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Abstract

Introduction

In this study, we provide novel in situ monitoring of strain during laser metal deposition of Inconel 718 by neutron diffraction. Thermal, phase and stress-related contributions to the lattice parameter evolution are addressed for the representative regions during processing: melt pool, near melt pool, and far-field. The evolution showed a strong dependency on the build height and distance to the melt pool, i.e., time and temperature gradient, as expected. The different regions of interest reached at different moments the processing stable regime, which is contrasted with microstructural characterization. A homogeneous microstructure of coarse epitaxial dendrites and Laves phase was found from the third printed layer on, with fine globular delta phase precipitation at the grain boundaries. In comparison, neutron diffraction strain monitoring highlighted an offset of process stabilization after 24 layers for the melt pool and near-melt pool regions. Keywords







Additive manufacturing Monitoring Strain Neutron diffraction




Inconel 718

S. Cabeza (&)
B. Özcan
T. Pirling
T. C. Hansen Diffraction Unit, Institute Laue Langevin, ILL, 71 Avenue des Martyrs, Grenoble, 38042, France e-mail: [email protected] J. Cormier
A. Vilalta-Clemente Institut Pprime, UPR CNRS 3346, ISAE-ENSMA, 1 avenue Clément Ader, BP 40109, Futuroscope-Chasseneuil, 86961, France S. Polenz
F. Marquardt
E. López
C. Leyens Additive Manufacturing Division, Fraunhofer IWS, Winterbergstraße 28, 01277 Dresden, Germany C. Leyens Institute of Materials Science (IfWW), TU Dresden, 01062 Dresden, Germany




A high demand for the additive manufacturing (AM) of Inconel 718 (IN718) in advanced engineering applications brings a priority to investigate the specific relationship between their properties and the fabrication parameters. During recent years, there has been a development of numerous viable 3D printing techniques and approximations for printing more stable and promising parts eligible for critical applications [1–3]. In particular, the laser metal deposition technique (LMD), based on full melting and solidification, is one of the most important techniques for producing large-scale parts since it combines high deposition rates, fast production, low cost, and a high buy-to-fly ratio [4]. Improvements in this technology gradually provide better near-net shaping, hence less machining requirements and more material savings [5]. Although the relationship between solidification, phase formation, and residual stress in welding and casting has been studied over the years, the impact of AM parameters on final material properties is yet to be fully understood. Intricate temperature gradients in 3D arise during fabrication, inherent to the layer-by-layer processing, scanning strategy, and complexity of geometry. As a result, heterogeneous distributions of microstructural features such as phases, texture, composition, and residual stresses within the printed part may appear, playing an essential role in the final product quality and per