Thermomechanical treatments and surface treatments to enhance the mechanical properties and fatigue performance of recycled cp-Ti

Recycled commercially pure Ti having different Fe and O contents was rotary swaged at 700 degrees C in order to break down the coarse as-cast microstructures. After swaging, materials were annealed at various temperatures to study potential coarsening of the recrystallized alpha-grains. While marked grain growth occurred in material A with low Fe and O contents after annealing for 1 hour at temperatures as low as 500 degrees C, the grain size in material B with higher Fe and O contents hardly increased even after a 1 hour exposure at temperatures as high as 800 degrees C. Yield stress, tensile strengformatth and high cycle fatigue strength in both as-cast and annealed conditions of material B were significantly higher than in the corresponding conditions of material A, presumably owing to more marked solid solution hardening and fine grain size strengthening of material B. In addition, precipitation hardening by fine Fe containing oxide particles may also contribute to the higher strength level of material B. Shot peening and roller-burnishing were found to drastically enhance the high cycle fatigue strengths relative to the electrolytically polished baseline conditions.