Advances in Titanium Technology: Phase Tranformation in Ti Alloys
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 - Psl Research University; Stoichko Antonov, National Energy Technology Laboratory; Rongpei Shi, Harbin Institute of Technology
Tuesday 8:00 AM
March 1, 2022
Location: Anaheim Convention Center
Session Chair: Stoichko Antonov, Max-Planck-Institut für Eisenforschung GmbH
Role of Defects in Alpha Precipitation in Metastable Beta Ti-5Al-5Mo-5V-3Cr Alloy: Dian Li1; Wenrui Zhao1; Stoichko Antonov2; Yufeng Zheng1; 1University of Nevada-Reno; 2Max-Planck-Institut für Eisenforschung
The mechanical performance of beta titanium alloys can be optimized by tuning hcp structured alpha precipitates in a matrix of bcc beta phase. Our previous study in Ti-5Al-5Mo-5V-3Cr (wt%, Ti-5553) has shown that fine-scale alpha microstructure can be generated, in which the pre-formed omega/beta interface may act as favorable nucleation sites for alpha precipitation. In this work, the role of other defects including dual-phase interface, twin boundary and grain boundary in tuning alpha precipitation in the metastable beta Ti-5553 alloy is studied using SEM, TEM, APT and FIB-SEM tomography. Fine-scale alpha precipitates form from pre-formed O”/beta interface; coarse alpha precipitates form along pre-formed twin boundary; while thick alpha layer forms from the grain boundary alpha. The possible microstructure evolution pathway to generate hierarchical alpha microstructure in Ti-5553 will be introduced.
β-titanium bcc-superalloys with Reinforcement by β' Ordered bcc TiFe Precipitates: Paraic O'Kelly1; Alexander Knowles1; 1University of Birmingham
The design and development of precipitate reinforced refractory-metal-based alloys has demonstrated the possibility of β-β' bcc-superalloys as a new class of high temperature materials. β-Ti alloys do not typically employ intermetallics reinforcement as in other high temperature alloys. Specifically, additions of Fe, a low cost β-Ti stabiliser, promotes formation of an ordered-bcc intermetallic phase, β' TiFe, offering a dual phase β-β' field yet to be widely exploited. However, key uncertainties exist in the base Ti-Fe binary. This current research evaluates ordered-bcc β' superlattice structures precipitated within a disordered-bcc β-Ti matrix matrix induced through varied heat treatment strategies. The optimised alloys reveal new insights into phase equilibria at near eutectoid temperatures in the purported dual phase field, where a complex interplay between β-Ti, β'-TiFe, α-Ti and ω has been found to exist. Preliminary investigation of mechanical properties have proven attractive, and further study is warranted to address ductility and oxidation performance.
Exploring Sub-stoichiometric Titanium Hydride Phase Space via Vacuum Hydrogen Annealing, X-ray Diffraction, and Combined Thermogravimetric Analysis/Mass Spectroscopy: Chad Macziewski1; Daniel Bufford1; 1Sandia National Laboratories
Titanium hydrides with formula TiHx exist over a range of compositions with 0 < x ≤ 2 (0 to 4 wt% hydrogen). Many applications focus on hydrogen as a processing aide or exploiting hydrogen content of near-stoichiometric hydrides (x ≈ 2). The intermediate range has been characterized to find pressure-composition-temperature relationships and is traversed frequently during hydride/dehydride processing of titanium sponge into powder. However, materials with intermediate hydrogen stoichiometry and techniques to quantify hydrogen in this region have seen less investigation. Here we produced sub-stoichiometric hydrides with 1.5 < x ≤ 2 from multiple feedstocks by manipulating processing temperature, pressure, and time utilizing multiple paths to sub-stoichiometric hydrides, including dehydriding TiH2 and hydriding Ti powders. X-ray diffraction and thermogravimetry coupled with quantitative mass spectrometry offer a means to quantify hydrogen content. Parallel development of these processing methods alongside analysis techniques reestablishes what accuracies are obtainable when processing sub-stoichiometric titanium powders.
Local Distortion Effects on the Dynamic Lattice Stability in the BCC Phase of Titanium and Its Alloys: An Ab-initio Study: Sri Ranga Jai Likith1; Benjamin Ellyson1; Amy Clarke1; 1Colorado School of Mines
Phase transformations in the β-Ti system are controlled by soft phonons and highly damped lattice vibrations. Here we use Density Functional Theory (DFT) calculations to examine the effects of solute additions (V, Cr, Mo) on local structural distortions and the elastic instabilities important to the properties of metastable β-Ti alloys. The latter is gleaned from analyzing phonon behavior of μ-Ti in the presence of V, Cr, and Mo solutes at low concentrations (6.25 at.%). Modeling results show that phonons in β-Ti are sensitive to small-scale distortions caused by Ti-solute atom interactions. These distortions are quantified, and their effects on phonon behavior have been analyzed; specifically, the phonon branches that play an important role in the β-α and β-ω phase transformations. The goal of this study is to inform subsequent efforts to understand the elastic and dynamic phenomena that govern phase transformations and microstructure evolution in metastable β-Ti alloys.
Monte Carlo Simulations for Texture-controlled Grain Growth during Beta-annealing of Ti-6Al-4V: Denielle Ricciardi1; Nate Levkulich1; Lee Semiatin1; Eric Payton1; 1Air Force Research Laboratory
Alpha\Beta Titanium alloys such as Ti-6Al-4V often undergo beta annealing to improve fatigue crack growth resistance. Under certain processing paths the grain growth may exhibit abnormal growth kinetics, which leads to coarse grains that may be detrimental to component durability. Previous studies have suggested this is a texture-controlled process which relies on spatial non-uniformities in grain boundary mobility and energy, giving a select few grains an advantage for growth. This work uses Monte Carlo simulations of grain growth to systematically study the most important factors leading to coarse grain development. The texture-controlled nature of coarse grain growth is explored by considering the influence of grain boundary mobility and energy as a function of misorientation, as well as the stored energy of the grains.