Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
11 results
Search Results
Item Combined effect of marine environment and pH on the impedance of reinforced concrete studied by electrochemical impedance spectroscopy(Springer, 2019) Goudar, S.K.; Das, B.B.; Arya, S.In the present investigation, behavior of OPC and fly ash based concretes were assessed by electrochemical impedance spectroscopy (EIS) technique after exposing the samples to the marine environment in combination with five pH levels (1, 4, 7, 10, and 13). Three different dosages of fly ash (15, 25, and 35%) were used to produce fly ash based concretes. After 90 days of exposure to the aggressive environment, the OPC and fly ash based concretes were tested for impedance analysis and corrosion resistance by electrochemical studies. For the equivalent electrical circuit in EIS study, a total of four electrical circuits were tried for the possible best fit of obtained Nyquist plots. The equivalent electrical circuits proposed by previous researchers failed to provide the best fit for the obtained Nyquist plots. A new equivalent electrical circuit is being proposed in this study which will provide the possible best fit of Nyquist plots when the concrete is being exposed to acidic and alkaline marine environment. It is observed that the pH of the marine environment has a decisive influence on the impedance of reinforced concrete. As the acidity of marine environment reduces to pH 1, the impedance of OPC and fly ash based concrete reduced significantly due to the severe deterioration of concrete composites especially because of acid attack and Cl− ions migration. However, in the case of alkaline nature of the marine environment (pH 13), there was comparably less deterioration of concrete composites which reflected in higher impedance values. The higher dosage of fly ash addition has led to substantial improvement in concrete impedance and also lower corrosion rate. © Springer Nature Singapore Pte Ltd. 2019.Item Hot corrosion resistance of air plasma sprayed ceramic Sm2SrAl2O7 (SSA) thermal barrier coatings in simulated gas turbine environments(Elsevier Ltd, 2018) Baskaran, T.; Arya, S.Samarium strontium aluminate (Sm2SrAl2O7-SSA) and Yttria-stabilized zirconia (YSZ) thermal barrier coatings (TBCs) were developed on NiCrAlY bond coated Inconel 718 superalloy substrate using air plasma spray process. The hot corrosion study was conducted in simulated gas turbine environments (molten mixtures of 50 wt% Na2SO4 + 50 wt% V2O5 and 90 wt% Na2SO4 + 5 wt% V2O5 + 5 wt% NaCl) for two different temperatures of 700 and 900 °C. A developed SSA TBCs showed about 8% and 22% lower lifetime at 700 and 900 °C, respectively than YSZ TBCs in 50 wt% Na2SO4 + 50 wt% V2O5 (vanadate). The hot corrosion life of SSA TBCs being found about 13% and 39% lower than YSZ TBCs in 90 wt% Na2SO4 + 5 wt% V2O5 + 5 wt% NaCl (chloride) at 700 and 900 °C, respectively. X-ray diffraction results showed the formation of SmVO4, SrV2O6, and SrSO4 as a major hot corrosion product in 50 wt% Na2SO4 + 50 wt% V2O5 and 90 wt% Na2SO4 + 5 wt% V2O5 + 5 wt% NaCl environments respectively for SSA TBCs. Similarly, YSZ TBCs also showed YVO4 as hot corrosion product in vanadate and chloride environments. Both the TBCs suffer a more severe hot corrosion attack in chloride environment at 900 °C. The leaching of Sr2+ and Y3+ ions from SSA and YSZ respectively play a vital role in the destabilization of coating in vanadate and chloride environments at 700 and 900 °C. In both SSA and YSZ TBCs, the leaching of ion has significantly low influence as compared to attack by chloride ions at the bond coat-top coat interface in the presence of chloride environment. The hot corrosion resistance of SSA TBCs was improved three times higher in the presence of MgO and NiO inhibitor in vanadate environment at 900 °C mainly due to the formation of a stable Ni3V2O8 phase at the surface. © 2018 Elsevier Ltd and Techna Group S.r.l.Item Effect of zinc and rare-earth element addition on mechanical, corrosion, and biological properties of magnesium(Cambridge University Press, 2018) Kottuparambil, R.R.; Bontha, S.; Ramesh, M.R.; Arya, S.; Jana, A.; Das, M.; Balla, V.K.; Amrithalingam, S.; Prabhu, T.R.The present work aims to understand the effect of zinc and rare-earth element addition (i.e., 2 wt% Gd, 2 wt% Dy, and 2 wt% of Gd and Nd individually) on the microstructure evolution, mechanical properties, in vitro corrosion behavior, and cytotoxicity of Mg for biomedical application. The microstructure results indicate that the Mg-Zn-Gd alloy consists of the lamellar long period stacking ordered phase. The electrochemical and immersion corrosion behavior were studied in Hanks balanced salt solution. Enhanced corrosion resistance with reduced hydrogen evolution volume and magnesium (Mg2+) ion release were estimated for the Mg-Zn-Gd alloy as compared to the other two alloy systems. At the early stage of corrosion, formation of the oxide film inhibited the corrosion propagation. However, at the later stages, the breaking of the oxide film leads to shallow pitting mode of corrosion. The ultimate tensile strength of Mg-Zn-Gd-Nd is better than the other two alloys due to the uniform distribution of the Mg12Nd precipitate phase. The moderate strength in the Mg-Zn-Gd alloy is due to the low volume fraction of the secondary phase. The MTT (methylthiazoldiphenyl-tetrazolium bromide) assay study was carried out to understand the cell cytotoxicity on the alloy surfaces. Studies revealed that all three alloys had significant cellular adherence and no adverse effect on cells. © 2018 Materials Research Society.Item On the corrosion resistance of some selective laser melted alloys(Elsevier B.V., 2018) Suryawanshi, J.; Baskaran, T.; Prakash, O.; Arya, S.; Ramamurty, U.The electrochemical corrosion resistances of selective laser melted (SLM) 316 L austenitic stainless steel (SS), 18(Ni) 300-grade maraging steel (MS), and Al-12 wt.% Si (AS) alloy in a 0.1 M NaCl solution at room temperature were evaluated. The effects of laser scanning strategy (single melt vs. checker board styles), post-SLM heat treatment, and corroding surface orientation (with respect to the scan and build directions) on the corrosion behavior were examined. In all cases, results were compared with those obtained on samples with the same compositions, but manufactured using conventional means. The experimental results show that, for the particular set of experimental conditions employed in this study, SLM in general improves the corrosion resistances of Al-12 wt.% Si and stainless steel alloys and degrades the corrosion resistance of the maraging steel, in comparison to the respective corrosion resistances of their conventionally manufactured counterparts. These results are discussed in terms of microstructural refinement and porosity that are common to the SLM alloys. © 2018 Acta Materialia Inc.Item Crosslinked polymer doped binary coatings for corrosion protection(Elsevier B.V., 2018) Kaur, H.; Sharma, J.; Jindal, D.; Arya, R.K.; Ahuja, S.K.; Arya, S.Solvent-based polymeric multilayer coatings prepared by ex-situ addition of crosslinked poly(styrene-co-divinyl benzene) in poly(styrene)-ethylbenzene solution were examined for corrosion protection of mild steel in a simulated water environment equivalent to sea water and acid rain. Electrochemical impedance spectroscopy (EIS) technique was used to determine the corrosion resistance behavior of the prepared polymeric coatings in 3.5 wt % of NaCl aqueous solution. EIS analysis suggested that the sample solution prepared by adding 1% crosslinked polymer in poly(styrene)-ethylbenzene solution, has better corrosion resistance as compared to the sample solutions prepared by adding 3% and 2% of crosslinked polymer in poly(styrene)-ethylbenzene solutions. Scanning electron microscopy (SEM) revealed that substrate coated with polymeric solution prepared by adding 1% of crosslinked polymer in poly(styrene)-ethyl benzene solution showed less corrosion as compared to the substrates coated with sample solutions prepared by adding 3% and 2% of crosslinked polymer in poly(styrene)-ethylbenzene solutions. © 2018 Elsevier B.V.Item Laser surface modification of Mg-Zn-Gd alloy: Microstructural, wettability and in vitro degradation aspects(Institute of Physics Publishing helen.craven@iop.org, 2018) Rakesh, K.R.; Bontha, S.; Ramesh, M.R.; Arya, S.; Das, M.; Balla, V.K.; Srinivasan, A.Mg-Zn-Gd have great potential for biomedical applications owing to excellent bioactivity and non-toxicity properties. In the present study, laser surface melting (LSM) was carried out on newly developed Mg-1Zn -2Gd (wt%) alloy. Effects of laser energy on microstructural evolution, corrosion properties, surface energy, and hardness have been investigated. The surface modified sample processed at different energy densities showed fine grain structure in the melt zone compared to the untreated substrate. Grain refinement in the laser melted region improved the hardness by 60%. The surface roughness was found to be increased with increasing laser energy density. At higher energy density, removal of materials from the surface is enhanced, resulting in deeper grooves and higher surface roughness. The wettability studies indicated that the variations in surface geometry, grain size and surface roughness of LSM samples strongly influence the surface energy and hydrophilicity. Improved wetting of LSM sample was achieved owing to grain refinement and low surface roughness. The corrosion resistance determined by immersion and electrochemical methods of laser melted sample in Hank's balanced salt solution improved considerably due to grain refinement, meltpool depth and uniform distribution of secondary phases. © 2018 IOP Publishing Ltd.Item Effects of combined multiaxial forging and rolling process on microstructure, mechanical properties and corrosion behavior of a Cu-Ti alloys(Institute of Physics Publishing helen.craven@iop.org, 2019) Ramesh, S.; Anne, G.; Shivananda Nayaka, H.; Sahu, S.; Arya, S.Combined multiaxial forging (MAF) and rolling was performed on Cu-3% Ti (wt%) alloy at room temperature with emphasis on microstructural evolution, improvement in mechanical properties, and corrosion resistance. Microstructural changes were confirmed from various characterization techniques, and co-related with mechanical properties. TEM analysis revealed high shear band density in the 3 pass MAF + 90% rolled sample appearing due to high strain. EBSD analysis revealed transformation to low angle grain boundaries from high angle grain boundaries. Maximum microhardness and UTS reached to 340 HV and 960 MPa, respectively in the processed samples. Significant grain refinement was observed in MAF processed Cu-3%Ti alloy, and after combined MAF + rolling, higher dislocation density and refinement of shear bands were observed. In addition, potentio-dynamic polarization test was used to study the corrosion behavior of the alloy. Scanning electron microscope (SEM) was used to analyze the corroded surface morphology. © 2019 IOP Publishing Ltd.Item Optimization of ball-burnishing process parameters on surface roughness, micro hardness of Mg-Zn-Ca alloy and investigation of corrosion behavior(Institute of Physics Publishing helen.craven@iop.org, 2019) Ramesh, S.; Aditya Kudva, S.; Anne, G.; Manne, B.; Arya, S.In this work, optimization of ball burnishing parameters (depth of press, feed, burnishing force, number of passes) and their effect on surface roughness, microhardness and corrosion behavior of Mg-4%Zn-1%Ca alloy is investigated. The Taguchi optimization technique was used to determine the number of experiments and by considering S/N ratios, right combination of ball burnishing parameters were selected. Results obtained from the experiments were investigated and it is understood that depth of press, feed and number of passes have a significant effect on surface roughness, microhardness and consequently improves corrosion resistance of Mg-4%Zn-1%Ca alloy. From ball burnishing experiments it is deduced that there is large increase in microhardness of 107 Hv and surface roughness of 129 nm, achieved for the depth of press 0.45 mm, burnishing force 250 N, feed 450 mm min-1 and number of passes: 2. Corrosion behavior of the alloys were analyzed using potentiodynamic polarization and electrochemical impedance spectroscopy techniques in Hank's balanced salt solution. The lowest corrosion rate was observed in DFN 442 sample (1.43 mm y-1) which is 4.7 times better than the homogenized alloy (6.73 mm y-1). It has been found that the ball burnishing plays an important role on surface roughness, microhardness and corrosion behavior of Mg-4%Zn-1%Ca alloy. © 2019 IOP Publishing Ltd.Item Influence of Multiaxial Cryoforging on Microstructural, Mechanical, and Corrosion Properties of Copper-Titanium Alloy(Springer, 2019) Ramesh, S.; Shivananda Nayaka, H.S.; Sahu, S.; Gopi, K.R.; Shivaram, M.J.; Arya, S.Multiaxial forging (MAF) was used to process Cu-4.5%Ti (wt.%) alloy at cryogenic temperature up to three cycles with a cumulative strain of 1.64. Microstructures, mechanical, and corrosion properties of as-received and deformed samples were analyzed. Microstructural analysis showed that average grain size decreased from 70 µm to 200 nm, and electron backscattered diffraction (EBSD) analysis revealed the transformation of high-angle grain boundaries (HAGBs) to low-angle grain boundaries (LAGBs). Variations in intensity of peaks were observed by x-ray diffraction (XRD) technique. Microstructural investigation showed elongated grains with shear bands having width ~ 200 nm for 3-cycle sample. Tensile testing and micro-hardness tests showed improvements in ultimate tensile strength (UTS), yield strength (YS), and micro-hardness, with the increase in MAF cycles. Ultimate tensile strength and hardness increased from 605 MPa and 252 HV (for as-received) to 1284 MPa and 428 HV for three cycles of MAF-processed sample, respectively. Improvement in strength and hardness was attributed to refined grain structure. Corrosion study was carried out for different cycles of MAF-processed samples using potentiodynamic polarization, and corroded surfaces were analyzed using scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) analysis. © 2019, ASM International.Item Corrosion Studies of Hf64Cu18Ni18 Metallic Glass in Acidic and Alkaline Media(Springer, 2021) Khond, A.; Arya, S.; Majumdar, B.; Bhatt, J.; Srivastav, A.K.In the present paper, the corrosion behavior of Hf-rich Hf64Cu18Ni18 (at%) metallic glass (MG) was studied in acidic and alkaline media using electrochemical polarization experiments. Three different molar solutions of NaOH and HCl were used for the experiments. The results show that the glassy alloy possesses significantly high corrosion resistance in alkaline solution than acidic one. Pits are observed on the sample in acidic media, whereas alkaline sample does not show pitting. In both the solutions, primarily, HfO2 is formed on the surface as a corrosion product. The corroded surface is non-uniformly distributed on the ribbon and found to decrease with concentration of NaOH. The non-uniform distribution is attributed to inhomogeneity in the ribbon sample. In case of HCl solution, corroded surface increases with the increase in HCl concentration. Furthermore, an attempt has been made to understand the corrosion mechanism of this MG in view of phases formed during the experiment. © 2021, The Indian Institute of Metals - IIM.