Browsing by Author "Nayak, U."

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Comparative study of the effect of section thickness of steel during quenching in neem and mineral oil
(ASM International joanne.miller@asminternational.org, 2017) Nayak, U.; Prabhu, K.N.
The cooling behavior of neem and mineral oil was obtained using instrumented ISO 9950 inconel probe. Flash, fire points and the viscosity of quenching media were measured. These oils were used to quench harden AISI 1045 and AISI 1090 grade steel probes of section diameters 25 and 50 mm. (The top and bottom faces of steel probes were coated with insulating paste to minimize end effects of heat transfer during quenching.) The measured temperature data in steel probes were used to estimate spatiotemporal heat flux by solving inverse heat conduction problem at the interface of the probe/quenching medium The estimated heat flux transients, microstructure, and hardness measurements were found to be similar for both oils indicating the potential application of neem oil as quenchant for heat treatment of steels. Â© Â© 2017 ASM Internationale All rights reserved.
Heat transfer and quench performance of aqueous CuO nanofluids during immersion quenching
(Inderscience Publishers, 2016) Nayak, U.; Prabhu, K.
The present work involves the assessment of quench performance of aqueous-copper oxide nanofluids. Distilled water-based copper oxide nanofluids of concentrations 0.01, 0.05, 0.1 and 1.0 vol.% were prepared by a two-step process. Cooling curves analysis was carried out using an inconel probe that was instrumented with thermocouples. The recorded temperature data during experiments was used to estimate spatiotemporal heat flux transients by solving inverse heat conduction problem. Quenching of probe in nanofluids resulted in longer vapour phase stage duration compared to distilled water. The addition of nanoparticles altered the peak flux and the time of its occurrence. Rewetting temperatures were found to be lower for nanofluids. The measured thermal conductivities and viscosities showed similar values for all quench media. © 2016 Inderscience Enterprises Ltd.
Heat transfer during immersion quenching in MWCNT nanofluids
(Trans Tech Publications Ltd ttp@transtec.ch, 2015) Nayak, U.; Prabhu, K.
Quench heat treatment consists of rapid cooling of steel alloys after austenetization by subjecting them to cooling in a suitable cooling medium. At the heart of quench treatment is the transient heat transfer that occurs between the metal surface and the quenchant at their interface. This governs the quality of the component as it influences phase transformation, residual quench stresses and mechanical properties developed. In the present research work, spatially dependent transient heat flux in the axial direction was estimated using cooling curve analyses coupled with inverse heat conduction technique. A standard Inconel 600 probe instrumented with multiple thermocouples and heated to 865Â°C was quenched in distilled water (DW) and DW based multi walled carbon nanotubes (MWCNT) quench media. For evaluating the cooling performance, nanoquenchants with concentrations of 0.01, 0.1 and 1.0g/lt. were prepared. The cooling rate curve calculated from the measured temperature at the geometric center of the probe and the estimation of spatially dependent heat fluxes showed that the heat extraction during quenching with MWCNT nanoquenchant (0.1g/lt.) was higher than the other quenchants. The measured values of thermal conductivity and viscosities of quenchants did not show any significant variation. Â© (2015) Trans Tech Publications, Switzerland.
Nano-ZnO particle addition to monolithic magnesium for enhanced tensile and compressive response
(Elsevier Ltd, 2014) Seetharaman, S.; Nayak, U.; Sabat, R.K.; Suwas, S.; Almajid, A.; Gupta, M.
In this study, the effects of nanoscale ZnO reinforcement on the room temperature tensile and compressive response of monolithic Mg were studied. Experimental observations indicated strength properties improvement due to nanoscale ZnO addition. A maximum increment in tensile yield strength by ?55% and compressive yield strength by 90% (with reduced tension-compression asymmetry) was achieved when 0.8 vol.% ZnO nanoparticles were added to Mg. While the fracture strain values under tensile loads were found to increase significantly (by ?95%, in case of Mg-0.48ZnO), it remained largely unaffected under compressive loads. The microstructural characteristics studied in order to comprehend the mechanical response showed significant grain refinement due to grain boundary pinning effect of nano-ZnO particles which resulted in strengthening of Mg. Texture analysis using X-ray and EBSD methods indicated weakening of basal fibre texture in Mg/ZnO nanocomposites which contributed towards the reduction in tension-compression yield asymmetry and enhancement in tensile ductility when compared to pure Mg. © 2014 Elsevier B.V. All rights reserved.
Wetting kinetics and cooling performance of PAG polymer quenchants
(Trans Tech Publications Ltd ttp@transtec.ch, 2015) Pai, A.; Nayak, U.; Pranesh Rao, K.M.; Prabhu, K.
The present research work is aimed at the estimation of quench severity Polyalkylene Glycol (PAG) polymer quenchants having varying concentrations. An Inconel600 probe instrumented with thermocouples was used for this purpose. The thermal history at various locations in the probe was used as an input to the inverse heat conduction model. The inverse analysis yields spatially dependent heat flux transients. The quench severity was assessed using the Grossmann technique. The wetting kinematics of quenching was studied by cooling curve analysis. The severity of quenching as measured by the Grossmannâ€™s technique was found to be higher for polymer quenchants. However, the heat flux transients estimated by the inverse technique and rewetting times measured form the cooling curve analysis suggested comparable and uniform heat transfer with polymer quenchants compared to water quenchants. Â© (2015) Trans Tech Publications, Switzerland.