In Situ Electron Backscatter Diffraction Study of Deformation Inhomogeneity under Uniaxial Tension of Laser Melting Deposited TA15 Alloy

The discourse of the anisotropic mechanical properties of a unit-built additively manufactured component depends on its microstructural features and inhomogeneous distribution. This work explores the microstructure distribution and deformation inhomogeneity during uniaxial tension of a laser melting deposited TA15 near-α titanium alloy via advanced in situ secondary electron microscopy and electron backscattered diffraction characterization. Microscopically, two major regions can be distinguished in the overall microstructure, including a Widmanstätten (αw) region along the prior β-grain boundary (GB) and a basketweave-α region within the columnar grains. These two different microstructural regions responded differently under the same tensile load conditions. In the early deformation stage, only conventional slip occurred in the basketweave-α region, whereas microscale shear bandings developed in both the basketweave-α and α_w regions. As the deformation progressed, the strain was optimally accommodated by the basketweave-α region. Nevertheless, the largest strain accumulation occurred along the prior β-GB because of a high misorientation angle, which resulted in the formation of cracks. Subsequently, the growth and propagation of the cracks along the prior β-GB were relatively fast due to the weak obstruction caused by the low angle of misorientation in the α_w region, resulting in early fracture of the sample.