Metastable Phases and Phase Equilibria: Towards Designing the Next Generation of Alloys: Session I
Sponsored by: TMS Materials Processing and Manufacturing Division, TMS: Phase Transformations Committee
Program Organizers: Bij-Na Kim; Rajarshi Banerjee, University of North Texas; Gregory Thompson, University of Alabama; Eric Lass, University of Tennessee-Knoxville; Mohsen Asle Zaeem, Colorado School of Mines; Mark Aindow, University of Connecticut; Peeyush Nandwana, Oak Ridge National Laboratory; Dinc Erdeniz, University of Cincinnati; Andrew Bobel, General Motors Corporation
Wednesday 8:30 AM
February 26, 2020
Room: 31A
Location: San Diego Convention Ctr
Session Chair: Bij-Na Kim, Carpenter Additive; Raj Banerjee, University of North Texas; Peeyush Nandwana, Oak Ridge National Laboratory
8:30 AM Keynote
New Strain-transformable Titanium Alloys Displaying Unprecedented Combination of Mechanical Properties: from Design Approaches to Deformation Mechanisms: Frederic Prima1; 1Chimie ParisTech
Owing to their high specific properties, titanium alloys have been, for a long time, highly competitive materials in fields such as aerospace industry. Among these alloys, research efforts were recently dedicated to design approaches for improved strength/ductility trade-off. Guided by electronic parameters calculations, new “strain-transformable” Ti alloys have been developed and both single phase and dual phase materials have been optimized. Thanks to the synergy between stress-induced martensitic transformation (TRIP effect), intense mechanical twinning (TWIP effect) and dislocations glide, these new materials display a combination of high fracture strength (up to 1400MPa), extra-large work-hardening and superior ductility (up to 45% at fracture).In this talk, design strategy and microstructural optimization approaches of this new family of alloys will be discussed regarding the occurrence, chronology, and synergy of the different deformation mechanisms. From this work, future directions towards both compositional and microstructural optimization pathways will be drawn and discussed.
9:10 AM Invited
Exploration of Nano-scaled Metastable Phases in Metastable Beta Titanium Alloys Using Advanced Electron Microscopy and Atom Probe Tomography: Yufeng Zheng1; Dong Wang2; Stoichko Antonov3; Dipankar Banerjee4; Rajarshi Banerjee5; Yunzhi Wang6; Hamish Fraser6; 1University of Nevada, Reno; 2Xi'an Jiaotong University; 3University of Science and Technology Beijing; 4Indian Institute of Science; 5University of North Texas; 6Ohio State University
Metastable beta titanium alloys have attracted a significant amount of attention in recent years, due to the fact that the microstructure of metastable beta titanium alloys is very sensitive to thermo-mechanical processes, and therefore its performance can be manipulated by accurately controlled processing conditions. In these alloys, the phase transformation pathways and deformation modes can be significantly influenced by the nano-scaled metastable phases. For example, the size and number density of alpha precipitates in Ti-5Al-5Mo-5V-3Cr can be modified by the pre-formed nano-scaled metastable isothermal omega phase in parent beta phase. In this work, four different nano-scaled metastable phases in the as-quenched or aged metastable beta titanium alloys, including athermal and isothermal omega phase, O' phase and O'' phase, have been systematically studied using advanced electron microscopy and atom probe tomography. The formation mechanism of each phase and their potential influence on microstructure evolution and deformation will be introduced.
9:40 AM
Tuning Strength in TRIP Titanium alloys: Benjamin Ellyson1; Amy Clarke1; Jonah Klemm-Toole1; Kester Clarke1; Yoafeng Guo1; 1Colorado School of Mines
Titanium (Ti) alloys are heavily used in defense, aerospace and bio-medical sectors, due to their exceptional specific strength and corrosion resistance. However, limited uniform elongation and low work-hardening restrict allowable deformation and absorbed energy of parts in service. TRansformation-Induced Plasticity (TRIP) has been heavily utilized in steels to increase crash-resistance in service, circumventing the traditional strength/ductility trade-off. Some metastable β-Ti alloys have been reported to exhibit TRIP, producing exceptionally high uniform elongation and work hardening rate (WHR). However, TRIP is fundamentally misunderstood in the Titanium system and these alloys have been plagued by uncommonly low yield stresses. Recent results have revealed that aging of athermal ω-phase precipitates permits highly reproducible tuning of the yield-stress of TRIP Titanium alloys. This aging behavior is shown to affect ω-phase morphology and volume fraction, which in turn strongly affects the transformation stress for martensite.
10:00 AM
Precipitation Kinetics and Mechanical Behavior of Oxygen-stabilized Metastable Beta Ti-Nb Alloys: Kathleen Chou1; Emmanuelle Marquis1; 1University of Michigan
Phase stability in metastable beta titanium has been actively investigated to develop alloys with controllable deformation behavior including superelasticity and TRIP/TWIP mechanisms. Oxygen has shown substantial influence through martensite suppression and stability changes in beta Ti that significantly affect deformation. In this work, a model Ti-20Nb (at. %) alloy was oxidized to obtain a dissolved oxygen gradient in the beta matrix, and subsequently aged to understand oxygen effects on metastable omega and stable alpha phase formation. During ageing, oxygen induced an increase in the omega number density and a change in the omega morphology from ellipsoid to rod-like. Elevated oxygen content expanded the omega phase stability region up to above 600 °C. Micropillar compression testing suggests enhanced work-hardening for oxygen-stabilized microstructures compared to oxygen-free specimens. These insights on oxygen as both an alpha and omega stabilizer open new avenues of microstructural control and design of beta Ti alloys.
10:20 AM Break
10:40 AM
The Intrinsic Coupling Between Twinning Plasticity and Transformation Plasticity in Metastable β Titanium Alloys: Yipeng Gao1; Yufeng Zheng1; Yunzhi Wang1; 1The Ohio State University
In addition to conventional dislocation plasticity, mechanical twinning and structural phase transformation are two important mechanisms that contribute to the plasticity of metals and alloys. Mechanical twinning and phase transformation are theoretically distinctive. In spite of established theories to treat mechanical twinning and phase transformation independently, the intrinsic coupling between them has not been well recognized due to the lack of a unified theoretical framework. We suggest a graph approach to analyze the deformation modes arising from the interplay of mechanical twinning and phase transformation. Using metastable β titanium alloys as an example, we show that mechanical twinning and phase transformation are intrinsically coupled in symmetry-breaking processes, which results in multiple interconnected deformation pathways and characteristic twinning modes. Our work not only reveals the physical origin of unique twinning modes observed in experiments, but also provides a new insight into the enhanced plasticity of β titanium alloys.
11:00 AM
Towards Work-hardenability of Ti-6Al-4V Through a Quenching and Partitioning Approach: Odeline Dumas1; Benjamin Hary1; Guilhem Martin2; Fan Sun3; Charlotte de Formanoir4; Frédéric Prima3; Stéphane Godet1; 1Université Libre de Bruxelles - 4MAT; 2SIMaP - CNRS; 3Chimie ParisTech-CNRS, Institut de Recherche de Chimie Paris, Université de recherche PSL; 4KU Leuven, Department of Mechanical Engineering
A quenching and partitioning strategy has been developed to provide insight into the possibilities to reach a work-hardening capacity very rarely reported in Ti-6Al-4V. Indeed, it was recently demonstrated that a sub-transus thermal treatment followed by water quenching could generate an α + α’ microstructure displaying a high work-hardening, strength and ductility. We performed a series of ‘quenching’ treatments using several solutionizing temperatures. The volume fraction of each phase, the size, the chemistry and the interfaces of the martensite are taken as microstructural variables to modify the work-hardenability of dual-phase Ti-6Al-4V. Then, annealing of the dual-phase microstructure was performed to bring about progressive martensite decomposition also involving a ‘partitioning’ of the alloying elements. Martensite was shown to be a very heterogeneous and discontinuous medium in which interfaces play a crucial role in the capacity of the material to progressively transform during the deformation and harden at a macroscopic scale.
11:20 AM
Composition, Processing, and Property Relationships in Fe and Al Modified Ti-12Cr Alloys: Joann Ballor1; Elizabeth Kautz2; Bharat Gwalani3; Masahiko Ikeda4; Jane Howe5; Takeshi Sunaoshi6; Arun Devaraj2; Carl Boehlert1; 1Michigan State University; 2Pacific Northwest National Laboratory; 3Pacific Northwest National Lab; 4Kansai University; 5Toronto University; 6Hitachi
Low-cost beta-stabilized Ti-12Cr-xFe-xAl(wt.%) alloys (where 0≤x≤3) were investigated to determine the effects of composition on microstructure and tensile properties. 400°C heat treatments were used to induce a phase transformation from the metastable BCC beta phase to the hexagonal omega phase and achieve higher tensile strengths. We investigated the impact of Fe and Al on the stability, volume fraction, distribution, and morphology of the omega and alpha phases in these alloys and their effect on mechanical performance under tensile loading conditions. Multi-modal characterization using optical microscopy, scanning electron microscopy, transmission electron microscopy, energy dispersive spectroscopy, and atom probe tomography resulted in a thorough understanding of composition-microstructure-property relationships that can be used to further optimize mechanical properties in these alloys, and can provide insight for the design of other beta-omega Ti alloys.
11:40 AM
Shape Memory Response of High Temperature NiTiHfPd: Soheil Saedi1; Guher Pelin Toker2; Ehsan Saghaian2; Dipak Banerjee1; Haluk Karaca2; 1University of Arkansas Little Rock; 2University of Kentucky
Materials that can act as an actuator at high temperature are rare. Not only attaining high transformation temperature is challenging, but also the strength and cyclic stability of the alloys are also diminished at such elevated temperatures. In this work, the effect of minor addition of precious Pd element to the promising high-temperature NiTiHf system is investigated in order to overcome the materials high brittleness and poor cyclic stability. The solid solution hardening is combined with post-processing heat treatments to increase the transformation temperature and enhance the shape memory response and ductility. Our studies show that with the addition of even minor (3-5 %at) Pd content and precipitate hardening it is possible to attain transformation temperatures above 250°C in this system. Furthermore, NiTiHfPd alloys could display large transformation strains under significantly high loadings that makes them a potential candidate for critical applications.