Additive Manufacturing: Length-Scale Phenomena in Mechanical Response: Modeling
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Nanomechanical Materials Behavior Committee
Program Organizers: Meysam Haghshenas, University of Toledo; Andrew Birnbaum, Us Naval Research Laboratory; Robert Lancaster, Swansea University; Xinghang Zhang, Purdue University; Aeriel Leonard
Wednesday 8:30 AM
March 22, 2023
Room: 23B
Location: SDCC
Session Chair: Andrew Birnbaum, NRL; Sezer Özerinç, Middle East Technical University
8:30 AM
Analytic Model for the Softening Factor within Stages of Work Hardening: Alan Jankowski1; 1Sandia National Laboratories
A formulation for a dimensionless coefficient has been derived that represents a microstructural scale of alloys which follow Kocks-Mecking (K-M) work hardening behavior as determined using the Considère criterion from the true plastic strain between the proportional limit and the strength at the instability. Further development is now made in formulating the softening factor coefficient for the individual and sequential stages 3 and 4 of plastic deformation in K-M work hardening behavior. Application is shown for tensile test results of Ti-6Al-4V made by different additively manufactured processes. It is found that the variation in plastic strain as a function of the coefficient produces a continuous curve representative of the alloy system. This model and the details presented for stages 3 and 4 enables the evaluation of other material parameters including the determination of the activation volume for the onset of plastic deformation.
8:50 AM
Quantitatively Describing Scan Strategies in Laser Powder Bed Fusion: Kahraman Demir1; Zhizhou Zhang1; Grace Gu1; 1University of California Berkeley
In laser powder bed fusion (LPBF), laser scan strategies are well known to be correlated with many properties; however, due to the lack of interpretable scan strategy descriptors and the consequential imposition of simple scan strategies, these correlations are not well understood and are difficult to investigate. This work proposes a methodology for an intuitive quantitative descriptor of scan strategies that has the potential to provide more insight into process-property correlations. Furthermore, a neural network is trained to predict post-print residual stress distributions using only the descriptor, demonstrating the correlative capacity of the descriptor.
9:10 AM
A Mixed Analytical/Empirical Model for Synthetic Generation of As-Printed Microstructures: Alexander Chadwick1; Peter Voorhees1; 1Northwestern University
Understanding the grain morphology after printing remains a critical step in designing predictive modeling frameworks of additive manufacturing processes. However, techniques such as phase-field or cellular automata are still computationally expensive at large scale. Here, we present a method that combines a semi-analytical solution of grain boundary trajectories around the solidifying melt pool with empirical rules to fill the remaining volume. This reduced-order model produces columnar, nonconvex grain morphologies that are consistent with those seen in phase-field simulations. However, we realize an orders of magnitude reduction in computational cost: single pass simulations require hours on a laptop instead of days on a supercomputer. This approach naturally scales to multiple scans or powder layers, which can be treated in a nearly identical manner to the original substrate. We demonstrate the model with various melt pool geometries and scan strategies. We also examine the feasibility of incorporating textural information into the model.
9:30 AM
Mesostructure-Based Model for Failure in Ti-6Al-4V Printed by Laser Powder-Bed Fusion: Kartikey Joshi1; Patcharapit Promoppatum2; Mark Jhon1; 1Institute of High Performance Computing; 2King Mongkut's University of Technology Thonburi
Additively manufactured alloys can exhibit mesoscale process-induced features such as lack-of-fusion defects, where incomplete melting leads to porosity. Although these defects are known to affect the mechanical properties of the printed alloy, the role of the defect distribution is unclear. In this work, we will describe a simulation-based method to systematically explore the effects of the size distribution and spatial distribution of the void structure on failure. We develop a model that explicitly represents the size and position of processing defects as measured from experiment and uses a micromechanics-based ductile damage model to represent failure in the matrix. Analysis of this model using different experimentally realized defect structures allows the identification of relevant metrics for porosity correlating to the measured mechanical properties.
9:50 AM Break
10:10 AM
Crystal Plasticity Study on Porosity and Anisotropic Fracture Behavior of Additively-manufactured 316L Stainless Steel: Ziyi Ding1; Jun Song1; 1McGill University
Heterogenous microstructure holding flaws affects heavily the large deformation response of stainless steel 316L fabricated by laser-based powder bed fusion(LPBF). Existing experimental studies have identified damage of void to the component, however, lacking quantifying value effect of pores to fracture. In this study, we have investigated the effects of keyhole pores and loading direction on the anisotropic tension behaviors of the as-built part through the crystal plasticity finite element model(CPFE), while a specific ductile mechanical threshold stress plasticity model (D-MTS) has been developed. Columnar-shaped grain with <001> texture orientation is particularly controlled. Based on more than hundreds of CPFE simulations having random pores with a series of relative densities, ranging from 95% to 99.9%, and different loading angles, results statistically demonstrate that there exist threshold porosity-fracture-values below which pores cause significant premature failure. The present study offers an optimal decision guide when applying the post-processing method to eliminate voids.
10:30 AM
Microscale Modeling of Solidification and Residual Stress in As-Built Additively Manufactured Parts: Lukasz Kuna1; Kirubel Teferra1; 1Naval Research Lab
As additive manufacturing (AM) technologies continue to progress and advance, so do capabilities to create more complex designs that are otherwise too difficult or expensive to build using traditional methods. As opposed to traditional methods, parts manufactured via AM undergo highly localized, large temperature gradients during high-frequency thermal cycles that result in high residual thermal stress. In this work, a cellular automata finite element (CAFE) approach has been developed and utilized to examine and better understand the microstructures of AM builds specifically with regards as to how various laser parameters influence not only the resulting microstructure, but also the mechanical properties. A combination of AMCAFE and MOOSE Multiphysics finite element simulations have been carried out to simulate the thermomechanical processes of solidification leading to residual stress development. The effects of processing parameters, and therefore microstructure, on stress and strain variability, including plastic response, will be presented for various thin-wall structures.
10:50 AM
Slip Localization in an Additively Manufactured 316L Stainless Steel: Christopher Bean1; Fulin Wang2; Marie Charpagne1; Patrick Villechaise3; Valery Valle3; Sean Agnew4; Dan Gianola5; Tresa Pollock5; Jean-Charles Stinville1; 1University of Illinois Urbana-Champaign; 2Shanghai Jiao Tong University; 3École nationale supérieure de mécanique et d'aérotechnique; 4University of Virginia; 5University of California Santa Barbara
The changes in the mechanical properties of additively manufactured (AM) 316L stainless steel is associated with the micro-scale cellular structures and complex grain and sub-grain structures that arise from heating and cooling during the additive manufacturing process. The sub-grain scale effects caused by these unique microstructural structures on plastic localization were investigated using high-resolution digital image correlation and multi-scale microstructure measurements. Significant heterogeneous slip localization was observed in the AM 316L stainless steel and related to the heterogeneity at the different microstructural scales. In addition, incipient plasticity in the AM material was observed to be mainly controlled by the cellular structures and the density of low-angle grain boundaries, significantly different from incipient plasticity in the wrought 316L stainless steel. In addition, relationships between strain localization and macroscopic mechanical properties are highlighted for the AM material.
11:10 AM
Hierarchical Investigations of Heterogeneities in an As-fabricated Electron Beam Melted Ni-based Superalloy: Bryan Lim1; Andrew Breen1; Xiaozhou Liao1; Sophie Primig2; Simon Ringer1; 1The University of Sydney; 2University of New South Wales
Many difficulties remain in creating usable electron beam powder bed fused Ni-based superalloys without further post processing for aerospace and maritime applications; especially as mission critical parts/replacements for in-service turbine blades and heat exchangers. The most promising and researched method insofar is to optimise the print parameters for commercial superalloys; to achieve comparable mechanical properties to traditional manufacturing methods. However, to do so is commonly costly due to the requirement of performing large empirical print parameter sweeps. Hence, there is a need to understand the entire processing-microstructure-property relationship and any instabilities and heterogeneities that arise from the atomic to macro length scale. Here, we present the inherent hierarchical microstructure and property heterogeneities of a commercial Ni-based superalloy, fabricated using a random spot melt scan strategy. Application of these multi-scale relationships to future thermodynamic/kinetic powder bed fusion simulations will allow a true materials engineering-based print parameter design of commercial superalloys.
11:30 AM Cancelled
Additive Manufacturing of Platinum-based Alloys for Industrial High Temperature Structural Applications: Parastoo Jamshidi1; Biao Cai2; Moataz Attallah2; Selassie Dorvlo3; Ian Campbell3; Martin Bach3; 1University of Birmingham; Cooksongold; 2University of Birmingham; 3Cooksongold
Additive manufacturing (AM) of platinum alloys is of great interests for production of structural components for high temperature industrial and aerospace applications in aggressive atmospheres due to their simultaneous creep resistance and outstanding chemical stability, oxidation and corrosion resistance. AM process can result in cost-efficient production, design flexibility, less material waste and with the potential of higher quality. In this study for the first time the potential for AM of Pt-Rh10wt% alloy for industrial applications was investigated. Laser Bed Powder Fusion (LBPF) was used to manufacture the test specimens for characterizations of density, hardness, ultimate tensile testing and oxidation rate at high temperature. The study illustrated the successful manufacture of Pt-Rh10 parts with porosity level as low as ~ 0.1% after AM process optimization. It was found that the LBPFed parts outperform that of the casted Pt-Rh10 in terms of mechanical performance. Assessment of oxidation rate at high temperature of 1550°C demonstrated low level of weight change confirming their acceptable oxidation rate for final use at high temperatures. Promisingly, this work illustrates the potential of combining AM process with Platinum-based alloys for the production of industrial high temperature structural.