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Jin H, Zhang J, Li P, Zhang Y, Zhang W, Qin J, Wang L, Long H, Li W, Shao R, Ma E, Zhang Z, Han X. Atomistic mechanism of phase transformation between topologically close-packed complex intermetallics. Nat Commun 2022; 13:2487. [PMID: 35513380 PMCID: PMC9072387 DOI: 10.1038/s41467-022-30040-0] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/05/2021] [Accepted: 03/28/2022] [Indexed: 11/18/2022] Open
Abstract
Understanding how topologically close-packed phases (TCPs) transform between one another is one of the challenging puzzles in solid-state transformations. Here we use atomic-resolved tools to dissect the transition among TCPs, specifically the μ and P (or σ) phases in nickel-based superalloys. We discover that the P phase originates from intrinsic (110) faulted twin boundaries (FTB), which according to first-principles calculations is of extraordinarily low energy. The FTB sets up a pathway for the diffusional in-flux of the smaller 3d transition metal species, creating a Frank interstitial dislocation loop. The climb of this dislocation, with an unusual Burgers vector that displaces neighboring atoms into the lattice positions of the product phase, accomplishes the structural transformation. Our findings reveal an intrinsic link among these seemingly unrelated TCP configurations, explain the role of internal lattice defects in facilitating the phase transition, and offer useful insight for alloy design that involves different complex phases. It is challenging to study how topologically close-packed phases (TCPs) transform between one phase to another. Here the authors use atomic-resolved tools to look at the transformation between μ and P phases, revealing an intrinsic link between seemingly unrelated TCP configurations.
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Affiliation(s)
- Huixin Jin
- Institute of Microstructure and Property of Advanced Materials, Beijing University of Technology, Beijing, 100124, China.,School of Materials Science & Engineering, Shandong University, Jinan, 250061, China.,Center for Alloy Innovation and Design (CAID), State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, 710049, China.,School of Materials Science & Engineering, Zhejiang University, Hangzhou, 310058, China.,Beijing Advanced Innovation Center for Intelligent Robots and Systems and Institute of Engineering Medicine, Beijing Institute of Technology, Beijing, 100081, China
| | - Jianxin Zhang
- School of Materials Science & Engineering, Shandong University, Jinan, 250061, China.
| | - Pan Li
- School of Materials Science & Engineering, Shandong University, Jinan, 250061, China.,Institute of Systems Engineering, AMS, PLA, Beijing, 100000, China
| | - Youjian Zhang
- School of Materials Science & Engineering, Shandong University, Jinan, 250061, China.,Shandong Laboratory of Yantai Advanced Materials and Green Manufacturing, Yantai, 264006, P. R. China
| | - Wenyang Zhang
- School of Materials Science & Engineering, Shandong University, Jinan, 250061, China
| | - Jingyu Qin
- School of Materials Science & Engineering, Shandong University, Jinan, 250061, China
| | - Lihua Wang
- Institute of Microstructure and Property of Advanced Materials, Beijing University of Technology, Beijing, 100124, China
| | - Haibo Long
- Institute of Microstructure and Property of Advanced Materials, Beijing University of Technology, Beijing, 100124, China
| | - Wei Li
- Institute of Microstructure and Property of Advanced Materials, Beijing University of Technology, Beijing, 100124, China
| | - Ruiwen Shao
- Beijing Advanced Innovation Center for Intelligent Robots and Systems and Institute of Engineering Medicine, Beijing Institute of Technology, Beijing, 100081, China
| | - En Ma
- Center for Alloy Innovation and Design (CAID), State Key Laboratory for Mechanical Behavior of Materials, Xi'an Jiaotong University, Xi'an, 710049, China.
| | - Ze Zhang
- Institute of Microstructure and Property of Advanced Materials, Beijing University of Technology, Beijing, 100124, China.,School of Materials Science & Engineering, Zhejiang University, Hangzhou, 310058, China
| | - Xiaodong Han
- Institute of Microstructure and Property of Advanced Materials, Beijing University of Technology, Beijing, 100124, China.
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2
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Origin of ω-phase formation in metastable β-type Ti-Mo alloys: cluster structure and stacking fault. Sci Rep 2020; 10:8664. [PMID: 32457317 PMCID: PMC7251116 DOI: 10.1038/s41598-020-65254-z] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2020] [Accepted: 04/08/2020] [Indexed: 11/21/2022] Open
Abstract
The ω-phase formation and its collapsed structures in metastable β-type Ti-Mo alloys were illustrated by first-principles calculations and experimental evidence of a partially collapsed ω-phase in the nano-scale Mo-depleted region under a rapid cooling via high-angle annular dark-field scanning transmission electron microscopy. The ease of ω-phase formation within -Mo-Ti-Mo- poor cluster structure was not only due to the low energy barrier in the collapse pathway, which was caused by the reduced lattice distortion, but also due to the softening of the shear modulus (G111) as a result of the small charge density difference. The most stable collapsed structure of the ω-phase strongly depended on the minimum stacking fault energy among different collapse degrees in accordance to the smallest charge density difference. Therefore, the concurrent compositional and structural instabilities of the ω-phase was attributed to the coupling effect of the cluster structure with stacking fault from the atomic and electronic basis.
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3
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Routes to control diffusive pathways and thermal expansion in Ti-alloys. Sci Rep 2020; 10:3045. [PMID: 32080304 PMCID: PMC7033225 DOI: 10.1038/s41598-020-60038-x] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/11/2019] [Accepted: 01/29/2020] [Indexed: 11/30/2022] Open
Abstract
β-stabilized Ti-alloys present several unexplored and intriguing surprises in relation to orthorhombic α″ phases. Among them are (i) the diffusion-controlled formation of transitional α″iso, α″lean and α″rich phases and ii) the highly anisotropic thermal expansion of martensitic α″. Using the prototypical Ti-Nb system, we demonstrate that the thermodynamic energy landscape reveals formation pathways for the diffusional forms of α″ and may lead to a stable β-phase miscibility gap. In this way, we derive temperature-composition criteria for the occurrence of α″iso and resolve reaction sequences during thermal cycling. Moreover, we show that the thermal expansion anisotropy of martensitic α″ gives rise to directions of zero thermal strain depending on Nb content. Utilizing this knowledge, we propose processing routes to achieve null linear expansion in α″ containing Ti-alloys. These concepts are expected to be transferable to other Ti-alloys and offer new avenues for their tailoring and technological exploitation.
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Zháňal P, Harcuba P, Hájek M, Stráský J, Śmilauerová J, Veselý J, Horák L, Janeček M, Holý V. In situ detection of stability limit of ω phase in Ti–15Mo alloy during heating. J Appl Crystallogr 2019. [DOI: 10.1107/s1600576719010537] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Phase transitions in a single crystal of a metastable β-titanium alloy (Ti-15Mo) were investigated in situ during heating by synchrotron X-ray diffraction. The results were compared with previous measurements of electrical resistance. Single-crystalline samples allowed different crystallographic families of ω-Ti and α-Ti phases to be distinguished. The observed evolution of the intensity of the reflections of the ω phase during heating is consistent with the evolution of electrical resistance, which proves that the resistance is affected by the presence of ω-phase particles. Between approximately 673 and 833 K, both the resistance and the intensity of ω peaks sharply decrease. At 833 K, ω reflections disappear, indicating a complete dissolution of the ω phase due to achieving the solvus temperature of the ω phase in the Ti–15Mo alloy. The synchrotron X-ray diffraction experiment proved that the disappearance of the ω phase during heating of Ti–15Mo with a heating rate of 5 K min−1 occurs by its dissolution back to the β phase and not by ω → α transformation.
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Šmilauerová J, Harcuba P, Cieslar M, Janeček M, Holý V. Anomalous X-ray diffraction from ω nanoparticles in β-Ti(Mo) single crystals. Acta Crystallogr A Found Adv 2019; 75:718-729. [PMID: 31475916 DOI: 10.1107/s2053273319008428] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2018] [Accepted: 06/13/2019] [Indexed: 11/11/2022] Open
Abstract
Anomalous X-ray diffraction (AXRD) is a technique which makes use of effects occurring near the energy of an absorption edge of an element present in the studied sample. The intensity of the diffracted radiation exhibits an anomalous decrease when the primary beam energy matches the energy needed to excite an electron from an atomic orbital. The characteristics of this step are sensitive to the concentration of the `anomalous' element and its spatial distribution in the sample. In the present investigation, AXRD was employed to study ω particles in a metastable β titanium alloy Ti-15Mo (in wt%). The experiments were done in an energy range around the Mo K edge at 20.0 keV, allowing investigation of the distribution of Mo in the material, which is rejected from the volume of ω particles during their diffusion-driven growth. This paper deals with diffuse scattering patterns around the (006)β diffraction maximum. It was observed that different regions of the diffuse scattering exhibited different variations of diffracted intensity with the incident photon energy near the absorption edge. Numerical simulations of diffuse scattering patterns as well as of energy dependences of the scattered intensity were performed. It was found that the observed patterns and their dependence on the primary beam energy can be explained by taking into account (a) elastic deformation of the β matrix arising from the presence of slightly misfitting ω particles and (b) the presence of a `cloud' of a higher Mo concentration around ω particles.
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Affiliation(s)
- Jana Šmilauerová
- Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 121 16 Prague, Czech Republic
| | - Petr Harcuba
- Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 121 16 Prague, Czech Republic
| | - Miroslav Cieslar
- Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 121 16 Prague, Czech Republic
| | - Miloš Janeček
- Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 121 16 Prague, Czech Republic
| | - Václav Holý
- Faculty of Mathematics and Physics, Charles University, Ke Karlovu 5, 121 16 Prague, Czech Republic
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6
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Composition of ω-Phase Particles in Ti(Mo) Alloys Studied by Anomalous X-ray Diffraction. CRYSTALS 2019. [DOI: 10.3390/cryst9090440] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Nanoparticles of hexagonal ω phase in bcc-Ti(Mo) single crystals ( β phase) occur due to a diffusionless athermal β to ω transformation and they grow during follow-up ageing at elevated temperatures, while the alloying atoms (Mo in our case) are expelled from the nanoparticle volumes. We investigated the Mo content in growing ω nanoparticles by anomalous X-ray diffraction and demonstrate that the Mo expulsion from the ω phase is not full; a thin shell of a nanoparticles where the β to ω transformation is not complete still contains a considerable amount of Mo atoms.
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8
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Precipitation of string-shaped morphologies consisting of aligned α phase in a metastable β titanium alloy. Sci Rep 2018; 8:2038. [PMID: 29391443 PMCID: PMC5794777 DOI: 10.1038/s41598-018-20386-1] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/23/2017] [Accepted: 01/17/2018] [Indexed: 11/08/2022] Open
Abstract
String-shaped morphologies consisting of preferentially aligned lath-shaped α precipitates were observed in the metastable β Ti-6Cr-5Mo-5V-4Al alloy after deformations at high strain rates and elevated temperatures. The morphology and 3-dimentional arrangement of this feature have been elaborated based on the characterizations via a combination of transmission electron microscopy, transmission kikuchi diffraction and atom probe tomography. The 2D projected morphology of the coalescent α laths observed in the etched samples by SEM depends on the metallographic section. All the microstructural observations indicate that dislocation structures are most likely the nucleation sites for the aligned α laths. In addition, an appropriate testing temperature, which can ensure a relatively high diffusion rate of solutes without inducing strong recovery of dislocation structures, is necessary for the occurrence of the string-shaped morphologies.
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9
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Giant thermal expansion and α-precipitation pathways in Ti-alloys. Nat Commun 2017; 8:1429. [PMID: 29127330 PMCID: PMC5681671 DOI: 10.1038/s41467-017-01578-1] [Citation(s) in RCA: 54] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2017] [Accepted: 09/29/2017] [Indexed: 11/08/2022] Open
Abstract
Ti-alloys represent the principal structural materials in both aerospace development and metallic biomaterials. Key to optimizing their mechanical and functional behaviour is in-depth know-how of their phases and the complex interplay of diffusive vs. displacive phase transformations to permit the tailoring of intricate microstructures across a wide spectrum of configurations. Here, we report on structural changes and phase transformations of Ti–Nb alloys during heating by in situ synchrotron diffraction. These materials exhibit anisotropic thermal expansion yielding some of the largest linear expansion coefficients (+ 163.9×10−6 to −95.1×10−6 °C−1) ever reported. Moreover, we describe two pathways leading to the precipitation of the α-phase mediated by diffusion-based orthorhombic structures, α″lean and α″iso. Via coupling the lattice parameters to composition both phases evolve into α through rejection of Nb. These findings have the potential to promote new microstructural design approaches for Ti–Nb alloys and β-stabilized Ti-alloys in general. Complex phase transformations in β-stabilised titanium alloys can dramatically change their α and β microstructures, providing tailorability for aerospace or biomaterial applications. Here the authors show that Ti-Nb alloys exhibit giant thermal expansions and identify two new pathways that lead to α phase formation.
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10
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Fan J, Li J, Zhang Y, Kou H, Ghanbaja J, Gan W, Germain L, Esling C. The origin of striation in the metastable β phase of titanium alloys observed by transmission electron microscopy. J Appl Crystallogr 2017; 50:795-804. [PMID: 28656040 PMCID: PMC5458594 DOI: 10.1107/s1600576717004150] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/26/2016] [Accepted: 03/14/2017] [Indexed: 11/10/2022] Open
Abstract
For the β phase of Ti-5553-type metastable β-Ti alloys, striations in transmission electron microscopy (TEM) bright- and dark-field images have been frequently observed but their origin has not been sufficiently investigated. In the present work, this phenomenon is studied in depth from the macroscopic scale by neutron diffraction to the atomic scale by high-resolution TEM. The results reveal that the β phase contains homogeneously distributed modulated structures, intermediate between that of the β phase (cubic) and that of the α phase or the ω phase (hexagonal), giving rise to the appearance of additional diffraction spots at 1/2, 1/3 and 2/3 β diffraction positions. The intermediate structure between β and α is formed by the atomic displacements on each second {110}β plane in the [Formula: see text] direction, whereas that between β and ω is formed by atomic displacements on each second and third {112}β plane in the opposite [Formula: see text] direction. Because of these atomic displacements, the {110}β and {112}β planes become faulted, resulting in the streaking of β diffraction spots and the formation of extinction fringes in TEM bright- and dark-field images, the commonly observed striations. The present work reveals the origin of the striations and the intrinsic correlation with the additional electron reflections of the β phase.
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Affiliation(s)
- Jiangkun Fan
- State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an, 710072, People’s Republic of China
- Laboratoire d’Étude des Microstructures et de Mécanique des Matériaux (LEM3), CNRS 7239, Université de Lorraine, Metz, 57045, France
- Laboratory of Excellence on Design of Alloy Metals for low-mAss Structures (DAMAS), Université de Lorraine, Metz, 57045, France
| | - Jinshan Li
- State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an, 710072, People’s Republic of China
| | - Yudong Zhang
- Laboratoire d’Étude des Microstructures et de Mécanique des Matériaux (LEM3), CNRS 7239, Université de Lorraine, Metz, 57045, France
- Laboratory of Excellence on Design of Alloy Metals for low-mAss Structures (DAMAS), Université de Lorraine, Metz, 57045, France
| | - Hongchao Kou
- State Key Laboratory of Solidification Processing, Northwestern Polytechnical University, Xi’an, 710072, People’s Republic of China
| | - Jaafar Ghanbaja
- Institut Jean Lamour, CNRS, Université de Lorraine, Parc de Saurupt, CS50840, Nancy, 54011, France
| | - Weimin Gan
- German Engineering Materials Science Centre (GEMS) at MLZ, Helmholtz-Zentrum Geesthacht, Garching, D-85748, Germany
| | - Lionel Germain
- Laboratoire d’Étude des Microstructures et de Mécanique des Matériaux (LEM3), CNRS 7239, Université de Lorraine, Metz, 57045, France
- Laboratory of Excellence on Design of Alloy Metals for low-mAss Structures (DAMAS), Université de Lorraine, Metz, 57045, France
| | - Claude Esling
- Laboratoire d’Étude des Microstructures et de Mécanique des Matériaux (LEM3), CNRS 7239, Université de Lorraine, Metz, 57045, France
- Laboratory of Excellence on Design of Alloy Metals for low-mAss Structures (DAMAS), Université de Lorraine, Metz, 57045, France
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11
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Šmilauerová J, Harcuba P, Kriegner D, Holý V. On the completeness of the β→ω transformation in metastable β titanium alloys. J Appl Crystallogr 2017. [DOI: 10.1107/s1600576716020458] [Citation(s) in RCA: 10] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/10/2022] Open
Abstract
The completeness of the β→ω transformation in ω particles in a Ti–8 at.%Mo (Ti–15 wt%Mo) single crystal was investigated by measuring the X-ray diffraction maximum 20{\overline 2}2, which is forbidden in both the pure body-centred cubic β phase and the hexagonal ω phase, and also the diffraction maxima 0001, 0002 and 10{\overline 1}1, which are forbidden in the β phase and allowed in ω. From a comparison of the integrated intensities and widths of the diffraction peaks with simulations, the effective (mean) degree of the transformation was determined and the radial profile of the transformation degree in an ω particle was estimated.
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12
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A low-cost hierarchical nanostructured beta-titanium alloy with high strength. Nat Commun 2016; 7:11176. [PMID: 27034109 PMCID: PMC4821990 DOI: 10.1038/ncomms11176] [Citation(s) in RCA: 157] [Impact Index Per Article: 19.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/02/2016] [Accepted: 02/26/2016] [Indexed: 11/22/2022] Open
Abstract
Lightweighting of automobiles by use of novel low-cost, high strength-to-weight ratio structural materials can reduce the consumption of fossil fuels and in turn CO2 emission. Working towards this goal we achieved high strength in a low cost β-titanium alloy, Ti–1Al–8V–5Fe (Ti185), by hierarchical nanostructure consisting of homogenous distribution of micron-scale and nanoscale α-phase precipitates within the β-phase matrix. The sequence of phase transformation leading to this hierarchical nanostructure is explored using electron microscopy and atom probe tomography. Our results suggest that the high number density of nanoscale α-phase precipitates in the β-phase matrix is due to ω assisted nucleation of α resulting in high tensile strength, greater than any current commercial titanium alloy. Thus hierarchical nanostructured Ti185 serves as an excellent candidate for replacing costlier titanium alloys and other structural alloys for cost-effective lightweighting applications. Lightweight materials with high strength are desirable for applications where they could reduce energy consumption. Here, the authors develop a low cost beta-titanium alloy that uses a hierarchical nanostructure of precipitates with different sizes to achieve high strength.
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Liu H, Niinomi M, Nakai M, Cho K, Narita K, Şen M, Shiku H, Matsue T. Mechanical properties and cytocompatibility of oxygen-modified β-type Ti-Cr alloys for spinal fixation devices. Acta Biomater 2015; 12:352-361. [PMID: 25449914 DOI: 10.1016/j.actbio.2014.10.014] [Citation(s) in RCA: 36] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2014] [Revised: 10/05/2014] [Accepted: 10/15/2014] [Indexed: 11/16/2022]
Abstract
In this study, various amounts of oxygen were added to Ti-10Cr (mass%) alloys. It is expected that a large changeable Young's modulus, caused by a deformation-induced ω-phase transformation, can be achieved in Ti-10Cr-O alloys by the appropriate oxygen addition. This "changeable Young's modulus" property can satisfy the otherwise conflicting requirements for use in spinal implant rods: high and low moduli are preferred by surgeons and patients, respectively. The influence of oxygen on the microstructures and mechanical properties of the alloys was examined, as well as the bending springback and cytocompatibility of the optimized alloy. Among the Ti-10Cr-O alloys, Ti-10Cr-0.2O (mass%) alloy shows the largest changeable Young's modulus following cold rolling for a constant reduction ratio. This is the result of two competing factors: increased apparent β-lattice stability and decreased amounts of athermal ω phase, both of which are caused by oxygen addition. The most favorable balance of these factors for the deformation-induced ω-phase transformation occurred at an oxygen concentration of 0.2mass%. Ti-10Cr-0.2O alloy not only exhibits high tensile strength and acceptable elongation, but also possesses a good combination of high bending strength, acceptable bending springback and great cytocompatibility. Therefore, Ti-10Cr-0.2O alloy is a potential material for use in spinal fixture devices.
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Affiliation(s)
- Huihong Liu
- Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan.
| | - Mitsuo Niinomi
- Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
| | - Masaaki Nakai
- Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
| | - Ken Cho
- Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
| | - Kengo Narita
- Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
| | - Mustafa Şen
- Graduate School of Environmental Studies, Tohoku University, Sendai 980-8579, Japan; Department of Biomedical Engineering, Faculty of Engineering and Architecture, Katip Celebi University, Izmir 35620, Turkey
| | - Hitoshi Shiku
- Graduate School of Environmental Studies, Tohoku University, Sendai 980-8579, Japan
| | - Tomokazu Matsue
- Graduate School of Environmental Studies, Tohoku University, Sendai 980-8579, Japan; WPI-Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan
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14
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Bönisch M, Calin M, Waitz T, Panigrahi A, Zehetbauer M, Gebert A, Skrotzki W, Eckert J. Thermal stability and phase transformations of martensitic Ti-Nb alloys. SCIENCE AND TECHNOLOGY OF ADVANCED MATERIALS 2013; 14:055004. [PMID: 27877611 PMCID: PMC5090374 DOI: 10.1088/1468-6996/14/5/055004] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/20/2013] [Accepted: 08/29/2013] [Indexed: 05/27/2023]
Abstract
Aiming at understanding the governing microstructural phenomena during heat treatments of Ni-free Ti-based shape memory materials for biomedical applications, a series of Ti-Nb alloys with Nb concentrations up to 29 wt% was produced by cold-crucible casting, followed by homogenization treatment and water quenching. Despite the large amount of literature available concerning the thermal stability and ageing behavior of Ti-Nb alloys, only few studies were performed dealing with the isochronal transformation behavior of initially martensitic Ti-Nb alloys. In this work, the formation of martensites (α' and α″) and their stability under different thermal processing conditions were investigated by a combination of x-ray diffraction, differential scanning calorimetry, dilatometry and electron microscopy. The effect of Nb additions on the structural competition in correlation with stable and metastable phase diagrams was also studied. Alloys with 24 wt% Nb or less undergo a [Formula: see text] transformation sequence on heating from room temperature to 1155 K. In alloys containing >24 wt% Nb α″ martensitically reverts back to β0, which is highly unstable against chemical demixing by formation of isothermal ωiso. During slow cooling from the single phase β domain α precipitates and only very limited amounts of α″ martensite form.
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Affiliation(s)
| | - Mariana Calin
- IFW-Dresden, PO Box 270116, D-01171 Dresden, Germany
| | - Thomas Waitz
- University of Vienna, Faculty of Physics, A-1090 Vienna, Austria
| | - Ajit Panigrahi
- University of Vienna, Faculty of Physics, A-1090 Vienna, Austria
| | | | - Annett Gebert
- IFW-Dresden, PO Box 270116, D-01171 Dresden, Germany
| | - Werner Skrotzki
- TU Dresden, Institut für Strukturphysik, D-01062 Dresden, Germany
| | - Jürgen Eckert
- IFW-Dresden, PO Box 270116, D-01171 Dresden, Germany
- TU Dresden, Institut für Werkstoffwissenschaft, D-01062 Dresden, Germany
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