Microstructural Analyses of ATI 718Plus® Produced by Wire-ARC Additive Manufacturing Process

Abstract

A detailed microstructural study of ATI 718Plus superalloy produced by the wire-arc additive manufacturing (WAAM) process was performed through the use of scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron probe micro-analysis (EPMA), and electron backscatter diffraction (EBSD). Extensive formation of eutectic solidification microconstituents including Laves and MC-type carbide phases, induced by micro-segregation, are observed in the build of the alloy in the as-deposited condition. Notwithstanding the significant segregation of niobium (Nb), which has been reported to promote the formation of the d-phase in ATI 718Plus, only g-phase particles are observed in the deposit. Excessive precipitation of g-phase particles is found to be linked to Laves phase particles that are partially dissolved in the deposit after post-deposition heat treatment (PDHT). The EBSD analysis shows a high textured build in the h100i directions with only a few misoriented grains at the substrate-deposit boundary and the top of the deposit. Investigation on the hardness of the build of the alloy, in the as-deposited condition, showed a softened zone about 2 mm wide at the deposited metal heat affected zone (DMHAZ), which has not been previously reported and potentially damaging to the mechanical properties. An extensive analysis with the use of both microstructural characterization tools and theoretical calculations shows that the DMHAZ has the lowest volume fraction of strengthening precipitates (c¢ and c¢¢) in terms of their number density, which therefore induces the observed softness. Delayed re-precipitation kinetics and the extent of the precipitation of c¢ and c¢¢ in the DMHAZ which is related to the diffusion of segregated solute elements from the interdendritic regions are attributed to this phenomenon. The microstructural analyses discussed in this work are vital to adequate understanding of properties of ATI 718Plus produced by the additive manufacturing process technique.

Predicting the Microstructural Evolution of Electron Beam Melting of Alloy 718 with Phase-Field Modeling

“…The local composition of the microstructure in Alloy 718 differs from its nominal composition value because of the segregation of the elements during solidification. A segregated microstructure behaves in a different manner compared with a microstructure in the nominal composition of the same alloy, [25] which is illustrated based on the CCT diagrams obtained (as explained in Section III-C) for Alloy 718 in the following.…”

CMT-Based Wire Arc Additive Manufacturing Using 316L Stainless Steel: Effect of Heat Accumulation on the Multi-Layer Deposits

“…Jinguo et al [7] investigated the cooling rate and 2 of 12 microstructure changes based on the height of the deposit in the cold metal transfer-WAAM process using 2Cr13 stainless steel; the authors claimed that the martensite content in the microstructure formed in each layer varied with the differences in the cooling rates of each layer. Asala et al [8] measured the temperature history during WAAM using Inconel 718, and studied the microstructure variation with respect to the height of the deposit; they observed that the lower and middle parts of the deposit remained for a longer period within the aging-temperature range of Inconel 718 during deposition compared to the upper part, resulting in increased precipitation hardening in the microstructure, thereby demonstrating enhanced mechanical properties.…”

Microstructure and thermal properties of unalloyed tungsten deposited by Wire + Arc Additive Manufacture

“…In particular, Wire + Arc additive Manufacturing (WAAM), which employs an electric arc as the heat source, and high-quality metal wire as the feedstock [19], can directly fabricate fully-dense large 3-D near-net-shape components, at much higher rates, than most other metal AM processes [18,19], the highest rate so far being of 9.5 kg/h [20]. The WAAM process has successfully produced large-scale parts in stainless steel [21], Inconel ® [22], titanium [23] and aluminium [24]. Furthermore, a previous research showed that unalloyed tungsten can be deposited via WAAM with a noteworthy absence of micro-cracks among the layers [25].…”