Friction-induced structural modifications of Mg and Ti surfaces

High-purity magnesium and titanium have been examined in order to study modifications to the near-surface layer during friction. Upsetting tests were conducted under atmospheric and imposed hydrostatic pressure to assess the plasticity and deformability of these metals. It is shown that the deformability of magnesium and to a lesser extent that of titanium can be considerably enhanced by superimposed hydrostatic pressure. Both metals were subjected to uniaxial, constant load, dry friction, pin-on-plate tests in air at room temperature and atmospheric pressure and the near-surface layer examined destructively and non-destructively in order to characterize induced changes. High-resolution X-ray diffraction examination of the worn and unworn surfaces suggested that the deformability of the near-surface layer in magnesium is associated with an increase in 〈a〉 Burgers vector screw dislocations able to cross slip and which contribute to recovery and recrystallization in the deformed region. A similar effect may be present for titanium although no recrystallization was observed.