PSI - Issue 52

Ivo Šulák et al. / Procedia Structural Integrity 52 (2024) 143–153 Author name / Structural Integrity Procedia 00 (2019) 000 – 000

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Fig. 9. a) Stress exponents for bulk and LPBF Alloy 400 at 650 °C; b) Activation energies for bulk Alloy 400 bulk crept at 125 MPa and LPBF Alloy 400 crept at 50 MPa. The strain rates are taken at the true strain of 2 %.

Fig.10. Creep curves for LPBF Alloy 400 at 30- 100 MPa and 650 °C.

The LPBF Alloy 400 has be en tested only at (650 ± 50) °C because the samples were available after the decision to follow on with lower temperatures. The tests followed the same pattern as for the bulk material – five tests at 650 °C for the stress exponent and two more at 600 °C and 700 °C for the activation energy. The creep curves for the LPBF Alloy 400 are shown in Fig. 10. The steady-state creep rates are in the range from 10⁻⁷ s⁻¹ and 10⁻⁵ s⁻¹, which are higher than for the bulk, and the applied stresses fall between 30 and 100 MPa. The time to fracture is shorter – from 82 minutes (100 MPa) to 170 hours (30 MPa). Also, the achieved true strain is somewhat smaller, from 3.3 % (100 MPa) to 10 % (30 MPa). The LPBF Alloy 400 thus shows significantly worse creep properties in comparison with the bulk material. The stress exponent for the LPBF Alloy 400 is n = 3.3 (Fig. 9a) which is considerably lower than for the bulk Alloy 400. In Fig. 11, the bulk and the LPBF Alloy 400 at 650 °C and 100 MPa are compared. Noticeable is also the achieved true strain, which is smaller for the LPBF Alloy 400 . The activation energy 292 kJ mol⁻¹ has been obtained from the tests at 50 MPa (Fig. 6) and is based on the strain rates at 2 % true strain.