Investigation of formability of commercially pure titanium in equal channel angular pressing process

Grain size refining down to sub-micrometer range using severe plastic deformation methods is known as an effective strengthening mechanism in metals and alloys. However, metals with low formability such as titanium are subjected to cracking and fracture when they are severely deformed. As a result, attempts to impose intense plastic strain to them which is essential for grain refinement are generally not successful. In the present study commercially pure titanium was severely deformed by equal channel angular pressing. In order to enhance the formability, a larger channel of 105˚ was selected instead of common angle of 90˚and the effect ECAP temperature (300, 250, and 200 ˚C), pressing speed (10, 1, 0.1, 0.01 mm/s), and the initial microstructure on the formability of titanium was investigated. The results indicate that by lowering the pressing speed the formability is improved. Also, the use of a larger channel angle provides the possibility of reducing the processing temperature by 150 ˚C compared to previous researches, such that the titanium bars were processed at a temperature of 250 ˚C safely and without cracking up to 10 passes. Moreover, it was seen that the initial equiaxed microstructure shows much better formability than lamellar one. Light microscopy observations of the microstructure of the processed bars indicate that cracks nucleate and grow from the regions in which the material experienced higher amounts of strain.