The Effect of Location and Post-treatment on the Microstructure of EBM-Built Alloy 718

Paper in proceeding, 2018

Alloy 718, usually referred to as Inconel 718, is a Ni-Fe based superalloy widely used in the aerospace industry by virtue of the excellent balance of mechanical properties and corrosion resistance that it affords at high temperature [1]. While Alloy 718 parts have been traditionally fabricated using conventional cast and wrought (C&W) techniques, there has been a growing interest in production of the complex high temperature service components through additive manufacturing (AM) processes due to the significant design freedom offered by the technology. Alloy 718 has been processed by laser (laser metal deposition, LMD; selective laser melting, SLM) and electron (Electron Beam Melting, EBM) beam based technologies [2]–[4]. AM, in general, involves high solidification rates and high thermal gradients, thus resulting in a finer microstructure compared to C&W products [5]. In EBM, a relatively high temperature is maintained throughout the process compared to SLM, thus resulting in lower residual stresses in as-manufactured parts [6]. However, as a relatively newer technology, the degree to which the EBM processing conditions (scanning strategies, preheat and melting parameters) affect the properties of EBM-built Alloy 718 material is less understood compared to the laser based techniques. Also, it has been challenging to date to build Alloy 718 parts that are free from issues such as defects, inhomogeneity, anisotropy, etc., thereby demanding post-treatment to achieve the required microstructure and intended part performance. Although post treatment of C&W Alloy 718 has been widely investigated over several decades [7]–[9], the inadequacy of conventional post-treatment protocols for EBM Alloy 718 [10]–[12], justifies further investigation of microstructural changes that occur in EBM-built Alloy 718 during post-treatment. A comprehensive study may eventually allow optimization of the combined build and post-treatment processes to obtain components with properties deployable in severe environments.