Advances in Titanium Technology: Session IV
Sponsored by: TMS Structural Materials Division, TMS: Titanium Committee
Program Organizers: Yufeng Zheng, University of North Texas; Zachary Kloenne, Ohio State University; Fan Sun, Cnrs Umr 8247 - Chimie Paristech Psl; Stoichko Antonov, National Energy Technology Laboratory; Rongpei Shi, Harbin Institute of Technology (Shenzhen)
Tuesday 2:30 PM
March 21, 2023
Room: Cobalt 500
Location: Hilton
Session Chair: Zachary Kloenne, The Ohio State University
2:30 PM Invited
Effect of the Vibratory Peening Parameters on Surface Properties of Ti-6Al-4V: Maxime Paques1; Benoit Changeux2; Anindya Das1; Hongyan Miao1; Martin Levesque1; Sylvain Turenne1; Etienne Martin1; 1Polytechnique Montréal; 2Safran Tech
Vibratory peening aims to combine both beneficial effects of shot peening and vibratory finishing. This work aims to understand the effect of the process parameters on surface integrity of Ti-6Al-4V. Mill machined and mirror polished specimen were vibratory peened with two different eccentricities and for two different processing times. Surface topography was evaluated using roughness profilometer, optical microscope and white light optical interferometry. The initial surface preparation had the most important effect on the surface roughness after vibratory peening. Mirror polished specimens resulted in the optimum surface finish, given for a given set of process parameters. The increase of processing time for vibratory peening on mill machined specimen allowed to reach the optimum surface finish. Micro-hardness measurements and SEM-EBSD cartographies were performed. It was highlighted that the XRD method is recommended to assess the plastic strain induced by vibratory peening in Ti-6Al-4V.
3:00 PM Invited
Computational Studies of Deformation Twinning in Metastable Titanium Alloys: Ganlin Chen1; Liang Qi1; 1University of Michigan
We applied computational studies to understand and tune the effects of diffusionless phase transformations on deformation twinning activities in beta Ti alloys. First-principle calculations were firstly performed to study the structures and energy stability of different phases (omega, beta, and alpha’’, etc.) at their local-minimum states in different alloy compositions. Secondly, we applied atomistic simulations with classical interatomic potentials to further analyze the structures of Ti binary alloys at finite temperatures. Both first-principle calculations and atomistic simulation results are used to construct the order parameters that can effectively describe the energy landscape and diffusionless transformation paths between multiple phases. Thirdly, with the aid of atomistic simulations and crystallographic theories, we investigate the energy landscape of the nucleation and growth of multiple types of deformation twinning in beta Ti alloys at finite temperatures and further explore how the diffusionless phase transformations affect the deformation twinning activities.
3:30 PM Invited
On the Heterogeneous and Cooperative Deformation in High-strength (α+β) Titanium Alloys: John Foltz1; Shaolou Wei2; C Tasan2; Bhuvi Nirudhoddi1; 1ATI Specialty Materials; 2Massachusetts Institute of Technology
(α+β) titanium alloys demonstrate diverse microstructural combinations that enable fruitful pathways to engineer the macroscopic load-bearing performances. However, plastic deformation coordination between α- and β-phases remain unclear, especially the underlying deformation micro-events that cause plastic strain inhomogeneity. Recent high-strength cold-workable titanium alloys developed by ATI (ATI 425®, ATI Titan 27TM) further trigger the fundamental interest in elucidating the underlying plasticity micro-mechanisms. By systematically assessing these two alloys and their processing variants using integrated in situ micro-DIC, in situ synchrotron X-ray diffraction, and crystallographic calculations, we will showcase the explorations of the following three fundamental topics: (1) what are the predominant deformation micro-events leading to plastic strain inhomogeneity; (2) what are the micro-mechanical consequences of interdependent plastic deformation modes? and (3) what are the microstructural and chemical dependencies of these plasticity micro-mechanisms. Broader indications for processing-microstructure-property correlations in cold-workable (α+β) titanium alloys will also be discussed.
4:00 PM Break
4:20 PM
Transformation-mediated Twin Nucleation and the Temperature Dependence in Hexagonal Close-packed Metals: Lei Cao1; Mehrab Lotfpour1; Amir Hassan Zahiri1; Jamie Ombogo1; 1University of Nevada
Though twinning plays an equally vital role to that of dislocation slips in accommodating deformation in the hexagonal close-packed Ti and its alloys, its atomic-level nucleation mechanism has long been under debate. Accordingly, there is a critical need to rigorously understand the atomic mechanism of twin nucleation. We performed large-scale molecular dynamics simulations to study the deformation process in titanium. We found the nucleation of various deformation twins through reversible martensitic phase transformations, via evanescent intermediate phases. Furthermore, the findings are applied to rationalize the anomalous temperature dependence of the activation of different twinning modes in Ti and Zr.
4:40 PM
Twin Interface Structures and Fault-energetics in HCP Materials: Gorkem Gengor1; Ahmed Sameer Khan Mohammed2; Huseyin Sehitoglu2; 1University of Illinois Urbana Champaign; 2University of Illinois Urbana Champaign
Twinning is a prominent deformation-mode in Hexagonal-Close-Packed (HCP) materials. Knowledge of energy-barriers of nucleation and migration is essential to predict twinning-onset and consequent mechanical-response. This study calculates energy-barriers for {101 ̅2} and {112 ̅1} twins in HCP materials such as Ti. These barriers have remained elusive due to ambiguity in understanding of the structure and twinning mechanism, caused by the complex crystallography of these planes. The equilibrium Twin-Boundary (TB) structure is established by defining and determining a lattice-offset through ab-initio Density Functional Theory (DFT) calculations. The lattice-offset specifies the relative position of twin- and matrix-phase lattices, and the offset minimizing the TB-energy is established. This offset leads to determination of the twinning-mechanism clarifying the shear-shuffle partition. The determined mechanism informs the calculation of the Generalized Planar Fault Energy (GPFE) landscape. To the best of our knowledge, the GPFE for these modes is calculated for the first time in literature.
5:00 PM
Cottrell Atmospheres around Screw Dislocations in alpha-Ti Alloys: Eric Rothchild1; Siying Li2; Daryl Chrzan2; David Jany2; 1Sandia National Laboratories; 2University of California, Berkeley
Generally, solute atoms interact with screw dislocations in HCP materials via contact interaction or by changing the relative stacking fault energies of possible slip planes. In simulations of HCP Ti, however, oxygen interstitials are shown to have a long-ranged interaction with the 〈a〉-type screw dislocation. While no interaction between a perfect screw dislocation and a point source of dilation is predicted by linear elasticity theory, the〈a〉-type screw dislocations in Ti may spread on multiple possible slip planes. Here we present a simple analysis that shows how dislocation core spreading can lead to a substantial linear elastic interaction between the dislocation and interstitial. As core structure controls dislocation dynamics, these interactions have profound consequences for the mechanical behavior of the alloy.
5:20 PM
Atomistic Molecular Dynamics Simulations of Crack Tip Behavior in alpha-Ti
: Satish Rao1; Michelle Harr1; Vikas Sinha1; Adam Pilchak1; Tom Broderick1; 1MRL Materials Resources LLC
Atomistic molecular dynamics crack simulations were performed to investigate the orientation-dependent mechanisms of crack growth in α-Ti. A more accurate potential for alpha-Ti, the MEAM-spline Ehemann potential was used in these simulations. 3D Molecular dynamics simulations of crack tip extension were performed for several crack orientations (crack plane and crack front) corresponding to either <a> type dislocation nucleation at the crack tip or <c+a> dislocation nucleation, in HCP α-Ti, at temperatures 5- 300K. Constant sigma simulations were performed. Free surface boundary conditions were applied along all three directions in 3D simulations. The mode of fracture, ductile (dislocation nucleation at the crack tip) or brittle (crack tip extension without or with very limited plastic deformation), for various crack orientations were determined. These simulation results are then correlated with surface energy at the cracks and unstable stacking fault energy on the basal, prism and pyramidal planes.