Additive Manufacturing: Building the Pathway towards Process and Material Qualification: Feedstock
Sponsored by: TMS Extraction and Processing Division, TMS Materials Processing and Manufacturing Division, TMS Structural Materials Division, TMS: Mechanical Behavior of Materials Committee, TMS: Powder Materials Committee, TMS: Process Technology and Modeling Committee, TMS: Additive Manufacturing Bridge Committee
Program Organizers: John Carpenter, Los Alamos National Laboratory; David Bourell, University of Texas - Austin; Allison Beese, Pennsylvania State University; James Sears, GE Global Research Center; Reginald Hamilton, Pennsylvania State University; Rajiv Mishra, University of North Texas; Edward Herderick, GE Corporate

Thursday 8:30 AM
March 2, 2017
Room: 8
Location: San Diego Convention Ctr

Session Chair: Chantal Sudbrack, NASA Glenn Research Center; Bryan McEnerney, Jet Propulsion Laboratory

8:30 AM  Invited
Investigation of Powder Feedstock Variability for SLM Alloy 718: Chantal Sudbrack1; David Ellis1; 1NASA Glenn Research Center
    Additive manufacturing stands to revolutionize the aerospace design and manufacturing paradigm, driving an important need to develop certification standards for flight-ready AM components. NASA has sponsored a multi-year effort to develop a NASA standard that covers all levels of component development and criticality. It would govern hardware fabricated by selective laser melting (SLM) under sanctioned projects, including Alloy 718 components for NASA’s Space Launch System engine. The impact of feedstock variability on the microstructure and durability of SLM 718 components is being examined using 12 off-the-shelf, gas-atomized powder lots, most with standard particle size distributions (PSDs). Well-blended, representative samples from each lot were obtained for chemistry, PSD, morphology, flow, rheological properties and SEM evaluation. The major, minor, and trace elements varied within the acceptable wide ranges for Alloy 718, allowing insight into compositional space. The relationship of this suite of measurements to the as-built and post-processed properties will be outlined.

9:00 AM  
The Influence of Gas Cooling in Context of Wire Arc Additive Manufacturing: A Novel Strategy of Affecting Grain Structure and Size: Philipp Henckell1; 1Technische Universitšt Ilmenau
    The continuous building process in additive manufacturing with gas metal arc welding (GMAW) provides the main advantage of a decreased processing time but leads to a high heat input in the built work piece. Especially geometrically small parts are affected by a coarse and constantly growing grain structure throughout the continuous reheating process. A novel approach of influencing the temperature-time regime during the additive manufacturing process is an application of additional cooling gas. Experimental trials with argon, hydrogen and nitrogen were carried out and analyzed by means of thermal imaging, hardness measurement and microscopy. The experimental results showed a significant influence of cooling gases on the temperature during the building process. Hence, grain structure and size can be modeled to a homogeneous microstructure by the composition of the gas.

9:20 AM  
Tomography and 3D Grain Mapping for Additive Manufacturing Qualification: Leah Lavery1; Hrishikesh Bale1; Jeff Gelb1; Arno Merkle1; 1Carl Zeiss X-ray Microscopy, Inc.
    Additive manufacturing techniques can produce complex anisotropic 3D structures. The reliability and performance of the produced parts relies heavily on the resultant microstructure from often-proprietary feedstock. Materials designed for high-stress applications can be quite sensitive to discrete, complex pore structure, therefore the need to investigate and understand the morphology in 3D at the appropriate pore scale to avoid premature failure. X-ray microscopy (XRM) for tomography using a laboratory source was used to characterize porosity in additive process control study for various steel input materials and Inconel alloys. For additional process and material qualification, a new XRM commercial development for 3D grain mapping termed diffraction contrast tomography (DCT) will be discussed. An example of this capability was used to follow the sintering of copper particles through a series of time-lapsed DCT measurements. XRM can provide accurate 3D internal structural information critical to aid computational design of next-generation materials.

9:40 AM  Invited
Qualification Development for AlSi10Mg for Robotic Spaceflight: Bryan McEnerney1; R. Dillon1; John Paul Borgonia1; Daniel Weinstock1; Andrew Shapiro-Scharlotta1; 1Jet Propulsion Laboratory
    NASA JPL has baselined the use of AlSi10Mg (SAE 4032) for use as an electronics enclosure on the upcoming International Space Station (ISS) instrument package, ECOSTRESS. Basic thermostructural and physical properties of alloy have been reasonably well characterized, but there is a lack of literature on the effects of aging on the fracture toughness, strength and impact energy of the alloy system. In addition, proof testing and non-destructive evaluation of the alloy systems, including techniques for determine precipitate or grain sizes will be examined and discussed to determine relevancy to accepting parts for robotic spaceflight.

10:10 AM Break

10:30 AM  
Numerical Investigations of the Coating Process during Powder Bed Additive Manufacturing: Mustafa Megahed1; Wolfgang Ottow1; 1ESI Group
     In spite of the significant time required to spread powder and the importance of obtaining a uniform powder bed for process stability and product quality, very few studies on powder coating have been reported. Preliminary numerical studies have shown unexpected low packing densities with large differences along the powder bed [Mindt, 2016]. This paper systematically analyzes the coating process numerically. Several metrics characterizing the powder layer are introduced prior to studying two different commercial powders. One powder has a high fraction of small particles and the other has larger particles. Multiple process parameters are analyzed. Results show the powder size distribution on the processing table and the recycled bin. One of the interesting findings with significant financial implications is that the quality of spread powder and recycled powder can be significantly enhanced (unified) if the coating parameters are fine tuned.

10:50 AM  
In-process Monitoring of Cross Contamination in Laser Powder Bed Fusion Additive Manufacturing: Mahdi Jamshidinia1; Paul Boulware1; Jacob Marchal1; Heimdall Mendoza1; Lance Cronley1; Scott Newhouse1; 1EWI
    Cross contamination in laser powder bed fusion (L-PBF) additive manufacturing (AM) could result in the formation of flaws, and consequently lower the mechanical performance of a component. In this study, the in-process monitoring and detection of cross contamination was investigated in L-PBF process, also known as direct metal laser sintering (DMLS). A setup was designed and fabricated at EWI, where contaminant materials could be introduced on the powder bed without pausing the fabrication process or breaking the chamber environment. Tungsten was used as the contaminant material, in the matrix of Inconel 625. Six levels of contamination were calibrated, and introduced in two stationary and mobile modes. Photodetector, spectrometer, and optical camera were used for the data acquisition. One of the sensors showed the most promising results for one of the materials. X-ray computed tomography (CT) and optical microscope were used to validate data collected by the sensors.

11:10 AM  
Microstructure and Mechanical Properties of Laser Deposited Ni/WC Metal Matrix Composite Coatings: Abhishek Ramakrishnan1; Amrinder Singh1; Guru Dinda1; 1Wayne State University
    The current study the effect of laser metal deposition of WC reinforced Nickel composite coatings was investigated for the application of hardfacing coating on copper. Ni/60WC MMC were fabricated on the surface of copper with a buffer layer of hastelloy C-276. An additional set of samples were deposited on a 1020 mild steel substrate. Metal deposition was carried out by a circular laser spot of 2 mm diameter to melt the metal powder particles. Three principal experiments were conducted in a systematic order to understand the microstructural evolution of Ni/60WC MMC. A multi-track, single track deposit and re-melting of the as deposited surface were systematically investigated by optical microscopy which revealed homogenous distribution of WC particles. Microstructural morphology of Ni/60WC particles were analyzed by scanning electron microscopy. The results revealed microstructural element such as equiaxed structure, columnar dendrites, eutectic structure and several other complex carbide structures. It was observed that the presence of three principle phases in the deposit consisted of the primary WC, dendritic Ni and a eutectic structure. Microhardness of the laser deposited samples indicated the gradual variation in hardness as the deposition transits from a highly conductive soft material to a hard facing coating. Homogenization of WC in Ni composite coating was well realized in this study.

11:30 AM  Invited
Phase-field Modeling of Microstructure Evolution during Additive Manufacturing of Ti-6Al-4V Alloys: Yanzhou Ji1; Lei Chen2; Long Qing Chen1; 1Penn State University; 2Mississippi State University
    Additive manufacturing (AM) of metallic alloys involves thermal cycles that result in microstructures differing drastically from their cast or wrought counterparts. Such different microstructure features critically affect the mechanical properties of the AM builds. In this presentation, we discuss a multi-scale computational framework based on the phase-field method for modeling microstructure evolution process during AM: (i) macroscopic finite element calculations for temperature distribution and thermal history; (ii) grain-scale phase-field model for solidification and grain growth; (iii) sub-grain-scale phase-field model for β →α phase transformations. We demonstrate the proposed framework by simulating the microstructure evolution during selective electron beam melting (SEBM) of a Ti-6Al-4V component in terms of both β-grain textures and (α+β) microstructure features. Upon the experimental validation, the proposed model predicts the <001>β// NZ columnar grain structure aligned with the build direction, as well as the inward curved β-grain structure in the skin layer. The effect of building parameters and build geometry on the microstructure features will also be discussed.