Additive Manufacturing: Microstructure and Material Properties of Titanium-based Materials: Modeling and Properties
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; Yufeng Zheng, University of North Texas

Wednesday 2:00 PM
November 4, 2020
Room: Virtual Meeting Room 8
Location: MS&T Virtual

Session Chair: Rongpei Shi, LLNL


2:00 PM  Cancelled
Predicting Properties in Additively Manufactured Titanium Alloys: Sunil Dhapola1; Andrew Temple1; Thomas Ales1; Peter Collins1; 1Iowa State University
    In recent years, we have demonstrated that it is possible to predict the yield strength of additively manufactured Ti-6Al-4V with a constitutive equation that has been developed using an approach that extracts physical phenomena from machine learning strategies. In this work, we will expand beyond predicting yield strength, and present our efforts to predict other properties for additively manufactured Ti-6Al-4V (including ultimate tensile strength), as well as rationalizing the deformation mechanisms that govern the mechanical behavior of not only Ti-6Al-4V, but also of other titanium alloys, including beta titanium alloys. We will look ahead at what it will take to predict properties such as ductility, fracture toughness and fatigue.

2:30 PM  
Microstructural Modeling of β to α Transformation Morphologies in Multi-layered Laser Wire Additively Manufactured Ti-6Al-4V Parts: Andrew (Drew) Huck1; Amit Verma1; Anthony Rollett1; Brandon Abranovich1; Elizabeth Chang-Davidson1; Ali Guzel1; Jack Beuth1; Zhening Yang1; Ze Geng1; Lonnie Smith1; Amaranth Karra1; 1Carnegie Mellon University
    The room temperature microstructure of Ti-6Al-4V in multi-bead laser weld deposited builds is characterized by predominantly lamellar α phase growth with interlamellar β within prior β grains. This microstructure is the result of a complex position dependent thermal history, with multiple heating cycles above and near the β transus from subsequent layer depositions. Several α morphologies and different lamellar sizes appear depending on local β character and cooling rates, which can affect the bulk mechanical properties of the material by causing local changes. This work attempts to model location referenced microstructural evolution in laser-wire deposited parts using a classical nucleation and growth model. Additive isothermal time steps in a JMAK type transformation with impingement correction are taken to approximate the cooling curves. Predicted values include area fractions of grain boundary, colony, basketweave, and martensitic α phase, as well as average lamella thickness.

2:50 PM  
Dynamic Transformations In AM Ti6Al4V Alloy: Sabina Kumar1; Rakesh Kamath2; Yan Chen3; Peeyush Nandwana3; Suresh Babu1; 1University of Tennessee; 2University Of Tennessee; 3Oak Ridge National Laboratory
    A complex interaction of process parameters, geometry and scan strategies in Additive Manufacturing (AM), can bring about spatial and temporal transients, i.e., Σ T (x,y,z,time), within a part. Published literature focusses on fluctuating thermal cycles on the microstructure evolution. However, the microstructural variations have not been correlated to dynamic flow behavior due to the macro- and micro-scale phenomena, i.e., accumulated plastic strains brought about by large thermal gradients, transformational strains and crystallographic misfit strains. Therefore, we studied the mechanical response of Ti6Al4V alloys produced by AM under externally imposed controlled thermo-mechanical reversals using a GleebleŽ thermo-mechanical simulator. The stress-strain behaviors were correlated to phase fractions, lattice strains, and also information on crystallographic texture using neutron diffraction techniques at the VULCAN Beamline at SNS, ORNL followed by metallographic analysis. The results are discussed and rationalized based on theories of static and dynamic phase transformations.

3:10 PM  
Fracture of additively manufactured Ti-6Al-4V under multiaxial loading: experiments and modeling: Alexander Wilson-Heid1; Allison Beese1; 1Pennsylvania State University
    The orientation dependent plasticity and fracture behavior of the titanium alloy Ti-6Al-4V manufactured via laser powder bed fusion (L-PBF) additive manufacturing (AM) was experimentally determined. Tests under uniaxial tension, pure shear, plane strain tension, and combined tension/shear loading showed that samples loaded in the vertical build direction had a higher ductility than corresponding samples loaded perpendicular to the vertical build direction. The experimental results were then used in conjunction with finite element analysis to calibrate and validate an anisotropic plasticity model. The fracture behavior was then evaluated with a combined experimental/computational approach to probe the strain to failure as a function of stress state (stress triaxiality and Lode angle parameter) of the material. Six existing fracture models were then calibrated using the experimental data, and their ability to capture and predict the anisotropic stress state dependent fracture of L-PBF Ti-6Al-4V will be discussed.

3:30 PM  
Influence of Different Post-printing Treatments on the In Vitro Biocompatibility of 3D Generated Titanium Plates: Jakob Schneider1; Elena Lopez1; Frank Brueckner1; Christoph Leyens1; Ute Botzenhart1; Bernhard Weiland1; Kiriaki Katerina Papadopoulos1; Andreas Schroeder1; 1Fraunhofer IWS
    Patient-individual bone plates from TiAl4V ELI can be 3D-printed. Directly after printing the samples have a very rough surface requiring further processing. The aim of this study was to analyse the effect of different grinding procedures on sample surface and in vitro biocompatibility, to make sure, that the clinically approved material properties of the Ti-alloy are satisfactory. Initial average surface roughness of 3D-printed titanium discs, produced by SLM was reduced by sandblasting followed by barrel finishing, electro-polishing or plasma-polishing and was then evaluated using tactile surface quality measurement. Biocompatibility of the different samples was assessed by quantification of metal-ion release, indirect cell viability and cytotoxicity tests as well as direct cell adhesion, analysed by fluorescence and SEM. Mouse fibroblasts, osteosarcoma cells, human primary gingival fibroblast as well as human gingival epithelial cells were used in this study. Statistical evaluation was performed by Kruskal Wallis test, followed by posthoc Dunn´s test.

3:50 PM  Cancelled
Measuring texture at large scales using spatially resolved acoustic spectroscopy: Thomas Ales1; Peter Collins1; 1Iowa State University
    A new technique, spatially resolved acoustic spectroscopy (SRAS) permits the characterization of grain orientation and their aggregated texture over very large areas (many square inches). This technique will be introduced for the first time to the MS&T community. In addition to establishing the first SRAS instrument in the western hemisphere, we are also integrating it into a serial sectioning instrument (a Robo-Met.3D), permitting 3D orientation information to be obtained over large volumes. It has been applied to study texture and microtexture in titanium alloys, both conventionally processed and additively manufactured. In this talk, we will explore the difference in texture in large-scale additively manufactured Ti-6Al-4V (both electron beam and laser based) and small-scale AM titanium alloys. Data will be presented in both 2D and 3D.

4:10 PM  
Understanding Microstructure and Mechanical Property Variations in Lase-based Powder Bed Fusion of Ti-6Al-4V and their Heat Treatment Design: Ebrahim Asadi1; Behzad Fotovvati1; Seyed Alireza Etesami1; 1University of Memphis
    This study presents a comprehensive investigation of microstructure and mechanical performance of laser-bases powder bed fusion (LPBF) of Ti-6Al-4V alloy (as-built) and several post-LPBF heat treatment cycles. First, the results of mechanical tensile testing and their associated microstructure, microhardness, porosity, and elemental analysis for LPBF of Ti-6Al-4V sheets are presented. The effect of thickness, orientation, distance from free edges, and height and their correlation to material microstructure (e.g. β nanoparticle volume fraction, martensitic α’ decomposition to α+β and α” orthorhombic structure) and thermal history as dictated by LPBF process parameters are investigate. For the second portion of the presentation, several heat treatments steps and cycles and their influence on mechanical properties and microstructure of Ti-6Al-4V alloys will be presented. These studies are utilized to design a heat treatment cycle to achieve α+α’ microstructure with improved elongation and mechanical strength combination needed for many applications in industries such as biodevice industry.