PSI - Issue 41

Danilo D’Andrea et al. / Procedia Structural Integrity 41 (2022) 199–207 D’Andrea et al./ Structural Integrity Procedia 00 (2019) 000–000

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under stress control, adopting a stress rate equal to 3 MPa/s, with a servo-hydraulic loading machine MTS 810 with a maximum load capacity of 250 kN (Fig. 2). The stress rate must be adopted in order to assure adiabatic conditions during the tensile tests, i.e. the specimen must not have the time to exchange heat with the surrounding environment. During the tests, the specimen surface temperature was monitored with an infrared camera FLIR A40, recording the temperature evolution every second. The maximum value of a rectangular area placed on the specimen was recorded and post processed with a rlowess filter, with a data span of 5%, to exclude outliers and enhance the linear trend.

Fig. 2. AISI 316L specimens and IR test setup.

A failure analysis was performed to characterize the microstructure of stainless steel AISI316L, and to correlate it with the differences in mechanical behaviour between the specimens obtained for AM and traditional ones. The failure analysis has been carried out through the use of an optical microscope (OM), a scanning electronic microscope (SEM) equipped with an EDS probe. The optical microscopy was carried out by means of a LEICA stereomicroscope (LEICA Microsystems GmbH, Germany), while the scanning electron microscopy was carried out using FEI Quanta 450 FEG (Thermo Fisher Scientific, Waltham, Massachusetts, US), operating at 20.00 kV in High Vacuum. In addition, XRD tests were performed to compare the crystalline characteristics of the alloys. In order to compare the composition of the AISI316L alloy of the two types of specimens, an XRF analysis was performed as shown in Table 1.

Table 1. AISI 316L composition (in wt%)

AISI 316L Traditional

Mn

Cr

Mo

Ni

Cu

Fe

1.73 1.81

16.68 16.99

1.98 2.57

10.22 12.83

0.37

68.6 63.9

AM

0.037

4. Results and Discussions 4.1. Static tensile test

Static tensile tests have been performed under stress control to assure adiabatic conditions and the superficial temperature has been monitored with an infrared camera. The applied stress level, evaluated as the ratio between the current force and the nominal cross section area, has been reported vs. time and specimen superficial temperature