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The ability to seed representative surrogate defects into otherwise nominal material can provide fundamental understanding of processing defects with LPBF and help advance additive process qualification and part certification.
The goal of this project is to develop and verify the controlled formation of process defects during laser powder bed fusion of additive manufacturing using nickel alloy IN718.
Laser powder bed fusion (LPBF) additive manufacturing (AM) has shown significant promise in creating complex component geometries manufactured with a number of useful metallic alloys. Understanding the mechanical performance of these components, however, still lags behind traditional processing methods, especially in fatigue and fracture. The mechanical performance debits are due to defects that are generated during the course of processing, which often exhibit a highly correlated nature due to the inherently linear and planar nature of the LPBF process. Understanding the formation of material/processing anomalies in LPBF and their effect on performance is critical to advancing analysis and model-based qualification methods.
The objective of this program is to quantify the impact of defects in LPBF with controlled and systematic evaluation of material performance as a function of defect characteristics in nickel alloy IN718. Specifically, the program seeks to develop an understanding of the mechanisms that trigger defect types commonly observed in LPBF; a processing approach for intentionally generating surrogate defects; targeted CT inspection, metallography, and fatigue testing responses of these surrogate defects for comparison to naturally occurring defects; a component scale demonstration of the methodology; and an initial implementation of a software tool for generating build files for controlling defect type, size and location.
In order to develop this fundamental understanding for processing defects with LPBF, it is necessary to generate representative defects in a controlled manner to enable quantitative studies of the mechanical property debits and probability of detection (PoD) of authentic LPBF defects. The technical approach and methodology include over a dozen LPBF build iterations in IN718, model-informed analysis of local processing conditions, in-situ process monitoring, post build computed tomography (CT), mechanical testing (fatigue), and user developed LPBF fusion machine control. Combining process modeling with in-situ monitoring accelerates determination of the key process parameters needed to control the formation and severity of typically observed LPBF defect types. CT and mechanical testing are being used to verify the presence of morphologically representative defects, as well as benchmark their mechanical performance debits relative to legacy data. Ohio State University (OSU) has demonstrated its ability to control numerous key processing parameters to achieve desired material response (high density) in the ongoing America Makes project #3014. The scope of this program acts as a continuation to elicit the opposite result in otherwise quality material. To ensure transition to America Makes and the DoD supply chain, OSU is partnering with a local small business AM supplier, Proto Precision Additive, and large aerospace and defense OEM/ Propulsion Supplier Rolls-Royce and Lockheed Martin.