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In this work CM247LC, a low weldable Ni-Based alloy, was produced using selective laser melting (SLM). Despite the initial process parameter optimization, the low defect volume fraction was still uncompliant with manufacturing standards. This condition is principally caused by the high γ’ volume fraction which strongly affects the alloy weldability. Nonetheless, a crack free condition was eventually achieved applying a γ’-sub-solvus Hot Isostatic Pressing Cycle (HIP) which lowered the defects fraction down to 0.04%. The HIP cycle also demonstrated to play an important role in the stabilization of the microstructure, considerably limiting the carbides coarsening during the following heat treatment. Apart from the effectiveness of the healing process brought by HIP, the material microstructure still needs an optimization process which will be described along this paper. In fact, the Initial microstructure obtained after the printing process (the as-built condition) as well as the one obtained after HIP (post-HIP) won’t meet the desired requirements. Namely, the dendritic and γ’ free microstructure of the as-built material or the one with coarse and disordered particles obtained right after HIP, still need a tailored homogenization process. This paper will show how the combined effect of the solution and first aging treatment will profoundly alter the γ’ precipitation. More specifically, here, a new heat treatment recipe was developed to promote the precipitation of ordered cuboidal primary γ’ so as to improve creep and high temperature fatigue resistance. Moreover, the use of a γ’ super-solvus temperature allowed to achieve a γ’ volume fraction as high as 73% reducing its average size to 520 nm. At the same time, such heat treatment caused a profound alteration of the crystalline structures of the material promoting a general grain coarsening and the formation of equiaxial grains.

More and more efforts are spent for manufacturing low-weldable nickel-based superalloys in contemporary research applied to additive manufacturing. One of the biggest difficulty with these kinds of alloys is reducing the flaws density obtaining a good final microstructure in the as-built state. Nevertheless, the complete densification of the alloys can be reached only after further heat treatments such as the Hot Isostatic Pressing (HIP). The SLM material microstructure is severely different with respect to that obtainable after traditional manufacturing. This will also impact the final mechanical properties as well as the microstructure stability. Very often, designing specifically tailored heat treatments become the most viable solution for enhancing these materials. In this work the effect of the HIP treatment Is discussed and, after performing DSC and TMA thermal analysis, the effects of two heat treatments on two Ni-based alloys are discussed

Hot isostatic pressing (HIP) is a post processing step commonly applied to Additive Manufactured (AM) parts, in order to increase their performances. In some sector HIP is a mandatory step of the AM parts fabrication route, e.g. aeronautic field. In front of the clear technical advantages, HIP is a cost and time consuming operation, especially due to the typical slow cooling. The combination of HIP step and following rapid queching is highly attractive in saving at least an unuseful cooling stage and the following heating ramp for the quench step.The paper addresses the benefits of an integrated design of AM-HIP-quench manufacturing route, in terms of fine control of the microstructure, of improving the integrity of fabricated parts and of containing the distortions related to heat treatment steps.Detailed microstructural analysis through optical and field emission scanning electron microscopy are given. Evidence of parts healing due to HIP steps are provided through X-ray tomography. Dimensionalaccuracy analysis after different steps of the fabrication route are reported. Major material grades considered within the paper are Ni superalloys.Final remarks on the integration of advanced fabrication routes for engineering components are given. &nbsp

This works is focused on the production of Nickel superalloys by Selective Laser Melting. It is investigatedhow different process parameters affects the densification and microstructure of different Nickel superalloyscharacterized by increasing amounts of γ′ former alloying elements thusstudying the balance between pores and cracks reduction and the resulting microstructure. The involved parameters are: laser power, scanning speed, hatching distance. &nbsp