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Linking pyrometry to porosity in additively manufactured metals

Additive Manufacturing

Mitchell, John A.; Ivanoff, Thomas I.; Dagel, Daryl; Madison, Jonathan D.; Jared, Bradley H.

Porosity in additively manufactured metals can reduce material strength and is generally undesirable. Although studies have shown relationships between process parameters and porosity, monitoring strategies for defect detection and pore formation are still needed. In this paper, instantaneous anomalous conditions are detected in-situ via pyrometry during laser powder bed fusion additive manufacturing and correlated with voids observed using post-build micro-computed tomography. Large two-color pyrometry data sets were used to estimate instantaneous temperatures, melt pool orientations and aspect ratios. Machine learning algorithms were then applied to processed pyrometry data to detect outlier images and conditions. It is shown that melt pool outliers are good predictors of voids observed post-build. With this approach, real time process monitoring can be incorporated into systems to detect defect and void formation. Alternatively, using the methodology presented here, pyrometry data can be post processed for porosity assessment.

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TYPE Journal Article YEAR 2020
DOIOSTIScopus

Development of a Generalized Residual Stress Inversion Technique

Johnson, Kyle J.; Bishop, Joseph E.; Reu, Phillip L.; Walsh, Timothy W.; Farias, Paul A.; Jared, Bradley H.; Susan, D.F.; Rouse, Jerry W.; Whetten, Shaun R.; Chen, Mark J.; Aquino, Wilkins A.; Bellotti, Aurelio; Jacobs, Laurence

Residual stress is a common result of manufacturing processes, but it is one that is often overlooked in design and qualification activities. There are many reasons for this oversight, such as lack of observable indicators and difficulty in measurement. Traditional relaxation-based measurement methods use some type of material removal to cause surface displacements, which can then be used to solve for the residual stresses relieved by the removal. While widely used, these methods may offer only individual stress components or may be limited by part or cut geometry requirements. Diffraction-based methods, such as X-ray or neutron, offer non-destructive results but require access to a radiation source. With the goal of producing a more flexible solution, this LDRD developed a generalized residual stress inversion technique that can recover residual stresses released by all traction components on a cut surface, with much greater freedom in part geometry and cut location. The developed method has been successfully demonstrated on both synthetic and experimental data. The project also investigated dislocation density quantification using nonlinear ultrasound, residual stress measurement using Electronic Speckle Pattern Interferometry Hole Drilling, and validation of residual stress predictions in Additive Manufacturing process models.

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TYPE SAND Report YEAR 2019
DOIOSTI

Nonlinear ultrasonic technique for the quantification of dislocation density in additive materials

AIP Conference Proceedings

Bellotti, Aurelio; Kim, Jin Y.; Bishop, Joseph E.; Jared, Bradley H.; Susan, D.F.; Jacobs, Laurence J.

This research applies nonlinear ultrasonic techniques for the quantitative characterization of additively manufactured materials. The characterization focuses on identifying the dislocation density produced during the additive constructive process in order to increase confidence on a part's performance and the success of the manufacturing process. Second harmonic generation techniques based on the transmission of Rayleigh surface waves are used to measure the ultrasonic nonlinearity parameter, β, which has proven a quantitative indicator of dislocations but has not been fully proven in additive manufactured materials. 316L and 304L stainless steel parts made from Powder Bed Fusion and Laser Engineered Net Shaping are compared between AM techniques and with wrought manufactured counterparts. β is consistently higher for additive manufactured parts. An annealing heat treatment is applied to each specimen to reduce dislocation density. β expectedly decreases by annealing in all specimens. A linear ultrasonic measurement is made to evaluate the effectiveness of using nonlinear techniques. The ultrasonic attenuation is higher for additive manufactured parts and increases at higher frequencies.

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TYPE Conference Poster YEAR 2019
DOIOSTIScopus
Results 51–75 of 220
Results 51–75 of 220