Additive Manufacturing: Solid-State Phase Transformations and Microstructural Evolution: Titanium Alloys
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
Wednesday 2:00 PM
March 17, 2021
Room: RM 5
Location: TMS2021 Virtual
Session Chair: Raj Banerjee, University of North Texas; Bij-Na Kim, Carpenter Additive
2:00 PM Invited
Prediction of Large Regions of Microstructure and Phase Distributions for Additive Manufactured Alloys Prediction of the Microstructure, Resultant Phases and Hardness of Additively Manufactured Ti6Al4V: Shunyu Liu1; Kyung-min Hong1; Yung Shin1; 1Purdue University
In this presentation, a quantitative link between thermal history and resulting solidification as well as solid-state phase transformation throughout multi-track Ti6Al4V built by laser direct deposition (LDD) is systematically established using three combined multi-physics predictive models. A three-dimensional (3D) LDD model was first employed to simulate the thermal behavior, from which the extracted temperature field was coupled to a 3D cellular automaton (CA) model to simulate the comparative growth of β grains during solidification. A phase prediction model was then incorporated with the simulated heating/cooling rates to quantify the β→α/α’ transformation in the final microstructure. Based on the predicted volume fractions of α and α’ in fusion zone and heat affected zone, microhardness for a given position in the deposition was assessed. The predicted thermal history, distribution and growth pattern of solidified β grains and microhardness were all in a good agreement with experimental measurements and microstructural characterization.
2:30 PM
Designing Duplex Microstructures in Additive Manufactured Ti Alloys: An Avenue to Achieve High Strength and Ductility: Jenniffer Bustillos1; Atieh Moridi1; 1Cornell University
Limited plasticity in additive manufactured (AM) Ti alloys is a long-standing challenge hindering the widespread adoption of the technology. Through a single hot isostatic pressing (HIP) treatment and deliberate introduction of “lack of fusion” defects, we demonstrate the ability to engineer a duplex microstructure with excellent combinations of strength (UTS=1.06±0.02GPa) and ductility (εf=18±0.06%). Interrupted tensile tests with concurrent microstructural analysis using electron backscatter diffraction, electron channeling contrast imaging, and digital image correlation are performed to capture the heterogenous distribution of strains in the duplex microstructure. Restrained dislocation interactions within α-laths and unhindered dislocation activity in globular α-grains are proposed as the key mechanisms enabling enhanced plasticity with moderate strengthening via work-hardening. Fundamental understanding of co-deformation interactions will pave the way to engineer damage-tolerant AM Ti structures with tunable mechanical properties by engineering the volume fraction of lamellar and globular grains.
2:50 PM
Controlled Thermal Post-processing of Additively Manufactured Ti-6Al-4V Parts in Order to Enhance their Mechanical Performance: Frederico Rossi Kaschel1; Rajani Vijayaraghavan1; Patrick McNally1; Mert Celikin1; Denis Dowling1; 1I-Form Advanced Manufacturing Centre
Parts fabricated by additive manufacturing often require post-thermal heat treatments, in order to reduce internal stresses, as well as to increase their density, yielding both enhanced microstructural properties and mechanical performance. In this study the impact of heat treatments of AM printed Ti-6Al-4V, on the alloy’s internal residual stress, on phase fraction and resultant mechanical properties, are systematically examined. Preliminary in-situ X-Ray Diffraction (XRD) analysis showed that stress relaxation occurs on heating between room temperature and 400°C, without any evidence of phase transformation. Tensile test results on samples annealed at different temperatures, were found to directly correlate with changes in phase fraction, as observed using in-situ XRD analysis. In addition, this investigation provides a further insight on the effect of varying input energy along with processing time during heat treatments, on both the microstructural and mechanical performance of the thermally annealed parts.
3:10 PM
Recyclability of Ti-6Al-4V Powders Used in Additive Manufacturing: Perspectives and Outlooks: Nicholas Derimow1; Nikolas Hrabe1; 1National Institute of Standards and Technology
Titanium alloys are widely used in aerospace and medical industries for their high strength-to-weight ratios and good corrosion resistance. However, the high affinity for oxidation often leads to costly processing environments to maintain the purity of the finished product. The lifetime of a Ti-6Al-4V powder batch in an electron beam powder bed fusion (EB-PBF) additive manufacturing (AM) production environment is determined by an individual manufacturer’s process optimization. In practice, Ti-6Al-4V powder is recycled across many builds until oxygen pickup increases to a level that is no longer acceptable. Findings and observations from the literature with respect to Ti-6Al-4V powder recycling and subsequent effects on part performance will be discussed in this review presentation. Potential knowledge gaps and opportunities to optimize this process will be highlighted in this talk to increase powder batch lifetime and potentially reduce overall process cost.
3:30 PM
Microstructure Control in a Beta Titanium Alloy via Selective Laser Melting: Sravya Tekumalla1; Alex Tan Sui Wei2; Krishnan Manickavasagam2; Matteo Seita1; 1Nanyang Technological University; 2Advanced Remanufacturing Technology Centre
Beta titanium alloys are promising materials for load-bearing biomedical implants due to their excellent biocompatibility and low elastic modulus (~60 GPa). Combining these unique properties with the design freedom offered by additive manufacturing provides the opportunity to produce parts with tailored mechanical properties that best match those of the human cortical bone. In this work, we study a titanium niobium alloy produced via selective laser melting (SLM) using a mixture of pure elemental powders. We investigate the processing-structure-property space to identify a fully dense, low elastic modulus alloy design using a combination of scanning electron microscopy and mechanical testing. The large matrix of experiments we carry out offers the opportunity to study the origin of the different microstructures in detail and demonstrates the potential of microstructure control and design in beta Ti alloys through SLM.
3:50 PM
Second Phase Precipitation during AM Processing of Metastable Beta Ti Alloys
: Mohan Sai Kiran Nartu1; Srinivas Aditya Mantri1; Abhishek Sharma1; Eugene Ivanov2; Kyu Cho3; Brandon McWilliams3; Narendra Dahotre1; Rajarshi Banerjee1; 1University of North Texas; 2Tosoh SMD; 3CCDC, US Army Research Laboratory
During the additive manufacturing (AM) of titanium alloys of a wide variety of compositions, including α + β alloys such as Ti-6Al-4 V, and β alloys, when the laser or electron beam hits the sample, grains in the previously deposited topmost layers transform into the β phase. Subsequently, during cooling cycle, depending on alloy composition, second-phase precipitation may occur within these layers via solid-state precipitation. This study compares two binary model β -Ti alloys, Ti-12Mo and Ti-20 V and two commercial metastable β-Ti alloys, Ti-1Al-8V-5Fe (Ti-185), Ti-10V-2Fe-3Al (Ti-10-2-3), that have been processed using laser engineered net shaping (LENS), AM technique. Compared to Ti-V, which exhibited grains of only the β phase in the as-built condition, the less β stabilized Ti-Mo, Ti-185, and Ti-10-2-3 had extensive second-phase precipitation (α/α''/ω) within the build. The location within the LENS build played a pivotal role in determining the size scale, area fraction, and morphology of the precipitates.
4:10 PM
Main Microstructural Characteristics of Ti-6Al-4V Components Produced via Electron Beam Additive Manufacturing (EBAM): Silvia Lopez-Castano1; Philippe Emile2; Claude Archambeau2; Florence Pettinari-Sturmel3; Joël Douin3; 1CEMES-CNRS / Airbus Operations S.A.S.; 2Airbus Operations S.A.S.; 3CEMES-CNRS
Electron Beam Additive Manufacturing (EBAM) has high deposition rates and big built envelopes which makes it a suitable additive manufacturing (AM) technology for the serial production of large metallic aeronautical parts. However, its complex periodic heat treatments with high temperature gradients produce heterogeneous and anisotropic microstructures throughout the built part compared to traditional technologies that has to be controlled in order to ensure its viability. In this study, a microstructural characterization of Ti-6Al-4V parts manufactured by EBAM technology is performed, providing a general idea of the main microstructural features that have to be taken into account for further improvement of this technology. After that, the influence of different key processing parameters on thermal history, microstructure and mechanical properties are investigated in order to reduce the large EBAM’s operating window to an operating zone where acceptable parts with the desired mechanical properties can be obtained.