High-temperature deformation and grain-boundary characteristics of titanium alloys with an equiaxed microstructure

The high-temperature deformation behavior of single-phase α (Ti–7.0Al–1.5V), near-α (Ti–6.85Al–1.6V), and two-phase (Ti–6Al–4V) titanium alloys with an equiaxed microstructure was examined, and the results were compared within the framework of an internal-variable theory of inelastic deformation. For this purpose, load-relaxation and tension tests were conducted at various temperatures. Stress–strain-rate curves obtained by load-relaxation tests for the three alloys were well described by the equations for grain-matrix deformation and grain-boundary sliding. With respect to boundary strength, the internal-strength parameter (σ*) for α–α boundaries was found to be ∼2 times higher than that for α–β boundaries. The friction stress parameter (Σg) of boundaries was the highest in the single-phase α alloy and the lowest in the two-phase (α + β) alloy. This indicates that grain-boundary sliding occurs preferentially at α–β interfaces rather than at α–α boundaries.