A combined experimental-computational investigation was performed in the first part of this work to quantify the relationship between plastic strain and crystallographic misorientation. Several material characterization techniques including tensile testing, Scanning Electron Microscopy (SEM), Digital Image Correlation (DIC), and Electron Backscatter Diffraction (EBSD) were combined to study the correlation between plastic strain and crystallographic misorientation at the microscale for two... Show moreA combined experimental-computational investigation was performed in the first part of this work to quantify the relationship between plastic strain and crystallographic misorientation. Several material characterization techniques including tensile testing, Scanning Electron Microscopy (SEM), Digital Image Correlation (DIC), and Electron Backscatter Diffraction (EBSD) were combined to study the correlation between plastic strain and crystallographic misorientation at the microscale for two body-centered cubic (bcc) titanium (Ti) alloys, namely Ti-13Cr-1Fe-3Al (wt.%) and TIMETAL-21S [Ti 15Mo-3Nb-3Al-0.2Si (wt.%)]. The results revealed that larger grains experienced more misorientation dispersion compared to smaller grains. An empirical equation was proposed to estimate the crystallographic misorientation at the grain scale as a function of plastic strain and grain size. Furthermore, the effects of crystallographic orientation and loading history on the misorientation were investigated. It was observed that {100} oriented grains (with respect to the tensile axis) exhibited more of a tendency for orientation change than {110} and {111} oriented grains. Interrupted loading resulted in higher crystallographic misorientation than monotonic (uninterrupted) loading. A qualitative comparison between the DIC-SEM strain field map and the misorientation maps revealed that there is a better correlation between the hot spots in the KAM map and the DIC-SEM strain field map compares with the correlation between the hot spots in the MD maps and the DIC-SEM stain field map. Some of the metrics, developed in the misorientation analysis, were implemented by EDAX-TSL, Inc. (Mahwah, NJ) in their latest orientation imaging microscopy (OIM) commercial software. Slip trace analysis was performed to characterize the distribution of the plastic deformation modes at RT, 200 ̊C, and 300 ̊C on three bcc Ti alloys: Ti-13Cr-1Fe-3Al (wt.%), TIMETAL-21S, and Ti-29Nb-13Ta-4.6Zr-xO (wt.%), where x is 0.1, 0.3, and 0.7 (wt.%). The results revealed that dislocation slip was the dominant plastic deformation mechanism for Ti-13Cr-1Fe-3Al (wt.%), TIMETAL-21S, Ti-29Nb-13Ta-4.6Zr-0.3O (wt.%), and Ti-29Nb-13Ta-4.6Zr-0.7O (wt.%). The {123}<111> slip systems exhibited the highest contribution, while the {110}<111> showed the least contribution of the observed traces. However, the normalized slip activity (according to the possible slip planes of each system) suggested that the activity of all the systems were relatively equal for the TCFA, while the activity of the {110}<111> was slightly greater than other two slip systems for the TIMETAL-21S. Three deformation mechanisms, i.e., stress-induced martensitic (SIM) transformation (β phase to α” phase), the {332}<113> mechanical twinning, and the slip activity activated and cooperated for the Ti-29Nb-13Ta-4.6Zr-0.1O (wt.%). In the second part of this work, the room temperature (RT) and elevated temperature strength of a low-cost Ti alloy were enhanced through thermomechanical processing (TMP). In-situ and ex-situ TMP treatments were systematically designed and conducted to increase the strength of a low-cost bcc Ti alloy. By performing heat treatments in the range of 300 ̊C to 600 ̊C, it was found that nanoscale and microscale precipitates formed in the bcc matrix, which led to enhance the strength. With an applied mechanical load, the phase transformation process was accelerated. The resulting mechanical properties depended on the type and duration of the TMP treatments. The maximum tensile strength of Ti-13Cr-1Fe-3Al (wt.%) reached approximately 1500 MPa at 410 ̊C. The TMP and alloy composition range was patented internationally. Show less
