Logo image
Back
Characterization of microstructure and residual strain in Inconel 625 fabricated by additive manufacturing
Thesis   Open access

Characterization of microstructure and residual strain in Inconel 625 fabricated by additive manufacturing

Kathryn Anderson Small
Master of Science (M.S.), Drexel University
Jun 2017
DOI:
https://doi.org/10.17918/D8WQ0Q
pdf
Small_Kathryn_20175.50 MBDownloadView
PDF Open Access Open Access (License Unspecified)

Abstract

Electron beams--Industrial applications Nickel alloys Industrial Engineering Materials Science
Inconel 625 is a Ni-based superalloy designed for use in extreme environments often exposed to high temperatures and corrosive substances and is widely used in aerospace, defense, and energy applications. However, the same properties that make this an ideal material for demanding environments also make this metal difficult and expensive to manufacture into complex geometries. Additive manufacturing (AM) is a group of fabrication techniques which add material in a layer-by-layer fashion using CAD data from a digital model of the final, desired part. AM is an area of intense development because of its potential to design and fabricate complex parts easily and quickly compared to traditional techniques. Unfortunately, essentially all AM methods are prone to inducing deformation in final parts because of repetitive thermal cycles and steep temperature gradients during fabrication. These internal strains result in residual stresses throughout the component, and could be detrimental to the mechanical properties of the part. Traditionally, residual stress has been characterized by bulk methods including neutron or X-ray diffraction and, more recently, digital image correlation; these techniques, however, do not take into consideration the effect of microstructural features on residual stress distribution, an understanding that is crucial if effective AM of complex parts is going to be developed. HR-EBSD methods have recently been introduced as a way of mapping the residual strain on a micro-level, allowing the comparison between microstructure and residual strain distribution to be observed. In this work, HR-EBSD methods are used to map internal strains in IN625 induced by three different AM methods and the reliability of the characterization method is explored. It was found that the HR-EBSD can be relied upon to produce strain maps reasonably consistent with Kernel Average Misorientation spreads produced from EBSD scans, but that HR-EBSD analysis resulted in a much lower average strain than other methods like ND or DIC. Because ND and DIC are on a bulk level instead of a micro-scale, some variation between methods is expected; however, the results produced here suggest that HR-EBSD is a promising method to map strain on a microstructural level.

Metrics

59 File views/ downloads
26 Record Views

Details

Logo image