Additive Manufacturing: Processing Effects on Microstructure and Material Performance: Microstructure and Mechanical Properties
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

Thursday 2:00 PM
February 27, 2020
Room: 6E
Location: San Diego Convention Ctr

Session Chair: Eric Lass, The University of Tennessee, Knoxville; Monnamme Tlotleng, University of Johannesburg


2:00 PM  
Micro-mechanical Characterization of Directed Energy Deposited 316L Stainless Steel with Hierarchical Microstructure: Baolong Zheng1; Xin Wang1; Sen Jiang1; Bingqing Chen2; Jiayu Liang2; Shuai Huang2; Yizhang Zhou1; Enrique Lavernia1; Julie Schoenung1; 1University of California, Irvine; 2Beijing Institute of Aeronautical Materials
    The evolution of microstructure that evolves during Directed Energy Deposition (DED) is rendered inhomogeneous due to complex thermal and fluid gradients in the melt pool. We applied DED to 316L stainless steel and report on the formation of an interesting hierarchical microstructure that evolves during the mesh-like laser scanning patterns, as multiple columnar colonies grow in different orientations. We used focused ion beam milling to prepare micron-sized pillars with different cellular orientations and evaluated the mechanical behavior, in compression, as a function of hierarchical microstructure. The yield stress and strain hardening varied with cellular orientation. Micro-pillars containing cells with multiple orientations exhibited high yield strength and strain hardening and deformed via the formation of multiple cross-shear bands. The formation of hierarchical microstructure is analyzed based on the thermal behavior and dynamics of the melt pool, and the deformation mechanisms are discussed based on the crystal orientations of the cellular microstructure.

2:20 PM  
Micromechanical Modeling of Length-scale Effects and Performance of SLM Stainless Steel Microstructures: Matti Lindroos1; Samuel Forest2; Tatu Pinomaa1; Anssi Laukkanen1; 1VTT Research Centre of Finland; 2MINES ParisTech
    Stainless steel 316L is known to develop cellular microstructure during selective laser melting. These cellular structures inside the grains contribute to the notably increased strength of the material. To estimate material performance, such as fatigue life of the SLM microstructures, modeling of the deformation behavior require attention to length-scale characteristics in addition to multiple deformation mechanisms, i.e., dislocation slip and deformation twining. A reduced micromorphic crystal plasticity model, akin to strain gradient plasticity, is used to analyze localized effects and provide reasonable regularization to strain localization produced by slip bands and twin concentrations in various 316L SLM microstructures. Emphasis is placed on providing cost-efficient and representative length-scale dependent crystal plasticity model that is usable in virtual materials design workflows. Performance outcomes of different rapidly cooled microstructures, produced by phase field simulations, are discussed, while the effect of local microstructure scale defects are analyzed, and an overall ICME workflow is presented.

2:40 PM  
Influence of Microstructure, Texture and Heat Treatments on the Mechanical Properties of Additively Manufactured Hastelloy X: Benedikt Diepold1; Steffen Neumeier1; Mathias Göken1; 1FAU Erlangen-Nuremberg
    The solid-solution strengthened Ni-base superalloy Hastelloy has an outstanding high temperature stability and good weldability. The processing of the alloy by the SLM-process results in different microstructures and phase fractions in comparison to conventionally processed material. The work examines the dendritic microstructures in the as-built condition and highlights differences in the grain morphology in the xz- and yz-plane, which have been found although a rotating scan pattern was used. Heat treatments are applied to reduce residual stresses and thus the formation of cracks. The standard heat treatment at 1177 °C causes the dissolution of fine dendritic structures and a partly recrystallization, which both leads to a decrease in strength compared to the as-built condition. Heat-treating at temperatures of around 900 °C leads to the formation of small precipitates and only to a partly dissolution of the fine dendrites resulting in an increased strength.

3:00 PM  
Effect of Build Size to the Final Microstructures in Ti6Al4V After Selective Laser Melting: Sinting Cynthia Chang1; Samy Hocine1; Steven Van Petegem1; Tuerdi Maimaityili1; Dario Ferreira Sanchez1; Daniel Grolimund1; Helena Van Swygenhoven1; 1Paul Scherrer Institute
    In this work, we study the as-built microstructures of Ti6Al4V samples that were printed by in operando selective laser melting (SLM) at the MicroSAXS beamline of the Swiss Light Source (SLS). Several samples were built with the same SLM parameters but with different cross-sections. During printing X-ray diffraction patterns were recorded with a frequency of 20Hz. The microstructures and textures on the build and the frontal planes were investigated by Electron Backscatter Diffraction (EBSD). The prior β phase was reconstructed from the orientation of the α’ phase in the EBSD data by using ARPGE. It is found that the microstructures and textures of the prior β grain and the α’ martensites laths are strongly related to the built size. We link the differences of the as-built microstructures to the different thermal history, obtained from the X-ray diffraction data.

3:20 PM  
Role of Thermal Gradients in the Microstructure Evolution in EBM Ti-6Al-4V Builds: Sabina Kumar1; Benjamin Stump2; Sudarsanam Babu1; 1University of Tennessee; 2Manufacturing Demonstration Facility
    Additive Manufacturing (AM) literature has shown that the final properties of components are influenced by complex interactions between geometry, process parameters and alloy chemistry. These interactions can be traced back to spatial and temporal variations of thermal and mechanical signatures (i.e., T {x, y, z, time}). With this constant fluctuation in thermo-mechanical signatures, we may induce constrained equilibrium conditions, leading to the decomposition of parent to product phases. A heat transfer simulation can be used to track the thermal gradients and interphase velocities of a build. In order to understand solid-state phase transformations under varying thermal gradients do so we printed cubes of Ti-6Al-4V with 3 different scan strategies. EBSD analysis show variations in the texture and microstructure at the bottom, middle and top sections. Correlating this to the microstructure we can get information on the effect of the thermal gradients on the product phase.

3:40 PM Break

4:00 PM  
High Temperature Anisotropic Mechanical Behavior of E-beam Ti6Al4V Material: Md Jamal Mian1; Jafar Razmi1; Leila Ladani1; 1Arizona State University
    Due to high strength, low weigh and high melting temperature Ti6Al4V is one of the key metals used in aerospace industry especially at higher temperatures such as jet engines. However, due to challenges involved with cutting and shaping this metal, manufacturing of it has been challenging. Therefore, additive manufacturing offers a convenient method for shaping this metal. However, powder bed processing has been suffering from issues such as surface roughness, anisotropic behavior and defects. Most studies have focused on room temperature mechanical behavior of the laser and e-beam powder bed methods. This study focuses on high temperature elastic and plastic behavior of Ti6Al4V under high temperatures up to 600C. Furthermore, the anisotropic behavior of parts made using E-beam in different orientations is investigated. Fractography and micro structural analysis is conducted to evaluate the failure mechanisms.

4:20 PM  
Simulating Microstructure in Metallic Materials Applied for Additive Manufacturing Processes: Javed Akram1; Thaddeus Low1; 1ANSYS
    The microstructure and composition of any metallic material highly influence the physical and mechanical properties at the macroscale level. A Cellular Automata-based microstructure model is implemented to simulate the temperature driven microstructure evolution of a material with the goal of linking Process-Structure-Property relation in AM processed metals. Nucleation and growth are the two main governing phenomena which describes the final microstructure and will be discussed in detail for both as-deposit and heat treatment phenomena. In this work, we will show particularly the setup of boundary conditions and assumptions made to simulate microstructure evolution in materials processed through metal based additive manufacturing process. The effect of different process parameters on the resulting grain morphologies and orientations of IN718 and Al357 alloy will be demonstrated using side-by-side comparison with experimental results. A Hall-Petch analysis is used to capture yield strength variation with respect to the predicted average grain size.

4:40 PM  
Microstructure and Mechanical Properties of Direct Laser Metal Deposited GRCop-84 Alloy: Ajay Bhagavatam1; Praveen Sreeramagiri1; Asit Biswas2; Dean Baker2; Guru Dinda1; 1Wayne State University; 2Advanced Powder Solutions
    In this study, dispersion strengthened GRCop-84 (Cu-8Cr-4Nb) alloy was successfully deposited without any defects using direct laser metal deposition. A diode laser with a spot size of 2 mm is used to deposit 30 mm x 10 mm single wall samples on a copper substrate. Scanning electron microscopy and electron dispersive spectroscopy investigation revealed the presence of dispersion particles Cr2Nb of 300 to 2000 nm in the copper matrix. In addition very fine Cr particles formed along the interdendritic regions of the copper matrix. It is also observed that these Cr2Nb precipitates are not formed, or the density of these particles is very less where there is segregation of Cr particles along the dendrite boundary. Tension test of the as-deposited samples displayed an average ultimate tensile strength of 410 MPa with 13 % elongation. This paper also reveals the effect of Cr addition on the development of unique eutectic microstructure

5:00 PM  
A Biomedical Titanium Alloy Manufactured by Selective Laser Melting (SLM): Xuan Luo1; Chao Yang1; Yuanyuan Li1; 1South China University of Technology
     We report a β-type Ti-35Nb-7Zr-5Ta alloy manufactured by selective laser melting under different laser energy density(LED). The microstructure, mechanical behavior, and strengthening mechanisms were investigated. The results show that the main phases consist of β-Ti together with minor α"by XRD analysis. The strip and zigzag formation of {112}<111>β twins were observed by the transmission electron microscopy at low and high LED, respectively. The SLM-produced sample with high LED exhibits enhanced strength (872MPa, 12%) but relatively low ductility compared with that by low LED(726MPa, 19%). This difference results from combination of fine grains, high density of dislocations and transformation-induced plasticity. An analysis of the strengthening mechanisms quantitatively established shows that a high density of dislocations and nanometer-sized hexagonal ω particles has a prominent contribution to strength. The obtained material exhibits a lowYoung's modulus(~64GPa) and high strength, which potentially allows for the development of implants.