The Dissolution Behaviors of Carbides During Solution Treatment for AMSC-DB Ni-Based Superalloys Fabricated by Laser-Directed Energy Deposition and Forging

Abstract

To gain insights into the microstructure evolution of as-fabricated Ni-based superalloys during post-heat treatments, a comparative microstructure analysis is made based on the AMSC-DB alloy samples fabricated by laser-directed energy deposition (L-DED) and forging. In L-DED samples, the (Nb,Ta)C carbides experience a continuous dissolution process during the solution treatment. In contrast, the coarsening behaviors of carbide particles in forge alloys are observed to take place simultaneously with their dissolution. Characterization results show that the carbides in L-DED alloy present uniformly distributed particle sizes and nodular shapes with much irregular surface curvatures. Also, less-pronounced Nb segregation behaviors in carbide vicinity are found in L-DED alloys. Therefore, the difference in carbide dissolution kinetics in L-DED and forge alloys can be ascribed to the combined effects of phase morphologies and local chemical driving forces. Correspondingly, the segmented changes in grain boundary misorientations and recrystallization process in forge alloys are observed to be highly coupled with the carbide dissolution behaviors, compared to the continuous microstructural evolution in L-DED alloy. The different recrystallization behaviors can be quantitatively reflected by the Zener pinning effect. This work sheds light on the proper design of post-heat treatments for L-DED alloys compared to the traditionally manufactured counterparts.