Regulating Strength and Ductility of Additively Manufactured Inconel 718 Alloy Through Nano-Tic Addition and Deep Cryogenic Treatment

Abstract

The morphology and size of Laves phase play a crucial role in influencing mechanical properties of additively manufactured Inconel 718 alloy. The present work investigates the effects of deep cryogenic treatment (DCT) and nano-TiC addition on the microstructure and tensile properties of Inconel 718 alloy manufactured through direct energy deposition (DED). It is found that the addition of 1.5 wt.% nano-TiC is conducive to transforming the long-striped Laves phase into granular shapes, and the reduced porosity and finer grains are obtained. Compared to the Inconel 718 alloy, the ultimate tensile strength of nano-TiC/Inconel 718 composite is improved by about 46.81 MPa. Through the thermodynamic simulations, the microstructure evolution induced by nano-TiC addition is discussed, which includes the suppression of Laves phase and precipitation of MC particles. Moreover, finer Laves phases, lower dislocation density and more uniform distribution are observed in the Inconel 718 alloy after the DCT. Dynamic recrystallization occurs inside the Inconel 718 alloy during the DCT process, and the grain refinement mechanism is facilitated by a high dislocation density. Consequently, the elongation increases by about 24.8%, while the strength remains almost unchanged. Furthermore, the synergistic effect of the nano-TiC addition and the DCT on Inconel 718 are investigated, and the elongation of nano-TiC/Inconel 718 composite is increased by about 32.7% with more uniform fracture dimples. This study provides a guidance for DED-fabricated Ni-based alloys with excellent strength and ductility.

Keywords: Direct energy deposition, Inconel 718, Deep cryogenic treatment, Microstructure evolution, Tensile properties