The Role of Deformation Twinning on Creep of Titanium Alloys

2007 ◽  
Vol 561-565 ◽  
pp. 121-126
Author(s):  
Sreeramamurthy Ankem ◽  
P. Gregory Oberson
Keyword(s):  
Titanium Alloys ◽  
Speed Of Sound ◽  
Critical Stress ◽  
National Science Foundation ◽  
Room Temperature ◽  
Deformation Twinning ◽  
Ti Alloys ◽  
National Science ◽  
Recent Developments

Normally, deformation twinning is a process that occurs at rates approaching the speed of sound in bulk metals once a critical stress has been reached. However, recently it has been shown that twins grow at speeds many orders of magnitude lower than the speed of sound during room temperature creep of titanium alloys. The net result is that this twinning process can contribute to the low-temperature (less than 0.25*Tm) creep behavior of α, α−β, and β−titanium alloys. For example, α-Ti alloys with small grain size do not extensively deform by twinning and hence show little overall creep strain. These recent developments are reviewed in this paper. This work is funded by the National Science Foundation under Grant Number DMR-0517351.

An Approach to Polar Research

ARCTIC ◽  
1963 ◽  
Vol 16 (3) ◽  
pp. 151
Author(s):  
T.O. Jones
Keyword(s):  
International Cooperation ◽  
Research Program ◽  
National Science Foundation ◽  
Basic Research ◽  
Upper Atmosphere ◽  
Common Interest ◽  
The Arctic ◽  
National Science

Discusses role of the National Science Foundation in U.S. research in the Arctic and Antarctic. For the latter NSF has fostered a coordinated basic research program. Some features of it and techniques developed might be utilized in a bipolar program on problems of common interest, e.g. conjugate phenomena of the upper atmosphere, international cooperation, etc. Proposals for basic research in the Arctic are welcomed.

Spectrofluorimetric Characterization of an Ionic Conductor: Sodium Sulfate High-Temperature Phases Doped with Europium(III)

1994 ◽  
Vol 369 ◽  
Author(s):  
Lowell R. Matithews ◽  
Edward T. Knobbe ◽  
Gamini Dharmasena ◽  
Renée Cole ◽  
Roger Frech
Keyword(s):  
Solid Solutions ◽  
Sodium Sulfate ◽  
National Science Foundation ◽  
Room Temperature ◽  
Local Environment ◽  
X Ray ◽  
National Science ◽  
Trivalent Cations ◽  
The Individual

AbstractThe highest-temperature polymorph of sodium sulfate, (I), has significant orientational disorder in its structure which allows it to readily accept substitution by di- and trivalent cations. Although Na2SO4 (I) exhibits reasonable ionic conductivity, it cannot be quenched to room temperature without changing phase. However, aliovalent solid solutions of (I) can be quenched to RT and resultant cation vacancies promote conduction via Na+ migration. The closely related but more ordered phase Na2SO4 (III) can also form aliovalent solid solutions which can be quenched to RT.The europium(III) ion is an extremely sensitive and useful probe of its immediate local environment. The presence, location, and intensity of its fluorescence transitions (particularly the 5D0→7F0-2 emissions) can provide detailed information about the symmetry, nature, and multiplicity of the individual Eu3+ site which cannot be gained from X-ray or neutron diffraction techniques.Our research (supported by the National Science Foundation and the State of Oklahoma) involves the structural characterization of two europium-doped sodium sulfate phases via fluorescence spectroscopy.

scholarly journals Deformation and fracture behavior of new strain-transformable titanium alloys: a multi-scale investigation

2020 ◽  
Vol 321 ◽  
pp. 11006
Author(s):  
Chloé VARENNE ◽  
Frédéric PRIMA ◽  
Cédrik BROZEK ◽  
Julie BOURGON ◽  
Jacques BESSON ◽  
...  
Keyword(s):  
Titanium Alloys ◽  
Coarse Grained ◽  
Multi Scale ◽  
Ti Alloys ◽  
Deformation And Fracture ◽  
Initiation And Propagation ◽  
Deformation Features ◽  
Deformation Work ◽  
Ductile Fracture Process

Titanium alloys possessing Twinning and Transformation Induced Plasticity effects show promising mechanical properties, particularly high ductility, hardenability, impact and fracture toughness. This work focuses on a strain-transformable, coarse-grained β-Ti-Cr-Sn alloy displaying TWIP effect. To account for the enhanced properties of this alloy, compared to more conventional β-Ti alloys, fracture and deformation features were correlated at different scales. Examinations evidenced a major role of twinning and, more generally, of plasticity-induced phenomena in the ductile fracture process. The resistance of this alloy to plastic deformation (work-hardening), and to crack initiation and propagation is interpreted in view of the progressive, multiscale twinning mechanisms that occur up to the very final stages of fracture.

Experimental and Modeling Studies on the Stress Relaxation Behaviour of Ti-6Al-4V Alloy

2021 ◽  
Author(s):  
Kali Prasad ◽  
Krishnaswamy Hariharan ◽  
Dilip K. Banerjee
Keyword(s):  
Stress Relaxation ◽  
Titanium Alloys ◽  
Room Temperature ◽  
Hold Time ◽  
High Strength ◽  
Uniaxial Tensile ◽  
Time Data ◽  
Transient Stress ◽  
Ti Alloys ◽  
Strain And Strain Rate

Abstract The transient mechanical behavior of materials during stress relaxation has evoked interest in manufacturing applications because of the effect of stress relaxation on formability enhancement. However, most of the previous studies have focused on advanced high strength steels and aluminum alloys. Limited transient stress relaxation studies have been conducted on titanium alloys in order to understand the influence of stress relaxation on forming behavior. Titanium alloys are widely used in aerospace components because of their high strength to weight ratios and excellent fatigue strengths. However, room temperature formability of Ti alloys is an important concern, which restricts their widespread use in various applications. To address these challenges, the present study is aimed to understand the role of transient stress relaxation on formability of Ti alloys. Toward this end, stress relaxation of a dual phase titanium alloy (Ti-6Al-4V) has been investigated experimentally. Stress relaxation tests were performed by interrupting uniaxial tensile tests in the uniform deformation regime for a pre-defined strain and hold time after which tests were continued monotonically until fracture. Single step, room temperature stress relaxation experiments were performed systematically to study the effect of hold time, pre-strain, and strain rate on mechanical properties. The stress relaxation phenomenon was found to contribute positively to the ductility improvement. The mechanisms responsible for enhancing the formability are discussed. The experimentally obtained stress vs. time data were analyzed using a advanced constitutive model for stress relaxation available in literature.

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