Observation of {110} cleavage in ⟨110⟩ axis tungsten single crystals

Tungsten is usually considered to cleave on the {100} plane although several theoretical calculations predict a lower surface energy for the {110} plane. It is shown that {110} clearvage can be produced in ⟨110⟩ axis single crystals of tungsten. A single experimental value obtained for the {110} plane implies that the surface energy of this plane is lower than that of the {100} plane. It is noted that relative values of surface energy do not alone dictate the cleavage plane in the completely brittle fracture of a single crystal. The direction of applied stress must also be considered.