Martensitic structures and deformation twinning in the U-Nb shape-memory alloys

Field, R. D.; Thoma, D. J.; Dunn, P.S.; Brown, Don W.; Cady, Carl M.

doi:10.1080/01418610108216633

Cited by 13 publications

(37 citation statements)

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“…[16] Thus, Vandermeer identified the diffuse maximum observed in the flow curve at 0.07 strain with the ''reversible strain limit'' beyond which the imparted strain was not fully recoverable. Brown et al, [19,20] Field et al, [21,22] and Clarke et al [23] used in-situ neutron diffraction and postdeformation electron microscopy to identify and characterize the active deformation mechanisms to 0.04 strain but did not investigate the details of the deformation in the large strain regime.…”

Section: Introductionmentioning

confidence: 99%

Large Strain Deformation in Uranium 6 Wt Pct Niobium

Tupper

Brown

Field

et al. 2011

Metall Mater Trans A

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The large strain deformation of polycrystalline uranium 6 wt pct niobium (U6Nb) was studied in situ during uniaxial tensile and compressive loading by time-of-flight neutron diffraction. Diffraction patterns were recorded at incremental strains to a maximum of approximately 0.13 tensile and 0.15 compressive true strain. A discrete reorientation of the crystallographic texture under tensile straining between 0.04 and 0.08 true strain is consistent with a previously unobserved mechanical deformation twinning mechanism, identified as either a (100) or (010) mechanical twin system. Beyond this, a continuous texture reorientation towards an (010) crystal orientations indicates that a slip mechanism is likely predominant. An analogous mechanical twin system was not observed in compression at large strain.

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Section: Introductionmentioning

confidence: 99%

Large Strain Deformation in Uranium 6 Wt Pct Niobium

Tupper

Brown

Field

et al. 2011

Metall Mater Trans A

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“…It has been reported that water-quenched U-6wt%Nb alloy containing extensively twinned α′′ martensite reveals shape memory effect and possesses low yield strength (∼200 MPa) and high tensile ductility (∼30%) [2,4,5]. Aging of the α′′ martensite in the range of 150°C to 400°C causes an increase of yield strength to ~1.3 GPa as a result of the formation of very fine-scale modulated structure presumably caused by spinodal decomposition [6].…”

Section: Introduction and Theoretical Backgroundmentioning

confidence: 99%

Spinodal Decomposition and Order-Disorder Transformation in a Water-Quenched U-6wt%Nb Alloy

Hsiung¹,

Zhou²

2006

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Objectives and accomplishmentsA combinative approach of microhardness testing, tensile testing, and TEM microstructural analysis has been employed to study phase stability and aging mechanisms of a water-quenched U-6wt%Nb (WQU6Nb) alloy subjected to different aging schedules that include artificial aging of WQ-U6Nb at 200°C, natural aging of WQ-U6Nb at ambient temperatures for 15 to18 years, and accelerative aging of the naturally aged (NA) alloy at 200°C. During the early stages of artificial aging at 200°C, the microhardness values continuously increase as a result of the development of a fine-scale compositional modulation (wavelength: 3 nm) caused by spinodal decomposition. Coarsening of the modulated structure occurs after prolonged aging of WQ-U6Nb at 200°C for 16 hours, which leads to a decrease of microhardness. Phase instability has also been found to occur in the NA alloy, in which the formation of partially ordered phase domains resulting from an atomic-scale spinodal modulation (wavelength: 0.5 nm) renders the appearance of antiphase domain boundaries (APBs) in TEM images. Although 18-year natural aging does not cause a significant change in hardness, it affects dramatically the aging mechanism of WQ-U6Nb subjected to the accelerative aging at 200°C. The result of microhardness measurement shows that the hardness values continuously increase until after aging for 239 hours, and the total hardness increment is twice in magnitude than that in the case of the artificial aging of waterquenched alloy at 200°C. The anomalous increment of hardness for the accelerative aging of NA alloy can be attributed to the precipitation of an ordered U 3 Nb phase. It is accordingly concluded that the long-term natural aging at ambient temperatures can detour the transformation pathway of WQ U-6Nb alloy; it leads to the order-disorder transformation and precipitation of ordered phase in the alloy. UCRL-TR-224432 Introduction and theoretical backgroundIt is well known that U-6wt%Nb (U-14at%Nb) alloy, as exploited for a variety of engineering applications, has a microstructure containing martensitic phases supersaturated with Nb that can be obtained by rapid quenching the alloy from γ (bcc)-field solid solution to room temperature [1,2]. The high cooling rate forces the γ-phase solid solution to transform diffusionlessly to variants of the low temperature α (orthorhombic) phase in which Nb is forced to retain in the supersaturated solid solution.It is noted that the crystal lattice of supersaturated solution formed by rapid quenching is unstable and is severely distorted since the solubility of Nb in the α phase at room temperature is nearly zero in stable equilibrium [3]. One variant phase has been designated as α′ martensite because its lattice parameters differ from the α phase as a result of the supersaturation. Two additional variant phases, a monoclinic distortion of α′ phase that is designated as α′′ martensite and a tetragonal distortion of γ phase that is Edmonds [7], who investigated the low-temperature aging beh...

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“…An elastic material response is observed below strains of approximately 0.3%. As the α ′ ′ phase is loaded beyond strains of 0.3%, the deformation process is dominated by continuous crystalline reorientation associated with a detwinning process, as reported by x-ray and neutron diffraction experiments [6,7]. That is, orientations (variants) that are favored by the loading direction increase in volume fraction at the expense of less favored orientations.…”

Section: Introductionmentioning

confidence: 82%

“…Based on experimental observations [6,7], it was determined that reorientation of the low-temperature phase ( α ′ ′ ) is initiated at a critical stress ( r τ ) and continues until dislocation slip is observed. This approach differs from previous methods [16,17] where it was concluded that an elastic region exists between the reorientation and dislocation slip regimes with the elastic moduli of the twinned and detwinned states being different.…”

Section: E Phase Diagrammentioning

confidence: 99%

Model for high-strain-rate deformation of uranium–niobium alloys

Addessio

Zuo

Mason

et al. 2003

Journal of Applied Physics

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A thermodynamic approach is used to develop a framework for modeling uranium–niobium alloys under the conditions of high-strain rate. Using this framework, a three-dimensional phenomenological model, which includes nonlinear elasticity (equation of state), phase transformation, crystal reorientation, rate-dependent plasticity, and porosity growth, is presented. An implicit numerical technique is used to solve the evolution equations for the material state. Comparisons are made between the model and data for low-strain rate loading and unloading as well as heating and cooling experiments. Comparisons of the model and data also are made for low- and high-strain-rate uniaxial stress and uniaxial strain experiments. A uranium–6 wt % niobium alloy is used in comparisons of the model and experiment.

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Martensitic structures and deformation twinning in the U-Nb shape-memory alloys

Cited by 13 publications

References 0 publications

Large Strain Deformation in Uranium 6 Wt Pct Niobium

Large Strain Deformation in Uranium 6 Wt Pct Niobium

Spinodal Decomposition and Order-Disorder Transformation in a Water-Quenched U-6wt%Nb Alloy

Model for high-strain-rate deformation of uranium–niobium alloys

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