Effect of prior cold rolling and test temperature on stress-strain rate behaviour of a Zr-2.5Nb alloy
TL;DR: In this paper, the authors investigated the effect of cold working on the stress (σ)-strain rate (έ) behavior over a strain rate range of ∼2 × 10−5 to 5 × 10 −3 s−1 and a temperature range of 625 to 700 °C.
Abstract: Zr-2.5 wt% Nb alloy sheet, obtained by unfolding and straightening a pressure tube, was further cold rolled upto 39% reduction in thickness to investigate the effect of cold working on the stress (σ)-strain rate (έ) behaviour over a strain rate range of ∼2 × 10−5 to 5 × 10−3 s−1 and a temperature range of 625 to 700 °C. Irrespective of the amount of rolling, the log σ vs log έ plots exhibit superplastic behaviour with strain rate sensitivity index, m, as high as 0.8, which decreases to 0.2 at higher strain rates. On the other hand, the activation energy for deformation, Q, increases from 171.1 kJ/mol for superplastic deformation to 249 kJ/mol in Region III. The tendency for improved superplasticity (m) is seen upon cold working by 22% or more at the test temperatures 675 and 700 °C.
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15 Feb 2005-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the effect of grain size on superplastic deformation in Zr −2.5% Nb was studied by constructing processing maps, which depict the variation of strain rate sensitivity with temperature and strain rate.
Abstract: The effect of grain size on superplastic deformation in Zr–2.5 wt.%Nb was studied by constructing processing maps (which depict the variation of strain rate sensitivity with temperature and strain rate) in the temperature range of 650–830 °C and strain rate range of 5 × 10 −6 to 2 × 10 −3 s −1 . The occurrence of superplastic domain with respect to temperature and strain rate was identified for three grain sizes (4, 10 and 16 μm). The 4 μm grain size material exhibited a domain centered around 800 °C and 10 −4 s −1 , exhibiting a ductility of 700%. With increasing grain size the domain shifts to higher temperatures and lower strain rates. A detailed characterization of deformed microstructure revealed equiaxed grain structure (curved boundaries) with considerable grain growth within the superplastic domain. Creep equation was used to evaluate the parameters of superplastic deformation, which resulted in activation energy of 125 kJ/mol and a grain size exponent of 1.6. The accommodation mechanism for superplastic deformation was deduced to be either non-conservative jog motion or grain boundary migration, with the rate controlling step for both being the grain boundary diffusion of Zr and Nb in β phase.
31 citations
TL;DR: In this article, the effect of microstructural evolution on superplastic deformation parameters, such as the nature of σ-e plots, strain-rate sensitivity parameter, and activation energy, were studied for unstable and thermally stable microstructures of a Zr-2.5 wt pct Nb pressure-tube alloy.
Abstract: The effect of microstructural evolution on superplastic deformation parameters, such as the nature of σ-e plots, strain-rate sensitivity parameter, and activation energy, were studied for unstable and thermally stable microstructures of a Zr-2.5 wt pct Nb pressure-tube alloy. Two types of differential strain-rate tests (increasing temperature (IT) and decreasing temperature (DT), in the temperature range of 610 °C to 810 °C at 20 °C intervals) were conducted within a strain-rate range of 10−5 to 10−3 s−1. Single specimens were used to obtain the σ-e plots for all the test temperatures in the aforementioned temperature range. The effect of orientation (with respect to the axial direction of the tube) on the superplastic deformation parameters was also studied. The microstructural evolution was studied along the three orthogonal planes of the tube by water quenching underformed samples in the beginning of differential strain-rate tests at each test temperature. The observed apparent activation-energy values associated with deformation were in the two distinct ranges of 287 to 326 and 151 to 211 kJ/mole. In the temperature range of 730 °C to 810 °C, the apparent activation-energy value depended on the direction of approach of the test temperature. The mechanisms of superplastic deformation in this alloy were found to be dislocation climb—controlled creep in region III and grain-boundary sliding accommodated by grain-boundary diffusion or lattice diffusion in the α or β phases in region II. Based on the observed microstructural features, a model to explain the σ-e plots and apparent activation energy has been proposed.
13 citations
TL;DR: In this article, the annealing behaviors of hot and cold-rolled Zr705 were investigated in a wide temperature range of 200∼850 °C and showed that the hot-rolled specimens exhibited lower hardness at temperatures
10 citations
TL;DR: In this article, a neural network model under Bayesian framework has been created to correlate the complex relationship between flow stress with its influencing parameters in various grades of zirconium alloys at different deformation conditions.
Abstract: Flow stress during hot deformation is essentially controlled by the chemistry of material, initial microstructure/texture, strain, strain rate, strain path, stress triaxility and the temperature of deformation. A comprehensive literature survey has been performed to realize this fact completely. In the present research, a neural network model under Bayesian framework has been created to correlate the complex relationship between flow stress with its influencing parameters in various grades of zirconium alloys at different deformation conditions. The network has been trained with published experimental database obtained from the different hot deformation experiments of zirconium alloys. Performance of the model has been evaluated; and excellent agreements between experimentally measured and model calculated data are obtained. The analysis permits the estimation of error bars whose magnitude strongly depends on their position in the input space. The model has been employed to different grades of zirconium alloys to confirm that the predictions are reasonably accurate in the context of basic metallurgical/solid mechanics theories and principles. The work has clearly identified the regions of the input space where further experiments should be encouraged and necessary. This model will be useful to design and manufacture the new generation zirconium alloys in future for the nuclear power plant components according to the needs of nuclear engineers/scientists by controlling the alloying elements and other possible conditions. The result shows that neural computation is a very effective tool to model the complex $$\textit{non-linear}$$
behaviour of flow stress of different zirconium alloys under any deformation conditions.
4 citations
TL;DR: In this article, a Zr-2.5Nb alloy was annealed at 900°C for 5-90 min and quenched in water, which resulted in formation of α′ martensite and primary α phase.
4 citations
References
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Book•
01 Jan 1949
TL;DR: In this paper, the authors present an X-ray analysis of metallic materials and their properties, such as elastic properties, damping capacity and shape memory alloys, as well as their properties of metal and alloys.
Abstract: General physical and chemical constants X-ray analysis of metallic material Crystallography Crystal chemistry Metallurgically important minerals Thermochemical data Physical properties of molton salts Metallography Equilibrium diagrams Gas-metal systems Diffusion in metals General physical properties Elastic properties, damping capacity and shape memory alloys Temperature measurement and thermoelectric properties Radiating properties of metals Electron emission Electrical properties Magnetic materials and their properties Mechanical testing Mechanical properties of metals and alloys Sintered materials Lubricants Friction and wear Casting alloys and foundry data Engineering ceramics and refractory materials Fuels Heat treatment Metal cutting and forming Corrosion Electroplating and metal finishing Welding Soldering and brazing Vapour deposited coatings and thermal spraying Superplasticity Metal-matrix composites Non-conventional and emerging metallic minerals modelling and simulation supporting technologies for the processing of metals and alloys.
3,593 citations
"Effect of prior cold rolling and te..." refers background in this paper
...Chemical diffusion Zr-Nb of various 900‐1600 217.9 to 333.1 Increases as Nb increases [ 15 ] compositions from 5 at % to 95 at %...
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...Homogeneous alloys Zr-2.3Nb 900‐1160 162.6 95 Nb diffusion [ 15 ]...
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...The present value of 171.1 kJ/mol, on the other hand, is comparable with the activation energy for lattice diffusion of Nb in Zr-2.3Nb alloy (162.6 kJ/mol) [ 15 ]....
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...Zr-Nb alloys 1445‐1690 196.9(Zr) Increases as Nb including pure metals 389.7 (Nb) increases from 0 to 100 at % [ 15 ] 95 Nb diffusion along the Zr-2.5Nb 702‐818 105/230 Q increases with temperature [16] fi/fl interphase boundaries 715‐818 288 Recalculated from Ref....
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...The similarity between these two activation energies can be understood by the fact that the Zr-2.5Nb alloy, as obtained from the phase diagram [ 15 ], contains 10‐19%fl-phase having Nb from 18.5 to 11.1 wt % as the temperature increases from 625 to 700 ‐ C. Thus, both the stress sensitivity...
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TL;DR: In this article, a new mechanism for superplastic deformation is described and modelled, which differs fundamentally from Nabarro-Herring and Coble creep in a topological sense: grains switch their neighbors and do not elongate significantly.
1,307 citations
Journal Article•
TL;DR: A general survey of plastic deformation can be found in this article, where Orowan and Bailey-Orowan equations are used to define deformation mechanism maps for pure metals.
Abstract: 1. Deformation and Creep. Deformation. Definition of creep. Time dependence of creep strain. Creep Curve. Mechanisms of plastic deformation: A general survey. Mechanical equation of state. Creep test compared with tensile test at constant strain rate and constant loading rate. Creep tests at constant load and constant stress. 2. Motion of Dislocations. Dynamic Recovery. Motion of dislocations. Free, mobile and moving dislocations. Dynamic recovery. 3. Temperature Dependence of Creep Rate. Activation energy of creep. Methods of determination of activation energy of creep. Correction of experimentally determined activation energy of creep for temperature dependence of elastic modulus. Activation energy or creep and activation enthalpy of diffusion. 4. Applied Stress Dependence of Creep Rate. Initial creep rate. Steady-state creep. Transient creep. 5. Influence of Grain Size and Stacking Fault Energy. Grain size. Stacking fault energy. 6. Orowan and Bailey-Orowan Equations. Orowan equation. Bailey-Orowan equation. Relation between Orowan equation and Bailey-Orowan equations. A consequence of the equivalence of Orowan and Bailey-Orowan equations. Experimental verification of Bailey-Orowan equation. Experimental determination of quantities r and h. Incubation period and ``Frictional'' stress. 7. Back Stress. Internal, threshold and frictional stress. Internal and effective stress. Concept of internal and effective stress and the mechanical equation of state. Definitions of experimental parameters. Interpretation of experimental parameters. 8. Dislocation Structure. Development of dislocation structure during creep. Basic quantitative characteristics of dislocation structure. Subgrain structure. Subgrain structure and long-range internal stress. Behaviour of sub-boundaries. Interaction of dislocations with sub-boundaries. Generation of dislocations. Structural steady state. Concept of hard and soft regions and measured internal stress. 9. Dislocation Creep in Pure Metals. Creep controlled by recovery. Creep controlled by dislocation glide. Models based on thermally activated glide and diffusion controlled recovery. Relation between constants A and n in the dorn creep equation and the natural third power law. Harper-Dorn creep. 10. Creep in Solid Solution Alloys. Introduction. Mechanisms of creep strengthening in solid solutions. Creep controlled by viscous dislocation glide. 11. Creep in Precipitation and Dispersion Strengthened Alloys. Models of Ansell and Weertman. Back stress concept. 12. Diffusional Creep. Nabarro-Herring and Coble creep. Subgrain boundaries as sources and sinks for vacancies. Diffusional creep and grain boundary sliding. Reactions on grain boundaries. Diffusional caritational creep. 13. Deformation Mechanism Maps. Equations used for construction of deformation mechanism maps. Examples of deformation mechanism maps. ``Generalized'' deformation mechanism map for pure metals. 14. Grain Boundary Sliding.
499 citations
TL;DR: The microstructural aspects of the superplastic phenomenon are reviewed in this article, where experimental results of a very large number of investigations are critically analysed in the context of: grain shape and size; grain growth; grain boundary sliding and migration, grain rotation and rearrangement; diffusion and dislocation activity.
Abstract: The microstructural aspects of the superplastic phenomenon are reviewed. The experimental results of a very large number of investigations are critically analysed in the context of: grain shape and size; grain growth; grain boundary sliding and migration, grain rotation and rearrangement; diffusion and dislocation activity. It is shown, that in spite of often conflicting evidence in the literature, a common pattern of microstructural behaviour emerges for all the materials and conditions investigated to date.
124 citations