scholarly journals Mechanistic basis of oxygen sensitivity in titanium

2020 ◽  
Vol 6 (43) ◽  
pp. eabc4060
Author(s):  
Yan Chong ◽  
Max Poschmann ◽  
Ruopeng Zhang ◽  
Shiteng Zhao ◽  
Mohammad S. Hooshmand ◽  
...  
Keyword(s):  
Titanium Alloys ◽  
Oxygen Sensitivity ◽  
Poisoning Effect ◽  
Extreme Sensitivity ◽  
Mechanistic Basis ◽  
Oxygen Poisoning ◽  
Temperature Strain ◽  
Mechanistic View ◽  
Oxygen Impurities ◽  
Solute Strengthening

One of the most potent examples of interstitial solute strengthening in metal alloys is the extreme sensitivity of titanium to small amounts of oxygen. Unfortunately, these small amounts of oxygen also lead to a markedly decreased ductility, which in turn drives the increased cost to purify titanium to avoid this oxygen poisoning effect. Here, we report a systematic study on the oxygen sensitivity of titanium that provides a clear mechanistic view of how oxygen impurities affect the mechanical properties of titanium. The increased slip planarity of Ti-O alloys is caused by an interstitial shuffling mechanism, which is sensitive to temperature, strain rate, and oxygen content and leads to the subsequent alteration of deformation twinning behavior. The insights from our experimental and computational work provide a rationale for the design of titanium alloys with increased tolerance to variations in interstitial content, with notable implications for more widespread use of titanium alloys.

scholarly journals On the mechanistic basis of deformation at the microscale in hexagonal close-packed metals

2015 ◽  
Vol 471 (2178) ◽  
pp. 20140881 ◽  
Author(s):  
T. B. Britton ◽  
F. P. E. Dunne ◽  
A. J. Wilkinson
Keyword(s):  
Single Crystal ◽  
Titanium Alloys ◽  
State Of The Art ◽  
Plastic Anisotropy ◽  
Deformation Mechanisms ◽  
Hexagonal Close Packed ◽  
Dwell Fatigue ◽  
Crystallographic Slip ◽  
Rate Effects ◽  
Mechanistic Basis

This is an overview of micromechanical deformation mechanisms in hexagonal close-packed metals. We start with an in-depth discussion of single-crystal behaviour concerning crystallographic slip, plastic anisotropy and deformation twinning. We move on to discuss some complexities involved in polycrystalline deformation and modelling approaches, focusing on rate effects in titanium alloys that are thought to play a significant role in dwell fatigue. We finish our review with a brief commentary on current understanding and state-of-the-art techniques, and outline some key areas where further study is recommended.

Dwell Sensitive Fatigue Response of Titanium Alloys for Power Plant Applications

2002 ◽  
Vol 125 (1) ◽  
pp. 241-245 ◽  
Author(s):  
M. R. Bache ◽  
W. J. Evans
Keyword(s):  
Titanium Alloys ◽  
Fatigue Testing ◽  
Cyclic Strain ◽  
Peak Stress ◽  
Strain Accumulation ◽  
Cleavage Facet ◽  
Fundamental Cause ◽  
Temperature Strain ◽  
Facet Formation

The phenomenon of “dwell sensitivity” in the α+β and near α titanium alloys and the intrinsic relationship with quasi-cleavage facet formation is discussed. In the present paper, particular emphasis is placed upon the role of “cold creep” and ambient temperature strain accumulation under cyclic loading. A process of stress redistribution between microstructurally distinct regions that demonstrate different strengths is proposed as the fundamental cause of facet development and subsequent dwell failures. A model to describe the redistribution process is validated through a matrix of fatigue testing designed to assess the effects of microstructural form, stress axiality, and periods of dwell loading at peak stress on cyclic strain accumulation.

scholarly journals Genetic basis of oxygen sensing in the carotid body: HIF2α and an isoform switch in cytochrome c oxidase subunit 4

2020 ◽  
Vol 13 (615) ◽  
pp. eaba1302 ◽  
Author(s):  
Tammie Bishop ◽  
Peter J. Ratcliffe
Keyword(s):  
Cytochrome C ◽  
Cytochrome C Oxidase ◽  
Carotid Body ◽  
Genetic Basis ◽  
Hypoxia Inducible Factor ◽  
Oxygen Sensitivity ◽  
Critical Importance ◽  
Glomus Cell ◽  
Oxidase Subunit ◽  
Mechanistic Basis

The mechanistic basis of the marked oxygen sensitivity of glomus cells in the carotid body has long puzzled physiologists. In this issue of Science Signaling, Moreno-Domínguez et al. show the critical importance of high levels of hypoxia-inducible factor, HIF2α/EPAS1, and the nuclear-encoded mitochondrial cytochrome c oxidase subunit, COX4I2, in glomus cell sensitivity to hypoxia.

Dwell Sensitive Fatigue Response of Titanium Alloys for Power Plant Applications

2001 ◽  
Author(s):  
Martin R. Bache ◽  
W. John Evans
Keyword(s):  
Titanium Alloys ◽  
Fatigue Testing ◽  
Cyclic Strain ◽  
Peak Stress ◽  
Strain Accumulation ◽  
Cleavage Facet ◽  
Fundamental Cause ◽  
Temperature Strain ◽  
Facet Formation

The phenomenon of “dwell sensitivity” in the α+β and near α titanium alloys and the intrinsic relationship with quasi-cleavage facet formation is discussed. In the present paper, particular emphasis is placed upon the role of “cold creep” and ambient temperature strain accumulation under cyclic loading. A process of stress redistribution between microstructurally distinct regions that demonstrate different strengths is proposed as the fundamental cause of facet development and subsequent dwell failures. A model to describe the redistribution process is validated through a matrix of fatigue testing designed to assess the effects of microstructural form, stress axiality and periods of dwell loading at peak stress on cyclic strain accumulation.

The Range of the Occurrence of α Phase in near β Titanium Alloys

2016 ◽  
Vol 682 ◽  
pp. 77-82
Author(s):  
Janusz Krawczyk ◽  
Łukasz Frocisz ◽  
Robert Dąbrowski ◽  
Edyta Rożniata ◽  
Tomasz Śleboda
Keyword(s):  
Heat Treatment ◽  
Titanium Alloys ◽  
Processing Time ◽  
Casting Process ◽  
Compression Tests ◽  
Phase Precipitation ◽  
Phase Dissolution ◽  
Β Phase ◽  
Α Phase ◽  
Temperature Strain

Two near β titanium alloys (Ti-3Al-8V-6Cr-4Mo-4Zr and Ti-10V-2Fe-3Al) were investigated in his research. Both materials contained disperse precipitations of α phase in β phase matrix. In the case of Ti-3Al-8V-6Cr-4Mo-4Zr alloy clear segregation of alloy constituents, resulting from casting process, were observed. This segregation caused different susceptibility to α phase precipitation in dendritic and interdendritic areas in the microstructure of the investigated alloy. The influence of the temperature, strain and processing time on α phase dissolution was determined. Gleeble compression tests were performed on both of the investigated alloys. The research showed different character of the influence of strain rate and processing time on the temperature of α phase dissolution for each alloy. The effect of heat treatment on α phase dissolution during ageing of the investigated alloys was also determined. The possibility of obtaining homogenous microstructure in these alloys by properly designed heat treatment was also discussed.

The Development of a Mechanistic Basis for Modelling Fuel Dissolution and Container Failures Under Waste Vault Conditions

1988 ◽  
Vol 127 ◽  
Author(s):  
D. W. Shoesmith ◽  
S. Sunder ◽  
B. M. Ikeda ◽  
F. King
Keyword(s):  
Experimental Data ◽  
Titanium Alloys ◽  
Nuclear Waste ◽  
Waste Disposal ◽  
Predictive Models ◽  
Crevice Corrosion ◽  
Electrochemical Techniques ◽  
Short Term ◽  
Mechanistic Basis ◽  
Radionuclide Release

ABSTRACTDue to the long containment periods required for radionuclides in a nuclear waste disposal vault, the justification that a particular containment system is acceptable will be based on relatively short-term experimental data used to support predictive models. To justify this approach, we must possess a sound mechanistic understanding of processes such as fuel dissolution, radionuclide release and container corrosion. Since these processes are driven by oxidants in the vault, it is natural to study them by electrochemical techniques. In this paper, we have reviewed a number of electrochemical methods used in the study of waste vault reactions. More detailed descriptions are given of the development of predictive models for the dissolution of UO2, the crevice corrosion of titanium alloys and the uniform dissolution of copper.

Direct Observation of the Diffusionless β → β + ω Transformation in Titanium Alloys

1971 ◽  
Vol 29 ◽  
pp. 122-123
Author(s):  
N. E. Paton ◽  
D. de Fontaine ◽  
J. C. Williams
Keyword(s):  
Electron Microscope ◽  
Titanium Alloys ◽  
Direct Observation ◽  
Dark Field ◽  
X Ray Diffraction ◽  
Resistivity Measurements ◽  
Selected Area Electron Diffraction ◽  
Ti Alloys ◽  
Thin Foils ◽  
Field Device

The electron microscope has been used to study the diffusionless β → β + ω transformation occurring in certain titanium alloys at low temperatures. Evidence for such a transformation was obtained by Cometto et al by means of x-ray diffraction and resistivity measurements on a Ti-Nb alloy. The present work shows that this type of transformation can occur in several Ti alloys of suitable composition, and some of the details of the transformation are elucidated by means of direct observation in the electron microscope.Thin foils were examined in a Philips EM-300 electron microscope equipped with a uniaxial tilt, liquid nitrogen cooled, cold stage and a high resolution dark field device. Selected area electron diffraction was used to identify the phases present and the ω-phase was imaged in dark field by using a (101)ω reflection. Alloys were water quenched from 950°C, thinned, and mounted between copper grids to minimize temperature gradients in the foil.

The Ordered Phase Formation in Ti-Al-Ga Alloys

1970 ◽  
Vol 28 ◽  
pp. 440-441
Author(s):  
Shiro Fujishiro ◽  
Harold L. Gegel
Keyword(s):  
Thermal Stability ◽  
High Temperature ◽  
Titanium Alloys ◽  
Growth Kinetics ◽  
Stoichiometric Composition ◽  
Good Potential ◽  
Alpha Titanium ◽  
Cold Rolled ◽  
Kinetics Of ◽  
Thermal Stability Of

Ordered-alpha titanium alloys having a DO19 type structure have good potential for high temperature (600°C) applications, due to the thermal stability of the ordered phase and the inherent resistance to recrystallization of these alloys. Five different Ti-Al-Ga alloys consisting of equal atomic percents of aluminum and gallium solute additions up to the stoichiometric composition, Ti3(Al, Ga), were used to study the growth kinetics of the ordered phase and the nature of its interface.The alloys were homogenized in the beta region in a vacuum of about 5×10-7 torr, furnace cooled; reheated in air to 50°C below the alpha transus for hot working. The alloys were subsequently acid cleaned, annealed in vacuo, and cold rolled to about. 050 inch prior to additional homogenization

TEM characterization of reaction zone in a SiC fiber-reinforced titanium alloy

1988 ◽  
Vol 46 ◽  
pp. 738-739
Author(s):  
G. Das ◽  
R. E. Omlor
Keyword(s):  
Titanium Alloys ◽  
Reaction Zone ◽  
Carbon Layer ◽  
Fiber Reinforced ◽  
Reaction Products ◽  
Sic Fibers ◽  
Sic Fiber ◽  
The Matrix ◽  
Immense Potential

Fiber reinforced titanium alloys hold immense potential for applications in the aerospace industry. However, chemical reaction between the fibers and the titanium alloys at fabrication temperatures leads to the formation of brittle reaction products which limits their development. In the present study, coated SiC fibers have been used to evaluate the effects of surface coating on the reaction zone in the SiC/IMI829 system.IMI829 (Ti-5.5A1-3.5Sn-3.0Zr-0.3Mo-1Nb-0.3Si), a near alpha alloy, in the form of PREP powder (-35 mesh), was used a茸 the matrix. CVD grown AVCO SCS-6 SiC fibers were used as discontinuous reinforcements. These fibers of 142μm diameter contained an overlayer with high Si/C ratio on top of an amorphous carbon layer, the thickness of the coating being ∽ 1μm. SCS-6 fibers, broken into ∽ 2mm lengths, were mixed with IMI829 powder (representing < 0.1vol%) and the mixture was consolidated by HIP'ing at 871°C/0. 28GPa/4h.

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