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Dive into the research topics where P. Nageswara Rao is active.

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Featured researches published by P. Nageswara Rao.


International Journal of Minerals Metallurgy and Materials | 2013

Microstructures and impact toughness behavior of Al 5083 alloy processed by cryorolling and afterwards annealing

Dharmendra Singh; P. Nageswara Rao; R. Jayaganthan

The influence of rolling at liquid nitrogen temperature and annealing on the microstructure and mechanical properties of Al 5083 alloy was studied in this paper. Cryorolled samples of Al 5083 show significant improvements in strength and hardness. The ultimate tensile strength increases up to 340 MPa and 390 MPa for the 30% and 50% cryorolled samples, respectively. The cryorolled samples, with 30% and 50% reduction, were subjected to Charpy impact testing at various temperatures from −190°C to 100°C. It is observed that increasing the percentage of reduction of samples during cryorolling has significant effect on decreasing impact toughness at all temperatures by increasing yield strength and decreasing ductility. Annealing of samples after cryorolling shows remarkable increment in impact toughness through recovery and recrystallization. The average grain size of the 50% cryorolled sample (14 μm) after annealing at 350°C for 1 h is found to be finer than that of the 30% cryorolled sample (25 μm). The scanning electron microscopy (SEM) analysis of fractured surfaces shows a large-size dimpled morphology, resembling the ductile fracture mechanism in the starting material and fibrous structure with very fine dimples in cryorolled samples corresponding to the brittle fracture mechanism.


Materials Science and Technology | 2013

Effect of annealing on microstructure and mechanical properties of Al 6061 alloy processed by cryorolling

P. Nageswara Rao; Dharmendra Singh; R. Jayaganthan

Abstract An ultrafine grained (UFG) structure developed in precipitation hardenable Al alloys through cryorolling by suppression of dynamic recovery followed by low temperature aging has received great research interest because of its high strength and very good ductility. In the present work, Al 6061 alloy was solution treated and deformed by cryorolling up to an effective true strain of 2·6 and then subjected to annealing at the temperature range from 150 to 350°C to study the effect of annealing on the microstructure and mechanical properties. The evolution of microstructure and precipitates was investigated by employing X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. Vickers hardness and tensile testings were performed at room temperature to evaluate the effect of annealing on the mechanical properties. It was observed that the strength and ductility increased upon annealing at 150°C, and further annealing at high temperatures (200–350°C) results in reduction in hardness and strength but increase in ductility. A significant improvement in strength observed at low temperature annealing (150°C) is due to the precipitation of metastable phase β″. It overcompensates the reduction in hardness that occurred due to the softening caused by the recovery effect. It was found that the cryorolled Al 6061 alloy with UFG structure is thermally stable up to temperatures 250°C with slight grain coarsening. At this temperature, the TEM studies revealed that second phase Mg2Si particles are effectively pinning the grain boundaries due to the Zener drag effect. Owing to the presence of heterogeneities in the material, a duplex structure was observed upon annealing at temperatures 150 and 200°C. Abnormal grain growth was observed after annealing at high temperatures (300°C).


Materials Science and Technology | 2014

High cyclic fatigue behaviour of ultrafine grained Al 5083 alloy

Dharmendra Singh; P. Nageswara Rao; R. Jayaganthan

Abstract The effects of cryorolling (CR) and CR followed by warm rolling (WR) on high cycle fatigue behaviour of Al 5083 alloy have been investigated in the present work. The Al 5083 alloy samples were rolled for different thickness reductions of 50 and 85% at cryogenic (liquid nitrogen) temperature. Fifty per cent cryorolled samples were subsequently warm rolled at 175°C for 70% reduction (WR). Hardness, tensile strength and fatigue life using constant amplitude stress controlled fatigue were investigated. The microstructural evolution of the alloy was characterised using optical microscopy, SEM and TEM techniques. The cryorolled Al alloy after 85% thickness reduction exhibits high dislocation density due to suppression of dynamic recovery, whereas WR alloy has shown fine subgrain structure in the range of 100–150 nm, associated with dynamic recovery and dynamic aging during WR. The Al 5083 alloy after WR has shown significant enhancement in fatigue strength as compared to the coarse grained solution treated (ST) bulk alloy and CR material. It can be attributed to the formation of fine precipitates during WR, which inhibits dynamic recovery during cyclic deformation; precipitate–dislocation tangled zones inhibits the crack propagation in the alloy.


Applied Mechanics and Materials | 2018

Effect of Pre-Ageing on the Age Hardening Response of Cryorolled Al-Mg-Si Alloy

Maruff Hussain; P. Nageswara Rao; Dharmendra Singh; R. Jayaganthan

The present work investigates about the effect of pre-ageing on hardening behavior of Al-Mg-Si alloys processed by cryorolling and its age hardening behavior. Ageing conditions were examined at natural ageing for 2days and pre-ageing at 100 °C, 130°C and 170 °C for 4 hours, 2 hours and 30 minutes respectively. The observations revealed that, the pre-ageing before cryorolling is useful to enhance the dislocation density during cryorolling. However artificial ageing of cryorolled samples is not influenced much with pre-ageing. It is revealed that, maturing at room temperature of CR samples for 30 days has resulted better hardening response during artificial ageing.


Materials & Design | 2012

Effects of warm rolling and ageing after cryogenic rolling on mechanical properties and microstructure of Al 6061 alloy

P. Nageswara Rao; R. Jayaganthan


Materials & Design | 2014

Mechanical properties and microstructural evolution of Al 6061 alloy processed by multidirectional forging at liquid nitrogen temperature

P. Nageswara Rao; Dharmendra Singh; R. Jayaganthan


Materials & Design | 2013

Effect of deformation temperature on mechanical properties of ultrafine grained Al–Mg alloys processed by rolling

Dharmendra Singh; P. Nageswara Rao; R. Jayaganthan


Materials Science and Engineering A-structural Materials Properties Microstructure and Processing | 2014

Effect of cryorolling and warm rolling on precipitation evolution in Al 6061 alloy

P. Nageswara Rao; B. Viswanadh; R. Jayaganthan


Journal of Materials Science & Technology | 2014

Effect of Post Cryorolling Treatments on Microstructural and Mechanical Behaviour of Ultrafine Grained Al-Mg-Si Alloy

P. Nageswara Rao; Dharmendra Singh; R. Jayaganthan


Procedia Engineering | 2014

Enhancement in Strength and Ductility of Al-Mg-Si Alloy by Cryorolling followed by Warm Rolling☆

P. Nageswara Rao; Amritha Kaurwar; Dharmendra Singh; R. Jayaganthan

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R. Jayaganthan

Indian Institute of Technology Madras

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Dharmendra Singh

Indian Institute of Technology Roorkee

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Maruff Hussain

Indian Institute of Technology Roorkee

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Amritha Kaurwar

Indian Institute of Technology Roorkee

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Ashoke Dr. Kumar

Motilal Nehru National Institute of Technology Allahabad

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Manpreet Singh

Government Engineering College Bikaner

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Mohd. Yunus Sheikh

Government Engineering College Bikaner

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Surendra Singh

Indian Institute of Technology Roorkee

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Heinz Günter Brokmeier

Clausthal University of Technology

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