Microstructure evolution of CP titanium during deformation in KoBo process followed by cold rolling

Abstract Evolution of microstructure and texture of commercial purity (CP) titanium grade 2 during two-step deformation process was investigated in this work. Deformation technique utilized in first step of samples preparation was the KoBo type extrusion. In the second step, further deformation was performed by the cold rolling process in order to facilitate high level of grain refinement. After the first step of deformation microstructure of titanium sample consists of equiaxed grains with no internal structure, but with distinct distribution of grain sizes. Texture of KoBo extruded Ti sample is typical with 0001 basal planes oriented parallel to the extrusion direction. During the cold rolling microstructure is significantly refined. Some grains are elongated in the rolling direction, however most of the microstructure is occupied by fine grains with close to equiaxed shape. Almost 50% of the microstructure consists of highly refined fraction of grains with diameter below one micrometer. Analysis of microstructure suggest that refined grains are produced due to dynamic recrystallization that occurs both during KoBo and during subsequent cold rolling in the fine grained areas of KoBo extruded sample.