Purveyors of Processing Science and ICME: A SMD Symposium to Honor the Many Contributions of Taylan Altan, Wei Tsu Wu, Soo-Ik Oh, and Lee Semiatin: Titanium Alloys
Sponsored by: TMS Structural Materials Division, TMS: Shaping and Forming Committee, TMS: Titanium Committee
Program Organizers: Adam Pilchak, Pratt & Whitney; Ayman Salem, MRL Materials Resources LLC; Viola Acoff, University of Mississippi; Nathan Levkulich, UES; Michael Glavicic, Rolls-Royce; Yufeng Zheng, University of North Texas; John Joyce-Rotella, Air Force Research Laboratory
Tuesday 8:30 AM
February 25, 2020
Room: 30E
Location: San Diego Convention Ctr
Session Chair: Adam Pilchak, Air Force Research Laboratory; Matthew Dunstan, US Army
8:30 AM Invited
Regulating Plastic Deformation by Structural Phase Transformations and Cice Vesa for Unprecedented Mechanical Properties: Yunzhi Wang1; 1The Ohio State University
In crystalline solids, plastic deformation can be carried out by dislocations, mechanical twinning (TWIP) and/or structural phase transformations (TRIP), while elastic deformation can be carried out by changing bond length and angle (intrinsic elasticity) and/or reversible structural phase transformations (pseudo-elasticity). All these plasticity and elasticity carriers could be intrinsically coupled together during a deformation process, which is particularly true in polymorphic crystals. In this presentation, using specific examples found in Ti-alloys, TiNi-shape memory alloys and Ni-base superalloys, we analyze such intrinsic couplings, either static or dynamic in nature, and demonstrate how they regulate the elastic and plastic deformation behavior of the alloys. Efficient and Judicious utilization of such couplings in alloy design and thermomechanical treatment could lead to unprecedented properties. This work is supported by DOE/BES program and NSF/DMREF program.
9:00 AM Invited
The Evolution of Abnormal Grains Structures during Beta Annealing of Ti-64 Wrought Products: Nicholas Byres1; Pratheek Shanthraj1; Benjamin Dod2; Jack Donoghue3; Alec Davis1; Joao Quinta da Fonseca1; Philip Prangnell1; 1University of Manchester; 2Airbus; 3The University of Manchester
Beta annealing of Titanium-6Al-4V (Ti64) forged components with a strong prior cube-related texture distributions, inherited from the deformation step, can lead to abnormal structures in semi-finished products that do not meet qualification requirements.The mechanisms behind the development of such abnormal grain structures during the beta annealing step are discussed, based on new evidence from in-situ heating experiments with high speed Electron Backscatter Diffraction (EBSD) analysis. These results have also been simulated using the phase field method, based on statistically representative starting texture distributions. This work has highlighted that a combination of factors may be involved, including the requirement for a strong starting matrix texture containing minor embedded highly misoriented grain components, that act as nuclei, and the heterogeneous dissolution of primary alpha grains, which allows such regions to achieve a sufficient size differential to obtain a ‘runaway’ growth advantage over the surrounding microstructure.
9:30 AM
Martensitic Variant Selection Under Applied Stress: A New Approach Applied to the β→𝛼 Transformation in Titanium: Zachary Brunson1; Adam Pilchak2; Eric Payton2; Aaron Stebner1; 1Colorado School of Mines; 2United States Air Force Research Laboratory
The problem of variant selection in Martensitic transformations has been explored in various aspects ever since the phenomenological theories were first developed by Wechsler, Lieberman, and Read in 1953 and by Bowles and Mackenzie in 1954. We tackle the scenario of variant selection under an applied stress using a new approach which combines aspects of the phenomenological theory as applied by Wang, Aindow, and Starink in 2003 for investigating variant cluster effects and an eigen-strain approach as described by Ledbetter and Dunn in 2000. The result is an approach for identifying the variant(s) and/or variant cluster(s) which minimize the strain energy of the system during a martensitic transformation under an imposed state of stress. We specifically apply the approach to the β→𝛼 transformation in Titanium, and explore various cases of imposed stress such as applied uniaxial and shear loadings and the strain field around dislocations in the parent phase.
9:50 AM
Manipulation of Microstructure and Microstructural Gradients through Dehydrogenation of Hydrogen-sintered Ti-6Al-4V: Matthew Dunstan1; James Paramore1; Z. Zak Fang2; Pei Sun2; 1United States Army Research Laboratory; 2University of Utah
In recent years, the powder metallurgy process known as hydrogen sintering and phase transformation (HSPT) has been employed to produce Ti-6Al-4V with mechanical properties that outperform traditional inert/vacuum sintered Ti-6Al-4V and compete with wrought processing. During HSPT processing, hydrogen is used as a temporary alloying element to improve densification and force phase transformations to occur, resulting in high relative density (>98%) and an ultra-fine grained microstructure. As part of hydrogen processing, residual hydrogen must be removed through a vacuum annealing step (known as dehydrogenation) to prevent the embrittling effects of excess hydrogen. In this work, dehydrogenation is shown to be a viable method to further manipulate the microstructure, thus producing a wider range of mechanical properties. Furthermore, by taking advantage of the β stabilizing effects of hydrogen, a functionally graded microstructure can be produced with an ultra-fine grained surface microstructure and a coarse-grained interior microstructure.
10:10 AM Break
10:30 AM Invited
Transformations, Recrystallization, Microtexture and Plasticity in Titanium Alloys: Dipankar Banerjee1; 1Indian Institute of Science
We describe different facets of the β to α transformation in titanium alloys. with special reference to dominant variant groupings. We then describe two distinct recrystallization processes during thermomechanical processing in the α/β regime with the help of fine scale, orientation image mapping techniques. The first is associated with the well-known α globularisation process. An alternative, dynamic recrystallization process is also observed in which newly recrystallized α and β grains form with the Burgers orientation relationship with each other. We call this process epitaxial recrystallization. We then present the role of transformation and recrystallisation texture on the plasticity of titanium alloys with emphasis on slip length through a quantitative EBSD /TEM based analysis of slip systems in the α phase and slip transfer between the α and β phases.
11:00 AM Invited
The Effects of Alpha-beta Interaction on the Texture Development of Zr and Ti Alloys during Hot Working: Joao Quinta da Fonseca1; Chi-Toan Nguyen1; Christopher Daniel2; Philip Prangnell2; Pratheek Shanthraj2; Benjamin Dod3; Peter Honniball4; 1University Of Manchester; 2University of Manchester; 3Airbus; 4Rolls-Royce
In Ti alloys, hot working is used to weaken the (micro-)texture, whereas in Zr alloys a strong texture is often desired. During hot working, the texture in these materials evolves through the simultaneous action of deformation, annealing and phase transformation. Here we present an overview of recent complementary work on the texture of hot deformed Zr and Ti alloys. Hot rolling produces a characteristic transverse basal texture in alpha and a strong rotated cube texture in beta. In uniaxial compression a cube fibre develops in beta, which is stronger in the alpha+beta regime than above the transus temperature, suggesting it is enhanced by the presence of alpha. The interaction between alpha and beta phases was studied using crystal plasticity finite element modelling. For particular alpha variants, its presence helps stabilize the cube-related components. The implication of this interaction for the development of texture in forgings is discussed.
11:30 AM Invited
The Role of Plastic Rotation in the Breakdown of Colony Microstructures in Two Phase Titanium Alloys: S. Keith Markham1; Mayo Mizak1; Adam Pilchak2; Victoria Miller3; 1North Carolina State University; 2Air Force Research Laboratory; 3University of Florida
The breakdown of the lamellar colony structure during the thermomechanical processing of two-phase titanium alloys is a critical step of primary processing. The alpha and beta phases of lamellar microstructures in titanium have a Burgers orientation relationship (BOR), which closely aligns several slip systems in each phase. Depending on the initial colony orientation, this alignment may cause both phases to rotate in the same direction hence preserving the BOR and potentially stymying spheroidization of the alpha phase and recrystallization of the beta phase. In other instances, plastic deformation causes rotation away from the BOR, which should enhance spheroidization kinetics. In this work, we hypothesize that the propensity for breakdown of the colony structure can be predicted by plastic rotation arguments. The viscoplastic self-consistent model is used to examine this hypothesis and results are compared to colony breakdown studies from literature.