Influence of different Heat Treatments on the microstructural Evolution and Microhardness of Laser Powder Bed Fusion manufactured Inconel 625

Abstract

Laser Powder Bed Fusion is an additive manufacturing technology that allows the production of parts with complex geometries. [8] The high energy focused laser beam that selectively melts the cold powder bed leads to high cooling rates which result in a fine microstructure and is often accompanied by internal stresses which may require a stress relief heat-treatment. Manufacturer recommended heat treatments are often based on the nominal powder composition and do not include the L-PBF produced microstructure. Inconel 625, a nickel-based superalloy, is frequently used for L-PBF processes. One of the major concerns is the precipitation of δ-phase at elevated temperatures, which has almost exclusively detrimental effects on the material’s mechanical properties. This thesis investigates the influence of heat treatments at 700 °C, 900 °C and 1050 °C for one and two hours on the microstructure and microhardness of the manufactured parts and shows that the secondary phases are hard to detect, that the change in lattice parameter can be used to indirectly show the nature of secondary phase formation and that a post-processing heat treatment should be carefully chosen in order to not be ineffective or even detrimental to the part’s performance.