Jayalakshmi Subramanian
Email Address
mpejs@nus.edu.sg
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19 results
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Publication Microstructural and mechanical properties of AZ31 magnesium alloy with Cr addition and CO 2 incorporation during processing(2012-06-15) Jayalakshmi, S.; Nguyen, Q.B.; Gupta, M.; MECHANICAL ENGINEERINGAZ31 Mg-alloy with ∼5 wt.% Cr and incorporated with CO 2 during processing were produced using the disintegrated melt deposition technique. The effect of Cr addition and CO 2 incorporation on the microstructural and mechanical properties was investigated after extrusion. Microstructural investigation revealed that the addition of Cr (AZ31-5Cr) significantly refined the grain size, and the incorporation of CO 2 (AZ31-5Cr-CO 2) resulted in the in situ formation of chromium carbide (Cr 23C 6) phase. The evaluation of mechanical properties indicated that when compared to the AZ31 base alloy, both AZ31-5Cr and AZ31-5Cr-CO 2 showed significant improvement in the strength properties. Based on the structure-mechanical properties correlation, it was identified that in AZ31-5Cr, Cr acted as a metallic reinforcement that improved the hardness, tensile and compressive yield strengths. In AZ31-5Cr-CO 2, the in situ formed Cr 23C 6 phase acted as a strengthening phase and enhanced the mechanical properties, which were significantly higher than those of AZ31 base alloy and AZ31-5Cr. © 2012 Elsevier B.V. All rights reserved.Publication Effect of ball milling the hybrid reinforcements on the microstructure and mechanical properties of Mg-(Ti + n-Al2O3) composites(2011-06-30) Sankaranarayanan, S.; Jayalakshmi, S.; Gupta, M.; MECHANICAL ENGINEERINGIn this study, composites containing pure magnesium and hybrid reinforcements (5.6 wt.% titanium (Ti) particulates and 2.5 wt.% nanoscale alumina (n-Al2O3) particles) were synthesized using the disintegrated melt deposition technique followed by hot extrusion. The hybrid reinforcement addition into the Mg matrix was carried out in two ways: (i) by direct addition of the reinforcements into the Mg-matrix, Mg-(5.6Ti + 2.5n-Al2O3) and (ii) by pre-synthesizing the composite reinforcement by ball milling and its subsequent addition into the Mg-matrix, Mg-(5.6Ti + 2.5n-Al2O3)BM. Microstructural characterization revealed significant grain refinement due to reinforcement addition. The evaluation of mechanical properties indicated a significant improvement in microhardness, tensile and compressive properties of the composites when compared to monolithic magnesium. For the Mg-(5.6Ti + 2.5n-Al2O3) composite, wherein the reinforcements were directly added into the matrix, the improvement in strength properties occurred at the expense of ductility. For the Mg-(5.6Ti + 2.5n-Al2O 3)BM composites with pre-synthesized ball-milled reinforcements, the increase in strength properties was accompanied by an increase/retention of ductility. The observed difference in behaviour of the composites is primarily attributed to the morphology and distribution of the reinforcements obtained due to the ball-milling process, thereby resulting in composites with enhanced toughness. © 2011 Elsevier B.V. All rights reserved.Publication Feasibility study on utilizing carbon dioxide during the processing of Mg-Al alloys(2011-08) Subramanian, J.; Guan, K.C.; Kuma, J.; Gupta, M.; CIVIL ENGINEERING; MECHANICAL ENGINEERINGThe feasibility of utilizing carbon dioxide (CO2) during magnesium-aluminium (Mg-Al) alloys processing was investigated by incorporating CO2 gas during melting and casting of the alloys. Mg-Al alloys containing ∼3 wt.% and ∼5 wt.% Al were processed with and without CO2 atmosphere using the disintegrated melt deposition (DMD) technique. The cast alloys after extrusion were characterized for their structural, physical and mechanical properties to identify the utilization of carbon dioxide during processing. Results indicated that sound, defect-free Mg-Alloys were produced with CO2 processing. Improvement in mechanical properties such as hardness, tensile strength and compressive yield strength were observed. The in situ formation of Al4C3 phase during processing was identified as the reason for the improvement in the properties, which indicated the utilization of carbon dioxide by the melt. © 2011 Elsevier B.V. All rights reserved.Publication Effect of addition of mutually soluble and insoluble metallic elements on the microstructure, tensile and compressive properties of pure magnesium(2011-12-15) Sankaranarayanan, S.; Jayalakshmi, S.; Gupta, M.; MECHANICAL ENGINEERINGIn the present study, pure magnesium incorporated with metallic elements was synthesized using the disintegrated melt deposition technique followed by hot extrusion. The metallic elements added include: (i) mutually soluble element, aluminium (Al), (ii) insoluble element, titanium (Ti) and (iii) a combination of mutually soluble and insoluble elements (Al and Ti). The addition of the combination of elements was carried out into two ways: (a) addition after prior ball milling and (b) direct addition. The developed Mg-based materials were investigated for their microstructural and mechanical properties. Microstructural investigation revealed significant grain refinement due to metallic addition. The evaluation of mechanical properties showed significant improvement in microhardness, tensile and compressive properties of all the Mg-materials when compared to pure magnesium. The addition of individual elements resulted in the formation of Mg-3Al alloy and Mg-5.6Ti composite, and improved both the strength and ductility. When the elements were ball milled, Al3Ti intermetallic was formed due to solid state reaction resulting in Mg-(3Al+5.6Ti)BM composite, which was absent during direct addition (Mg-3Al-5.6Ti). The Mg-(3Al+5.6Ti)BM composite showed the highest strength, however at the expense of ductility, while the Mg-3Al-5.6Ti showed relatively lower strength properties. The observed difference in behaviour between Mg-3Al-5.6Ti and Mg-(3Al+5.6Ti)BM is primarily attributed to the Al3Ti intermetallic phase formation and the change in morphology and distribution of the metallic elements due to the ball-milling process. © 2011 Elsevier B.V..Publication Development of novel Mg-Ni60Nb40 amorphous particle reinforced composites with enhanced hardness and compressive response(2014-01) Jayalakshmi, S.; Sahu, S.; Sankaranarayanan, S.; Gupta, S.; Gupta, M.; MECHANICAL ENGINEERINGDevelopment of amorphous alloy/glassy particle reinforced light metal composites is an emerging research field. In this investigation, we have synthesized and characterized Ni60Nb40 amorphous alloy particle reinforced Mg-composites with varying volume fractions. Microwave-assisted two-directional rapid sintering technique followed by hot extrusion was used to produce these pure Mg-based composites. The structural and mechanical properties of the developed composites were investigated, and are discussed using structure-property relationship. Structural analysis indicated the retention of amorphous structure of the reinforcement in all the composites. It was found that the distribution of the reinforcement was strongly dependent on the volume fraction (Vf). The addition of Ni60Nb40 amorphous alloy particles modified the preferred crystal orientation of Mg, as was observed fromX-ray diffraction (XRD) analysis. The composites showed significant improvement in hardness (increment up to 120%) and compressive strength (~85% increase at 5% Vf). Comparison of mechanical properties of the developed composites with those of conventional Mg-composites having ceramic/metallic reinforcements, highlight the effectiveness of using amorphous particles as promising reinforcement materials. © 2014 Elsevier Ltd.Publication Effect of Ag and Cu trace additions on the microstructural evolution and mechanical properties of Mg-5Sn alloy(2013-07-15) Jayalakshmi, S.; Sankaranarayanan, S.; Koh, S.P.X.; Gupta, M.; MECHANICAL ENGINEERINGIn this study, the effect of trace additions of Ag (0.175 wt.%) and Cu (0.035 wt.%) on the microstructural evolution and mechanical behavior of extruded Mg-5Sn alloy is investigated. Microstructural studies revealed that all the alloys have fine grains (2-6.5 μm), and that the binary Mg-5Sn alloy has polygonal and submicron-sized lath/rod-like Mg2Sn second phase particles. While Ag addition (TQ50 alloy) induced a change in morphology from lath/rod-shaped Mg2Sn to short-rod/oblong-shaped Mg-Sn-Ag particles, the presence of Ag and Cu (TQC500 alloy) resulted in an additional Mg 2(Cu, Sn) nano-sized phase. From XRD analyses, it was identified that the trace addition of Ag and Cu modified the preferred Mg-crystal orientation of the Mg-5Sn alloy that had basal planes strongly aligned parallel to the extrusion direction. Both Ag and Cu contributed to a remarkable decrease in the coefficient of thermal expansion and better static salt-water corrosion resistance. When compared to pure Mg, all the alloys showed significant improvement in hardness, tensile and compressive strength values, with Ag and Cu trace additions contributing to enhanced tensile ductility. The effect of trace additions of Ag and Cu on the material behavior was identified based on structure-property correlation. © 2013 Elsevier B.V. All rights reserved.Publication Effect of hybridizing micron-sized Ti with nano-sized SiC on the microstructural evolution and mechanical response of Mg-5.6Ti composite(2013) Sankaranarayanan, S.; Sabat, R.K.; Jayalakshmi, S.; Suwas, S.; Gupta, M.; MECHANICAL ENGINEERINGIn this work, the effect of hybridizing micro-Ti with nano-SiC particulates on the microstructural and the mechanical behaviour of Mg-5.6Ti composite were investigated. Mg materials containing micron-sized Ti particulates hybridized with different amounts of nano-size SiC particulates were synthesized using the disintegrated melt deposition method followed by hot extrusion. The microstructural and mechanical behaviour of the developed Mg hybrid composites were studied in comparison with Mg-5.6Ti. Microstructural characterization revealed grain refinement attributed to the presence of uniformly distributed micro-Ti particles embedded with nano-SiC particulates. Electron back scattered diffraction (EBSD) analyses of Mg-(5.6Ti + 1.0SiC)BM hybrid composite showed relatively more localized recrystallized grains and lesser tensile twin fraction, when compared to Mg-5.6Ti. The evaluation of mechanical properties indicated that the best combination of strength and ductility was observed in the Mg-(5.6Ti + 1.0SiC)BM hybrid composites. The superior strength properties of the Mg-(5.6Ti + x-SiC)BM hybrid composites when compared to Mg-5.6Ti is attributed to the presence of nano-reinforcements, the uniform distribution of the hybridized particles and the better interfacial bonding between the matrix and the reinforcement particles, achieved by nano-SiC addition. © 2013 Elsevier B.V. All rights reserved.Publication Characteristics of Ni-Nb-based metallic amorphous alloys for hydrogen-related energy applications(2012-02) Jayalakshmi, S.; Vasantha, V.S.; Fleury, E.; Gupta, M.; MECHANICAL ENGINEERINGIn hydrogen-related energy technologies, materials selection is critical as hydrogen tends to decrease the mechanical stability of the metallic alloys. Amorphous alloys are known to exhibit high hydrogen solubility and significant embrittlement resistance. The current work is focussed towards the properties of several (Ni-Nb)-based amorphous alloys for use in hydrogen-related energy applications. Based on the studies pertaining to hydrogenation characteristics and mechanical stability, it was observed that the Ni-Nb-based amorphous alloys have high absorption capacity, with hydrogen-to-metal ratio (H/M)∼1.8 (∼2.30wt.% of hydrogen) and excellent embrittlement resistance (H/M∼0.8), due to their unconventional structure and high hydrogen solubility, but these properties are strongly dependent on the alloy compositions. Investigations carried out to study the hydrogen permeation behavior of various Ni-Nb base amorphous alloys under gas permeation conditions for application as permeation membranes indicated that the Ni-Nb-based amorphous alloys exhibit high hydrogen permeabilities (∼1.1×10-8molm-1s-1MPa-1/2), comparable to that of Pd-Cu, in the temperature range 300-550°C. The corrosion behavior of the Ni-Nb alloys investigated under simulated proton-exchange membrane fuel cells (PEMFC) conditions, for use as bipolar plates in PEMFC exhibited excellent corrosion resistance, with corrosion and passivation current densities nearly comparable to those of graphite, the currently used material for bipolar plates. From these studies, it was understood that the inherent structure of the alloys and the constituent alloying elements played an important role in determining the properties. Based on our investigations, and from the hydrogen storage properties of amorphous alloys existing from literature, it is envisioned that amorphous alloys are most promising as future-generation materials for hydrogen-related energy applications. © 2011 Elsevier Ltd.Publication Influence of micron-Ti and Nano-Cu additions on the microstructure and mechanical properties of pure magnesium(2012) Seetharaman S.; Subramanian J.; Gupta M.; Hamouda A.S.; MECHANICAL ENGINEERINGn this study, metallic elements that have limited/negligible solubility in pure magnesium (Mg) were incorporated in Mg using the disintegrated melt deposition technique. The metallic elements added include: (i) micron sized titanium (Ti) particulates with negligible solubility; (ii) nano sized copper (Cu) particulates with limited solubility; and (iii) the combination of micro-Ti and nano-Cu. The combined metallic addition (Ti + Cu) was carried out with and without preprocessing by ball-milling. The microstructure and mechanical properties of the developed Mg-materials were investigated. Microstructure observation revealed grain refinement due to the individual and combined presence of hard metallic particulates. The mechanical properties evaluation revealed a significant improvement in microhardness, tensile and compressive strengths. Individual additions of Ti and Cu resulted in Mg-Ti composite and Mg-Cu alloy respectively, and their mechanical properties were influenced by the inherent properties of the particulates and the resulting second phases, if any. In the case of combined addition, the significant improvement in properties were observed in Mg-(Ti + Cu)BM composite containing ball milled (Ti + Cu) particulates, when compared to direct addition of Ti and Cu particulates. The change in particle morphology, formation of Ti3Cu intermetallic and good interfacial bonding with the matrix achieved due to preprocessing, contributed to its superior strength and ductility, in case of Mg-(Ti + Cu)BM composite. The best combination of hardness, tensile and compressive behavior was exhibited by Mg-(Ti + Cu)BM composite formulation. © 2012 by the authors; licensee MDPI, Basel, Switzerland.Publication Hydrogenation properties of Ni-Nb-Zr-Ta amorphous ribbons(2010-10) Jayalakshmi, S.; Choi, Y.G.; Kim, Y.C.; Kim, Y.B.; Fleury, E.; MECHANICAL ENGINEERINGIn this paper, we present the hydrogenation properties of two compositions of Ni-Nb-Zr-Ta amorphous ribbons. The importance of the alloy composition, particularly the role of Zr, in determining the stability of the structure, hydrogenation kinetics and mechanical properties are brought out. It was observed that the partial replacement of Zr by Nb in the Ni42Nb 28Zr25Ta5 amorphous alloy induced a reduction of the hydrogen absorption kinetics, a larger dilatation of the amorphous structure and a lower value of hydrogen permeability for temperature larger than 450 °C. These properties are interpreted based on the possible occupation sites of hydrogen atoms in structural models recently proposed for these Ni-Nb-Zr-based amorphous alloys. © 2010 Elsevier Ltd. All rights reserved.