The Experts below are selected from a list of 267 Experts worldwide ranked by ideXlab platform
David C. Dunand - One of the best experts on this subject based on the ideXlab platform.
-
Modeling the creep Threshold Stress due to climb of a dislocation in the Stress field of a misfitting precipitate
Acta Materialia, 2011Co-Authors: Matthew E. Krug, David C. DunandAbstract:A model for creep Threshold Stresses in alloys strengthened by coherent, misfitting precipitates is developed for the case where the precipitate is not sheared, and where there are elastic interactions between a dislocation and the precipitate over which it climbs. Calculations of the particle Stress field due to a positive stiffness and lattice parameter mismatch between precipitate and matrix predict that the mismatch forces help the dislocation climb/glide process over the precipitates but that they trap it at the departure side of the particle. This results in a true Threshold Stress, rather than a slowing of the kinetics of dislocation climb as in previous models, which is given by the applied Stress necessary to free the dislocation by a glide mechanism. Model predictions and experiment are compared for precipitation-strengthened aluminum alloys containing nanosize Al3Sc, Al3(Sc, Li) and Al3(Sc, Yb) precipitates with various sizes and mismatches. In agreement with experimental creep results, the model predicts that the Threshold Stress increases nearly linearly with precipitate radius, and also with the magnitude of the precipitate/matrix lattice mismatch.
-
Model for creep Threshold Stress in precipitation-strengthened alloys with coherent particles
Scripta Materialia, 2002Co-Authors: Emmanuelle A. Marquis, David C. DunandAbstract:Abstract The general climb model for creep Threshold Stress for dislocations interacting with incoherent particles is modified for the case of coherent precipitates, by taking into account elastic interactions between matrix dislocations and particles due to particle/matrix stiffness and lattice mismatches. The model is in qualitative agreement with experimental data for the Al–Sc system.
-
Creep of metals containing high volume fractions of unshearable dispersoids—Part I. Modeling the effect of dislocation pile-ups upon the detachment Threshold Stress
Acta Materialia, 1997Co-Authors: David C. Dunand, A.m. JansenAbstract:Abstract The high creep resistance of dispersion-strengthened metals is the result of a Threshold Stress, which is determined in existing models by considering the interaction of a single dislocation with dispersoids. This paper presents a new model which takes into account the effect of dislocation pile-ups upon the detachment Threshold Stress of dispersion-strengthened metals. First, it is shown that dislocation pile-ups are expected to form at dispersoids when the volume fraction and/or size of the dispersoids is large. Then, the equilibrium dislocation positions within the pile-ups are calculated and the resulting shear Stress exerted upon the detaching dislocations pinned at the dispersoids is determined. Finally, this pile-up Stress is added to the athermal detachment Threshold Stress determined with existing models to find a total Threshold Stress. Calculations for aluminum containing 25 vol.% alumina dispersoids show that the magnitude of the pile-up Stress is comparable to the athermal Threshold Stress, and thus contributes significantly to the total Threshold Stress. The model also predicts a creep activation energy much higher than that of the unreinforced metal as a result of the temperature dependence of the number of dislocations in the pile-ups.
Gollapudi S. Murty - One of the best experts on this subject based on the ideXlab platform.
-
Threshold Stress for superplastic flow in the Zn-Al eutectoid alloy
Materials Transactions JIM, 1993Co-Authors: Sanjeev Tandon, Gollapudi S. MurtyAbstract:The high temperature deformation of a commercial Zn-Al eutectoid alloy was investigated over the grain size range of 0.8 to 2.6 μm and the temperature range of 423 to 473 K, with a view to assessing the interpretation of region I in terms of a Threshold Stress for superplastic flow. The Threshold Stress evaluated by an extrapolation procedure is observed to decrease with increasing temperature and grain size. The activation energy and grain size exponent for the Threshold process are 34 kJ/mol and 0.85, respectively. Boundary sliding controlled by boundary migration is the likely origin of the Threshold Stress
-
Microstructural evolution and Threshold Stress for superplastic flow in the Zn-Al eutectoid
Journal of Materials Science, 1993Co-Authors: Sanjeev Tandon, Gollapudi S. MurtyAbstract:The microstructural evolution and the Stress-strain rate behaviour of superplastic Zn-Al eutectoid alloy were investigated by prestraining specimens at two strain rates corresponding to Regions I and II. Even though the scale of microstructure was similar, the Stress-strain rate curves of differently prestrained specimens were distinctly different in the lower strain-rate regime. While Region I of low rate sensitivity was more prominent when prestrained at a lower strain rate of Region I, it was less distinct because of prestrain in Region II. The Threshold Stress for superplastic flow, as assessed by an extrapolation procedure, varied with the nature of prestrain. The interphase boundaries were more rounded (higher mean curvature) on prestraining on Region II, compared to Region I. The correlation between the changes in the mean curvature of phase boundaries and the Threshold Stress arising from the nature of prestrain was consistent with the boundary-migration controlled sliding mechanism to interpret the Threshold Stress for superplastic flow.
E. Kovács-csetényi - One of the best experts on this subject based on the ideXlab platform.
-
Evaluation of the true activation enthalpy of superplastic flow including a Threshold Stress
Journal of Materials Science, 1994Co-Authors: Nguyen Q. Chinh, P. Tasnádi, András Juhász, István Kovács, E. Kovács-csetényiAbstract:A new method is suggested for the evaluation of the true activation enthalpy for alloys where the strain rate of the superplastic flow varies with a power of an effective Stress σe = σ-σo, where σ and σo are the applied Stress and a Threshold Stress, respectively. Some earlier results concerning superplastic AlMgZnCu alloys containing chromium and in which a strongly temperature-dependent Threshold Stress can be revealed, are reanalysed. The results are in good agreement with the previous ones. It has been shown further that for the alloys investigated the true activation energy increases with increasing chromium content.
Sanjeev Tandon - One of the best experts on this subject based on the ideXlab platform.
-
Threshold Stress for superplastic flow in the Zn-Al eutectoid alloy
Materials Transactions JIM, 1993Co-Authors: Sanjeev Tandon, Gollapudi S. MurtyAbstract:The high temperature deformation of a commercial Zn-Al eutectoid alloy was investigated over the grain size range of 0.8 to 2.6 μm and the temperature range of 423 to 473 K, with a view to assessing the interpretation of region I in terms of a Threshold Stress for superplastic flow. The Threshold Stress evaluated by an extrapolation procedure is observed to decrease with increasing temperature and grain size. The activation energy and grain size exponent for the Threshold process are 34 kJ/mol and 0.85, respectively. Boundary sliding controlled by boundary migration is the likely origin of the Threshold Stress
-
Microstructural evolution and Threshold Stress for superplastic flow in the Zn-Al eutectoid
Journal of Materials Science, 1993Co-Authors: Sanjeev Tandon, Gollapudi S. MurtyAbstract:The microstructural evolution and the Stress-strain rate behaviour of superplastic Zn-Al eutectoid alloy were investigated by prestraining specimens at two strain rates corresponding to Regions I and II. Even though the scale of microstructure was similar, the Stress-strain rate curves of differently prestrained specimens were distinctly different in the lower strain-rate regime. While Region I of low rate sensitivity was more prominent when prestrained at a lower strain rate of Region I, it was less distinct because of prestrain in Region II. The Threshold Stress for superplastic flow, as assessed by an extrapolation procedure, varied with the nature of prestrain. The interphase boundaries were more rounded (higher mean curvature) on prestraining on Region II, compared to Region I. The correlation between the changes in the mean curvature of phase boundaries and the Threshold Stress arising from the nature of prestrain was consistent with the boundary-migration controlled sliding mechanism to interpret the Threshold Stress for superplastic flow.
Arturo Domínguez-rodríguez - One of the best experts on this subject based on the ideXlab platform.
-
Correlation between yttrium segregation at the grain boundaries and the Threshold Stress for plasticity in yttria-stabilized tetragonal zirconia polycrystals
Philosophical Magazine, 2003Co-Authors: Diego Gómez-garcía, C. Lorenzo-martin, A. Muñoz-bernabé, Arturo Domínguez-rodríguezAbstract:Nowadays, the high-temperature plasticity of yttria-stabilized tetragonal zirconia polycrystals (YTZPs) is successfully explained in terms of a Threshold Stress. Despite the fact that its existence is very well proved experimentally, the origin and nature of the Threshold Stress are still unexplained. This work develops a possible explanation for the Threshold Stress in YTZPs. The model developed in this paper is able to explain quantitatively the dependence of this Threshold Stress with temperature and grain size. The model is able to predict the influence of a glassy phase present at grain boundaries and the values of the Threshold Stress in YTZP nanocrystals. The theoretical results are discussed and compared with the available data in the literature.
-
The Influence of the Threshold Stress in the Superplastic Flow of YSZP
Materials Science Forum, 1999Co-Authors: Manuel Jiménez-melendo, Arturo Domínguez-rodríguezAbstract:Creep tests at constant load have been performed on high purity, fine-grained 3 mol% yttria-stabilized tetragonal zirconia polycrystals (YTZP). The apparent activation energy measured by the temperature change procedure depends on Stress, temperature and grain size. The results can be rationalized within a Threshold Stress approach.
-
Grain size and temperature dependence of the Threshold Stress for superplastic deformation in yttria-stabilized zirconia polycrystals
Materials Science and Engineering A-structural Materials Properties Microstructure and Processing, 1998Co-Authors: Arturo Domínguez-rodríguez, A. Bravo-león, Manuel Jiménez-melendoAbstract:Abstract The influence of the Threshold Stress on the value of the activation energy ( Q ) and Stress exponent ( n ) measured during creep tests in fine-grained Y 2 O 3 -doped ZrO 2 polycrystals has been investigated in the low-Stress region at intermediate temperatures. A significant increase of the measured value of Q and n with decreasing Stress has been observed, consistent with the existence of a Threshold Stress for superplastic deformation.
