Laser powder bed fused Inconel 718 in stress-relieved and solution heat-treated conditions

N. Hasani*, C. Dharmendra, M. Sanjari, F. Fazeli, B. S. Amirkhiz, H. Pirgazi, G. D.Janaki Ram, M. Mohammadi

*Corresponding author for this work

Research output: Contribution to journalArticleScientificpeer-review

Abstract

Inconel 718 superalloy cylindrical rods were fabricated using the laser powder bed fusion (L-PBF) technology in the vertical orientation. The rods were stress-relieved at 980 °C for 15 min before cutting them from the build plate. The microstructure in this condition exhibited a significant amount of undesirable needle-like δ-phase precipitates and a small amount of interdendritic Laves phase that is finer in size. Differential Scanning Calorimetry (DSC) was used to determine the temperatures for solid-state phase transformations and appropriate temperature for solution-treatment. Solution-treatment was performed at 1065 °C for 1 h, followed by air cooling. The microstructures were characterized with specific reference to δ-phase and Nb segregation. Solution-treatment at 1065 °C was found to result in a significant elimination of micro-segregation (mainly Nb), complete dissolution of δ phase, considerable Laves dissolution, and partly undissolved carbide particles (few nm in size). Solution-treatment did not produce a significant change in the grain morphology (columnar dendritic) on a plane parallel to the build direction but more recrystallized and equiaxed grains were formed on a plane perpendicular to the build direction. The hardness of the solution-treated sample is comparable with wrought 718 alloys but lesser (115 HV) than in the stress-relieved condition attributing to the annihilation of dislocation tangles.

Original languageEnglish
Article number111499
Number of pages16
JournalMaterials Characterization
Volume181
DOIs
Publication statusPublished - 2021

Keywords

  • Electron microscopy
  • Inconel 718
  • Laser powder bed fusion
  • Secondary phases
  • Solution treatment
  • Stress-relieving

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