The effect of initial grain size on the mechanical properties and deformability of titanium alloy in a direct extrusion process

This study determines the effect of grain size on the mechanical properties and the deformability of titanium bar in a direct extrusion process. The specimen of commercially pure grade 2 (CP2) with a diameter of 5 mm is annealed at various temperatures, to obtain different grain sizes, and extruded with die angles of 5, 10 and 15°. The results show that the initial grain size of α-phase microstructure is in the range of 59.7 to 122.1. The strength coefficient, yielding stress and hardness of the annealed specimen with an α-phase microstructure decreases as the grain size increases. β-phase microstructure forms when the annealing temperature exceeds 800°C, which leads to a reduction in the ductility and extrusion deformability, but an increase in the hardness. The grain evolution sequences are coarse columnar, thin columnar and refined grain. The initial grain size has no significant effect on extrusion force. The hardness of the refined grains is close to that of the initial grains.