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Metals 2017, 7(6), 196; doi:10.3390/met7060196

Structure, Texture and Phases in 3D Printed IN718 Alloy Subjected to Homogenization and HIP Treatments

1
Mechanical and Materials Engineering Department, Khalifa University of Science and Technology, Masdar Institute, P.O. Box 54224 Abu Dhabi, UAE
2
Department of Mechanical Engineering, École de Technologie Supérieure, 1100, Notre-Dame Street West, Montreal, QC H3C 1K3, Canada
3
Mechanical Engineering Department, Concordia University, 15151 Rue Sainte Catherine west, Montreal, QC H3G 2W1, Canada
*
Author to whom correspondence should be addressed.
Academic Editor: Johannes Henrich Schleifenbaum
Received: 11 April 2017 / Revised: 17 May 2017 / Accepted: 19 May 2017 / Published: 30 May 2017
(This article belongs to the Special Issue Selective Laser Melting)

Abstract

3D printing results in anisotropy in the microstructure and mechanical properties. The focus of this study is to investigate the structure, texture and phase evolution of the as-printed and heat treated IN718 superalloy. Cylindrical specimens, printed by powder-bed additive manufacturing technique, were subjected to two post-treatments: homogenization (1100 °C, 1 h, furnace cooling) and hot isostatic pressing (HIP) (1160 °C, 100 MPa, 4 h, furnace cooling). The Selective laser melting (SLM) printed microstructure exhibited a columnar architecture, parallel to the building direction, due to the heat flow towards negative z-direction. Whereas, a unique structural morphology was observed in the x-y plane due to different cooling rates resulting from laser beam overlapping. Post-processing treatments reorganized the columnar structure of a strong {002} texture into fine columnar and/or equiaxed grains of random orientations. Equiaxed structure of about 150 µm average grain size, was achieved after homogenization and HIP treatments. Both δ-phase and MC-type brittle carbides, having rough morphologies, were formed at the grain boundaries. Delta-phase formed due to γ″-phase dissolution in the γ matrix, while MC-type carbides nucleates grew by diffusion of solute atoms. The presence of (Nb0.78Ti0.22)C carbide phase, with an fcc structure having a lattice parameter a = 4.43 Å, was revealed using Energy dispersive spectrometer (EDS) and X-ray diffractometer (XRD) analysis. The solidification behavior of IN718 alloy was described to elucidate the evolution of different phases during selective laser melting and post-processing heat treatments of IN718. View Full-Text
Keywords: Inconel 718; additive manufacturing; 3D printing; hot isostatic pressing (HIP); homogenization treatment; selective laser melting (SLM); Electron backscattered diffraction (EBSD) Inconel 718; additive manufacturing; 3D printing; hot isostatic pressing (HIP); homogenization treatment; selective laser melting (SLM); Electron backscattered diffraction (EBSD)
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Mostafa, A.; Picazo Rubio, I.; Brailovski, V.; Jahazi, M.; Medraj, M. Structure, Texture and Phases in 3D Printed IN718 Alloy Subjected to Homogenization and HIP Treatments. Metals 2017, 7, 196.

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