Investigation of GH3625 alloy: Contrasting microstructures, mechanical properties, and corrosion performance via conventional and extreme high speed laser material deposition

The GH3625 nickel alloy, known for its exceptional mechanical properties and corrosion resistance, has been widely adopted. Nonetheless, the current additive manufacturing (AM) of GH3625 alloy presents compromised strength and significant segregation, thus limiting its potential applications. To address these challenges, the utilization of the extreme high-speed laser material deposition (EHLA) process with its rapid cooling capabilities has been investigated, aiming to enhance grain refinement and suppress segregation. In this study, a comparative analysis was conducted between GH3625 nickel alloy sample fabricated by conventional laser material deposition (LMD) and the EHLA technique. The investigation covered thermal processes, microstructural evolution, mechanical properties, and corrosion resistance. The EHLA-fabricated specimen exhibits a refined microstructure and elevated dislocation density attributed to the rapid solidification process. This leads to an impressive ultimate tensile strength of 1005 MPa, surpassing the LMD-deposited counterpart by 20 %. The Clyne-Kurz model outperforms the classic Scheil model in evaluating AM processes sensitive to cooling rates. Notably, the EHLA sample demonstrates reduced Nb segregation compared to the LMD sample. Furthermore, the formation of the precipitated Laves phase is reduced, and the concentrations of Nb and Mo within the dendritic structure are increased in the EHLA sample. Consequently, enhancements in pitting corrosion resistance and the protective effectiveness of passive films are observed.