Additive Manufacturing of Metals: Applications of Solidification Fundamentals: Poster Session
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Additive Manufacturing Committee, TMS: Solidification Committee
Program Organizers: Wenda Tan, The University of Michigan; Alex Plotkowski, Oak Ridge National Laboratory; Lang Yuan, University of South Carolina; Lianyi Chen, University of Wisconsin-Madison

Monday 5:30 PM
March 20, 2023
Room: Exhibit Hall G
Location: SDCC

Session Chair: Wenda Tan, University of Michigan


A-11: A New Cellular Automaton Model for Simulating the Formation of Aluminum Microstructure in Laser Powder Bed Fusion Process: Michael Moodispaw1; Buwei Chen1; Qiqui Wang2; Andy Wang2; Alan Luo1; 1The Ohio State University; 2General Motors
    Additive manufacturing (AM) processes, such as laser powder bed fusion (LPBF), have been extensively researched and are increasingly being used in industrial applications. Since the mechanical properties of LPBF parts are determined by solidification microstructure and defect population, accurate microstructure prediction is required for AM product development and process optimization. In this study, a new cellular automaton model was developed to simulate the solidification of aluminum grain structure in the LPBF process. Thermal diffusion was calculated to determine the local undercooling, which is the driving force for grain structure nucleation and growth in the model. The simulation results were compared to the microstructure of LPBF samples of Al-10Si-Mg alloy with specified process conditions. The new model provides quantitative and visual understandings of the effects of various processing conditions, such as laser scan speed, on the solidification structure of AM products.

A-12: A Study on the Effect of VED, Particle Size Distribution, Moisture content, and Powder Reuse on the Densification and Mechanical Properties of L-PBFed Nickel Alloy 718 Using Design of Experiment and ANOVA: Peter Morcos1; David Shoukr1; Tayler Sundermann1; Thomas Dobrowolski2; Nicholas Barta2; Jayesh Jain2; Raymundo Arroyave1; Ibrahim Karaman1; Alaa Elwany1; 1Texas A&M University; 2Baker Hughes
     Laser-Powder bed fusion of nickel alloy 718 has been widelystudied in the literature. However, the effect of powder characteristics such as particle size distribution (PSD), inclusion of fine particles, moisture content, and powder reuse was not studied comprehensively. In this study, two levels of powder type, particle size distribution, (includes particle size range and median particle size), moisture content, VED, and powder type were used. Statistical design of experiment (DOE) techniques was implemented to reduce the experimental cost and burden. The observed results were analyzed using analysis of variance to determine the effect of the different powder characteristics on the quantities of interest (QoI). The QoI in this study are the densification and mechanical properties. The study reveals that VED, powder type, and range are the commonly significant factor for the QoI, while moisture content was significant for Charpy impact energy test only.

A-13: Achieving Single Crystals of Pure Ni via Laser Powder Bed Fusion with a Flat-top Laser Profile: Dennis Edgard Jodi1; Tomonori Kitashima1; Yuichiro Koizumi2; Takayoshi Nakano2; Makoto Watanabe1; 1National Institute for Materials Science; 2Osaka University
    The microstructure control in laser powder bed fusion (LPBF) using a flat-top laser profile to achieve a single crystal pure Ni structure was investigated. Using the flat-top profile, a parametric optimization yielded a planar melt pool. There was no usage of powder stage heating or SX seed. Based on the optimized parameters, at the high building heights, a suppression of high-angle grain boundary (HAGB, misorientation > 15°) was obtained, yielding the formation of an SX structure with a homogeneous configuration of near-{001}<100> parallel to the build direction. The SX structure was supplemented by a lower strain accumulation, which was beneficial in preventing HAGB formation from the continuous dynamic recrystallization process. This study showed that it is feasible to use a flat-top profile in the LPBF process to achieve an SX structure.

Additive Manufacturing Process Map of Ti6Al4V Using In Situ and Operando Synchrotron Radiography: Elena Ruckh1; Samy Hocine1; Sebastian Marussi1; Andy Farndell2; Ruben Lambert-Garcia1; Maureen Fitzpatrick3; Anna Getley1; Caterina Iantaffi1; Saurabh Shah1; Marta Majkut3; Alexander Rack3; Nick Jones2; Peter Lee1; Chu Lun Alex Leung1; 1University College London; 2Renishaw plc; 3European Synchrotron Radiation Facility
    Laser Powder Bed Fusion (LPBF) of Ti-alloys opens the opportunity to manufacture lightweight and complex components for medical, automotive, aerospace and space applications. The reliability of these builds needs to be very high. However, the influence of the process parameters on the melt pool dynamics and feature formation are not fully understood. Using a unique 4 laser AM machine, the Quad In-Situ and Operando powder bed Process Replicator (Quad-ISOPR), we can quantify the phenomena in the weld pool using ultra-high-speed synchrotron radiography, together with an additional coaxial high-speed optical camera and a photodiode. Here we present a process map of the melt pool dynamics for a Ti6Al4V in continuous wave and modulated mode. This process map can help optimise process parameter selection while reducing the probability of associated defects.

A-14: Directed Energy Deposition of Al-0.5Sc-0.5Si Alloy: Effect of Thermal Cycles in Microstructure and Mechanical Properties: Amit Singh1; Yasham Mundada2; Priyanshu Bajaj3; Sushil Mishra1; Amit Arora2; 1Indian Institute of Technology Bombay; 2Indian Institute of Technology Gandhinagar; 3Max-Planck-Institut für Eisenforschung GmbH
    Additive Manufacturing application has significantly increased in aerospace, automobile, health, and electronic industries as complex features can be built with the specimen in a single step. Similarly, post-processing such as machining and heat treatment can also be eliminated to obtain an engineered specimen with better mechanical properties. However, there are numerous challenges in studying the microstructure and mechanical properties of the deposited specimen due to the very complex heating and cooling cycle. A heat transfer and material flow model is developed to compute the thermal cycle and correlated with the structure and mechanical properties of the specimen in the multi-layer deposition of Al-0.5Sc-0.5Si alloy. The thermal cycles, melt pool dimension, and cooling rates are computed around the melt pool for multi-layer deposition, and solidification morphologies are predicted using the CET solidification map. The solidification morphologies are further correlated with the microhardness in the multi-layer deposition of Al-0.5Sc-0.5Si alloy.

Effects of Nanoscale Compositional Inhomogeneity on the Mechanical Properties of a Cu-9Al Alloy Produced by Wire Arc Additive Manufacturing: Hao Wang1; Bosheng Dong2; Huijun Li2; Simon Ringer1; Xiaozhou Liao1; 1University of Sydney; 2University of Wollongong
     (MURI and AUSMURI Collaborative Research)Wire arc additive manufacturing (WAAM) is a technique that uses metal wires as the feedstock and electric arc as the heating source. The manufacturing processes are highly non-equilibrium such that alloys are subjected to abrupt and complex thermal and stress gyrations that are far from those encountered in conventional metallurgical processing. It creates a wholly new process dynamic resulting in local compositional and microstructural inhomogeneity. Compositional homogenization would be a necessary materials processing step for components produced by WAAM. However, recent studies stuggest that nanoscale compositional inhomogeneity is benefitial for ductility retainsion in nanocrystalline alloys. Here, we use WAAM to produce a coarse-grained Cu-9Al alloy with a face-centred cubic structure. Systematic electron microscopy and atom probe tomography studies were conducted to reveal the degree of nanoscale compositional inhomogeneity in the as-fabricated samples. The impact of compositional inhomogeneity on mechanical properties is investigated in detail.

A-15: Effects of Thermal Cycling on Microstructural Evolution in Ni-Mo-Al Single Crystals: Ruben Ochoa1; Adriana Eres-Castellanos1; Gus Becker1; Kamel Fezzaa2; Jonah Klemm-Toole1; Kester Clarke1; Tresa Pollock3; Amy Clarke1; 1Colorado School of Mines; 2Argonne National Laboratory; 3University of California Santa Barbara
    A major drawback of metal additive manufacturing (AM) is the lack of understanding of microstructural evolution and control during the build process due to rapid solidification conditions. Local thermal conditions within AM parts favor the formation of columnar grains, which may lead to hot cracking and anisotropy. Thus, understanding solidification conditions associated with the interactions between multiple melt pools is crucial to controlling microstructural development. This work explores the relationship between melt pool interactions and thermal cycling on microstructural evolution in model Ni-Mo-Al single crystals. Solidification velocities of overlapping spot and raster melts were obtained by in-situ synchrotron x-ray radiography captured at the Advance Photon Source. Resulting microstructures can then be understood by coupling solidification velocities with simulated thermal gradients modeled using FLOW-3D. This work seeks to fundamentally develop an understanding between processing conditions and microstructural evolution. MURI and AUSMURI Collaborative Research.

A-16: Feasibility Study of Solidification Microstructure Control in Laser Powder Bed Fusion Based on Thermal Analysis and Microstructure Simulation: Masahiro Kusano1; Makoto Watanabe1; 1National Institute for Materials Science
    Because of the very fast cooling rate in a laser powder bed fusion (LPBF) process, the solidification microstructure is much finer than in conventional processes. Such microstructure determines the material properties of the fabricated parts. In this study, the effects of processing parameters, especially scanning strategy, on the solidification structure were investigated experimentally and numerically. By coupling thermal analysis and microstructure simulation by using finite element method and cellular automaton, it was demonstrated that the solidification microstructure can be controlled by changing the scanning pattern and hatching space. Such microstructures were confirmed by microscopic observations of nickel-based superalloy samples fabricated by LPBF.

A-17: Hot Cracking during Powder Direct Energy Deposition: Experimental and Numerical Study: Pilar Rodriguez1; Monica Gonzalez1; Mustafa Megahed2; 1AIMEN; 2ESI Group
    316L is considered to be a weldable material easily processed using direct energy deposition (DED). The standard composition does however allow for certain levels of impurities that could affect processability. In this study the influence of impurities on hot cracking susceptibility showed that higher levels of impurities lead to increased cracking. Different process parameters and deposition strategies are investigated experimentally and numerically to ensure crack free as-built material. A crack susceptibility model utilizes CALPHAD property predictions in combination with a process model to study the influence of processing parameters on crack distribution. Whereas improvements could be achieved, the influence of alloy composition could not be completely mitigated by adapting processing parameters. Crack free printing is achieved by reducing impurities.

A-18: Impact of Laser Power and Scanning Velocity on Microstructure and Mechanical Properties of Inconel 738LC Alloys Fabricated by the Constant Volumetric Energy Input of Laser Powder Bed Fusion (LPBF): Yixuan Chen1; Weihao Wang1; Yao Ou1; Yingna Wu1; Zirong Zhai1; Rui Yang2; 1ShanghaiTech University; 2The Institute of Metal Research (IMR), Chinese Academy of Sciences (CAS)
    The microstructure and mechanical properties of Inconel 738LC fabricated by laser powder bed fusion (LPBF) were investigated in this work. Three processing parameters were chosen with a specific volumetric energy density of 55.56 J/mm3 input but varying scanning velocity and laser power. The electron backscatter diffraction (EBSD) results revealed that the fraction of the recrystallized grains increased by 15% and the average grain size became smaller with the increased scanning velocity and laser power. Moreover, it was found that the first dendrite arm spacing also showed a slight difference caused by cooling rate variation. Vickers hardness of three sets of parameters varied from 367.6±8.0HV to 396.5±10.9HV. The tensile test results also indicated that better mechanical properties were achieved by choosing a high-speed scanning speed strategy. In addition, computational fluid dynamics (CFD) was performed to verify the melt pool morphology and cooling rate distribution. The CFD results revealed that the more uniform cooling rate distribution caused by low-speed scanning velocity in the melt pool resulted in smaller surface tension of the liquid phase.

A-19: In-situ Homogenization of Inconel 718 during Induction Heating Assisted-laser Direct Energy Deposition: Junmyoung Jang1; Juyeong Lee1; Taehwan Ko1; Jaeheon Lee1; Geonmin Kim1; Seung Hwan Lee1; 1Hanyang University
    In this study, we propose a in-situ homogenization heat treatment of Inconel 718 during induction heating-assisted laser direct energy deposition. In this method, the in-situ homogenization is performed by maintaining the temperature of the deposit at the homogenization temperature for Inconel 718, thereby the total time required for post-heat treatment process could be shortened. In order to investigate the effect of induction heating during the deposition, two thick walls were deposited with and without the induction heating. Additionally, a 3D transient heat transfer model of the deposition process was built to calculate the temperature profiles during the process. The temperature profiles were correlated with the microstructural features of the deposits. Furthermore, an as-deposit sample without induction heating was homogenization heat-treated using furnace and compared with the in-situ homogenized sample.

A-20: IN939 Fabricated by the Laser Powder Bed Fusion: The Effect of Process Parameters on the Density, Surface Roughness and Microstructural Properties: Merve Dogu1; Muhannad Ahmed Obeidi1; Hengfeng Gu2; Dermot Brabazon1; 1Dublin City University; 2ANSYS
    IN939 is a Ni-based superalloy which is used for the land-based gas turbine engines thanks to its outstanding properties such as high temperature microstructural and mechanical stability, along with high corrosion resistance. The production of intrinsic geometries is not possible in a single step with conventional manufacturing techniques (casting and forging). Laser powder bed fusion (L-PBF) offers many advantages such as the design of freedom and single-step production of intrinsic geometries with nearly zero waste material. IN939 has recently been applied with the L-PBF process. There is still, however, much more work required to understand the effects of the process parameters of the L-PBF on the microstructural and mechanical properties of IN939. In this study, the effect of the process parameters such as laser power, scanning speed and hatch distance of the L-PBF on the microstructural and mechanical properties of IN939 was investigated.

A-21: Laser Powder Bed Fusion of 17-4 PH Stainless Steel: Multiscale Microstructure and Property Relationships: Maxwell Moyle1; Nima Haghdadi1; Xioazhou Liao2; Simon Ringer2; Sophie Primig1; 1The University of New South Wales; 2The University of Sydney
    Processing by many additive manufacturing (AM) techniques generally exposes alloys to vastly different conditions than those usually experienced during conventional subtractive processing routes, such as sharp thermal gradients, high solidification rates, and numerous reheating cycles. This results in distinct microstructural features including hierarchical and anisotropic grain structures as well as metastable phases. These features in turn have a knock-on effect on mechanical properties, for reasons including residual stress and transformation toughening. The current work reveals these phenomena occurring in 17-4 PH stainless steel produced by laser powder bed fusion, highlighting differences in microstructural behaviour both in the as printed state as well as after heat treatments. Correlative investigations of these effects were undertaken using a broad range of techniques including neutron scattering, electron backscattered diffraction, and atom probe microscopy. This allowed for a multiscale evaluation of the AM builds in terms of residual stress, texture, phase, and nanoscale precipitation.

Cancelled
A-22: LPBF Fabrication of Thin Cross Sections; Challenges and Printability: Shahrooz Nafisi; John Daniel Arputharaj1; Reza Ghomashchi1; 1University of Adelaide
    Additive Manufacturing (AM) as a prototyping technique has recently evolved into a stand-alone manufacturing process. Laser Powder Bed Fusion (LPBF), also known as Selective Laser Melting (SLM), as the most commonly used technique for metal additive manufacturing uses a laser as the energy source to melt and shape complex designs. The increased freedom in design has offered a shorter assembly line, lower parts weight, shorter lead time, and efficient materials usage. However, the high demand in the aerospace, medical, and automotive industries for even lighter artifacts has opened a new field for designing and fabricating lattice-architectured metamaterials. These miniature networked designs have been mainly researched to establish the variation in the macro-mechanical properties while ignoring the strut’s topological integrity and microstructure, all controlled by the process parameters. To have a clearer understanding of the topological and microstructural evolution in thin sections, this work aims at studying the geometrical and microstructural features of single struts of varying diameters ranging from 0.1mm to 1mm within the XY plane and angles from 10˚ to 90˚ in the z-direction to establish the capability of LPBF machines in printing struts as the essential constituent of the lattice structures. In this regard, the printability of struts with respect to their diameter, length, angle of inclination, circularity, and surface integrity are studied and discussed. The analysis of the results suggests that to successfully manufacture a lattice structure, struts as the main constituent of lattice architecture should have any diameter above 0.2mm with an angle of inclination between 40˚ and 60˚ to exhibit good geometrical accuracy, lower surface roughness, and lower hardness.

A-23: Machine Learning Based Parameters Optimization for Selective Laser Melting: Jiahui Zhang1; Yu Zou1; 1University of Toronto
    For the selective laser melting process, the printing parameters play a vital role in the mechanical properties of the components while the traditional design of experiments (DOE) method is time-consuming and costly to find the optimized parameters. In this study, we show an easy-deployed and accurate machine learning method to find the possible optimized parameters based on a few experimental results. The microstructure of the components fabricated by random parameters and optimized parameters will be characterized by electron microscopy. The mechanical properties of these components are also compared and analyzed. Our work provides an efficient and reliable method to establish "building process-structure-property" relationships for newly designed materials or alloys.

A-24: Microsegregation Model Dedicated to Rapid Solidification – Application to Multicomponent Alloys of Industrial Interest.: Paul Martin1; François Pichot2; Nicolas Leriche2; Gildas Guillemot1; Charles-André Gandin1; 1CEMEF; 2Safran Additive Manufacturing Campus
     The soundness of parts produced by Laser Powder Bed Fusion (L-PBF) depends on the possibility to limit the occurrence of defects. Among them, hot cracking represent a key issue for industries. These cracks are due to the persistence of a liquid film at the end of the solidification stage together with large stresses. A microsegregation model that predicts the solidification path for materials produced by LPBF is thus required, not only to account for the initial undercooling of the microstructure but also to follow the composition of the interdendritic chemical species during LPBF.Several phenomena are considered: i- solute redistribution based on unsteady diffusion, ii- dendrite tip growth model and iii- kinetic phase diagram. Cross-diffusion of solute species in the liquid is also taken into account, as well as coupling with CALPHAD. Results are compared to experimental data in the Ag-Cu system before applications dedicated to nickel-base superalloys.

A-25: Microstructures of 316L Steel Processed by Laser Powder Bed Fusion: Carlos Capdevila-Montes1; Adriana Eres-Castellanos2; Ana Santana1; Rosalia Rementeria3; Francisca Caballero1; 1CENIM CSIC; 2Colorado School of Mines; 3ArcelorMittal Global R&D SLab
    Grade 316L is one of the most versatile austenitic stainless-steel products whose potential in laser powder bed fusion has been recently evaluated. This process allows manufacturing parts with complex shapes to be used in fields such as power generation, oil and gas, water treatment, petrochemical, and construction. The way of improving its properties is to promote dispersion hardening and to control texture. In this work, the effect of dispersion hardening and texture on the behavior at high temperature of a 316L steel was evaluated. Two 316L samples were manufactured by laser powder bed fusion, where the powder of one of them was inoculated with TiC nanoparticles. Advanced characterization proved that inoculation did not affect the solidification structure or the grain size, although it did modify the bulk texture.

A-26: Modification of H950 Condition for 17-4 PH Stainless Steel Processed by DED: Ipfi Mathoho1; 1CSIR Pretoria
    The current study embarked on developing the H950 aging condition for 17-4 PH stainless steel that was manufactured through the DED process. The driving force for carrying out this study was that, when the H950 condition was applied to 17-4 PH that was processed by DED, then the mechanical properties were not similar to those of 17-4 PH (as-received) manufactured through the traditional method. The printing of tensile specimens was done using the LENS technique. Subsequently, the specimens were subjected to homogenization treatment (1100°c for 2 hours followed by air cooling) and aging treatment at 400°c, 450°c, and 500 °c for a specific period followed by air cooling. Additionally, a material characterization which includes porosity evaluation mechanical properties testing, and microstructural evolution analysis was done. It was established that 400°c was the aging temperature that produced specimens with mechanical properties similar to the as-received specimens.

A-27: Phase Field Simulation of Microstructure Evolution during Epitaxial Solidification in Additive Manufacturing Processes: Abdur Al Azad1; Philip Cardiff1; David Browne1; 1University College Dublin
    Rapid solidification occurs in Metal Additive Manufacturing (MAM) processes, and the properties of the 3D printed components depend on the solidified microstructure. Fundamental knowledge about the microstructural evolution during the process is useful in producing tailored components with desired properties. Phase field models are powerful computational tools to simulate the development of microstructure in the MAM process. Due to high thermal gradients, the growth morphology is usually columnar or epitaxial. Such directional solidification was simulated using a quantitative phase field model in a two-dimensional domain. A convergence study was carried out to study the effects of diffuse interface width in our simulations. The influence of different processing parameters such as thermal gradient and scan speed on the microstructure is investigated through simulation. Consideration is also given to solute trapping in such rapid solidification. The simulated grain morphology agrees well with an analytical model and experimental findings.

A-28: Printability of Nickel Alloy 718 Using a Systematic Process Optimization Framework with Different Layer Thicknesses: David Shoukr1; Peter Morcos1; Tayler Sundermann1; Thomas Dobrowolski2; Chad Yates2; Jayesh Jain2; Raymundo Arroyave1; Ibrahim Karaman1; Alaa Elwany1; 1Texas A&M University; 2Baker Hughes
     Laser-powder bed fusion is used in the literature to fabricate nickel alloy 718 successfully. However, the selection of the process parameters was based on experimentally-intensive methods or computationally-expensive simulations. Hence, these methods can test only a small region of the parameter space. Moreover, studies combine the process parameters into linear or volumetric energy densities. Both factors have proven to provide partial information about the part and inconsistent mechanical properties and microstructures. The current framework covers the entire scanning speed-laser power space, determines the hatch spacing, and detects the printability region which is the porosity-free region determined by the elimination of the porosity defects. Furthermore, layer thicknesses of 60 and 90 μm are investigated to increase the volumetric build rate (VBR).Printability is assessed using porosity measurements while performance is evaluated using tensile tests. Fully-dense parts were fabricated with tensile strengths and VBR of up to 1063.5 MPa and 7.10 mm3/s.

Probing Surface Structures in Metal Powders Produced by Abrasion and Rapid Solidification: Harish Singh Dhami1; Puli Saikiran1; Koushik Viswanathan1; 1Indian Institute of Science
    Metal powder particles show a range of interesting surface structures that are quite reminiscent of those seen in conventional casting. Given their central importance for manufacturing processes such as metal 3D printing and powder metallurgy, understanding their evolution during rapid solidification has remained an area of active interest. This work attempts to understand the dynamic evolution of surface morphologies on spherical metal particles produced via an abrasion process. In order to surmount the technical challenges posed by high cooling rates (10^5 K/s) and very small time/length scales, we use a controllable low-melting organic substitute to mimic the process. Containerless solidification conditions were set up using acoustic levitation techniques and controlled thermal environment, to study the solidification dynamics of a single levitated drop using in situ imaging and tracking techniques. Complementary analytical and numerical calculations are also presented in the context of transitions between different surface morphologies.

A-29: Process Modification and Alloy Design of Ni-base Superalloys: Mohammad Tashfiul A Chowdhury1; John M. O'Connell1; Nathaniel Badgett1; Anthony E. Lavelle1; Bhaskar S. Majumdar1; 1New Mexico Institute of Mining and Technology
    High temperature Ni-base superalloys, whose application temperatures exceed those of Inconel 718 have been challenging to fabricate defect-free using additive manufacturing (AM). These alloys contain a high volume fraction of gamma-prime phase in the gamma matrix, and also contain refractory elements for strengthening the gamma matrix. These phases/elements provide strength, but simultaneously influence segregation and solidification behavior, and residual stresses that lead to cracking. This work was focused on alloy CM247LC, which has so far resisted crack-free AM. Using CALPHAD and crack susceptibility models along with methods to reduce deleterious carbides, alloy design was carried out, and validated using single laser scans on arc melted buttons. Subsequently, the desired alloy powder was fabricated, and AM studies conducted on them. The microstructure and mechanical properties of these AM fabricated samples will be provided, along with insight on the effects of process parameters.

A-30: Quantification of the Microstructure of Additively Manufactured Parts Utilizing Local Orientation Image Analysis: Sahar Beigzadeh1; Jeffrey Shield1; 1University of Nebraska-Lincoln
    All additively manufactured (AM) parts have meltpool formation during solidification and dendritic microstructure because of the high thermal gradient and high cooling rate. By measuring the dendritic growth orientation inside each meltpool, it would be possible to differentiate the meltpool microstructures and analyze the related characteristics. For this aim, we used the “SkeletonOrientation” algorithm to analyze meltpool microstructures, allowing subtle variations in dendritic structures and orientations to be quantified. For example, we analyzed the dendritic microstructure of 300 maraging steel, printed using laser powder bed fusion. The dendritic growth directions have been measured for several meltpools and the results revealed that the dendrites inside each meltpool are mostly orientated in directions perpendicular to each other. The dendrite orientation misalignment was also observed to be dependent on build height, presumably related to the different cooling rates from the bottom to the top of the build.

A-31: Rapid Solidification in Ternary Alloys: A Phase-Field Study: Yitao Wang1; Fadi Abdeljawad1; 1Clemson University
    Recent advances in metal additive manufacturing techniques have highlighted non-equilibrium effects during the solidification of metallic alloys. Solute trapping can become significant during rapid solidification, which in turn influences the microstructural evolution, and microstructure length scales and, as a result, the properties of such alloys. However, the effect of alloy chemical thermodynamics on solidification properties in multi-component systems remains poorly understood. In the present work, we employ the recently developed finite interface dissipation phase-field modeling framework to examine solidification kinetics in ternary alloys. Analytical and computational studies are used to systematically examine the influence of off-diagonal interdiffusion coefficients and interface “permeability” on solidification rates and solute trapping. Our studies show that the liquid phase off-diagonal transport coefficients play a non-trivial role in solidification growth rates and solute redistribution around the advancing solid-liquid interface.

Cancelled
A-32: Strength Enhancement of Al Alloy via Microstructure Design Strategy Using Laser Powder Bed Fusion: Ankita Roy1; Saket Thapliyal1; Ravi Haridas1; Priyanka Agrawal1; Abhijeet Dhal1; Rajiv Mishra1; Eric Faierson1; 1University of North Texas
    Variability in solidification kinetics and growth dynamics via additive manufacturing techniques have led to the inception of microstructure customization at various length scales. Novel Al-3Ni-Ti-0.8Zr alloy had been meticulously designed to explore both the wide solidification range and the eutectic solidification regimes of Al alloys. Heterogenous nucleation of equiaxed grains has been imposed at various locations within a melt pool from the in-situ precipitation of different Al intermetallics. The solidification pathway progressively introduces several nucleants, particles, segregations and heterogenous grains, thus increasing the number of deformation pathways. A basic understanding of the synergistic influences of process parameters and volume energy density associated with laser-powder bed fusion (L-PBF) warrants the introduction of heterogeneity at all hierarchical levels. Our research highlights the role played by process variables in tuning the granular refinement and tailoring sub-granular intricate morphologies that goes into shaping its mechanical attributes.

Cancelled
A-33: Thermal and Mechanical Behavior of Powder Blown Directed Energy Deposited Nickel-Titanium Shape Memory Alloys: Dyuti Sarker1; Aaron Stebner1; Samad Firdosy2; Ali Komilian1; Zachary Haataja1; 1Georgia Institute of Technology; 2Jet Propulsion Laboratory
    Additive manufacturing (AM) is a promising technique for the fabrication of NiTi shape memory alloy (SMA) parts with intricate geometry which are attractive for biomedical and aerospace applications. Most of the AM fabricated NiTi SMA focus to date has been on the development of laser powder bed fusion process parameters. However, powder blown directed energy deposition (DED) has several desirable characteristics including better oxygen control of the printing chamber to minimize oxide formation, easier mixing of multiple composition powders into the powder blown gas stream during manufacture to enable local control of phase transformation temperatures. Here, we investigate the thermal and mechanical properties that arise from low temperature single step and double step heat treatments. We report upon new characterizations of defects and oxides, microstructures, martensite and R-phase transformation temperatures, and superelastic performances during compression and tensile cycle as a function of DED process parameter and post-process heat treatment variations.

A-34: Thermal Cycles Induced Phase Evolution in IN718 during Additive Manufacturing: a Gleeble Study: Nana Kwabena Adomako1; Nima Haghdadi1; Xiaozhou Liao2; Simon Ringer2; Sophie Primig1; 1UNSW Sydney; 2The University of Sydney
    Additive manufacturing (AM) has recently received significant attention due to its ability to produce complex, near-net-shape components with minimal material waste. It has been widely adopted for making parts of high-performance nickel-based superalloys such as IN718, for applications in modern aero-engines. However, a complete understanding of the microstructural evolution, such as γ′, γ′′, Laves, and δ phases transformations during printing, is still lacking. The complex AM thermal cycles cause several morphological changes to these phases. However, observing these transformations during printing is challenging as an in-situ measurement technique is needed. In this study, we introduce alternate techniques to investigate the effects of thermal cycles on the phase evolution of IN718 components during additive manufacturing. This involves using the Gleeble physical simulator to perform cyclic heating and quenching experiments and the thermokinetic analysis software package, MatCalc, as a guide to determine the expected phases under equilibrium.

A-35: Ultrafine Austenite in Laser Powder Bed Fusion Processed Duplex Stainless Steels Through Microstructural Engineering: Xinyi He1; Xiaozhou Liao2; Simon Ringer2; Sophie Primig3; Nima Haghdadi1; 1UNSW Sydney, NSW 2052; 2Australian Centre for Microscopy & Microanalysis, The University of Sydney, NSW 2006; 3 UNSW Sydney, NSW 2052
    The highly non-equilibrium microstructures resulted from metal additive manufacturing (AM) can offer unique opportunities for microstructural engineering. One example is duplex stainless steel that first solidifies as delta-ferrite at high temperature. In these steels, the further solid-state phase transformation during AM and post-processing can be engineered to obtain desirable properties through the formation of ultrafine austenite. Mechanical and corrosion properties of these steels are dependent on the phase ratio, size and chemistry of austenite and ferrite, precipitates, and dislocation density. The current research aims to unravel the relationship between AM process parameters and character of austenite in duplex stainless steels fabricated by laser powder bed fusion. A detailed insight into the capability of microstructural manipulation in these steels can not only contribute to tailoring the properties of these steels but also be extended to other similar allotropic alloys processed by AM.

A-82: Understanding the Effect of Solute Elements on the Evolution of Equiaxed and Columnar Grains in AM Processed Beta Titanium Alloys: Mohan Sai Kiran Nartu1; Srinivas Mantri1; Brian Welk2; Narendra Dahotre1; Hamish Fraser2; Rajarshi Banerjee1; 1University of North Texas; 2The Ohio State University
    Virtually, all additive manufacturing (AM) processes involving complete melting of metal powders/wires produce significantly textured columnar grains along build-direction, which are deleterious for mechanical properties. Therefore, understanding growth and texture of these columnar grains become crucial for AM alloys. Significant research in the last decade has been focused on extending the concept of growth restriction factor (GRF) (a classical theory originally developed for conventional casting) to AM. However, there are some critical concerns regarding the applicability of GRF model to AM and there is a need to understand and validate this model. Current work analyzes the evolution of grain morphology and texture in few commercial as well as model metastable beta titanium alloys processed via AM. Results indicate that the GRF model fails to interpret the grain growth behavior in these alloys. Alternatively, an approach based on solidification range has been proposed for the first time to rationalize the observations.

A-36: Understanding the Impact of Residual Stresses on Microstructure Evolution in Additive Manufacturing: Michael Haines1; Nima Haghdadi1; Sophie Primig1; 1University of New South Wales
    Residual stresses after powder bed fusion (PBF) additive manufacturing processes contribute to defect formation though delamination and cracking in builds. Further, they are known to introduce additional dense networks of dislocations, resulting in yield stress increments. Yet, the current understanding of how changes in these residual stresses due to variations in geometry and/or the temporal and spatial thermal conditions may impact the microstructure evolution and property control remains limited. This work utilizes an approach to print specific geometries with the expressed interest in looking at the impact of residual stress on microstructural constituents. Thermo-mechanical simulations were carried out to get an estimate on the stress and strain distributions in special geometries designed for this study. These geometries were then printed from IN718 and Ti-6Al-4V alloys under electron beam – PBF. Advanced characterization techniques were used to better understand how variation in residual stress impact the microstructure.

A-37: Using Analytical Solidification Models to Solve Solidification Cracking in Laser Powder Bed Fusion Processed Ni-based Alloys: Dan McConville1; Ruben Ochoa1; Benjamin Rafferty2; Kevin Eckes2; Jeremy Iten2; Amy Clarke1; Jonah Klemm-Toole1; 1Colorado School of Mines; 2Elementum 3D
    Many Ni-based superalloys are known to be susceptible to a wide range of cracking mechanisms, which occur during solidification as well as in the solid state. This cracking susceptibility is responsible for many Ni-based alloys being considered “unweldable” or “unprintable.” In this presentation, we show how we used analytical solidification models to design and introduce nucleation sites during solidification that modify the as-solidified microstructure and eliminate solidification cracking in both solid solution and precipitation hardened Ni-based alloys. We discuss how our method of using analytical solidification models can be applied to solve cracking in other materials systems or additive manufacturing processes.

A-80: Using Laser Powder Bed Fusion to Exploit Transformation Induced Plasticity in Beta-Titanium: Chris Jasien1; Alec Saville1; Jonah Klemm-Toole1; Kamel Fezzaa2; Kester Clarke1; Amy Clarke1; 1Colorado School of Mines; 2Advanced Photon Source, Argonne National Laboratory
    The continued development of metal additive manufacturing (AM) has expanded the metallic alloys for which these processes can be applied. However, rapid cooling rates inherent in AM have presented difficulties in producing crack-free parts. One possible solution is to use alloys that can accommodate the stresses developed during the build process. For example, transformation induced plasticity (TRIP) may not only resist cracking that has plagued traditional AM of titanium alloys, but also promotes good combinations of strength and ductility with deformation. A better understanding of where and when TRIP occurs during AM is needed to exploit it. Simulated laser-powder bed fusion (L-PBF) of the beta-titanium alloy Ti-10V-2Fe-3Al (wt.%) was performed at the Advanced Photon Source at Argonne National Laboratory under varying conditions. TRIP was observed in the melt pools, and the effects of process parameters and scan strategy were determined through post-mortem microstructural characterization. MURI and AUSMURI Collaborative Research.