Improvement of tensile properties of laser directed energy deposited IN718/316L functionally graded material via different heat treatments

Functionally graded materials (FGMs) always serve under rigorous circumstances requiring specific local properties. However, the inhomogeneity of FGMs makes their heat treatment (HT) difficult. Herein, the better HT method for laser directed energy deposited (LDED) IN718/316L FGM was achieved by investigating the microstructural evolution and mechanical properties after different HTs. The results showed that the ultimate tensile strength (UTS) and elongation of the specimen soluted at 1080 °C (HT2 specimen) were greater than those of both the as-built specimen (AB specimen) and the specimen soluted at 980 °C (HT1 specimen). The wear resistance in the building direction increased owing to increasing In718 powder content. After HT, the Laves phase was dissolved, and the δ, γ′, and γ′′ phases were reprecipitated at the top region of the specimen (Region 1). Meanwhile, the thinner grains boundaries and transition from ferrite to austenite can be observed at both the middle region (Region 2) and bottom region (Region 3) of the specimen. Finally, the effect of HT on the mechanical properties was revealed.