Additive Manufacturing of Metals: Establishing Location-Specific Processing-Microstructure-Property Relationships: Defects and Fatigue
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: High Temperature Alloys Committee, TMS: Shaping and Forming Committee, TMS: Additive Manufacturing Bridge Committee
Program Organizers: Eric Lass, NIST; Judy Schneider, University of Alabama-Huntsville; Mark Stoudt, National Institute of Standards and Technology; Lee Semiatin, AFRL; Kinga Unocic, Oak Ridge National Laboratory; Joseph Licavoli, Michigan Technological University; Behrang Poorganji, YTC America Inc.

Wednesday 2:00 PM
March 1, 2017
Room: 7B
Location: San Diego Convention Ctr

Session Chair: Kinga Unocic, Oak Ridge National Laboratory; Michael Kirka, Oak Ridge National Laboratory

2:00 PM  Invited
An Integrated Platform for Predicting the Mechanical Behavior of Additive Manufactured Metal Parts: Jian Cao1; Wing Liu1; Sarah Wolff1; Steven Lin1; Wei Xiong1; Puikei Cheng1; Gregory Wagner1; Eric Faierson2; Federico Sciammarella3; Kornel Ehmann1; Greg Olson1; 1Northwestern University; 2Quad City Manufacturing Laboratory & Western Illinois University; 3Northern Illinois University
    Additive manufactured (AM) metal components are growing in ubiquity in biomedical and aerospace industries for their complexity and flexibility. Our recent work aims to predict localized inhomogeneity and anisotropy of direct material deposition processed materials. A collaboration of simulation methods and material characterization were used in this study, including an in-house code that captures the thermal history and material development at each point during a build, material characterization of pore shape and size using optical microscopy and X-ray micro-tomography, and a modified GTN material model to predict pore coalescence and ductile failure of a component at localized points. Direct relationships between localized thermal history and structure were found. By understanding the relationships between process, cooling rate, porosity and mechanical behavior at localized areas of a DMD-processed component, closed-loop control of process parameters can be achieved for desirable and controlled material properties.

2:30 PM  
Microstructural Evolution and Fatigue Behavior of SLM Processed Alloy IN625: John Samuel Dilip Jangam1; Md Anam1; Deepankar Pal1; Brent Stucker2; 1University of Louisville; 23D SIM LLC
    Microstructural evolution and fatigue properties of alloy IN625 processed using selective laser melting (SLM) were investigated. Samples were fabricated in horizontal, vertical and inclined (45°) orientations. Microstructures of the as-built and heat treated samples were investigated using optical and scanning electron microscopes, X-ray diffraction, and electron backscattered diffraction techniques. As-built specimens showed coarse columnar grains with internal cellular substructure. EBSD of the as-built samples showed a considerable amount of texture developed in the as-built parts. Fatigue tests were carried out on the specimens built in different orientations and heat treated ones. The present study will summarize the effect of build orientation on the fatigue properties in alloy IN625.

2:50 PM  
Investigating the Role of Porosity in DMLS IN718 by Crystal Plasticity Modeling with Experimental Validation: Veerappan Prithivirajan1; Todd Book1; Diwakar Naragani1; Michael Sangid1; 1Purdue University
    Direct metal laser sintering (DMLS) can be used for aerospace applications to realize numerous advantages, which have been well documented. However, prior to their use in safety critical components, the failure mechanisms have to be well understood, especially for the unique defects in DMLS materials, especially porosity. In our work, fatigue crack initiation of a Ni-based superalloy, IN 718, produced by DMLS is studied via crystal plasticity finite element (CPFE) simulations and experimental tools such as (i) concurrent digital image correlation and electron backscatter diffraction (DIC-EBSD) and (ii) high energy x-ray diffraction microscopy (HEDM). Hot spots obtained from the CPFE simulations are used to identify the possible location of the crack initiation. Also, the role of pore size on the crack nucleation is investigated. Finally, the strain fields obtained from the CPFE simulations are compared to experimental data obtained from DIC-EBSD and HEDM.

3:10 PM  
Anisotropic Mechanical Behavior of AlSi10Mg Parts Produced by Selective Laser Melting: Ming Tang1; Petrus Pistorius1; 1Carnegie Mellon University
    As one metal additive manufacturing process, selective laser melting (SLM) is usually accompanied by the development of anisotropy, which arises from sample geometry and building orientation. To date, there have been only a limited number of studies on this topic. In this work, anisotropic behavior of AlSi10Mg parts produced by SLM was investigated by performing tension and fatigue tests, employing microscopy to examine the internal porosity and microstructure development at the fracture surface, and nanohardness measurements to quantify the local decrease in strength. The results shows that Z-oriented samples have appreciably lower ductility and shorter fatigue life, and tearing along the coarser heat-affected zone is observed. The coarser solidification microstructure at the heat-affected zone is responsible for the loss of ductility, and porosity distribution brought by the laser scanning strategy dominates orientation-dependent performance during fatigue tests.

3:30 PM Break

3:50 PM  
Microstructure Evolution, Tensile and Dynamic Properties, and Computational Modeling in Ti-6Al-4V and Inconel 718 Alloys Manufactured by Laser Engineered Net Shaping: Yuwei Zhai1; Diana Lados1; Eric Brown2; Greg Vigilante2; Robert Warren1; 1Worcester Polytechnic Institute; 2Benet Labs
    Laser Engineered Net Shaping (LENS) is a directed energy deposition process able to fabricate fully dense metallic parts. Applying LENS to structural components and repair requires a fundamental understanding of the microstructure, static and dynamic properties, and damage mechanisms of the LENS-fabricated materials. In this study, Ti-6Al-4V and Inconel 718 alloys were deposited using two laser power levels for each material, and investigated in both as-fabricated and heat treated conditions. The effects of processing parameters and heat treatments on microstructure and room temperature tensile and fatigue crack growth (FCG) properties were systematically studied. FCG tests (R=0.1, 0.8) were performed in different orientations with respect to the deposition direction, in order to establish the FCG mechanisms at the microstructural scale of the alloys at different growth stages, and further correlate them to the processing conditions using thermal simulations results. The findings will be compared and critically discussed for processing-microstructure-properties optimization.

4:10 PM  
Fracture and Fatigue Behavior of Additively Manufactured Austenitic Stainless Steel: Chris San Marchi1; Josh Sugar1; Michael Maguire1; Dorian Balch1; 1Sandia National Laboratories
    Innovation in additive manufacturing (AM) has propagated methods for producing net-shape or near net-shape components. The microstructures of the materials produced by additive manufacturing are distinct from conventional casting and wrought product in addition to being as diverse as the multitude of strategies that are being employed for additive manufacturing. For component design in high-value applications, such as in aggressive environments, the effect of the unique microstructures on mechanical performance must be evaluated. This report explores the microstructure as well as bulk mechanical properties of austenitic stainless steels produced by additive manufacturing. In particular, fracture and fatigue properties are reported and compared to performance of wrought materials. In addition, the environmental effects of hydrogen on mechanical properties are explored in relationship to the unique microstructure of these materials as well as in the context of our existing knowledge of the microstructure and performance of wrought product.

4:30 PM  
Classification, Effects, and Prevention of Build Defects in Powder-bed Fusion Printed Inconel 718: Arthur Brown1; Zachary Jones1; William Tilson2; 1NASA-Marshall Space Flight Center; 2 Jacobs-ESSSA Group
    The development of aerospace quality 3D printed Inconel 718 is predicated on producing defect-free material. Successfully producing and qualifying such material will reduce not only cost but also production times of many engine components. Therefore, knowledge of causal relationships between build process variables and possible generation of defects is considered essential. For a given set of build process variables, the known defects have been classified by their morphologies, consequence, and method of prevention. An example of each defect type along with it’s known cause and effect on the materials performance is given. Lastly, strategies for defect prevention are discussed.

4:50 PM  
Investigating Strain Localization in DMLS TI-6Al-4V Using CPFE Modeling and DIC: Kartik Kapoor1; Todd Book1; Michael Sangid1; 1Purdue University
    Ti-6Al-4V, an extensively used titanium alloy, produced via Additive Manufacturing (AM) techniques offers tremendous benefits over conventional manufacturing processes. However, there is inherent uncertainty associated with material properties, preventing their use as critical components. Since these uncertainties arise due to varying microstructures, there is a growing need to link the underlying microstructure to the properties of the final part. This work investigates Ti-6Al-4V produced via direct metal laser sintering (DMLS) by carrying out crystal plasticity finite element (CPFE) simulations and digital image correlation (DIC) on the samples. Possible sites for damage nucleation are identified, which correspond to regions of high plastic strain accumulation. Results indicate that prior beta boundaries play an important role in strain localization within the grains. This is significant as the size and orientation of the prior beta grains may be controlled via AM process parameters.

5:10 PM  
Mechanical Properties of SS316L Manufactured by Laser Powder Bed Additive Manufacturing: Håkan Brodin1; 1Siemens Industrial Turbomachinery AB
    The current paper is providing an insight in the mechanisms that control damage development and fracture in laser powder bed additive manufactured stainless steel 316L.. Mechanical testing has also been performed. SS316L is typically available as a hot-rolled material and results are compared to results on the conventional material. Tensile and fatigue properties of 316L manufactured by additive manufacturing and hot-rolling are reported. The additive manufactured material has a morphology with high aspect ratio grains, where e grains are elongated in the additive manufacturing build direction. Material manufactured by hot-rolling is equiaxed with a larger grain size. The grain size difference is reflected in the material strength, where a fine-grained material exhibits a higher strength accompanied by a reduction in ductility. Fatigue properties of the additive manufactured material are also influenced by the manufacturing process, where inherent material defects in the additive manufactured material reduces resistance to crack initiation.