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Purpose Directed energy deposition (DED) with laser powder-feed is an additive manufacturing process that is used to produce metallic components by simultaneously providing a supply of energy from a laser and mass from a powder aerosol. The breadth of alloys used in DED is currently limited to a very small range as compared to wrought or cast alloys. The purpose of this paper is to develop the new alloys for DED is limited because current models to predict operational processing parameters are computationally expensive and trial-and-error based experiments are both expensive and time-consuming. Design/methodology/approach In this research, an agile DED model is presented to predict the geometry produced by a single layer deposit. Findings The utility of the model is demonstrated for type 304 L stainless steel and the significance of the predicted deposition regimes is discussed. The proposed model incorporates concepts from heat transfer, welding and laser cladding; and integrates them with experimental fits and physical models that are relevant to DED. Originality/value The utility of the model is demonstrated for type 304 L stainless steel and the significance of the predicted deposition regimes is discussed.

Additively manufacturing tantalum is a challenging process in which obstacles are stemming from the high melting temperature and susceptibility to oxidation of tantalum. Several combinations of deposition parameters were considered in an effort to obtain fully dense additively manufactured tantalum produced on an EOSINT M280 DMLS system. Deposition parameters significantly affect the resulting microstructure of additively manufactured tantalum, altering grain morphology, grain size, crystallographic preferred orientation, and deposition porosity. Due to the nature of the laser sintering process applied, which implies large directional temperature gradients, the resulting microstructures were strongly columnar along the building direction. Microstructural differences for different deposition conditions manifested themselves in both grain morphology and preferred crystal orientations in the columnar grains. Deposition speed and laser power were important parameters to consider for obtaining porosity-free material. Stripe width had the most significant effect on grain growth.

A two-color pyrometer is aligned co-axially to the laser inside a Laser Engineered Net Shaping machine to gather thermal data during a single layer two-pass deposit. Several molten pool metrics are calculated from the pyrometer data, and anomalies in the data are used to flag potential defect locations. The depositions are scanned using x-ray Computed Tomography (XCT) with a 4.13 micron voxel, and void size and location are recorded. XCT void data is then compared to the thermal analysis to determine the efficacy of the anomaly detection technique. In this build, four voids > 40 microns in diameter were found with XCT. Three defects appeared in the interfacial region between the deposit and substrate and produced signatures that were detected by analyzing the in-situ pyrometer data.

Recent work in both 304L and 316L stainless steel produced by additive manufacturing (AM) has shown that in addition to the unique, characteristic microstructures formed during the process, a fine dispersion of sub-micron particles, with a chemistry different from either the powder feedstock or the expected final material, are evident in the final microstructure. Such fine-scale features can only be resolved using transmission electron microscopy (TEM) or similar techniques. The present work uses electron microscopy to study both the initial powder feedstock and microstructures in final AM parts. Special attention is paid to the chemistry and origin of these nanoscale particles in several different metal alloys, and their impact on the final build. Comparisons to traditional, wrought material will be made.

In order for metallic additive manufacturing (AM) to find application in industrial production environments, methods for quality control need to be developed. Presently, even precisely calibrated process parameters cannot prevent the stochastic occurrence of defects resulting from elements in the AM process which are difficult to control. This study utilizes low framerate (10 Hz) pyrometry to record in situ temperature measurements of the molten pool and surrounding substrate in LENSTM AM. The data is statistically analyzed in search of anomalous behavior which is compared to the actual population of voids and inclusions found using X-ray Computed Tomography. This statistical analysis technique was able to identify volumetric defects as small as 40 μm in diameter as well as inclusions such as powder contamination. This study shows that the thermal analysis parameters can be tuned specifically for detecting different anomalies in the build.

Irradiations were performed with 1.5 MeV protons to 0.6 dpa at 40–150 °C on additively manufactured (AM) 304L stainless steel and the changes in microstructure and mechanical behavior after irradiation were compared to wrought 304L stainless steel. All microstructural and hardness results after irradiation suggest the samples evolve toward a similar state, despite significant differences in the unirradiated microstructures and hardness values. A TEM and nanoindentation-based investigation of before and after proton irradiation at 40–150 °C is presented. Results are interpreted in terms of initial dislocation content, dislocation structures, and microstructural and chemical homogeneity.

The certification and qualification paradigms required for additively manufactured (AM) metals and alloys must evolve given the absence of any broadly accepted “ASTM- or DIN-type” AM certification/qualification processes or fixed AM-material produced specifications. This is in part due to the breath of the evolved microstructures produced across the spectrum of AM manufacturing technologies including powder bed and directed energy systems. Accordingly, design and microstructure optimization, manufacture, and thereafter implementation and insertion of AM-produced materials to meet the wide range of engineering applications requires detailed quantification of the structure/property behavior of AM-materials, across the spectrum of metallic AM methods, in comparison/contrast to conventionally-manufactured metals and alloys. The scope of this talk is a discussion of some present opportunities and challenges to achieving qualification and certification of AM produced metals and alloys for engineering applications.

This study utilizes in situ thermal imaging to monitor the melt pool during a LENS additive manufacturing (AM) process. A software tool is created which gathers metrics for each frame and summarizes them over every build. Plotted metrics allow a user to visually inspect the data, but the software tool also automatically identifies anomalies and flags them for further review. Anomalies are then correlated to physical locations in the build which are inspected for defects. This type of process monitoring could lead to fast detection of defects during a build, thus increasing the confidence in production quality and eliminating the acceptance of parts with abnormalities. An anomalous event was identified by the software tool and investigated with X-ray computed tomography. Defects were observed in the location identified by the software tool.

Certification and product qualification of an engineering component generally involves meeting engineering and physics requirements tied to its functional requirements.. In this paper, the results of a study quantifying the microstructure and the dynamic damage evolution of Tantalum (Ta) fabricated using an EOS laser-powder-bed machine are presented. The microstructure of the AM-Ta is detailed and compared / contrast to wrought Ta. The dynamic damage evolution and failure response of the AM-Ta material, as well as wrought Ta, was probed using flyer-plate impact driven spallation experiments. The differences in the spallation response between the AM and wrought Ta were measured using in-situ velocimetry as well as post-mortem quantification of damage in “soft-recovered” samples. The damage evolution of the AM and wrought Ta were characterized using optical metallography.

For additive manufacturing (AM) of metallic materials, the certification and qualification paradigm needs to evolve as there currently exists no broadly accepted “ASTM- or DIN-type” additive manufacturing certified process or AM-material produced specifications. Accordingly, design, manufacture, and thereafter implementation and insertion of AM materials to meet engineering applications requires detailed quantification of the constitutive (strength and damage) properties of these evolving materials, across the spectrum of metallic AM methods, in comparison/contrast to conventionally-manufactured metals and alloys. This report summarizes the 316L SS research results and presents initial results of the follow-on study of 304L SS. For the AM-316L SS investigation, cylindrical samples of 316L SS were produced using a LENS MR-7 laser additive manufacturing system from Optomec (Albuquerque, NM) equipped with a 1kW Yb-fiber laser. The microstructure of the AM-316L SS was characterized in both the “as-built” Additively Manufactured state and following a heat-treatment designed to obtain full recrystallization to facilitate comparison with annealed wrought 316L SS. The dynamic shock-loading-induced damage evolution and failure response of all three 316L SS materials was quantified using flyer-plate impact driven spallation experiments at peak stresses of 4.5 and 6.35 GPa. The results of these studies are reported in detail in the first sectionmore » of the report. Publication of the 316L SS results in an archival journal is planned. Following on from the 316L SS completed work, initial results on a study of AM 304L SS are in progress and presented herein. Preliminary results on the structure/dynamic spallation property behavior of AM-304L SS fabricated using both the directed-energy LENS and an EOS powder-bed AM techniques in comparison to wrought 304L SS is detailed in this Level 2 Milestone report.« less

For Certification and qualification of an engineering component generally involves meeting engineering and physics requirements tied to its functional requirements. In this paper, the results of a study quantifying the microstructure, mechanical behavior, and the dynamic damage evolution of Tantalum (Ta) fabricated using an EOS laser-powder-bed machine are presented. The microstructure and quasi-static mechanical behavior of the AM-Ta is detailed and compared / contrasted to wrought Ta. The dynamic damage evolution and failure response of the AM-Ta material, as well as wrought Ta, was probed using flyer-plate impact driven spallation experiments. The differences in the spallation response between the AM and wrought Ta were measured using in-situ velocimetry as well as post-mortem quantification of damage in “soft-recovered” samples. The damage evolution of the AM and wrought Ta were characterized using both optical metallography and electron-backscatter diffraction.