PSI - Issue 68

Yuki Tampa et al. / Procedia Structural Integrity 68 (2025) 681–686 Y. Tampa et al. / Structural Integrity Procedia 00 (2025) 000–000

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tests were carried out at an initial strain rate of 2.0 × 10 –3 s –1 and 1.33 × 10 –3 s –1 for the micrometer - and millimeter -scale specimens, respectively.

3. Results and Discussion 3.1. Stress–strain curves and slip behaviour of single-crystalline specimens

Figure 3 shows the nominal stress–nominal strain curves obtained for single-crystalline specimens of FC-O, FCV-O and FCV D. The FC-O specimen exhibited significant strain hardening after the onset of yielding at ~270 MPa, and then fractured after plastic instability at the ultimate tensile stress of ~915 MPa. The FCV-O specimen exhibited moderate strain hardening after the onset of yielding at ~450 MPa, and the final fracture occurred after plastic instability at the ultimate tensile stress of ~720 MPa. In contrast, the FCV-D specimen, a sudden stress drop occurred after the onset of yielding at ~590 MPa, and then the flow stress was decreased to half the tensile strength of the FCV-O specimen. Figure 4 shows the deformation morphology showing the lateral views of micro single-crystalline specimens after failure. In FC-O and FCV-O, specimen bending occurred under uniaxial tensile loading conditions (Figs. 4a and 4b). This may be associated with shear banding due to the activation of {101}< 11 1> and {001}<0 1 0> slips. For the FCV-D specimen, yielding occurred by slip localisation at the specimen shoulder region. The localised slip bands contained wavy slip lines (Fig. 4c). This presumably caused the sudden stress drop and the reduced flow stress (Fig. 3) through short-range order hardening followed by cross-slipping with the common [ 1 11] slip direction.

Fig. 3 Nominal stress–nominal strain curves obtained for micro single-crystalline specimens.

Fig. 4 SEM images showing the lateral views of micro single-crystalline specimens after failure.