| Summary: | Titanium (Grade 2) was processed by cryogenic milling and subsequently sintered by spark plasma sintering (SPS) method with the aim of creating and preserving the ultra-fine grained (UFG, < 1 μm) microstructure. Microstructural investigation was performed after both cryogenic milling and spark plasma sintering. An advanced technique of transmission Kikuchi diffraction (TKD) was used to characterize the individual milled powder particles.
Investigations of milled powders showed significant grain refinement down to 50 nm after milling in liquid argon with tungsten carbide balls. We assume that this is the equilibrium grain size resulting from the balance of deformation, recovery and dynamic recrystallization. A texture, resembling the rolling texture in Ti, was also found in the milled particles, which can be explained by the nature of deformation during milling.
UFG microstructure was not maintained after sintering, with the mean grain size of 2.6 μm. Although the grains are completely recrystallized, a texture, similar to the powder texture, was also found in these samples as a result of packing of the powder particles and the nature of the recrystallization process (continuous static recrystallization).
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