Influence of β Grain Orientation on the Stress-Induced Martensite Formation in Cold-Rolled Metastable β Ti-5Mo-5V-5Al-3Cr Alloy

Solution-treated metastable beta Ti-5Mo-5V-5Al-3Cr (Ti 5553) alloy processed through cold rolling at strain levels of 5-45% results in stress-induced martensitic transformations (SIMT). Further, the cold-deformed sample is annealed at 860 degrees C for 5 min to achieve recrystallization and relieve internal stresses. The influence of recrystallized beta grain orientations on Ti-5553 deformation behavior is characterized using nanoindentation tests. As beta grain orientation changes from near <111> to <001> direction, the alloy exhibits an increase in hardness (from approximate to 6.3 to approximate to 6.6 GPa) and a decrease in elastic modulus (from approximate to 127 to approximate to 120 GPa). It can be inferred that a threshold stress is necessary to activate SIMT in each orientation due to the stress gradient from the top surface to the indent tip at a certain penetration depth in the sample. Additionally, the influence of alloying elements (e.g., Mo, V, Al, and Cr) on beta phase stability as a function of grain orientations is confirmed using the electron probe microanalyzer. Observations indicate that <111> grain orientation is most preferred, followed by <101> for promoting stress-induced martensite, while <001> is least preferred.