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B. Vamsi Krishna

Bio: B. Vamsi Krishna is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Powder metallurgy & Deformation (engineering). The author has an hindex of 8, co-authored 16 publications receiving 309 citations.

Papers
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Journal ArticleDOI
TL;DR: In this paper, the influence of cryo-rolling reduction and annealing of commercially pure (CP) Al is evaluated in four aspects: microstructure, mechanical properties, electrical conductivity and general corrosion.
Abstract: Influence of cryo-rolling reduction and annealing of commercially pure (CP) Al is evaluated in four aspects: microstructure, mechanical properties, electrical conductivity and general corrosion. It is shown that by selecting optimal cryo-rolling reduction and subsequent annealing condition result in ultrafine grains in CP Al with good combination of high strength and ductility. Electrical conductivity of the cryo-rolled samples decreased due to increased number of the electron scattering centers (lattice defects and grain boundary area). However, optimization of cryo-rolling and annealing treatment could restore the conductivity coupled with high strength in CP Al. Corrosion behaviour of cryo-rolled CP Al improved after annealing treatment. High dissolution rate and low thermal stability of the ultrafine grain structure could override the anticipated advantage of uniform corrosion in ultrafine grain CP Al.

188 citations

Journal ArticleDOI
TL;DR: In this article, the results of preliminary studies, carried out for the first time, related to the production of bimetallic tubes by tailoring the initial materials characteristics through powder metallurgy (P/M) and cold extrusion route were reported.
Abstract: The present article reports the results of preliminary studies, carried out for the first time, related to the production of bimetallic tubes by tailoring the initial materials characteristics through powder metallurgy (P/M) and cold extrusion route. It is shown that the domination of consolidation (volume change) during simultaneous deformation of P/M preforms reduces the differential velocity between the core and the sleeve as indicated by lower failure propensity of extrudes. High interfacial friction at the dissimilar P/M preform interface and in turn the high interfacial bond aids the sound flow over a wide range of processing conditions. In addition, the non-uniformities of deformation would be accommodated by the softer preform near the interface through micro-mechanical interactions. It is believed that the current approach of producing the bimetals greatly enhances the manufacturing flexibility and reduces the tool cost.

33 citations

Journal ArticleDOI
TL;DR: In this paper, the effect of current pulse frequency on weld bead microstructure, tensile strength, and hardness in joining of powder metallurgical steel preform sheets to wrought copper was studied.
Abstract: Pulsing of the welding current is one approach for refining the fusion zone microstructure in materials joined by fusion welding. The effect of current pulse frequency on weld bead microstructure, tensile strength, and hardness in joining of powder metallurgical steel preform sheets to wrought copper was studied. Considering weld strength as the quality characteristic in the selection of process parameters, the Taguchi method is used to analyse the effect of each process parameter individually and of their interaction on weld strength, and subsequently to determine the process parameters leading to optimum weld strength. The application of pulsed current causes iron dendrites to become more equiaxed and uniformly distributed owing to dendrite fragmentation. Further, there was an optimum frequency range over which the microstructural refinement was maximal. The same optimum frequency range corresponded to maximum tensile strength. Enhanced fluid flow and reduced thermal gradients are thought to be ...

21 citations

Journal ArticleDOI
TL;DR: In this article, a sound transition joint between two dissimilar metal tubes by tailoring the initial materials characteristics through powder metallurgy (P/M) and cold extrusion route is described.
Abstract: The present investigation describes about producing a sound transition joint between two dissimilar metal tubes by tailoring the initial materials characteristics through powder metallurgy (P/M) and cold extrusion route. An attempt has been made to analyse the influence of process parameters such as density ratio, volume ratio, interfacial angle and strain on successful solid state joining of steel–Cu and Cu–Al P/M preform tubes. The correlation between the process parameters and failure propensity, weld strength, extrusion force, change in interfacial angle, strain in each material and microstructural features of the joints is also presented.

21 citations

Journal ArticleDOI
TL;DR: In this article, the authors proposed a method for analyzing cylindrical shells with viscoelastic treatment, which obviates the discretisation of liquid domain by treating fluid domain with Bessel function and shell domain based on first-order shear deformation theory.

15 citations


Cited by
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Journal ArticleDOI
TL;DR: A brief overview of the available SPD technologies is given in this paper, along with a summary of unusual mechanical, physical and other properties achievable by SPD processing, as well as the challenges this research is facing, some of them generic and some specific to the nanoSPD area.

1,451 citations

Book ChapterDOI
01 Jan 1987
TL;DR: In this article, the authors presented a theory of liquid alloys and assembled all the necessary tools for the ab initio construction of an alloy phase diagram, which they used to construct a phase diagram.
Abstract: With the presentation of a theory of liquid alloys, we have now assembled all the necessary tools for the ab initio construction of an alloy phase diagram.

417 citations

Journal ArticleDOI
TL;DR: A review of the state-of-the-art in the area of dynamic analysis of composite shells can be found in this article, where the main aim is to provide a broad perspective of the current state of the art in this field.

364 citations

Journal ArticleDOI
TL;DR: The results demonstrate that non-recrystallized grains, which are generally avoided in conventional alloys because of their deleterious effect on ductility, can be useful in achieving high-strength high-entropy alloys.
Abstract: The excellent cryogenic tensile properties of the CrMnFeCoNi alloy are generally caused by deformation twinning, which is difficult to achieve at room temperature because of insufficient stress for twinning. Here, we induced twinning at room temperature to improve the cryogenic tensile properties of the CrMnFeCoNi alloy. Considering grain size effects on the critical stress for twinning, twins were readily formed in the coarse microstructure by cold rolling without grain refinement by hot rolling. These twins were retained by partial recrystallization and played an important role in improving strength, allowing yield strengths approaching 1 GPa. The persistent elongation up to 46% as well as the tensile strength of 1.3 GPa are attributed to additional twinning in both recrystallized and non-recrystallization regions. Our results demonstrate that non-recrystallized grains, which are generally avoided in conventional alloys because of their deleterious effect on ductility, can be useful in achieving high-strength high-entropy alloys.

267 citations

Journal ArticleDOI
TL;DR: In this article, the authors present an overview of the Directed Energy Deposition (DED) process and its role in the repairing of metallic components and confirm the significant capability of DED process as a repair and remanufacturing technology.
Abstract: In the circular economy, products, components, and materials are aimed to be kept at the utility and value all the lifetime. For this purpose, repair and remanufacturing are highly considered as proper techniques to return the value of the product during its life. Directed Energy Deposition (DED) is a very flexible type of additive manufacturing (AM), and among the AM techniques, it is most suitable for repairing and remanufacturing automotive and aerospace components. Its application allows damaged component to be repaired, and material lost in service to be replaced to restore the part to its original shape. In the past, tungsten inert gas welding was used as the main repair method. However, its heat affected zone is larger, and the quality is inferior. In comparison with the conventional welding processes, repair via DED has more advantages, including lower heat input, warpage and distortion, higher cooling rate, lower dilution rate, excellent metallurgical bonding between the deposited layers, high precision, and suitability for full automation. Hence, the proposed repairing method based on DED appears to be a capable method of repairing. Therefore, the focus of this study was to present an overview of the DED process and its role in the repairing of metallic components. The outcomes of this study confirm the significant capability of DED process as a repair and remanufacturing technology.

223 citations