Sushanta Kumar Panigrahi

Bio: Sushanta Kumar Panigrahi is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topic(s): Alloy & Microstructure. The author has an hindex of 28, co-authored 81 publication(s) receiving 2594 citation(s). Previous affiliations of Sushanta Kumar Panigrahi include Indian Institute of Technology Roorkee & École centrale de Nantes.

Effects of grain size on the corrosion resistance of wrought magnesium alloys containing neodymium

Abstract: A range of grain size from 70 μm to 0.7 μm was studied for corrosion resistance of Mg–Y–RE magnesium alloy using electrochemical and constant immersion testing in 3.5 wt.% NaCl solution. The linear polarization resistance ( R p ) showed a clear trend of increasing R p value with grain refinement. The ultrafine grained sample showed the most positive pitting potential as compared to coarse grained samples. One order of magnitude decrease in corrosion rate was observed between coarsest and ultrafine grained microstructure.

Influence of grain size and texture on Hall–Petch relationship for a magnesium alloy

Abstract: Friction stir processing was applied to a magnesium alloy to generate various grain sizes with the same intense basal texture. Subsequent tensile deformation along two orthogonal directions by easy activation or inhibition of basal slip follows the Hall–Petch relationship between yield stress and grain size in both directions. The Hall–Petch parameters are texture dependent. Easy activation of basal slip introduces lower values, while inhibition of basal slip leads to higher values. The Hall–Petch parameters are interpreted by texture and microstructural factors.

A study on the mechanical properties of cryorolled Al–Mg–Si alloy

Abstract: The mechanical properties of a precipitation hardenable Al–Mg–Si alloy subjected to cryorolling and ageing treatments are reported in this present work. The severe strain induced during cryorolling of Al–Mg–Si alloys in the solid solutionised state produces ultrafine microstructures with improved mechanical properties such as strength and hardness. The improved strength and hardness of cryorolled alloys are due to the grain size effect and higher dislocation density. The ageing treatment of cryorolled Al–Mg–Si alloys has improved its strength and ductility significantly due to the precipitation hardening and grain coarsening mechanisms, respectively. The reduction in dimple size of cryorolled Al–Mg–Si alloy upon failure confirms the grain refinement and strain hardening mechanism operating in the severely deformed samples.

Effect of ageing on microstructure and mechanical properties of bulk, cryorolled, and room temperature rolled Al 7075 alloy

Abstract: The effect of ageing on mechanical properties and microstructural characteristics of a precipitation hardenable Al 7075 alloy subjected to rolling at liquid nitrogen temperature and room temperature are has been investigated in the present work employing hardness measurements, tensile test, XRD, DSC, and TEM. The solution-treated bulk Al 7075 alloy was subjected to cryorolling and room temperature rolling to refine grain structures and subsequently ageing treatment to simultaneously improve the strength and ductility. The solution treatment combined with cryorolling up to a true rolling strain of 2.3 followed by low temperature ageing at 100 °C for 45 h has been found to be the optimum processing condition to obtain fine grained microstructure with improved tensile strength (642 MPa) and good tensile ductility (9.5%) in the Al 7075 alloy. The combined effect of suppression of dynamic recovery, partial grain refinement, partial recovery, solid solution strengthening, dislocation hardening, and precipitation hardening are responsible for the significant improvement strength–ductility combination in the cryorolled Al 7075 alloy subjected to peak ageing treatment. The cryorolled and room temperature rolled Al 7075 alloy, upon subjecting to peak ageing treatment, have shown higher strength and ductility in the former than the latter. It is due to presence of high density of nanosized precipitates in the peak aged cryorolled sample.

Corrosion behavior of a friction stir processed rare-earth added magnesium alloy

Abstract: Effect of grain refinement and heat treatment on corrosion behavior of a friction stir processed Mg-Y-RE alloy was studied The ennoblement of pitting potential by ∼250 mV vs SCE of processed samples as compared to parent alloy was attributed to grain refinement and uniform second phase distribution as a result of friction stir processing Lower currents and positive open circuit potentials were observed in friction stir processed samples under free corroding conditions Friction stir processing prior to peak hardening resulted in improved pitting potential when compared to the peak aged and processed samples Electrochemical testing and constant immersion testing showed differing trends

Extreme grain refinement by severe plastic deformation: A wealth of challenging science

Abstract: This article presents our take on the area of bulk ultrafine-grained materials produced by severe plastic deformation (SPD). Over the last decades, research activities in this area have grown enormously and have produced interesting results, which we summarise in this concise review. This paper is intended as an introduction to the field for the “uninitiated”, while at the same time highlighting some polemic issues that may be of interest to those specialising in bulk nanomaterials produced by SPD. A brief overview of the available SPD technologies is given, along with a summary of unusual mechanical, physical and other properties achievable by SPD processing. The challenges this research is facing—some of them generic and some specific to the nanoSPD area—are identified and discussed.

Mechanical Behavior and Strengthening Mechanisms in Ultrafine Grain Precipitation-Strengthened Aluminum Alloy

Abstract: To provide insight into the relationships between precipitation phenomena, grain size and mechanical behavior in a complex precipitation-strengthened alloy system, Al 7075 alloy, a commonly used aluminum alloy, was selected as a model system in the present study. Ultrafine-grained (UFG) bulk materials were fabricated through cryomilling, degassing, hot isostatic pressing and extrusion, followed by a subsequent heat treatment. The mechanical behavior and microstructure of the materials were analyzed and compared directly to the coarse-grained (CG) counterpart. Three-dimensional atom-probe tomography was utilized to investigate the intermetallic precipitates and oxide dispersoids formed in the as-extruded UFG material. UFG 7075 exhibits higher strength than the CG 7075 alloy for each equivalent condition. After a T6 temper, the yield strength (YS) and ultimate tensile strength (UTS) of UFG 7075 achieved 734 and 774 MPa, respectively, which are ∼120 MPa higher than those of the CG equivalent. The strength of as-extruded UFG 7075 (YS: 583 MPa, UTS: 631 MPa) is even higher than that of commercial 7075-T6. More importantly, the strengthening mechanisms in each material were established quantitatively for the first time for this complex precipitation-strengthened system, accounting for grain-boundary, dislocation, solid-solution, precipitation and oxide dispersoid strengthening contributions. Grain-boundary strengthening was the predominant mechanism in as-extruded UFG 7075, contributing a strength increment estimated to be 242 MPa, whereas Orowan precipitation strengthening was predominant in the as-extruded CG 7075 (∼102 MPa) and in the T6-tempered materials, and was estimated to contribute 472 and 414 MPa for CG-T6 and UFG-T6, respectively.

Nanostructured aluminium alloys produced by severe plastic deformation: New horizons in development

Abstract: In recent years, much progress has been made in the studies of nanostructured Al alloys for advanced structural and functional use associated both with the development of novel routes for the fabrication of bulk nanostructured materials using severe plastic deformation (SPD) techniques and with investigation of fundamental mechanisms leading to improved properties. This review paper discusses new concepts and principles in application of SPD processing to fabricate bulk nanostructured Al alloys with advanced properties. Special emphasis is placed on the relationship between microstructural features, mechanical, chemical, and physical properties, as well as the innovation potential of the SPD-produced nanostructured Al alloys.

Developing stable fine-grain microstructures by large strain deformation - Discussion

Abstract: Methods of deforming metals to large strains are reviewed and the process of equal channel angular extrusion is analysed in detail. The development of microstructure during large strain deformation is discussed, and it is concluded that the main criterion for the formation of a sub–micron grain structure is the generation of a sufficiently large fraction (> 0.7) of high–angle grain boundary during the deformation process. For aluminium alloys, it is found that a low–temperature anneal is required to convert the deformed microstructure into an equi–axed grain structure. The material, microstructural and processing factors that influence the formation of such fine–grain microstructures are discussed, and the stability of these microstructures at elevated temperatures is considered.

Surface composites by friction stir processing: A review

Abstract: Surface composites are suitable materials for engineering applications encountering surface interactions. Friction stir processing (FSP) is emerging as a promising technique for making surface composites. FSP can improve surface properties such as abrasion resistance, hardness, strength, ductility, corrosion resistance, fatigue life and formability without affecting the bulk properties of the material. Initially, FSP was used for making surface composites in aluminum and magnesium based alloys. Recently surface composites including steel and titanium based alloys have also been reported. While influence of process parameters and tool characteristics for FSP of different alloys has been considerably reviewed during the last decade, surface composites fabrication by FSP and the relation between microstructure and mechanical properties of FSPed surface composites as well as the underlying mechanisms have not been wholesomely reviewed. The present review offers a comprehensive understanding of friction stir processed surface composites. The available literature is classified to present details about effect of process parameters, reinforcement particles, active cooling and multiple passes on microstructure evolution during fabrication of surface composites. The microstructure and mechanical characteristics of friction stir processed surface micro-composites, nano-composites, in-situ composites and hybrid composites are discussed. Considering the importance of tool wear in FSP of high melting point and hard surface composites, a brief note on tool materials and the limitation in their usage is also provided. The underlying mechanisms in strengthening of friction stir processed surface composite are discussed with reported models. This review has revealed few gaps in research on surface composites via FSP route such as fabrication of defect-free composites, tailoring microstructures, development of durable and cost effective tools, and understanding on the strengthening mechanisms. Important suggestions for further research in effective fabrication of surface composited by FSP are provided.