Additive Manufacturing: Processing Effects on Microstructure and Material Performance: Residual Stress and Texture
Sponsored by: TMS: Additive Manufacturing Committee
Program Organizers: Eric Lass, University of Tennessee-Knoxville; Joy Gockel, Wright State University; Emma White, DECHEMA Forschungsinstitut; Richard Fonda, Naval Research Laboratory; Monnamme Tlotleng, University of Johannesburg; Jayme Keist, Pennsylvania State University; Hang Yu, Virginia Polytechnic Institute And State University
Wednesday 2:00 PM
February 26, 2020
Room: 6E
Location: San Diego Convention Ctr
Session Chair: Hang Yu, Virginia Polytechnic Institute and State University
2:00 PM
Interface Texture Development of Additively Manufactured Materials: David Rowenhorst1; Aeriel Murphy-Leonard1; Richard Fonda1; 1U.S. Naval Research Laboratory
During the additive manufacturing process, the complex processing conditions of overlapping rapidly solidified melt pools, with preferred solidification directions changing from layer-to-layer leads to a highly complex grain morphology. Using automated mechanical serial-sectioning combined with EBSD, we reveal this complex morphology of the as-built material in 316L stainless steel produced through laser-powder based fusion. The 3D reconstruction shows that grain morphologies are more complex and that the sizes are much larger than expected from 2D cross-sections. Additionally, we show that the interface texture is at a highly non-equilibrium condition, with most of the interfaces within the as-built material occupying relatively high energy configurations. We also show that with subsequent heat treatments, that this interface texture, through processes of recrystallization and grain growth will approach that of the equilibrium state.
2:20 PM
Grain Boundary Engineering of Additively Manufactured Stainless Steel: Shubo Gao1; Hu Zhiheng2; Chin Kai Siang1; Song Xu2; Matteo Seita1; 1Nanyang Technological University; 2Singapore Institute of Manufacturing Technology
Grain boundary engineering (GBE) is a processing strategy aimed at increasing the fraction of ∑3 grain boundaries in metals via a sequence of strain-annealing cycles. Despite the positive impact of GBE on the physical and mechanical properties of materials, it is impractical to employ it for the production of advanced alloys due to its high costs and energy requirements. In this study, we propose the integration of GBE in selective laser melting (SLM) processes as a more viable processing route for enhancing materials performance. Our strategy combines the inherent thermal strains induced during SLM with mechanical strains, which may be applied layer by layer during the additive process. Using 316L stainless steel as a case study material, we produce samples with up to 40% ∑3 boundaries. Our study provides the groundwork for designing and developing a hybrid SLM technology that integrates in-situ mechanical deformation capabilities for GBE of structural parts.
2:40 PM
Crystallographic Texture Control in Additively Manufactured Stainless Steel: Sudharshan Raman1; Bernard Gaskey1; Ekta Jain1; Shubo Gao1; Kishore Venkatesan2; David Ritchie3; Darren Fraser3; Sri Lathabai3; Matteo Seita1; 1Nanyang Technological Unviersity; 2CSIRO ; 3CSIRO
Site-specific microstructure control in metal additive manufacturing (AM) is a new paradigm aimed at producing parts with complex geometries which integrate multiple properties. In powder bed fusion technologies—such as selective laser melting (SLM)—microstructure control may be achieved by tailoring the solidification direction of the melt pool, layer by layer. In this work, we demonstrate this capability by varying the laser scanning angle during SLM to produce stainless steel samples with controlled crystallographic textures. The resulting microstructures range from quasi-single crystalline, to layers of controlled thickness with distinct and narrow grain orientation distribution. This strategy paves the way to a new generation of additively manufactured metals with optimized, site-specific properties to suit a wide range of applications.
3:00 PM
Crystallographic Texture Evolution in Additive Manufactured Metals as a Function of Build Height and Strategy: Alec Saville1; Jonah Klemm-Toole1; Sven Vogel2; Adam Creuziger3; Sudarsanam Babu4; Amy Clarke1; 1Colorado School of Mines; 2Los Alamos National Laboratory; 3National Institute of Standards and Technology; 4Oak Ridge National Laboratory/University of Tennessee-Knoxville
Metals produced via additive manufacturing (AM) exhibit non-uniform loading responses or anisotropy due to the directional growth of crystals during solidification. Understanding the process parameters involved with the formation of microstructure and anisotropy is critical to the qualification and certification and use of AM parts for high-performance structural applications. One of the primary causes of anisotropy is preferred crystal orientations (crystallographic texture), which can be controlled by altering AM processing parameters. This work presents a study on the texture evolution of AM-built Ti-6Al-4V via neutron diffraction, and demonstrates the influence of varying scan strategy on crystallographic texture at the bulk and local scales as a function of build height. The findings presented here are discussed in the context of improved process-microstructure-property relationships and the production of born-qualified parts.
3:20 PM
Controlling Residual Stress and Phase Transformations during Laser Powder Bed Fusion through large-area Surface Heating: John Roehling1; William Smith1; Tien Roehling1; Gabriel Guss1; Bey Vrancken1; Joseph McKeown1; Michael Hill2; Manyalibo Matthews1; 1Lawrence Livermore National Laboratory; 2University of California, Davis
Residual stresses are large in additively manufactured parts because of the high thermal gradients inherent to the process. In this work, residual stresses are effectively reduced by using a large-area heating beam in conjunction with the typical, tightly-focused, scanning beam to control the thermal history of fabricated parts. A reduction up to 90% of the effective residual stress was realized in bridge test specimens. Control of the thermal history is demonstrated and its effects on the microstructure and residual stress distribution are examined in stainless steel 316L. The decomposition and/or avoidance of the martensite transformation in Ti6Al4V is also demonstrated in test specimens.This work was performed under the auspices of the U.S. Department of Energy (DOE) by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
3:40 PM Break
4:00 PM
Influence of Selective Laser Melting Strategies and Post Treatment on the Residual Stresses and Microstructure of Alloy 718: Jan Capek1; Efthymios Polatidis1; Robert Pederson2; Christophe Lyphout3; Markus Strobl1; 1Paul Scherrer Institute; 2University West; 3Research Institute of Sweden
Selective Laser Melting (SLM) involves numerous building parameters and subsequently, numerous post-building treatment options that affect the geometrical integrity, surface quality, microstructure and mechanical behavior. SLM provides valuable prospects also for nickel-based superalloys that are used in many applications in aerospace or automotive, chemical and nuclear industry. However, the microstructure and mechanical properties of these materials are especially sensitive to building conditions and post-treatment, as they are susceptible to the formation of secondary phase precipitates.Coin-shaped samples of Alloy 718 , were built with different SLM building strategies. Residual stresses in the bulk of the specimen were measured by neutron diffraction experiment at the POLDI instrument at the Paul Scherrer Institute. In addition, electron backscatter diffraction and energy-dispersive X-ray spectroscopy were used to investigate the effect of building conditions on the microstructure, crystallographic texture and chemical variations.
4:20 PM
Residual Stress and Distortion Modeling of a LENS Ti-6Al-4V Thin Wall Using the Evolving Microstructural Model of Inelasticity: Matthew Dantin1; Matthew Priddy1; 1Mississippi State University
Predictive capabilities within additive manufacturing (AM) research have been a limiting factor for quality control and part qualification; however, AM modeling can reduce the time required for process optimization compared to traditional trial-and-error methods. This work focuses on the implementation of the Evolving Microstructural Model of Inelasticity (EMMI) into the Abaqus/Standard framework to examine the thermally induced residual stresses and distortion incurred from the Laser Engineered Net Shaping (LENS) of a Ti-6Al-4V thin wall. A 3D finite element thermal model calibrated using dual-wave pyrometer images was used to generate the temperature history of the thin wall build. The EMMI material constants were fitted based on tension, compression, and torsion tests. The results of the mechanical model are compared with experimental results found in literature along with results using the Bammann-Chiesa-Johnson mechanical model and an elastic-plastic mechanical model.
4:40 PM
Evaluation of Additively Manufactured Functionally Graded Titanium Alloys Tailored for Thermal Expansion Applications: Skyler Hilburn1; Timothy Simpson1; Todd Palmer1; 1Pennsylvania State University
Thermal stresses can be generated within a part due to a difference in thermal expansion at the interface with another component. Specific space applications require components to maintain accurate alignment with temperature changes. This research effort employs functional grading to tailor the thermal expansion of titanium through alloying with pure copper or pure silver. Directed energy deposition was used to produce three different compositions in each alloy system, evaluating if a rule-of-mixtures prediction was valid and determining how high the coefficient of thermal expansion could be raised. Post-build analysis showed that the phase fractions were not as predicted. Phase changes were observed after dilatometry testing and hot isostatic pressing, altering the thermal expansion behavior. Using these initial results, a functional gradient was developed to tailor the coefficient of thermal expansion. Mechanical properties were evaluated for individual compositions as well as fully graded samples to asses performance.
5:00 PM
Residual Stress Prediction in Metal Additive Manufacturing: Numerical Simulation and Experimental Validation: Tao Wu1; Thomas Niendorf1; 1University of Kassel
In the metal additive manufacturing (AM), the induced large thermal gradients lead to the appearance of high residual stresses within manufactured components, which may result in part failure. In this work, a well-established thermal-mechanical model will be employed for predicting the residual stress profile in the components built by AM. Not only laser parameters and scanning strategy will be accounted for, but also other factors poorly investigated in the open literature such as the position on the base plate as well as the interactions among different parts in the build chamber. Parametric studies will be carried out for establishing a thorough understanding of the relation between the utilized process parameters and the induced residual stresses. Numerical results will be validated by reliable residual stress measurements through, e.g. deep-hole drilling and X-ray diffraction, accounting for the microstructural features of the additively manufactured metallic components characterized by anisotropy and strong texture.
5:20 PM
Additive Manufacturing Simulation Comparison Using Commercial Tools: Charles Fisher1; Adam Gershen1; John Michopoulos2; Athanasios Iliopoulos2; John Steuben2; Andrew Birnbaum2; 1Naval Surface Warfare Center - Carderock; 2Naval Research Laboratory
The present study is part of an integrated computational materials engineering (ICME) thrust to expand the use of computational simulations for additive manufacturing (AM) components within shipbuilding. Finite element analysis (FEA)-based tools have been developed to simulate the entire build process, including distortion and residual stress. To address this, recently developed computational tools are under a validation investigation for laser powder-bed fusion (L-PBF) builds. The on-going investigation includes physical validation of unique, complex AM-enabled parts to understand how modification of the process can improve build efficiency and reduce instances of failed builds. Additionally, the thermal modeling of the build process will likely influence the developed microstructure, thereby giving insight into how to modify build processes in order to obtain designed alloy systems. The project goal is to validate the computational tools to determine best practices for insertion of computational AM simulation into shipyard fabrication.