Additive Manufacturing: Solid-State Phase Transformations and Microstructural Evolution: Poster Session
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Additive Manufacturing Committee, TMS: High Temperature Alloys Committee, TMS: Phase Transformations Committee
Program Organizers: Bij-Na Kim; Andrew Wessman, University of Arizona; Chantal Sudbrack, National Energy Technology Laboratory; Eric Lass, University of Tennessee-Knoxville; Katerina Christofidou, University of Sheffield; Peeyush Nandwana, Oak Ridge National Laboratory; Rajarshi Banerjee, University of North Texas; Whitney Poling, General Motors Corporation; Yousub Lee, Oak Ridge National Laboratory

Tuesday 5:30 PM
March 16, 2021
Room: RM 5
Location: TMS2021 Virtual


A Comparison of the Microstructure in Blown Powder Deposition Inconel 718 for Various Heat Treatments: Giancarlo Puerto1; Chris Hill2; Judy Schneider1; 1University of Alabama in Huntsville; 2NASA Space Flight Center
    Additive Manufacturing (AM) provides a low-cost method to fabricate near net shape complex parts, such as rocket combustion chambers and rocket turbomachinery impellers, in one process. However, the nature of printing a part layer by layer can result in non-homogeneity of the microstructure due to the repeated heating and cooling gradients. To mitigate undesirable microstructures, heat treatments are being developed to reduce residual stresses, increase homogeneity, and promote desirable phase formation. As these heat treatments are based on those developed for wrought Inconel 718, the response of AM materials to similar heat treatments is unknown. In this study a rocket turbopump inducer was fabricated using blown powder direct energy deposition (DED). This inducer was sectioned, and various heat treatments were applied in order to evaluate the microstructural evolution. The resulting microstructures were the basis for optimizing the heat treatment processes for blown powder DED Inconel 718 material.

Constituent Phases and Microstructure of Cu-10Sn Alloy Produced by Laser Powder Bed Fusion: Le Zhou1; Binghao Lu2; Holden Hyer2; Abhishek Mehta2; Sun Hong Park3; Yongho Sohn2; 1Marquette University; 2University of Central Florida; 3POSCO Technical Research Laboratories
    Cu-10Sn alloys were additively manufactured by laser powder bed fusion. With constant hatch spacing of 0.12 mm and slice thickness of 0.03 mm, near full density of Cu-10Sn alloys could be produced using appropriate laser power and scan speed (200 – 350 W and 500 – 1000 mm/s). When the scan speed decreased, the fraction of porosity increased due to the keyhole melting associated with excessive energy density. The melt pool depth and width increased when the laser power increased or the scan speed decreased. The grains within the top melt pool layer, which was last to solidify, exhibited a fan-like structure, whereas all other areas had small columnar grains aligned parallel to the build direction. The α-Cu dendrites and interdendritic δ-Cu41Sn11 phase was observed in all samples. In addition, formation of thin laths (~100 nm) was observed by TEM presumably due to martensitic transformation.

Cancelled
Effect of Hot Isostatic Pressing Conditions on Microstructure Evolution and Hardness of Laser Powder Bed Fusion Processed Alloy 718: Hamza Fagiha1; Runbo Jiang2; Joseph Pauza2; Magnus Ahlfors3; Chad Beamer3; Anthony Rollett2; Amir Mostafaei1; 1Illinois Institute of Technology; 2Carnegie Mellon University; 3Quintus Technologies
    Alloy 718 is fabricated by laser powder bed fusion (LPBF) with standard EOS parameters to attain fully dense parts. Various post-heat treatment conditions including (1) pressureless and under an applied pressure of 102 MPa and 200 MPa, and (2) soaking times of 90 min and 240 min at the holding temperature of 1120 °C are employed. We aim to investigate the role of hot isostatic pressing on the microstructural evolution at the horizontal and vertical directions compare to the as-built alloy 718. LPBF alloy 718 shows heterogeneous columnar grains with inter-dendritic micro-segregation; while, post-heat treatments alter grain structure by formation of recrystallized grains with carbide precipitates. Grain morphology and phase formation are characterized by scanning electron microscopy in conjunction with electron backscatter diffraction and X-ray diffraction. Hardness mapping is carried out on cross-sections including perpendicular and along the build direction to understand the hardness distribution of different heat treated parts.

In Situ Observation of Phase Evolution in Ti-6Al-4V upon Laser Processing with Synchrotron X-ray Diffraction Analysis: Seunghee Oh1; Rachel Lim1; Joseph Aroh1; Joseph Pauza1; Andrew Chuang2; Benjamin Gould2; Niranjan Parab2; Joel Bernier3; Tao Sun4; Robert Suter1; Anthony Rollett1; 1Carnegie Mellon University; 2Argonne National Laboratory; 3Lawrence Livermore National Laboratory; 4University of Virginia
    Ti-6Al-4V, α+β titanium alloy, is one of the extensively studied alloys for additive manufacturing. For the optimization of the printed Ti-6Al-4V parts, the phase configuration accompanied by the solid-state phase transformation needs to be understood. However, the phase evolution in laser-based manufacturing occurs over milliseconds at any given location. We used a high-speed synchrotron X-ray diffraction system to observe the laser melted region in Ti-6Al-4V during melting and subsequent cooling with high temporal and spatial resolution. Qualitative and quantitative analysis was performed through single-peak fitting that reveals the transient phase evolution in individual grains. From the estimated temperature via thermal expansion, the evolution is related to the predictions of equilibrium thermodynamics. The β phase appears to show recalescence and the lattice parameters of certain α peaks exhibit spatial anisotropy, indicative of residual stress.

Microstructure-defect Printability in Laser Powder Deposition of Ni-based Superalloys: Huang Xueqin1; 1Texas A&M University
    The understanding of Ni-based binary alloys is essential for studying Additive Manufacturing in materials design. Considering the alloys Ni-Cu, Ni-Zr and, Ni-Al the simulation shows that the microsegregation rises as the freezing zone range increases, indicating that the solute is trapped in the solid phase. Furthermore, the cellular structure is more apparent in the materials with a larger freezing zone. The microstructure is finer due to higher cooling rates and solidification speeds. The simulations use COMSOL, a thermal model numerical solver platform, to calculate two thermal parameters, temperature gradient and the solidification speed, that are used as inputs in the finite interface dissipation Phase-field model. By the integral model, the defect-free and microstructure-homogeneous printable region is predicted to give a prescription for the proper process parameters selection.

Microstructure Evolution in Laser Deposited AISI 420 Stainless Steel: Effect of Post-processing Heat Treatment: Madhavan Radhakrishnan1; Md Mehadi Hassan1; David Otazu2; Thomas Lienert2; Osman Anderoglu1; 1University of New Mexico; 2Optomec Inc
    AISI 420 martensitic stainless steels (0.4%C, 12.7%Cr, in wt.%) were successfully deposited onto 316L substrate by Laser Engineered Net Shaping (LENSŪ) process. The process produced a near-fully dense deposit (99.5% relative density). The cross-sectional examination by electron microscopy and XRD confirms dual-phase microstructure of martensitic needles and austenite. Phase fraction calculations show that near the substrate and top of the build, the microstructure is almost martensite and the austenite area fraction is about 2%. The austenite fraction peaks to about 20% at the center of the build. The observed microstructure gradient is attributed to the repeated heating cycles and fast cooling rates of the individual build layers. Preliminary mechanical characterization by micro-Vickers hardness tests shows uniform hardness trend across the build. The talk would explore the effects of processing heat input and post-processing heat treatment conditions on the evolution of local chemistry, phase transformation, and mechanical performance of 420 steel.

Tailoring Microstructure of Selective Laser Melted TiAl-alloy with In-situ Heat Treatment via Multiple Laser Exposure: Igor Polozov1; Artem Kantyukov1; Anatoly Popovich1; Vera Popovich2; 1Peter the Great St. Petersburg Polytechnic University; 2Delft University Of Technology
    Intermetallic titanium aluminide (TiAl) alloys are considered as attractive materials for high temperature applications in aerospace, automotive and energy industries. Additive manufacturing is a promising way of producing complex TiAl-alloy parts, however it still remains challenging due to brittleness of the alloy. While high-temperature preheating can mitigate cracking during selective laser melting, the microstructure of TiAl-alloys still needs to be optimized to achieve better mechanical performance. In this work, multiple laser exposures were used during selective laser melting of TiAl-based alloy to tailor its microstructure. Applying additional laser exposure of up to 20 times per layer induced an in-situ heat treatment, which allowed to modify volume fraction and size of different phases. Microstructure, phase and chemical compositions, and hardness of TiAl-alloys were investigated with regards to a number of laser exposures during the selective laser melting process.

Well-aligned nanoprecipitates in Nickel alloy produced by direct metal laser sintering: Bo Yang1; Zhongxia Shang1; Jie Ding1; Jack Lopez2; William Jarosinski2; Tianyi Sun1; Yifan Zhang1; Nicholas Richter1; Haiyan Wang1; Xinghang Zhang1; 1School of Materials Engineering, Purdue University; 2Praxair Surface Techonologies Inc.
    Nanostructured metallic materials have widespread industrial applications due to their high strength and radiation tolerance. Most bulk nanostructured alloys have been produced by severe plastic deformation. Here we show that direct metal laser sintering can be employed to produce fully dense Ni alloys with nanoprecipitates. Scanning electron microscopy studies on as-printed specimen identified well aligned arrays of nanoprecipitates decorated at dislocation cell walls. After stress relief treatment, dislocation cell walls dissolved and a different type of nanoprecipitates emerges with no obvious change in the separation distance. Transmission electron microscopy studies reveal the nanoprecipitates can form several aligned orientation relationships with the matrix. The nanoprecipitates also improve the work hardening ability of the alloy. This study suggests that additive manufacturing may open a new avenue to produce bulk nanostructured alloys for various applications.