November passed quite quickly and almost unnoticeable while I was busy shopping for books and titanium. Also the atmospheric conditions wasn’t making any clues of time passing by, maintaining the impression that we are stuck in late summer rather than falling straight into the jaws of winter. However amidst raging summer and shopping frenzy I managed to read through another portion of literature, paving my way into the temple of PhD grade knowledge.
My literature research remains focused on the field of titanium grain refinement by means of plastic deformation methods. While method of equal channel angular pressing (ECAP) is highly developed and described and also can produce satisfying results when combined with other methods of deformation (ex. cold rolling) it exhibits some disadvantages, especially with titanium when substantial grain refinement is desirable. First, titanium has to be heated in order to be plastically deformed in ECAP. Heating of metal during deformation increases recrystallization rates and thus limits maximum grain refinement level. Second, by introduction of large amounts of dislocations and internal stress ECAP makes it difficult to obtain sufficient crystallographic data with good spatial resolution in order to quantitatively characterize nanostructured material.
KOBO method (named after inventors: Korbel, Bochniak) resolves some of that problems by change of deformation mode into heterogeneous plastic flow. Change of deformation mode is performed by cyclic change of deformation path (for instance by cyclically reversible plastic twisting ), which leads to destabilization of the structure, and organized dislocation motion. The structure of material is refined by propagating of coarse slip bands and creation of transgranular shear bands. In process no increase of internal stress or dislocation density is produced.
There is no literature regarding titanium processed by KOBO method at the moment and performing such procedure involving this metal might indeed produce some interesting results.