Effect of Bimodal Grain Structure on the Yielding Behavior of Commercial Purity Titanium Under Quasi-static Tension

In this work, a bimodal grain structure was developed for commercial purity Ti(CP-Ti) via powder metallurgy processing, followed by free hot forging and then heat treatment. The bi-modal grains were characterized with electron backscatter diffraction. The mechanical tests showed that in comparison to the uniform and equiaxed grain structure, the bimodal grains improved the yield strength of CP-Ti significantly, while it maintains a merely changed ultimate tensile strength and elongation to failure. In addition, an interesting yield plateau was observed in the bimodal CP-Ti. To explore underlying mechanisms behind the phenomenon, the microstructures of the samples before and after testing were carefully examined. The results revealed that geometrically necessary dislocations accumulating at the interface between coarse and fine grains induced back stress hardening, which together with the statistically stored dislocations also accounted for the yield plateau in the bimodal CP-Ti. Graphical abstract: [Figure not available: see fulltext.].