Investigation of Inhomogeneous Plastic Deformation Behavior of LDED TA15 Alloy Using In-Situ EBSD Tensile Technique

Abstract

Laser direct energy deposition (LDED) of titanium alloys often results in diverse grain structures, causing sequential or simultaneous deformation of multiple grains under dynamic loading. This microstructural diversity causes localized damage and deformation heterogeneity, leading to inconsistent mechanical properties and limiting the application of LDED TA15 titanium alloy in the aerospace industry. Real-time monitoring of these deformation mechanisms at the grain level is crucial for understanding the alloy's behavior. In this study, the grain deformation and texture evolution of LDED TA15 titanium alloy with a basketweave lamellar structure were examined using an in-situ SEM-EBSD tensile test conducted at 300°C. The results showed that the coarse grains accommodate more dislocations and exhibit lower deformation rates, while fine, thinner lamellar α grains fragment early due to geometrical constraints. Moreover, despite having a high Schmid factor (SF), coarse grains exhibited low intragranular misorientation at high deformation levels and maintained their morphology. Dislocations nucleated from low-angle boundaries, and the high dislocation density in neighboring grains caused boundary distortion. Microcracks formed along thin lamellar grain boundaries and prior α boundaries, eventually connecting and leading to fracture under increasing load.