Sokkalingam Rathinavelu
@kau.se
Associate Senior Lecturer (Assistant Professor)
Karlstad University
RESEARCH, TEACHING, or OTHER INTERESTS
Engineering, Industrial and Manufacturing Engineering, Mechanical Engineering, Mechanics of Materials
Scopus Publications
Scopus Publications
Riddhi Shukla, R. Sokkalingam, and K.G. Prashanth
Elsevier BV
Rathinavelu Sokkalingam, Zhao Chao, Katakam Sivaprasad, Veerappan Muthupandi, Jayamani Jayaraj, Parthiban Ramasamy, Jürgen Eckert, and Konda Gokuldoss Prashanth
Wiley
CoCrFeMnNi high‐entropy alloy (HEA)/AISI 316L stainless steel bimetals were additively fabricated using selective laser melting (SLM). The bimetal structure comprises three regions, i.e., CoCrFeMnNi‐HEA, AISI 316L stainless steel, and an interface between CoCrFeMnNi‐HEA, AISI 316L stainless steel. SLM processing results in the formation of columnar grains extending over many built layers epitaxially in a preferential <100> growth direction. The Vickers microhardness ranges mainly between 250 and 275 HV0.5 in all three observed regions. In addition, only a marginal variation in tensile strength is observed between the CoCrFeMnNi‐HEA, AISI 316L stainless steel, and the CoCrFeMnNi‐HEA/AISI 316L stainless steel bimetal. The unique higher work hardening behavior of the CoCrFeMnNi‐HEA prevents failure along the CoCrFeMnNi‐HEA side in the bimetallic structure during plastic deformation. The CoCrFeMnNi‐HEA shows higher pitting susceptibility than the AISI 316L stainless steel in the bimetallic structure due to its lower pitting potential. Further, the presence of pores and lack of fusion spots further decreases the pitting resistance of the CoCrFeMnNi‐HEA. Hence, the bimetal is prone to more preferential corrosion attack along the CoCrFeMnNi‐HEA side due to its anodic behavior and defects.
N. Singh, Raghunandan Ummethala, Kumar Babu Surreddi, J. Jayaraj, Rathinavelu Sokkalingam, Monika Rajput, Kaushik Chatterjee, and K.G. Prashanth
Elsevier BV
R. Sokkalingam, K. Sivaprasad, N. Singh, V. Muthupandi, P. Ma, Y. D. Jia, and K. G. Prashanth
Springer Science and Business Media LLC
R. Sokkalingam, B. Pravallika, K. Sivaprasad, V. Muthupandi, and K. G. Prashanth
Springer Science and Business Media LLC
AbstractHigh-entropy alloy, a new generation material, exhibits superior structural properties. For high-temperature applications, where dissimilar materials are in demand, HEAs may be joined with commercially available structural materials to improve their performance-life ratio. In this connection, a dissimilar joint was fabricated by gas tungsten arc welding between Al0.1CoCrFeNi-HEA and Inconel 718. The columnar dendritic grains are growing epitaxially at the Al0.1CoCrFeNi-HEA/weld metal interface, where their compositions are matching. While the composition misfit at the weld metal/Inconel 718 interface, reveals the non-epitaxial mode of solidification. In addition, the fusion zone exhibits the porosity and micro-segregation of NbC and Laves phases. The joint shows a joint efficiency of ~ 88%, where the strength is observed to be 644 MPa with 21% ductility. The results demonstrate the applicability of GTAW in fabricating the dissimilar weld joints between HEA and Inconel 718 for structural applications. Graphic abstract
Raghunandan Ummethala, J. Jayaraj, Phani S. Karamched, Sokkalingam Rathinavelu, Neera Singh, Kumar Babu Surreddi, and K. G. Prashanth
Springer Science and Business Media LLC
Rathinavelu Sokkalingam, Marek Tarraste, Kumar Babu Surreddi, Rainer Traksmaa, Veerappan Muthupandi, Katakam Sivaprasad, and Konda Gokuldoss Prashanth
Hindawi Limited
Abstract Al0.1CoCrFeNi-high entropy alloy (HEA) /tungsten carbide (WC)metal matrix composite was successfully prepared by mechanical alloying and subsequent spark plasma sintering. The different vo ...
Neera Singh, Raghunandan Ummethala, Phani Shashanka Karamched, Rathinavelu Sokkalingam, Vasanth Gopal, G. Manivasagam, and Konda Gokuldoss Prashanth
Elsevier BV
R. Sokkalingam, P. Mastanaiah, V. Muthupandi, K. Sivaprasad, and K. G. Prashanth
Informa UK Limited
ABSTRACT An autogenously dissimilar Al0.1CoCrFeNi-high entropy alloy/stainless steel (i.e., AISI 304) weld joint was produced by an electron-beam welding technique. The weld metal followed mode A of solidification and resulted in a fully austenitic columnar dendritic microstructure due to rapid cooling and lower chromium equivalent to nickel equivalent (Creq/Nieq) ratio (1.12–1.14). Tensile test sample fractures at the base metal (Al0.1CoCrFeNi-high entropy alloy) and illustrates higher strength (the yield and ultimate strength of 310 ± 10 MPa and 560 ± 15 MPa, respectively) than that of Al0.1CoCrFeNi-high entropy alloy, ensuring the suitability of the electron-beam welding for the Al0.1CoCrFeNi-high entropy alloy/AISI 304 stainless steel joint structures designed with respect to Al0.1CoCrFeNi-HEA properties. The influence of the manufacturing process (electron beam welding) is highlighted in terms of microstructure and mechanical properties.
Raghunandan Ummethala, Phani S. Karamched, Sokkalingam Rathinavelu, Neera Singh, Akash Aggarwal, Kang Sun, Eugene Ivanov, Lauri Kollo, Ilya Okulov, Jürgen Eckert,et al.
Elsevier BV
Rathinavelu Sokkalingam, Marek Tarraste, Kumar Babu Surreddi, Valdek Mikli, Veerappan Muthupandi, Katakam Sivaprasad, and Konda Gokuldoss Prashanth
Springer Science and Business Media LLC
Al_0.1CoCrFeNi high-entropy alloy (HEA) was synthesized successfully from elemental powders by mechanical alloying (MA) and subsequent consolidation by spark plasma sintering (SPS). The alloying behavior, microstructure, and mechanical properties of the HEA were assessed using X-ray diffraction, electron microscope, hardness, and compression tests. MA of the elemental powders for 8 h has resulted in a two-phased microstructure: α-fcc and β-bcc phases. On the other hand, the consolidated bulk Al_0.1CoCrFeNi-HEA sample reveals the presence of α-fcc and Cr_23C_6 phases. The metastable β-bcc transforms into a stable α-fcc during the SPS process due to the supply of thermal energy. The hardness of the consolidated bulk HEA samples is found to be 370 ± 50 HV_0.5, and the yield and ultimate compressive strengths are found to be 1420 and 1600 MPa, respectively. Such high strength in the Al_0.1CoCrFeNi HEA is attributed to the grain refinement strengthening.
Neera Singh, Raghunandan Ummethala, Pearlin Hameed, Rathinavelu Sokkalingam, and Konda Gokuldoss Prashanth
Hindawi Limited
P. V. Satyanarayana, B. Blessto, R. Sokkalingam, C. Rambabu, and K. Sivaprasad
Springer Science and Business Media LLC
R. Sokkalingam, K. Sivaprasad, M. Duraiselvam, V. Muthupandi, and K.G. Prashanth
Elsevier BV
P. V. Satyanarayana, R. Sokkalingam, P. K. Jena, K. Sivaprasad, and K. G. Prashanth
MDPI AG
Tungsten heavy alloy composite was developed by using novel CoCrFeMnNi high-entropy alloy as the binder/reinforcement phase. Elemental tungsten (W) powder and mechanically alloyed CoCrFeMnNi high-entropy alloy were mixed gently in high energy ball mill and consolidated using different sintering process with varying heating rate (in trend of conventional sintering < microwave sintering < spark plasma sintering). Mechanically alloyed CoCrFeMnNi high-entropy alloy have shown a predominant face-centered cubic (fcc) phase with minor Cr-rich σ-phase. Consolidated tungsten heavy high-entropy alloys (WHHEA) composites reveal the presence of Cr–Mn-rich oxide phase in addition to W-grains and high-entropy alloys (HEA) phase. An increase in heating rate restricts the tungsten grain growth with reduces the volume fraction of the Cr–Mn-rich phase. Finally, spark plasma sintering with a higher heating rate and shorter sintering time has revealed higher compressive strength (~2041 MPa) than the other two competitors (microwave sintering: ~1962 MPa and conventional sintering: ~1758 MPa), which may be attributed to finer W-grains and reduced fraction of Cr–Mn rich oxide phase.
Rathinavelu Sokkalingam, Veerappan Muthupandi, Katakam Sivaprasad, and Konda Gokuldoss Prashanth
Springer Science and Business Media LLC
High-entropy alloys (HEAs) have been proven to exhibit superior structural properties from cryogenic to high temperatures, demonstrating their structural stability against the formation of complex intermetallic phases or compounds as major fractions. These characteristics can find applications in nuclear and aerospace sectors as structural materials. As the dissimilar joint design is necessary for such applications, an attempt is made to fabricate the dissimilar transition joint between Al_0.1CoCrFeNi-HEA and AISI304 austenitic stainless steel by conventional tungsten inert gas welding. Microstructural characterization by SEM and EBSD clearly revealed the evolution of columnar dendritic structures from the interfaces and their transformation to equiaxed dendritic grains as they reach the weld center. Also, considerable grain coarsening was observed in the heat-affected zone of the HEA. The tensile test results depict that the dissimilar weld joint showed significantly higher tensile strength (590 MPa) than the HEA (327 MPa), making it suitable for structural applications.
Shikai Zhang, Pan Ma, Yandong Jia, Zhishui Yu, Rathinavelu Sokkalingam, Xuerong Shi, Pengcheng Ji, Juergen Eckert, and Konda Gokuldoss Prashanth
MDPI AG
In this study, a combination of Al–12Si and Al–20Si (Al–(12-20)Si) alloys was fabricated by selective laser melting (SLM) as a result of increased component requirements such as geometrical complexity and high dimensional accuracy. The microstructure and mechanical properties of the SLM Al–(12-20)Si in as-produced as well as in heat-treated conditions were investigated. The Al–(12-20)Si interface was in the as-built condition and it gradually became blurry until it disappeared after heat treatment at 673 K for 6 h. This Al–(12-20)Si bi-material displayed excellent mechanical properties. The hardness of the Al–20Si alloy side was significantly higher than that of the Al–12Si alloy side and the disparity between both sides gradually decreased and tended to be consistent after heat treatment at 673 K for 6 h. The tensile strength and elongation of the Al–(12-20Si) bi-material lies in between the Al–12Si and Al–20Si alloys and fracture occurs in the Al–20Si side. The present results provide new insights into the fabrication of bi-materials using SLM.
M.P. Shankar, R. Sokkalingam, Katakam Sivaprasad, and V. Muthupandi
Trans Tech Publications, Ltd.
AA2014 is a heat treatable aluminium alloy found its application in light weight structures owing to its superior strength to weight ratio. The alloy was welded with automatic gas tungsten arc welding. The microstructure and mechanical properties of each zone such as parent metal (PM), heat affected zone (HAZ) and fusion zone (FZ) of the weldment were studied using optical microscopy, microhardness survey and micro-tensile testing. The PM with elongated grains with evenly distributed Al2Cu phases showed a tensile strength of 456 MPa and 24% elongation; the HAZ and FZ offered a reduction in strength and ductility. The grain coarsening with segregation of continuous string of Al2Cu along grain boundaries in HAZ and the formation of coarse dendritic grains with continuous network of brittle Al2Cu and a minor fraction of porosity at interdendrite in FZ were attribured to the observed strength reduction in these regions. Keywords: AA2014 alloy; gas tungsten arc welding; optical microscopy; microhardness; micro-tensile testing.
M.P. Shankar, R. Sokkalingam, Bhavani Kosuri, Katakam Sivaprasad, and V. Muthupandi
Trans Tech Publications, Ltd.
The microstructure and corrosion properties of weld fusion zone and the heat affected zones of gas tungsten arc (GTA) welded AA2014 alloy, welded at varying speeds of 1.5mm/s, 2.5 mm/s and 3.5 mm/s were examined for gaining knowledge on the effect of welding speed on corrosion behavior at localized regions of the weldment. The macrostructure and microstructure of the welds were evaluated with optical microscope. The corrosion properties were examined with potentiodynamic polarization in aqueous 3.5% NaCl solution. The GTA welding has resulted in grain refinement fusion zone and dispersion of coarse Al2Cu phases within the grains and along the grain boundaries of heat affected zones. With increase in welding speed the grain size of AA2014 at the fusion zone reduces significantly and also the corrosion resistance of the fusion zone and heat affected zone could decrease as it shows higher negative corrosion potential.
R. Sokkalingam, K. Sivaprasad, V. Muthupandi, and Muthukannan Duraiselvam
Trans Tech Publications, Ltd.
High-entropy alloys (HEA), a new generation alloy system offer superior mechanical properties with solid solution strengthening. AlxCoCrFeNi-HEA is one such system being received more attention because of its specific yield strength and ductility. In the present work, Al0.5CoCrFeNi-HEA was prepared by vacuum arc melting. The laser beam welding (LBW) was carried out on 1mm thick forged and homogenized HEA, with a beam power of 1.5 kW and at a traverse speed of 600 mm/min. The microstructural features of different regions of the weld were studied using scanning electron microscopy. The homogenized Al0.5CoCrFeNi-HEA have shown equiaxed grains of average size 60 μm. The weld metal showed a typical weld fusion zone microstructure with dendritic structure with a reduction in BCC phase due to minimal Al and Ni segregation ratio at interdendrites. Micro-chemical analysis with energy dispersive spectroscopy confirmed that there was no major segregation of elements in the weld fusion zone. The microhardness survey performed across the weld evidenced a reduction in hardness, as a consequence of significant reduction in Al-Ni rich hardening factor.
R. Sokkalingam, Sourav Mishra, Srinivasa Rakesh Cheethirala, V. Muthupandi, and K. Sivaprasad
Springer Science and Business Media LLC
P.V. Satyanarayana, R. Sokkalingam, K. Sivaprasad, and A.K. Mukherjee
Trans Tech Publications, Ltd.
Tungsten heavy alloy of two different compositions (93W-4.0Ni-2.0Co-1.0Fe and 90W-6.1Ni-3.0Fe-0.5Co-0.4Mo in wt%) was synthesized in conventional powder metallurgy route through the liquid phase sintering. Studies have been carried out on the effect of alloying elements, tungsten particle size, and amount of matrix on mechanical properties. The alloy with 93% W had shown the higher tensile strength value and lower elongation along with double the value of impact energy than that of 90% W due to lower tungsten particle size and weight fraction in addition to an increase in cobalt and increase in ratio of iron to nickel. Relatively higher porosity could also have resulted in reduced properties.