Additive Manufacturing Benchmarks 2022 (AM-Bench 2022): Mechanical Behavior III
Program Organizers: Brandon Lane, National Institute of Standards and Technology; Lyle Levine, National Institute of Standards and Technology
Tuesday 1:30 PM
August 16, 2022
Room: Regency Ballroom I & II
Location: Hyatt Regency Bethesda
Session Chair: Jake Benzing, National Institute of Standards and Technology
1:30 PM Invited
Powder Oxygen Heterogeneities and Significant Intra-build Tensile Strength Variation from Common EB-PBF Ti-6Al-4V Powder Reuse Methods: Nicholas Derimow1; Jake Benzing1; Newell Moser1; Orion Kafka1; Nik Hrabe1; Priya Pathare2; Frank DelRio2; 1National Institute of Standards and Technology; 2Sandia National Laboratories
Tensile strength was found to vary significantly (15% changes in UTS and YS) within a single build of electron beam powder bed fusion (EB-PBF) Ti-6Al-4V, and heterogenous local oxygen content was found to be the major contributor to this strength variability. No significant correlation was found between tensile behavior (375 specimens tested) and plate location (X-Y), porosity (x-ray CT, fractography), alpha lath thickness (SEM-BSE), or crystallographic texture (SEM-EBSD). Strength was found to correlate with local oxygen content (inert gas fusion and TOF-SIMS) and build height (Z). Oxygen variation most likely arises from current EB-PBF Ti-6Al-4V powder reuse methods, which commonly involve frequent mixing of powders with differing oxygen content. Changes to powder reuse methodology to avoid significant differences in mechanical behavior for identical parts on the same build plate will be discussed. SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525.
2:00 PM
Combining Fractal and Topological Analyses to Quantify Fracture Surfaces in Additively Manufactured Ti-6Al-4V: Ian Wietecha-Reiman1; Albert Segall1; Xiaoliang Zhao2; Todd Palmer3; 1The Pennsylvania State University; 2Intelligent Automation; 3Pennsylvania State University
The quantitative analysis of fracture surfaces has long been hindered by the lack of tools capable of quickly providing usable information on fracture modes and crack initiation locations. An easily implementable non-destructive image analysis-based tool utilizing a combination of fractal analysis and topological techniques has been developed. This tool can be used to analyze selected locations across a fracture surface by processing high resolution images and calculating both the fractal dimension to quantify feature complexity and the lacunarity for defining feature directionality. With the incorporation of topology measurements, the connectivity of fracture features can also be characterized, thus enhancing the fidelity of the quantitative analysis and the ability to differentiate fracture micro-mechanisms in a quantitative fashion. Validation was performed on complex multi-mode fracture surfaces in additively manufactured Ti-6Al-4V materials subjected to static and fatigue loading conditions. Fracture initiation sites at both sub-surface and internal defects were identified using this tool.
2:20 PM
Effect of Process-specific Defects on the Tensile and Constant-amplitude Tatigue Behavior of As-built Ti-6Al-4V Alloy Produced by Laser Powder Bed Fusion Process: Saikumar Reddy Yeratapally1; Erik Frankforter2; George Weber2; Peter Spaeth2; Christapher Lang2; Albert Cerrone3; Edward Glaessgen2; 1National Institute of Aerospace; 2NASA Langley Research Center; 3University of Notre Dame
The influence of various process parameters on the mechanical behavior (including tensile strength, strain-to-failure and constant-amplitude fatigue performance) of as-built Ti-6Al-4V alloy, produced via laser powder bed fusion (L-PBF) process, is demonstrated using complementary information obtained from mechanical tests, fractography analysis, metallographic analysis and micromechanical simulations. Four different build conditions were considered such that the laser power and velocity were varied for each build while holding the build orientation, hatch spacing, layer thickness, laser spot size and hatch rotation constant. Two coupons per build were subjected to constant-amplitude fatigue loading while one coupon per build was subject to uniaxial tensile loading at room temperature. The effect of process-specific defects will be contextualized by using complementary information obtained from X-ray computer tomography (CT), fractography imaging and micromechanical simulations. The resultant mechanical performance will be correlated to pore distribution, crack profiles from fractography imaging and the estimated strain fields from micromechanical simulations.
2:40 PM
Tunable PBF-EB Ti-6Al-4V Fatigue Performance via Controlled Powder Recovery: Nicholas Derimow1; Keenan Hanson2; Jake Benzing1; Newell Moser1; Orion Kafka1; Nik Hrabe1; 1National Institute of Standards and Technology; 2Stryker Orthopaedics
A surface layer comprised of globular alpha has been identified in electron beam powder bed fusion (PBF-EB) titanium alloy (Ti-6Al-4V), and the effect of this surface layer on rotating bending fatigue behavior (ISO 1143) will be discussed during this talk. The globularization of alpha occurs due to post-build plastic deformation during normal sintered powder removal blasting, followed by standard Ti-6Al-4V hot isostatic pressing heat treatment. Three surface layer thickness conditions were studied by varying blasting working distance, i.e. the separation of the blasting nozzle from the part being blasted. An additional condition with no surface layer was studied by replacing blasting with ultrasonic techniques to remove powder. Microstructure (SEM-EBSD), porosity (x-ray CT), and surface roughness (optical profilometry) were characterized. The influence of this globular alpha surface layer on fatigue behavior will be discussed in the context of the ability to tune fatigue response through control of the surface layer thickness.
3:00 PM Break