Cyclic twinning in fatigued close-packed hexagonal metals

Abstract

A study has been made of the behaviour of {1012} ⟨011⟩ type deformation twins in fatigued cadmium, zinc, magnesium and titanium. Plastic deformation is accentuated at twin interfaces, which subsequently become serrated : the serrations are accommodated by closely spaced kink boundaries. Pre-existing twins are broken up into smaller irregularly shaped twin fragments and cracks are present at twin fragment interfaces after ∼ 25% of the life has elapsed. A model based on the pinning of twin boundaries by lattice defects explains qualitatively the effects observed.