PSI - Issue 7

Gianni Nicoletto et al. / Procedia Structural Integrity 7 (2017) 133–140 Gianni Nicoletto/ Structural Integrity Procedia 00 (2017) 000–000

136

4

3. Results 3.1. Microstructures

Microstructures after heat treatment were investigated using metallographic methods and presented in Fig.3. The microstructures shown in Fig. 3 are characterized by a lighter alpha phase and darker beta phase. In HT1 and HT2 samples the laser scanning path is visible even after the heat treatment, while in the other two samples this particular feature is not observed.

Fig. 3 Microstructures of SLM Ti6Al4V after the four post fabrication heat treatments a) HT1, b) HT2, c) HT3, d) HT4

The characteristic α lamellar morphology can be identified in almost the whole section of HT1 and HT2 specimens, (see Fig. 3a and 3b). In particular, islands of fine martensitic grains are identifiable in a complex structural network, which is defined “Widmanstӓtten structure ”, see Vranken et (2012). HT3 specimen of Fig. 3c shows a remarkable grain coarsening due to the high temperature it has been subjected to during the heat treatment. The α” lamellar microstructure(see Morri) can also be observed in this metallographic section. Finally, HT4 sample of Fig. 3d is characterized by a homogeneous α microstructure, in which lamellar grains are slightly coarsened and shorter in size if compared to the ones obtained after HT1 and HT2.The cooling rate is the most important parameter that determines the phases and the morphology. Furnace cooling results in lamellar α+β and Argon cooling results in “ Widmanstӓtten