Peeyush Nandwana

Recyclability study on Inconel 718 and Ti-6Al-4V powders for use in electron beam melting

Powder bed-based additive manufacturing technologies offer a big advantage in terms of reusability of the powders over multiple cycles that result in cost savings. However, currently there are no standards to determine the factors that govern the powder reuse times. This work presents the results from a recyclability study conducted on Inconel 718 and Ti-6Al-4V powders. It has been found that the Inconel 718 powders are chemically stable over a large number of cycles and their reuse time is limited by physical characteristics of powders such as flowability. Ti-6Al-4V, on the other hand, finds its reuse time governed by the oxygen pick up that occurs during and in between build cycles. The detailed results have been presented.

Electron beam melting of Inconel 718: effects of processing and post-processing

ABSTRACT This study reports the effect of process temperature on microstructure evolution of electron beam melted Inconel 718. Samples fabricated at 915°C had fine grain boundary δ (∼200 nm) along with coarse intragranular δ spanning through the length of the grains. On the other hand, samples fabricated at 990°C, only had grain boundary δ along with secondary carbides. During hot isostatic pressing, the distribution of carbides governs the grain growth vs. lack of it. The samples fabricated at 990°C having grain boundary carbides had no grain growth owing to the pinning effect of carbides. In contrast, the sample processed at 915°C had significant grain growth owing to dissolution of grain boundary δ phase and absence of grain boundary carbides.

Progress in the Processing and Understanding of Alloy 718 Fabricated Through Powder Bed Additive Manufacturing Processes

This paper reviews currently available information on the processing and understanding of Alloy 718 fabricated through powder bed additive manufacturing processes, specifically selective laser melting, electron beam melting, and binder jet additive manufacturing. In each instance, the microstructures formed exhibit attributes unique to the process used. Through post-processing, these materials are capable of achieving property behaviors similar to that of the long utilized wrought material. While AM processes are complex, computational modeling has been successfully applied to capture the heat and mass transfer, microstructure evolution, and constitutive response of the material.

Correlation of Microstructure to Creep Response of Hot Isostatically Pressed and Aged Electron Beam Melted Inconel 718

Creep rupture samples were fabricated by additive manufacturing (AM) via electron beam melting (EBM) to study the effects of grain morphology (equiaxed/columnar grains) and loading direction (longitudinal/transverse) with respect to build direction on creep deformation at 923 K (650 °C) with applied stresses of 580 and 600 MPa. The observed minimum creep rates and creep rupture lives of EBM Inconel 718 after post-processing by hot isostatic pressing (HIP) were found to be comparable to wrought material. The material with equiaxed grains exhibited low creep strain (2 pct) and short creep lifetimes (800 hours), whereas longer times (approximately 4500 hours) and high creep strain (up to 23 pct) were observed for material with columnar grains. The high stress exponent (n > 14) reflected the resistance to dislocation motion by γ” particles during creep. A precipitate-free zone (PFZ) was observed around the grain boundary δ phase. Creep damage occurred as voids and cracks in the PFZ. Optimal post-processing of EBM Inconel 718 material should be explored to prevent δ phase embrittlement.