Effect of post-heat treatment on microstructure and mechanical properties of nickel-based superalloy fabricated by ultrasonic-assisted wire arc additive manufacturing

Ultrasound as a novel auxiliary means has been gradually used in additive manufacturing (AM) process. Ul-trasonic cavitation and acoustic streaming can effectively control the columnar to equiaxed transition of grain structures, which can improve the anisotropy of mechanical properties. In addition, post-heat treatment (PHT) was considered to improve the microstructure uniformity and mechanical properties of alloys prepared by AM. In this study, we investigated the effect of PHT on the microstructure and mechanical properties of IN625 super-alloy fabricated by ultrasonic-assisted wire arc additive manufacturing (UA-WAAM). The results showed that ultrasonic successfully inhibited the growth of columnar grains, and the microstructure was replaced by equiaxed grain structure. When the PHT temperature reached 1200 degrees C, the grain morphology changed, and a large number of annealing twins were generated in the alloy. Further, with the increase of PHT temperature, Laves phase disappeared and carbide particle size decreased. The results of mechanical properties showed that the micro-hardness and yield strength of the IN625 superalloy decreased with increasing PHT temperature, but the elon-gation and strain hardening ability increased significantly. The combination of UA and PHT provided an opportunity to achieve excellent strength-ductility balance in metals and alloys fabricated by AM.