Tailoring the deformation characteristics of commercial purity titanium through hot deformation of a martensitic microstructure

The control of microstructure, texture and deformation inhomogeneity is critical for the hot working of titanium alloys and to optimize their mechanical properties. Herein, a new approach to control the grain refinement, texture and deformation anisotropy of commercial purity titanium (CP-Ti) was established through hot working of a martensitic starting microstructure. The deformation characteristics of the martensitic CP-Ti were investigated through uniaxial hot compression testing at 800 degrees C and compared with the same alloy with an equiaxed starting microstructure. The associated microstructure, texture development and grain refinement mechanisms were elucidated using electron backscatter diffraction (EBSD) and flow behavior analysis. The equiaxed microstructure displayed a typical flow behaviour of metals undergoing continuous dynamic recrystallization (CDRX). This was accompanied by moderate grain refinement to -8.2 mu m and macroscopically non-uniform expansion of specimen. In comparison, the martensitic microstructure revealed a stress-strain curve of continuous softening beyond the peak strain. An enhanced grain refinement to -5 mu m was obtained also via CDRX in the form of kinking of laths and progressive lattice rotation without noticeable macroscopic deformation anisotropy. This distinct deformation behaviour was mainly attributed to the unique microstructure and texture formed through the martensitic transformation, which altered the activation of slip systems, grain refinement kinetics and texture development during hot deformation.