Issue 50

L. Romanin et al., Frattura ed Integrità Strutturale, 50 (2019) 251-263; DOI: 10.3221/IGF-ESIS.50.21 261 Little differences in cooling rates could be attributed to the presence of transport phenomena in the molten region that increase the heat loss and that cannot be taken into account in the phenomenological approach. Another reason could be found in the non-linearity of the emissivity coefficient that is not included for sake of simplicity in the present model. Irradiation is the primary heat transfer phenomenon at high temperature because EBW is performed in vacuum. A higher emissivity coefficient at high temperature could justify the steeper cooling rate. From the work of Palmer et al. [22] it seems more plausible that neglecting convective heat transfer in FZ is the cause of the small discrepancies in Fig. 14. Therefore, the thermal conductivity should be adjusted for temperatures that are higher than the melting temperature. Figure 13: Top view (a) of the calculated thermal field. Cross sections (b). Figure 14: Comparison between numerical and experimental the temperature histories at different distance from the weld line: 6 mm (a), 2.5 mm (b). C ONCLUSIONS metallurgical and thermal study of Inconel 625 electron-beam welded joints was carried out. The welding parameters were first optimized in order to obtain a sound weld. The EBW didn’t promote a grain grow in HAZ. Microhardness profiles didn’t show any depression that may suggest a significant reduction in mechanical properties compared to that of the parent metal. Small traces of Leaves phases were detected in FZ that are thought not to affect the structural integrity of the joint. Finally, a thermal numerical model of the EBW process was developed. In order to reproduce the correct FZ shape, two different power density distribution functions have been superimposed. A A (a) (b) T (°C)