On the role of Al or Ti alloying in additively manufactured IN718 alloys

Abstract

Although Al or Ti addition is promising to improve the performance of IN718, traditional metallurgical processing methods encounter difficulties in manufacturing superalloys with higher Al and Ti content. Laser powder bed fusion (LPBF) exhibits great potential to address these challenges, but the effects of Al or Ti content on additively manufactured IN718 stay unclear. In this work, we fabricated crack-free modified IN718 alloys with elevated Al or Ti content through in-situ alloying using laser powder bed fusion. The results revealed that the alloy 1 wt.% Ti addition outperformed IN718 in strength at both ambient and elevated temperatures by about 120 and 70 MPa, respectively, while the addition of 1 wt.% Al decreases the yield strength due to the significant decrease of γʹʹ phase fraction. However, the addition of 3 wt.% Al leads to precipitation of σ-phase, while 3 wt.% Ti addition leads to growth of coarse η-phase of micrometers at grain boundaries. After aging treatment at 720 °C for 50 h, it is also found that the thermal stability of γʹʹ phase is substantially improved by Ti alloying due to the formation of γʹʹ/γʹ/γʹʹ sandwich structure. These findings highlight the advantages of Ti alloying in enhancing thermal stability and mechanical performance.