Mechanical characterization of cp-Ti produced by investment casting

Abstract

The influence of hot swaging (SW) and annealing treatment on microstructure and mechanical properties of commercially pure titanium produced by investment casting was evaluated. The as-cast samples showed a typical microstructure consisting of a variety of α-morphologies, while the hot swaged samples exhibited a kinked lamellar microstructure. Annealing at 500 °C did not significantly change this microstructure while annealing at 700 and 870 °C led to recrystallization and formation of equiaxed microstructures. The cast bars exhibited a typical hard α-layer in near-surface regions with a maximum depth and maximum hardness of 720 μm and HV 0.5 660, respectively. Due to SW, the tensile strength of the as-cast material drastically increased from 605 MPa to 895 MPa. Annealing at 500 °C decreased the tensile strength slightly from 895 to 865 MPa while annealing at 700 °C led to a further pronounced drop in tensile strength from 865 to 710 MPa. No additional decrease in tensile strength was noticed with increasing the annealing temperature from 700 to 870 °C. The true fracture strain of the as-cast and hot swaged samples was in the range of 0.05 to 0.12, while the annealed samples showed values in the range of 0.25 to 0.53. In addition, the as-cast and hot swaged samples revealed a brittle cleavage fracture surfaces. However, the annealed samples showed a transgranular ductile fracture with formation of dimples.