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Microstructural and Microhardness Evolution from Homogenization and Hot Isostatic Pressing on Selective Laser Melted Inconel 718: Structure, Texture, and Phases


Microstructural and Microhardness Evolution from Homogenization and Hot Isostatic Pressing on Selective Laser Melted Inconel 718: Structure, Texture, and Phases

Seede, Raiyan, Mostafa, Ahmad ORCID: https://orcid.org/0000-0001-5625-1106, Vladimir, Brailovski, Mohammad, Jahazi and Medraj, Mamoun (2018) Microstructural and Microhardness Evolution from Homogenization and Hot Isostatic Pressing on Selective Laser Melted Inconel 718: Structure, Texture, and Phases. Journal of Manufacturing and Materials Processing, 2 (2). p. 30. ISSN 2504-4494

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In this work, the microstructure, texture, phases, and microhardness of 45° printed (with respect to the build direction) homogenized, and hot isostatically pressed (HIP) cylindrical IN718 specimens are investigated. Phase morphology, grain size, microhardness, and crystallographic texture at the bottom of each specimen differ from those of the top due to changes in cooling rate. High cooling rates during the printing process generated a columnar grain structure parallel to the building direction in the as-printed condition with a texture transition from (001) orientation at the bottom of the specimen to (111) orientation towards the specimen top based on EBSD analysis. A mixed columnar and equiaxed grain structure associated with about a 15% reduction in texture is achieved after homogenization treatment. HIP treatment caused significant grain coarsening, and engendered equiaxed grains with an average diameter of 154.8 µm. These treatments promoted the growth of δ-phase (Ni3Nb) and MC-type brittle (Ti, Nb)C carbides at grain boundaries. Laves phase (Fe2Nb) was also observed in the as-printed and homogenized specimens. Ostwald ripening of (Ti, Nb)C carbides caused excessive grain growth at the bottom of the HIPed IN718 specimens, while smaller grains were observed at their top. Microhardness in the as-fabricated specimens was 236.9 HV and increased in the homogenized specimens by 19.3% to 282.6 HV due to more even distribution of secondary precipitates, and the nucleation of smaller grains. A 36.1% reduction in microhardness to 180.5 HV was found in the HIPed condition due to phase dissolution and differences in grain morphology.

Divisions:Concordia University > Gina Cody School of Engineering and Computer Science > Mechanical, Industrial and Aerospace Engineering
Item Type:Article
Authors:Seede, Raiyan and Mostafa, Ahmad and Vladimir, Brailovski and Mohammad, Jahazi and Medraj, Mamoun
Journal or Publication:Journal of Manufacturing and Materials Processing
Date:16 May 2018
  • Masdar Institute of Science and Technology
Digital Object Identifier (DOI):10.3390/jmmp2020030
Keywords:Inconel 718; additive manufacturing; 3D printing; selective laser melting (SLM); hot isostatic pressing (HIP); homogenization; hardness; precipitation; microstructure; texture
ID Code:983890
Deposited On:22 May 2018 13:19
Last Modified:22 May 2018 13:19
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