74 research outputs found
The effect of wire drawing speed on the dislocation substructures and mechanical properties in aluminum
No full textAbstract not availabl
Virtual 3D microstructures with specified characteristics of state variable distributions
No full textFor a wide variety of model calculations a hypothetical 3D microstructure is required as input. Although experimental data are frequently used to this purpose, 3D microstructures are difficult to measure experimentally. In order to circumvent these difficulties, a virtual microstructure generator to simulate a specific 3D material microstructure is proposed. Such a virtual microstructure could serve as input for different types of models, would allow a faster model prototyping, would help to explore the boundary conditions of models and reduces the number of unnecessary experimental measurements. In the current paper, the method to generate and to control the grain size distribution as well as texture are discussed
Role of S[(123)〈634〉] orientations in the preferred nucleation of cube grains in recrystallization of FCC metals
No full textFriction stir processing of AZ31 magnesium alloy
No full textMagnesium alloys are known to be one of the lightest structural alloys and hence they are of interest to the potential applications in aerospace and automobile industry. However, widescale commercial usage of magnesium alloys is limited given its low formability at room temperature. Conventional processing techniques fail to alter the formability and other mechanical properties significantly. A severe plastic deformation processing technique called friction stir processing (FSP) developed on the principles of friction stir welding (FSW) is touted to significantly change the microstructure, texture and hence the mechanical properties of magnesium alloys. This thesis is primarily based on investigating the mechanisms of microstructure and texture evolution during FSP of a commercial AZ31 magnesium alloy. The work presented in the thesis comprise of four projects, all under the broad theme of investigating the microstructure and texture evolution in AZ31 alloy: (i) Microstructural origin of friction stir processed zone in a magnesium alloy, (ii) Microstructural evolution during multipass friction stir processing of a magnesium alloy, (iii) Friction stir processing under different thermal history, and (iv) Study of grain structure evolution during annealing of a twin roll cast AZ31 Mg alloy. In (i) microstructural and texture evolution at the edge regions of a friction stir processed (FSP) magnesium alloy AZ31 was studied which was aimed at explaining the mechanism of the microstructural evolution during FSP. A model of microstructural development through grain boundary sliding of the ultra-fine grains was proposed based on the texture and microstructural observations in the concerned regions. Further, in (ii) the microstructure and texture developments and also prediction of texture using visco-plasticself-consistent (VPSC) modelling of commercial magnesium alloy AZ31 being friction stir processed through multi-pass and multi-directional (unidirectional, reverse and transverse tool movements) was studied. Later, in (iii) the effect of various coolant mediums viz. air, liquid nitrogen and water on the microstructural and thermal profiles in the friction stir processed zone was investigated. Experimental observations, on the process zone dimensions and temperature profiles, showed significant differences: which highlighted the effect of the thermal history. A numerical simulation was made using multi-physics finite element method. A three-dimensional steady-state coupled laminar fluid flow and heat transfer model was developed, which could capture the experimentally observed process zone dimensions and temperature profiles. Lastly, in (iv) evolution of microstructure under static annealing at 300°C and 500°C for different times of twin-roll-cast (TRC) magnesium alloy AZ31 was outlined. Grain path envelope analysis was used for quantitatively analyzing the microstructural evolution. Twin-rolled structure had bimodal grain size which was preserved after annealing at 300°C. However, annealing at 500°C led to a unimodal grain size. A deformation induced recrystallization recovery (DIRR) model was proposed which could explain the observed microstructural features.Thesis submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy of the Indian Institute of Technology Bombay, India and Monash University, Australia
X-ray diffraction for the determination of residual stress of crystalline material: an overview
No full textThough there are a variety of experimental techniques available for residual stress measurements, diffraction-based measurements have the unique advantage of estimating the individual components of the residual strain matrix in a crystalline material. This is then converted to residual stresses with appropriate continuum elasticity model(s) and X-ray elastic constants. In particular, measurements based on electron or neutron diffractions have their complexities or availability issues. The laboratory X-ray diffraction, on the other hand, may provide an easy resource and an effective tool. Such measurements range from two tilt methods to more extended d-sin2ψ measurements and multiple {hkil} grazing incident X-ray diffraction. Measurements can even be conducted on single crystals with micro-Laue diffraction and extended to stress ODF (orientation distribution function) calculations. These techniques are unquestionably extremely specialized, where measurement uncertainty plays an important role in the effectiveness plus reproducibility of the data. Unfortunately, standard textbooks or review articles typically describe some, but not all, of the techniques. In this overview, different techniques of X-ray diffraction for the determination of residual stresses in crystalline material have been summarized. It is hoped that potential users may benefit from the deliberations
Microstructural and Mechanistic Insights into the Tension-Compression Asymmetry of Rapidly Solidified Fe-Cr Alloys: A Phase Field and Strain Gradient Plasticity Study
No full textRapid solidification in Additively Manufactured (AM) metallic materials
results in the development of significant microscale internal stresses, which
are attributed to the printing induced dislocation substructures. The resulting
backstress due to the Geometrically Necessary Dislocations (GNDs) is
responsible for the observed Tension-Compression (TC) asymmetry. We propose a
combined Phase Field (PF)-Strain Gradient Plasticity (SGP) framework to
investigate the TC asymmetry in such microstructures. The proposed PF model is
an extension of Kobayashi's dendritic growth framework, modified to account for
the orientation-based anisotropy and multi-grain interaction effects. The SGP
model has consideration for anisotropic temperature-dependent elasticity,
dislocation strengthening, solid solution strengthening, along with GND-induced
directional backstress. This model is employed to predict the solute
segregation, dislocation substructure and backstress development during
solidification and the post-solidification anisotropic mechanical properties in
terms of the TC asymmetry of rapidly solidified Fe-Cr alloys. It is observed
that higher thermal gradients (and hence, cooling rates) lead to higher
magnitudes of solute segregation, GND density, and backstress. This also
correlates with a corresponding increase in the predicted TC asymmetry. The
results presented in this study point to the microstructural factors, such as
dislocation substructure and solute segregation, and mechanistic factors, such
as backstress, which may contribute to the development of TC asymmetry in
rapidly solidified microstructures.Comment: 30 pages, 12 figure
Solidification morphology and shrinkage behavior of Mg-alloys in chill- and sand casting
No full text
New insights into Cube nuclei in deformed aluminium
No full textInternational audienceThe formation of Cube oriented elements in plane strain compressed aluminium has been studied by EBSD for both hot and cold deformations. By following the orientation changes of the same set of 176 grains deformed at 400 degrees C up to a strain of 1.2 using a split sample, it is shown that about 15% of the grains can break up into several regions of very different orientations, characterized by very large orientation gradients. In particular those grains oriented within about 30 degrees of Cube develop Cube oriented zones in contact with other rolling texture components. Finite element crystal plasticity simulations confirm this mechanism of creation of Cube by plastic deformation. The same type of microstructure can also be observed after heavy cold rolling (strain of 2.3), but at a scale that is much finer by at least an order of magnitude. In this case the micron-sized Cube fragments are located along many grain boundaries or in some particular grains. When the cold deformed sample is annealed, EBSD observations of the same areas reveal that the intergranular Cube fragments are very efficient recrystallization nucleation sites, apparently since they possess mobile high angle boundaries with the local environment
Resistance to sensitization and intergranular corrosion through extreme randomization of grain boundaries
No full textTwo grades of austenitic stainless steel, type 304 and 316L, were cold rolled to different reductions by unidirectional and by cross rolling. Subsequent solutionizing of the cold rolled samples produced noticeable textural differences in type 304, but insignificant differences in type 316L. Both the solutionized materials had however the same trend in grain boundary character distribution (GBCD): an increasing fraction of random boundaries with an increasing presolutionizing reduction percentage. The degree of sensitization (DOS) was measured by the double loop electrochemical potentiokinetic reactivation (DL-EPR) test in both the alloys. The susceptibility to intergranular corrosion was assessed by the standard weight loss technique (practice B, A262 ASTM) in type 304 alloy. These increased with increase in random boundary concentration, but then dropped significantly beyond a 'critical' concentration-a pattern observed in both the grades. Such a pattern may be explained from a balance between nucleation rate of Cr-carbides and grain boundary Cr-flux, though postulating an exact model is premature at this stage. The present study, however, demonstrates a clear possibility of remarkable improvement in DOS and IGC through extreme grain boundary randomization. (C) 2002 Acta Materialia Inc. Published by Elsevier Science Ltd. All rights reserved.sponsorship: Indian Inst Technol, Dept Met Engn & Mat Sci, Bombay 400076, Maharashtra, India; Bhabha Atom Res Ctr, Div Sci Mat, Bombay 400085, Maharashtra, India; Katholieke Univ Leuven, Dept MTM, B-3001 Louvain, Belgiumstatus: Publishe
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