Additive Manufacturing: Nano/Micro-mechanics and Length-scale Phenomena: Microstructural Features II
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Additive Manufacturing Committee, TMS: Nanomechanical Materials Behavior Committee
Program Organizers: Meysam Haghshenas, University of Toledo; Robert Lancaster, Swansea University; Andrew Birnbaum, Us Naval Research Laboratory; Jordan Weaver, National Institute Of Standards And Technology; Aeriel Murphy-Leonard, Ohio State University
Wednesday 8:30 AM
March 2, 2022
Room: 260A
Location: Anaheim Convention Center
Session Chair: Kavan Hazeli, The University of Arizona; Andrew Birnbaum, US Naval Research Laboratory (NRL)
8:30 AM
Understanding the Influence of Microstructure and Voids during Induced Spall Failure of Additive Manufactured Stainless Steel: Josh Kacher1; Katie Koube1; Taylor Sloop1; Kevin Lamb2; Suresh Babu3; 1Georgia Institute of Technology; 2Y-12 National Security Complex; 3University of Tennessee Knoxville
Additive manufactured stainless steel has a rich hierarchy of defect structures, including dense dislocation cell networks at the microscale, coarse and refined grain structures at the mesoscale, and void structures ranging from microns to millimeters. Multiple studies have focused on the influence of these defect structures on mechanical properties, though primarily under quasistatic loading conditions. In this study, we investigated the influence of microstructural features and intentional voids on spall initiation under high strain rate loading conditions. By varying the size and distribution of voids in the printed materials, we explored the relative importance of voids verses melt pool boundaries on spall initiation and dislocation accumulation. Post mortem, we used multiscale electron microscopy characterization, including high resolution electron backscatter diffraction and site specific transmission electron microscopy characterization, to characterize the defect structures accompanying spall initiation and crack propagation. Discussion will focus on the micro and mesoscale mechanisms dictating spall initiation.
8:50 AM
Effect of Skin Microstructure on the Bending Properties of Additively Manufactured IN625 Beams: Arunima Banerjee1; Sara Messina2; William Musinski3; Paul Shade3; Marie Cox3; Matthew Begley2; Kevin Hemker1; 1Johns Hopkins University; 2UCSB; 3Air Force Research Laboratory
Additively manufactured (AM) metallic structures often have location-dependent microstructures that depend on the laser raster pattern and thermal history. This can lead to spatial variations in the attendant mechanical properties. This study was undertaken to determine the location-specific material properties of IN625 beams fabricated via laser powder bed fusion approach. Samples either retained their as-printed microstructure consisting of smaller grains in the outer skin and larger grains in the interior region or were polished to remove the outer skin. Micro-bending tests were performed on both sets of samples to compute the contribution of the outer skin to the measured properties. The samples with the outer skin had a higher bending strength and hardening rate. These observations provide insight into the material properties and modeling approaches that need to be employed to capture the spread of plasticity in complex, printed thin-walled structures with similar microstructural variations.
9:10 AM
Effect of LPBF Parameters on Post Heat Treatment Microstructure and Sub-sized Tensile Properties of LPBF Inconel 718: Jayaraj Radhakrishnan1; Punit Kumar2; Upadrasta Ramamurty2; 1Nanyang Technological University; 2NTU
Novel LPBF processing strategies have shown to enhance tensile properties of IN718 by designing mesostructure and controlling texture evolution. In light of such efforts, there is a need to scrutinize the applicability of standard heat treatment on different as-fabricated microstructures. Moreover, it is important to study the cascading effect of in-built texture and sub-grain boundary fraction on post heat treatment grain growth and precipitate evolution. In the present work, quasi-static sub-sized tensile tests of heat-treated IN718 fabricated using two distinct LPBF machines were conducted. Five heat treatments were conducted by selecting solutionizing temperature above and below the solvus of δ and Laves phase to vary the proportion of strengthening precipitates. Role of cellular structure, microstructure, texture, and precipitates on the strengthening mechanism and ductility was examined to elucidate the observed differences in tensile properties of IN718.
9:30 AM
Microstructure and Mechanics of Hydrogel Enabled Additively Manufactured Metals and Metal Alloys: Rebecca Gallivan1; Max Saccone1; Thomas Tran1; Julia Greer1; 1California Institute of Technology
Microstructural features such as twins and grain boundaries directly impact mechanical behavior in metals and when engineered can push properties to new extremes. We have recently developed an additive manufacturing technique which converts hydrogels printed via vat polymerization into metal and metal alloy structures through a calcination and reduction process. With this unique manufacturing methodology, we can push materials into non-equilibrium microstructures, such as heavily twinned grains, opening a new space for material design and fundamental investigation of nano-plasticity. Through EBSD, TEM, and a suite of nanomechanical experiments, we show the impact of processing on microstructural features and mechanical properties. This work provides direct insight to micro- and nano-scale mechanical properties of materials made through this unique process and highlights the opportunities for novel microstructural engineering of additively manufactured metals and metal alloys.
9:50 AM Break
10:10 AM
On the Influence of the Representative Volume Elements Size on Predicting Dislocation Microstructure Evolution in Laser Additive Manufacturing Metals: Markus Sudmanns1; Jaafar El-Awady1; 1Johns Hopkins University
Selective Laser Melting (SLM) is a promising technique for additive manufacturing (AM) of metallic components, however, modeling dislocation microstructure evolution during processing and mechanical loading involves significant challenges due to imposed constraints in domain size, time scale, and boundary conditions. The complex interactions induced by the multi-scale nature of the process with high temperatures, induced residual stresses, and microsegregation requires careful consideration of the influence of the simulation domain on the predicted results. We combine Finite Element Analysis of thermo-mechanical stresses induced by single track SLM scans of various alloys and the associated dislocation microstructure evolution with large-scale 3D discrete dislocation dynamics simulations to investigate the relationship between time scale and simulation domain in mesoscale simulations and properties of evolving microstructural features. The results here provide an understanding of requirements for simulation domains in mesoscale simulations for being sufficiently representative of the overall process under consideration.
10:30 AM
Temperature-dependent Evolution of Dislocation Microstructure and Mechanical Properties of SLM-316L Stainless Steel: Markus Sudmanns1; Andrew Birnbaum2; Yejun Gu1; Athanasios Iliopoulos2; John Michopoulos2; Jaafar El-Awady1; 1Johns Hopkins University; 2US Naval Research Laboratory
Selective Laser Melting (SLM) has evolved into a promising technique of additive manufacturing (AM) for building three-dimensional (3D) components with high resolution. However, the relationship between processing conditions and the observed microstructures and mechanical properties is still poorly understood. This prevents a reliable prediction of mechanical properties of SLM manufactured parts. We investigate the multi-scale nature of SLM processing by Finite Element Analysis (FEA) of induced thermo-mechanical stresses and dislocation microstructure evolution by large-scale 3D d6iscrete dislocation dynamics (DDD) simulations of SLM-316L stainless steel in comparison with experiments. The complex interplay and transient nature of temperature, residual stresses, and chemical segregation on the evolution of the dislocation microstructure during the cool-down phase is studied. Further, we investigate the influence of the dislocation microstructure and chemical environment on the mechanical response of the manufactured part. Thereby we provide a unique mechanistic perspective on the complex, multi-scale nature of SLM processing.