to 50 mm min⁻¹. Fracture surface energies were ∼ 10 kJ m⁻², consistent with the large plastic extensions before failure and also with the large amounts of ductile shear seen on the fracture face. Both the fracture surface energy and also the crack nucleation stress increased with extension rate. The crack growth direction showed a very strong preference for the {100} planes even when large misorientations existed between the tensile and crystallographic axes.