PSI - Issue 69

Diego Scaccabarozzi et al. / Procedia Structural Integrity 69 (2025) 80–88

82

120 65 30 ° < 20

Point distance, d p Laser spot size

Platform temperature

Oxygen level

Fig. 1. Schematic of the principal process parameters in the LPBF process: a) exposure time cycle, b) laser spot and related hatch and point distances.

Samples were oriented at a 45° angle relative to the building platform during fabrication. This orientation improved residual stress distribution and maximised the build volume efficiency. After the printing, the produced samples were subjected to two ageing treatments aimed at improving their functional properties. The treatments were carried out at 500 °C for 5 (T500-5’) and 10 minutes (T500-10’) in a muffle furnace, followed by water quenching. Martensitic Transformation Analysis The martensitic transformation was analysed using differential scanning calorimetry (DSC, model Q25 from TA Instruments, USA). Measurements were conducted on small samples (15-20 mg) with a heating/cooling rate of 10 °C/min, in a temperature range from -80°C to 100°C. Measurement method description The range for the acoustic excitation to vibrate the sample was numerically determined through a modal analysis in free conditions, conducted using commercial software. The material properties used in the simulation were density (6450 kg/m³), modulus of elasticity (44.1 GPa), and Poisson's ratio (0.30). These parameters were derived from testing of the manufactured samples by mechanical testing. Fig.2 shows the first mode of vibration and the theoretical position of the nodal lines. The location of these lines is critical for conducting the vibration tests since additional fictitious damping can be introduced in the measured frequency response function if the component is not vibrating on the nodal lines. Thus, the theoretical position of nodal lines was used as a reference to mount the samples on the testing setup.