R. Jayaganthan

Bio: R. Jayaganthan is an academic researcher from Indian Institute of Technology Madras. The author has contributed to research in topics: Surface roughness & Ultimate tensile strength. The author has an hindex of 4, co-authored 6 publications receiving 31 citations.

Effect of multiaxial forging followed by hot rolling on non-basal planes and its influence on tensile and fracture toughness behaviour of Mg–4Zn–4Gd alloy

Abstract: Large true strain (up to ~ 4.7) through hybrid severe plastic deformation (HSPD) technique was imparted to Mg–4Zn–4Gd alloy, to study its influence on microstructural evolution, fracture toughness and tensile properties in the present work. The tensile and fracture toughness of processed Mg alloy were compared with solutionized bulk Mg alloy. The tensile properties are found to be superior in multiaxially forged followed by repetitive rolled specimen at 723 K compared to ST sample. The key strengthening mechanisms such as microstructural bimodality, coherency of the twin boundaries, and precipitation are characterized in detail, to elucidate the enhancement in hardness ( ~ 61 % ) , tensile ( ~ 62 % ) , yield ( ~ 42 % ) and elastic-plastic fracture toughness ( ~ 40 % ) properties. These improvements are observed in the optimised thermo-mechanically processed condition “6 pass hot forged followed by 75% repetitive hot rolled (6PF-75R) specimen”. However, high dislocation density observed in 6PF-75R specimen leads to lower the ductility compared to other HSPDed conditions but still found higher than that of the solutionized specimens. The fracture phenomena were also explored through post-deformation processed samples through scanning electron microscopy based fractograph to understand the response of different processed specimens using tension and fracture tests. Various microstructural features such as microshear bands, nano-twinning, slip clusters and especially the effect of continuous dynamic recrystallization upon varying true strain are examined by using high-resolution transmission electron microscopy (HR-TEM) and low angle annular dark field scanning transmission electron microscopy (LAADF-STEM) techniques. Correlation of these features with tensile and fracture behaviour are made with the support of light microscopy and X-ray diffraction techniques.

Understanding the dielectric and mechanical properties of self-passivated Al–epoxy nanocomposites

Abstract: Epoxy nano passivated aluminium composites with optimised size and filler contents were fabricated. Variation in contact angle and surface roughness is insignificant with increasing filler into nanocomposites but it showed a drastic reduction on corona ageing. Water droplet initiated corona inception voltage (CIV) is high under the negative DC voltage followed with positive DC and AC voltages. The bandwidth of ultra-high frequency signal generated due to water droplet initiated corona discharge lies in the range of 0.5–1.2 GHz. Surface potential measurements have shown that the decay in the potential was fast initially, and it became slower and sluggish subsequently. The trap energy density versus trap depth plot exhibits shallow traps and deep traps at around 0.8 and 0.87 eV, respectively. Permittivity, conductivity and loss factor have increased with an increase in the filler content in nanocomposites. The bulk resistance and capacitance of samples were determined for obtaining the equivalent parallel RC circuit model. Incorporation of nanofillers increases the glass transition temperature and reduces the tan δ with increasing frequencies as evident from dynamic mechanical analysis studies. A direct correlation is observed between the plasma temperature measured through laser-induced breakdown spectroscopy spectra and hardness of the material.

Investigation and measurement of porosity in Al + 4.5Cu/6wt%TiB2 in situ composite: optimization and statistical modelling

Abstract: Present work investigates the adequacy of stir casting technique using mixed salt route method to fabricate in situ Al-4.5Cu-6wt%TiB2 composites and further the variation of porosity present in cast composite with varying pouring temperature, pouring time and different types of gating systems. The casting was found to be effective and economical for top gating system amongst rest of the gating design. The microstructural analysis of cast composite was carried out to determine the physical morphology and distribution of the TiB2 and Al2Cu phases in the matrix with the help of scanning electron microscopy (SEM). X-ray diffraction (XRD) analysis of cast composite shows the formation of TiB2 particles in the absence of intermetallic, hard and brittle compound Al3Ti. Microstructural characterization was tandem with optical and high-resolution transmission electron microscopy (HR-TEM) results. These castings were checked for surface defects or sub-surface cracks using dye penetrant and ultrasound test. The amount of porosities present in all the castings was then determine precisely using Archimedes’ Principle of buoyancy. The experimental results thus found were validated with the simulation results obtained by AutoCAST simulation tool and improvements were incorporated by optimization of gating systems using modelling and simulation technique.

Effect of multiaxial forging followed by hot rolling on non-basal planes and its influence on tensile and fracture toughness behaviour of Mg–4Zn–4Gd alloy

Abstract: Large true strain (up to ~ 4.7) through hybrid severe plastic deformation (HSPD) technique was imparted to Mg–4Zn–4Gd alloy, to study its influence on microstructural evolution, fracture toughness and tensile properties in the present work. The tensile and fracture toughness of processed Mg alloy were compared with solutionized bulk Mg alloy. The tensile properties are found to be superior in multiaxially forged followed by repetitive rolled specimen at 723 K compared to ST sample. The key strengthening mechanisms such as microstructural bimodality, coherency of the twin boundaries, and precipitation are characterized in detail, to elucidate the enhancement in hardness ( ~ 61 % ) , tensile ( ~ 62 % ) , yield ( ~ 42 % ) and elastic-plastic fracture toughness ( ~ 40 % ) properties. These improvements are observed in the optimised thermo-mechanically processed condition “6 pass hot forged followed by 75% repetitive hot rolled (6PF-75R) specimen”. However, high dislocation density observed in 6PF-75R specimen leads to lower the ductility compared to other HSPDed conditions but still found higher than that of the solutionized specimens. The fracture phenomena were also explored through post-deformation processed samples through scanning electron microscopy based fractograph to understand the response of different processed specimens using tension and fracture tests. Various microstructural features such as microshear bands, nano-twinning, slip clusters and especially the effect of continuous dynamic recrystallization upon varying true strain are examined by using high-resolution transmission electron microscopy (HR-TEM) and low angle annular dark field scanning transmission electron microscopy (LAADF-STEM) techniques. Correlation of these features with tensile and fracture behaviour are made with the support of light microscopy and X-ray diffraction techniques.

Investigation on space charge and charge trap characteristics of Al–epoxy nanocomposites

Abstract: Optimised quantity of nano-aluminium (Al) filler mixed with epoxy resin using percolation threshold criteria was adapted to fabricate nanocomposite with desired space-charge and charge-trap properties. Surface potential variation due to charge deposition on to the insulating material under transient voltages was investigated, and it showed the improved decay rate with reduced trap depth for the nanocomposites with nanofillers addition in the range between 0.5 and 5 wt%. Threshold electric field calculated based on space-charge density variation by pulsed electroacoustic measurement was found to be between 7–9 kV/mm and maximum electric field calculated through polarity reversal test is about 9 kV/mm, for 5 wt% (for the optimised value of nanofiller) epoxy nano-Al composites.