Ashutosh Sahu | NIT ROURKELA (original) (raw)

Papers by Ashutosh Sahu

Social Science Research Network, 2019

After exploring space for more than 50 years for research, study and defense purposes, the region... more After exploring space for more than 50 years for research, study and defense purposes, the region above the atmosphere of earth is highly polluted by orbital debris. Figure 1 shows the total number of rocket launches in period of nine years. This has become a concern for placing satellites in their respective orbits and their safe functioning during their mission. Space debris or orbital debris colloquially known as space junk are parts of the non-functional satellites, thermal blankets, booster stages of the rockets. Those satellites are placed in the several orbits according to their missions. Mainly, they are placed in LEO (Low Earth Orbit), an earth centered orbit ranging from 200 to 2000 kilometers. Some are also placed in GEO (Geostationary Earth Orbit), at an altitude of 36000 kilometers and some are placed in the Higher Earth Orbit. Since the dawn of space age, approximately 7000 rockets have been launched, placing their payloads in several orbits of the Earth, revolving at several kilometers per second. And more than half of these objects are present in LEO. It is estimated that their sizes vary from a few millimeters to few meters, the largest being the European Envisat. Because of their high speeds, pieces of debris not more than a millimeter apart also poses a huge risk to current and upcoming space missions. Since the risk is increasing exponentially and is of great concern for all the space-faring nations, there is a need for the active removal of space debris. Hence, in this paper, the authors have analyzed the threat that space debris poses, and some of its removal techniques that have been proposed by scientists and space organizations. The authors have also suggested a few more of these Active Debris Removal techniques. <br>

Materials Today: Proceedings, 2015

International Journal of Research in Engineering and Technology, 2017

Nowadays, automobiles in the market are prone to heightened level of emissions due to fresh charg... more Nowadays, automobiles in the market are prone to heightened level of emissions due to fresh charge and scavenging losses. Furthermore, there is no practice of lean operation resulting in poor fuel economy. Carburetors have served the role of fuel supply system in spark ignition engines since a long time. Earlier due to the high initial cost and limited understanding, fuel injection system was used only in aircraft engines or racing cars. But due to increasing stress on air pollution control, the re is a strong need of adoption of technical amendments in the prevailing spark ignition engines. Hence this need gave rise to the development of newer systems like MPFI and GDI, which aim at satisfying the forthcoming stringent pollution norms. Also the innovations made needed to be affordable by the common people and also small in size so as to meet the space constraint. We made an attempt to compare the various fuel supply systems with special emphasis given on MPFI &GDI. So the report aims to suggest a gasoline direct injection in automobiles to increase the efficiency as well as a reduction in emissi on levels so that it complies with the EURO-VI norms. The basic objectives of the report are: (i) Incorporation of Gasoline Direct Injection in a 4-wheeler vehicle along with the inclusion of advanced technologies like EMS, turbo charging etc., for the overall engine improvement. (ii) Basic downsizing principles and techniques like turbo charging to reduce cost, increase power output and improve efficiency. (iii) Meet the existing EURO-VI emission norms, using EGR and controlling particulate matter emission.

Acta Metallurgica Sinica (English Letters), 2021

In the present study, Al86Ni8Y6 and Al86Ni6Y4.5Co2La1.5 bulk amorphous nanocomposites were synthe... more In the present study, Al86Ni8Y6 and Al86Ni6Y4.5Co2La1.5 bulk amorphous nanocomposites were synthesized by spark plasma sintering of milled melt spun ribbon particles. The as-cast ribbons were of near amorphous nature with minute amount of FCC Al embedded in the amorphous matrix. Milling of the ribbons resulted in partial devitrification due to mechanical crystallization. The milled ribbon particles were sintered in the temperature and pressure range of 300–500 °C and 500–700 MPa, respectively. It was observed that nominal amount of amorphous phase was retained at 500 °C and 500 MPa. With increase in sintering pressure and decrease in sintering temperature, the amount of crystalline phase evolution decreased, and maximum amount of amorphous phase was retained at 300 °C and 700 MPa. The microstructure consisting of amorphous phase embedded with hard intermetallic phases led to increase in the nanohardness of Al86Ni8Y6 and Al86Ni6Y4.5Co2La1.5 as-cast ribbons from 3.26 ± 0.59 GPa and 3.81 ± 0.58 GPa to 6.06 ± 0.70 GPa and 6.14 ± 0.82 GPa, respectively, for the corresponding consolidated amorphous nanocomposite. Microhardness of the three and five component system bulk samples was 4.19 ± 0.13 GPa and 3.6 ± 0.13 GPa, respectively.

Metallurgical and Materials Transactions A, 2020

In this work, the effects of milling and spark plasma sintering on crystalline phase evolution of... more In this work, the effects of milling and spark plasma sintering on crystalline phase evolution of Al 86 Ni 8 Y 6 and Al 86 Ni 6 Y 4.5 Co 2 La 1.5 amorphous ribbons and subsequently on nanoindentation behavior have been studied. The as-cast ribbons of both compositions exhibited three-stage crystallization behavior. The first stage of crystallization disappeared completely and onset of second stage shifted to lower values in the sintered samples compared to those in the corresponding as-cast ribbons, ascribed to evolution of various crystalline phases. The nanohardness of Al 86 Ni 8 Y 6 and Al 86 Ni 6 Y 4.5 Co 2 La 1.5 ribbons and the corresponding sintered samples were 3.26 ± 0.59, 3.81 ± 0.58, 6.06 ± 0.7, and 6.14 ± 0.82 GPa, respectively. The wear volume loss of Al 86 Ni 8 Y 6 and Al 86 Ni 6 Y 4.5 Co 2 La 1.5 as-cast ribbons at 3 mN load were 1.73 and 1.79 lm 3 , which decreased to 0.78 and 0.5 lm 3 , respectively, in the corresponding consolidated samples. The increase in nanohardness and decrease in wear volume loss in bulk samples can be ascribed to the formation of hard intermetallic phases in amorphous matrix. Average coefficient of friction for Al 86 Ni 8 Y 6 and Al 86 Ni 6 Y 4.5 Co 2 La 1.5 bulk samples at 3 mN were 0.36 and 0.32, which increased to 0.43 and 0.45, respectively, at 200 mN, attributed to the increase in the lateral force.

Thermochimica Acta, 2020

In the present work, thermal behavior of Al 86 Ni 8 Y 6 and Al 86 Ni 6 Y 4.5 Co 2 La 1.5 as-cast ... more In the present work, thermal behavior of Al 86 Ni 8 Y 6 and Al 86 Ni 6 Y 4.5 Co 2 La 1.5 as-cast amorphous ribbons, corresponding milled ribbon particles and spark plasma sintered samples has been studied. Activation energies of crystallization at all transition temperatures of the samples were determined by Kissinger, Ozawa and Augis-Bennett equations. The first stage of crystallization for both the as-cast ribbons, related to formation of nanocrystalline FCC Al disappeared completely in case of the milled ribbon particles and consolidated samples. In comparison to as-cast ribbons, the onset of second stage crystallization with corresponding activation energies shifted to lower values in the milled ribbon particles; whereas the onset and peak temperatures of third stage crystallization and related activation energies shifted to higher values. Formation of higher amount of crystalline phases during sintering led to decrease in all transition temperatures and corresponding activation energies of bulk samples compared to that of the milled ribbon particles.

Surface and Coatings Technology, 2018

Abstract Ti2AlC based MAX phase coatings were successfully deposited on Inconel 625 substrate by ... more Abstract Ti2AlC based MAX phase coatings were successfully deposited on Inconel 625 substrate by a cold spraying technique. A dense coating of 70 μm thickness was deposited. Ball-on-disk wear behavior of Ti2AlC coating at room temperature (25 °C), and high temperature (600 °C) were studied. The coefficient of friction (COF) and wear volume loss at 600 °C reduced by ~ 21% and ~ 40% respectively, due to the lubricious nature of oxide layer formed at a higher temperature. Mechanical properties of the Ti2AlC coating were also studied by carrying out nanoindentation and nano-scratch tests at room temperature and 300 °C and varying loads. For a low load of 7000 μN at room temperature, Ti2AlC coating exhibited a higher elastic modulus of 273 GPa compared to the elastic modulus of 191 GPa at high temperature (300 °C). The room temperature nano-scratch at 7000 μN displayed brittle behavior with fracture, chipping and wear debris formation along the scratch path. However, high temperature (300 °C) scratch path exhibited ductile nature with plowing, cutting and no wear debris formation. The wear volume loss was several orders of magnitude higher at 8 N load scratch. The overall wear behavior in MAX phase Ti2AlC coating at multiple load scales is elucidated in terms of the interaction volume varying from a single to several splats in the cold sprayed structure.

Progress in Natural Science: Materials International, 2019

Al 86 Ni 6 Y 4.5 Co 2 La 1.5 amorphous powders were synthesized by mechanical alloying for 200 h.... more Al 86 Ni 6 Y 4.5 Co 2 La 1.5 amorphous powders were synthesized by mechanical alloying for 200 h. Subsequent consolidation was performed via spark plasma sintering in the temperature range of 250°C to 500°C at the pressure of 500 MPa. The role of viscous flow on densification was investigated by studying the viscosity change of the amorphous phase at different consolidation temperatures. The decrease in viscosity at higher sintering temperatures resulted in better particle bonding and densification of consolidated samples. The formation of only FCC Al was observed in the consolidated samples at sintering temperatures ≤ 300°C and the intermetallic phases formed at temperatures ≥ 400°C. The mechanical properties of the bulk samples were measured by Vickers microhardness and nanoindentation tests. The testing results showed that the average values of microhardness, nanohardness and elastic modulus of the sample consolidated at 500°C were 3.06 ± 0.14 GPa, 4.85 ± 1.14 GPa and 89.53 ± 9.25 GPa, respectively. The increase in hardness and elastic modulus of the higher temperature consolidated samples is attributed to the improvement in particle bonding, densification and distribution of various hard intermetallic phases in the amorphous matrix.

Advanced Powder Technology, 2019

In this research work, the sintering characteristics of Al 86 Ni 6 Y 4.5 Co 2 La 1.5 mechanically... more In this research work, the sintering characteristics of Al 86 Ni 6 Y 4.5 Co 2 La 1.5 mechanically alloyed amorphous powders and milled melt spun ribbon have been compared. Mechanically alloyed amorphous powders were synthesized via 200 h high energy ball milling. Melt spun ribbons were synthesized by single roller melt spinning technique and grounded to powder form by ball milling. Mechanically induced partial crystallization occurred in the ribbons during milling. Significantly higher amount of contaminations such as carbon, oxygen and iron were observed in the mechanically alloyed amorphous powders compared to the milled ribbons. Both powders were consolidated via spark plasma sintering. Superior particle bonding was found in the sample consolidated from milled ribbons, ascribed to the lower amount of contamination that could not effectively restrict the viscous flow and diffusion of atoms. Various complex crystalline phases evolved in the sample consolidated from milled ribbon particles due to the presence of crystalline phases in the powders which acted as nucleation sites, whereas the amorphous phase was mostly retained in its counterpart. Vickers microhardness of the consolidated alloys from milled ribbon and mechanically alloyed amorphous powders were 3.60 ± 0.13 GPa and 2.53 ± 0.09 GPa, respectively. The higher hardness in the former case was attributed to the superior particle bonding and distribution of hard intermetallic phases in the amorphous matrix.

Advanced Materials Letters, 2016

Materials & Design, 2016

The aim of the present work was to understand the phase transformation sequence in Al 86 Ni 8 Y 6... more The aim of the present work was to understand the phase transformation sequence in Al 86 Ni 8 Y 6 powder blend, subjected to prolonged mechanical alloying and in the bulk amorphous alloy consolidated via spark plasma sintering at various temperatures. The powder blend, mechanically alloyed up to 300 h, exhibited cyclic phase transformation by yielding (i) amorphous-crystalline matrix phase with distributed nanocrystalline phases at 80 h, (ii) fully amorphous phase at 140 h and again (iii) amorphous-crystalline matrix phase with distributed nano-crystals at 200 h of milling. The phase reversal due to the prolonged milling after achieving complete amorphization was attributed to mechanical crystallization. Amorphous powders were consolidated via spark plasma sintering in the temperature range of 250°C to 500°C. Quantitative phase analysis performed on the sintered alloys revealed at least 80% amorphous phase fraction in alloys sintered up to 350°C. The higher temperature (450°C and 500°C) sintered alloys exhibited higher amount of nanocrystalline FCC-Al and various intermetallic nano-precipitates (Al 3 Ni, Al 3 Ni 2 AlY, Al 2 Y and Al 2 NI 6 Y 3) distributed in the retained amorphous matrix.

Materials Science and Engineering: A, 2016

Mechanically alloyed amorphous Al 86 Ni 8 Y 6 powders were consolidated by spark plasma sintering... more Mechanically alloyed amorphous Al 86 Ni 8 Y 6 powders were consolidated by spark plasma sintering (SPS) and the effect of varying sintering pressure (100-400 MPa) on phase transformation and resulting mechanical property was studied. Fully amorphous Al 86 Ni 8 Y 6 powder obtained via mechanical alloying exhibited good thermal stability with a wide glass transition range of 45°C. Higher sintering pressure (400 MPa) during SPS resulted in (i) better densification (98%) with improved inter-particle bonding and moreover, (ii) retention of higher volume fraction ($ 92 vol%) of amorphous phase with lower amount of intermetallic nano-precipitates, indicating improvement in thermal stability of the amorphous phase. Vickers microhardness test showed improvement in hardness with increasing sintering pressure attributed to a larger fraction of the retained amorphous phase and better inter-particle bonding. Nanoindentation test exhibited similar trends in hardness and elastic modulus with wide variation in hardness and elastic modulus values attributed to the distribution of comparatively soft nanocrystalline Al and very hard intermetallic precipitates in the amorphous matrix.

Indian heart journal

Pulmonary arterial hypertension is a life-threatening disease for which continuous intravenous in... more Pulmonary arterial hypertension is a life-threatening disease for which continuous intravenous infusion of prostacyclin has proved effective. However, it carries the risk of serious complications arising from the complex delivery system. Prostacyclin analogs, endothelin antagonists, and the phosphodiesterase-5 inhibitor sildenafil are emerging promising therapies. This study was aimed at evaluating the utility of oral sildenafil in patients with pulmonary hypertension of varied etiology, poorly controlled on conventional treatment. Ten consecutive patients with pulmonary hypertension, either primary or related to previous left-to-right shunts, thromboembolism, or interstitial lung disease, poorly controlled on conventional therapy such as warfarin, calcium antagonists, digitalis, and diuretics, were included. A thorough clinical, laboratory, and comprehensive echo Doppler evaluation was performed before enrollment in the trial to establish the diagnosis and obtain baseline data. Sub...

International Journal of Cardiology, 2004

International Journal of Materials Research, 2020

The present work is focused on the investigation of hardness and scratch behavior of mechanically... more The present work is focused on the investigation of hardness and scratch behavior of mechanically alloyed and various temperature (300 °C–500 °C) spark plasma sintered Al86Ni8Y6 glassy alloys. Glassy alloy sintered at higher temperature, exhibited significantly improved hardness attributed to the increase in metallurgical bonding, relative density and nanocrystalline phases. A large variation in hardness of sintered alloys was attributed to the diffusion controlled crystallization mechanism depending on the nucleation rate during spark plasma sintering, which led to the different degree of microstructural phase evolution in a different part of the sample as confirmed by the scanning probe microscopy revealing the varying depth of indentation. Nanoindentation conducted at lower load resulted in higher hardness attributed to the indentation size effect. The scratch test exhibited decrease in coefficient of friction from 0.40 to 0.30 with the increase in sintering temperature from 300 ...