Process development and application of hot forging arc-based additive manufacturing on Haynes® 282 for microstructural and mechanical improvements

Haynes® 282, a nickel-based superalloy, is renowned for its exceptional strength, thermal stability, and resistance to oxidation and creep. While directed energy deposition arc-based additive manufacturing of this alloy has been explored, the formation of large columnar grains and high texture leading to anisotropy and suboptimal mechanical performance remains a significant challenge. This study introduces an interlayer in-situ mechanical deformation approach, known as hot forging, to address these issues. The hot forging process, applied at high temperatures, aims to refine grain structure, reduce porosity, and enhance mechanical properties. The dynamic analysis of the process using a high-speed camera imaging allowed to calculate a forging force exceeding 1000 N. Two single-bead multi-layered walls were fabricated, one with hot forging and one without. Results demonstrated a 22 % reduction in porosity upon hot forging. Electron backscatter diffraction analysis indicated that the hot forged sample has less texture, and the average grain size decreased from 1746 to 1262 μm and from 1053 to 696 μm in the top and middle wall regions, respectively. Synchrotron X-ray diffraction revealed a small variation in phase composition and confirmed that hot forging promotes refined grain structures with less texture. The ultimate tensile strength in the horizontal direction improved by 8 % with hot forging, while elongation decreased by 30 %. Electrical conductivity and microhardness measurements were similar for both processes. The findings confirm the efficacy of in-situ hot forging in enhancing microstructure and mechanical performance, highlighting its potential for high-cost and low-machinability materials in arc-based additive manufacturing.