Additive Manufacturing: Processing, Microstructure and Material Properties of Titanium-based Materials: Session II
Sponsored by: TMS Titanium Committee
Program Organizers: Ulf Ackelid, Freemelt AB; Ola Harrysson, North Carolina State University; Peeyush Nandwana, Oak Ridge National Laboratory; Rongpei Shi, Harbin Institute of Technology
Monday 4:00 PM
October 18, 2021
Room: A120
Location: Greater Columbus Convention Center
Session Chair: Anthony Rollett, Carnegie Mellon University
4:00 PM
An Automated Tool for Porosity Characterization and Classification in LPBF: Evan Diewald1; Jack Beuth1; 1Carnegie Mellon University
Minimizing the percentage of porosity within fabricated samples has long been a primary optimization target in laser powder bed fusion (LPBF) and other AM processes. Due to improvements in system control and parameter development, parts are now consistently built with >99.5% density. However, in many situations, this baseline density metric does not adequately summarize process quality. In this work, we present an automated tool for porosity characterization and classification. The end-to-end processing pipeline ingests micrographs of sample cross-sections, identifies and indexes individual pores, extracts geometric properties for each flaw, and classifies each defect according to its formation mechanism using a trained machine learning model. We will also demonstrate the utility of the tool through three use cases involving Ti-6V-4Al: process mapping, evaluation of a novel scan strategy, and automated identification of rogue defects.
4:20 PM
Time-resolved Characterization of Evolving Phase and Microstructure of Ti-6Al-4V during Laser Processing with Synchrotron X-ray Diffraction: Seunghee Oh1; Rachel Lim2; Joseph Aroh1; Andrew Chuang3; Benjamin Gould3; Behnam Amin-Ahmadi4; Joel Bernier5; Tao Sun6; P. Chris Pistorius1; Robert Suter1; Anthony Rollett1; 1Carnegie Mellon University; 2Penn State University; 3Argonne National Laboratory; 4Colorado School of Mines; 5Lawrence Livermore National Laboratory; 6University of Virginia
Ti-6Al-4V (Ti64), one of the extensively studied alloys for additive manufacturing, is a α+β titanium alloy involving the solid-state phase transformation. The phases and microstructures of Ti64 are crucial components in determining material properties. However, their evolution is complicated depending on the process conditions and the examination of the transformation of β to α is limited owing to its high transformation temperature. Moreover, the extremely fast process in small volumes makes it more challenging to characterize the development during laser processing. In this study, an in-situ synchrotron X-ray diffraction with a high temporal and spatial resolution was utilized to observe the rapid phase evolutions in the differently developed melt pools. The estimated temperature based on the lattice parameter change is compared with the simulated temperature to interpret the phase evolution during laser processing. Microscopy provides complementary information to the X-ray measurements to evaluate, e.g., the occurrence of martensitic transformation.
4:40 PM
Modeling of True Stress-Strain in the Plastic Regime of Additively Manufactured Ti-6Al-4V: Andrew Temple1; Maria Quintana1; Peter Collins1; 1Iowa State University
The continued development of additive manufacturing, and the rapid expansion of AM process variants, necessitates the development of materials qualification methods that are able to predict the material properties and performance for a given composition and microstructure. In this way, it is possible to qualify the material independent of the additive manufacturing process. In this work, we have demonstrated that it is possible to not only predict the ultimate tensile strength, but also the full true stress-strain curves for more than 100 specimens of the alloy Ti-6Al-4V that were produced via wrought and three markedly different additively manufactured processes (large-volume electron beam, large-volume laser hot wire, and small-volume selective laser melting). Nearly all of the predictions for ultimate tensile strength, which ranges from ~910MPa to ~1170MPa, are within 5% of the experimentally measured values for both the wrought and additively manufactured samples, including samples that underwent post-deposition processing.
5:00 PM
On the Use of Energy Dispersive Spectroscopy to Inform on Local Property Variations and Defect Formation across AM Processes: Katie O'Donnell1; Maria Quintana1; Matthew Kenney1; Andrew Temple1; Scott Blazanin1; Shraddha Vachhani1; Peter Collins1; 1Iowa State University
Metallic additive manufacturing (i.e., 3D printing) techniques typically generate melt pools with both higher thermal gradients and smaller length scales than those achieved through traditional manufacturing methods. Fluid flow during the build process is complex, and can vary locally based on machine parameters, powder properties, scanning strategy and many other mechanisms. Within melt pools, local composition can vary due to thermal gradients, fluid flow, solute segregation, selective vaporization, contaminants or other means. Analysis of the post-deposition compositional fluctuations in Ti-6Al-4V parts printed through electron beam melting, selective laser melting, and laser hot wire melting, have been used to showcase variations in local properties that lead to or influence the formation (and location) of defects, microstructure, and micro-texture across additive manufacturing processes. Revelations in compositional fluctuations shown through energy dispersive spectroscopy have been paired with microstructural imaging, electron backscatter diffraction, and nanoindentation to couple chemical, microstructural, and mechanical property variations.
5:20 PM
Reactiviting Transformation Induced Plasticity (TRIP) in an Additively Manufactured β-Ti Alloy: Srinivas Aditya Mantri1; MSKKY Nartu1; Narendra Dahotre1; Rajarshi Banerjee1; 1University of North Texas
A commercially available, metastable β-Ti alloy, Ti-10V-2Fe-3Al, was processed via both Laser powder bed fusion (LBPF) technique, using an Aconity MIDI system and a direct energy deposition (DED) technique, using Optomec LENS-750. With regards to titanium alloys, the use of AM technology has been well established; but most of the literature is limited to the α/β alloy Ti-6Al-4V. In the current study, site-specific microstructure and texture analysis, and mechanical properties along and across the build direction will be presented of this metastable β-Ti alloy. A change in the deformation behavior is noted in the sample, going from planar slip in the as-deposited condition to deformation via transformation induced plasticity in the solutionized sample. To put this in context, mechanical properties and deformation behavior of the bulk sample will also be presented.