Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
16 results
Search Results
Item Development and characteristics of accumulative roll bonded Mg-Zn/Ce/Al hybrid composite(Elsevier Ltd, 2017) Anne, G.; Ramesh, M.R.; Shivananda Nayaka, H.; Arya, S.B.; Sahu, S.Accumulative roll bonding (ARB) process have been used develop Mg-2%Zn/Ce/Al hybrid composite and microstructure, mechanical and corrosion properties were investigated. The electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM) revealed that the grains are significantly reduced and reaches up to 1 ?m in Mg-2%Zn layer and 1.8 ?m in Al layer having high angle misorientation of grain boundaries after subjected to 5-passes of the ARB process. The Al17Mg12, AlMg4Zn11 and Al11Ce3 intermetallic phases were observed through the XRD analysis. Mechanical properties of the hybrid composite improved with increase in the number of ARB passes which is attributed to work hardening, grain refinement and uniform distribution of Ce particles. Presence of Ce in the hybrid composite restricts the phenomenon of dynamic recrystallization and prevents the grain growth during ARB process. The corrosion rate of Mg-Zn/Ce/Al hybrid composite (0.72 mm/y) improved about 3.3 times as compared to that of Mg-2%Zn alloy (2.37 mm/y). © 2017 Elsevier B.V.Item HVOF sprayed Ni3Ti and Ni3Ti+(Cr3C2+20NiCr) coatings: Microstructure, microhardness and oxidation behaviour(Elsevier Ltd, 2018) Reddy, N.C.; Kumar, B.S.A.; Reddappa, H.N.; Ramesh, M.R.; Koppad, P.G.; Kord, S.This paper reports the development of Ni3Ti and Ni3Ti+(Cr3C2+20NiCr) coatings on AISI 420 stainless steel (MDN-420) and titanium alloy ASTM B265 (Ti-15) by HVOF technique. Microstructure, microhardness and high temperature oxidation behaviour of coatings were investigated. Microstructure of coatings was dense and displayed layers depicting lamellar structure. The microhardness of coatings was significantly higher than that of substrate owing to higher density and cohesive strength between individual splats of coating materials. Cyclic oxidation studies conducted on Ni3Ti and Ni3Ti+(Cr3C2+20NiCr) coatings showed oxide scale was composed of various oxides like NiO, NiCr2O4 and Cr2O3 phases. The formation of compact and protective NiO phase in case of Ni3Ti coatings; NiO and Cr2O3 phases in Ni3Ti+(Cr3C2+20NiCr) coatings stabilised the weight gain exhibited slow oxidation rate at higher temperatures. © 2017 Elsevier B.V.Item Microstructure and Adhesion Strength of Ni3Ti Coating Prepared by Mechanical Alloying and HVOF(Pleiades Publishing compmg@maik.ru, 2018) Reddy, N.C.; Ajay Kumar, B.S.; Ramesh, M.R.; Koppad, P.G.In the present work we report the development of Ni3Ti intermetallic compound by high energy ball milling of Ni and Ti powders. The ball milled powders were taken at various intervals (4, 6, 8, 10, and 11 h) to analyze the formation of NixTix intermetallic compounds. The ball milled powders were analyzed using scanning electron microscopy and X-ray diffraction. The layered shaped powder particles of Ni3Ti phase were formed after 11 h of ball milling, which was confirmed by X-ray peaks. Further High-Velocity Oxy-Fuel (HVOF) process was used to coat Ni3Ti and Ni3Ti + (Cr3C2 + 20NiCr) on MDN 420 steel. Both the coated materials displayed excellent cohesion with minimal porosity less than 2%. The tensile adhesion strength test was carried out on these coatings to check the bond strength. Out of the two the Ni3Ti coating showed excellent bond strength of 41.04 MPa compared to that of Ni3Ti + (Cr3C2 + 20NiCr) coating. © 2018, Pleiades Publishing, Ltd.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 Experimental Investigation on Effects of Wire Electro Discharge Machining of Ti50Ni45Co5 Shape Memory Alloys(Springer Netherlands rbk@louisiana.edu, 2018) Soni, H.; Narendranath, S.; Ramesh, M.R.TiNiCo shape memory alloy is most popular shape memory alloy for biomedical applications due to their outstanding properties such as shape memory effect, pseudoelasticity and transformation temperature. Machining of such kind of alloys is very difficult through conventional machining process is very difficult because they may affect their internal properties of these alloys. However conventional machining processes give poor surface quality during the machining hence non-conventional machining processes such as (wire electro discharge machining, water jet machining and electro discharge machining etc.) are more suitable for machining of such kind of alloy. From the literature it has been found that Wire electro discharge machining (WEDM) is more suitable non-conventional machining process for such kind of alloy. Present study exhibits the effects WEDM characteristics of Ti50Ni45Co5 shape memory alloy. L-9 orthogonal array has been created by using Taguchi as a design method for machining of selected alloy and machined surface characterization has been carried out at the optimized process parameters with respect to microstructures, surface topography, microhardness, XRD analysis and residual stresses. To find the optimum setting of the input process parameters a couple of optimization techniques are used, namely principal component analysis (PCA) and Gray relational analysis (GRA) technique. 125?s pulse on time (Ton), 35?s pulse off time (Toff) and 40V servo voltage (SV) were found as an optimal setting for the higher material removal rate (MRR) with better surface roughness (SR) in the present study. Moreover, characterization of the machined surface is performed with respect to microstructures, surface topography, microhardness analysis, XRD and residual stresses. Harder surface observed near the cutting edge and TiNio3 Tio2 and CuZn were noticed on the surface of machined component through XRD analysis. However, compressive residual stress has been noticed on the machined surface during WEDM process. © 2018, Springer Science+Business Media B.V., part of Springer Nature.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 High-temperature wear and frictional behavior of partially oxidized Al with NiCr composite coating(Institute of Physics Publishing helen.craven@iop.org, 2019) Medabalimi, S.R.; Ramesh, M.R.; Kadoli, R.The influence of composite coating in improving wear and frictional behavior from room temperature to 600 °C was investigated. Partially oxidized Al powder was prepared with a flame spray process by spraying pure Al powder into distilled water. The composite powder is the mixture of 30 weight percent of partially oxidized Al and 70 weight percent of NiCr alloy powder. The composite powder was subsequently coated on MDN321 steel by air plasma spray process. The composite coatings are characterized with respect to adhesion strength, porosity, micro-hardness, and density. Wear and frictional behavior of coatings are evaluated under disc speed of 1 and 2 m s-1, loads of 10, 20 and 30 N and 3000 m sliding distance. The test results indicated that at room temperature, frictional heat generated due to applied load produce three-body abrasion at the interface caused to increase the wear and friction in the coating. The oxide film formed at high temperature due to plastic deformation avoids surface degradation at the interface and reduce the wear and friction. The worn surfaces at 600 °C consist phases of ?-Al2O3, NiO, and Cr3O. These phases are contributing to improving the wear resistance of the coating more than 4-times compared to uncoated steels under varying load and sliding velocities. The coefficient of friction reduced with increase in temperature due to generated oxides act as lubricants at the interface. © 2019 IOP Publishing Ltd.Item Influence of Multidirectional Forging on Microstructural, Mechanical, and Corrosion Behavior of Mg-Zn Alloy(Springer New York LLC barbara.b.bertram@gsk.com, 2019) Ramesh, S.; Anne, G.; Shivananda Nayaka, H.S.; Sahu, S.; Ramesh, M.R.Multidirectional forging (MDF) was applied to Mg-6%Zn alloy up to 5 passes successfully at 280 °C. MDF-processed materials were characterized using optical microscope, scanning electron microscope, electron backscatter diffraction, transmission electron microscope, and x-ray diffraction. Obtained results showed a significant reduction in grain size (up to 3.8 ?m) having a large fraction of high-angle grain boundaries after 5 passes of MDF process. Maximum tensile strength of 230 MPa was achieved for 5-pass MDF-processed Mg-6%Zn alloy which is about ~ 2.0 times higher in comparison with that of homogenized alloy (117 MPa) and was attributed to higher dislocations density and grain refinement. Corrosion behavior of the alloy was investigated in 0.1 M NaCl solution using potentiodynamic polarization test, electrochemical impedance spectra analysis, and immersion tests. It was found that the corrosion rate of 5-pass MDF sample improved (0.34 mm/year) ~2.5 times in comparison with that of homogenized Mg-6%Zn alloy (0.86 mm/year) due to fine grain structure, which creates more grain boundaries that act as a corrosion barrier. © 2019, ASM International.Item Hot corrosion behaviour of HVOF sprayed Ni3Ti and Ni3Ti + (Cr3C2 + 20NiCr) coatings in presence of Na2SO4-40%V2O5 at 650 °c(IOP Publishing Ltd custserv@iop.org, 2019) Reddy, N.C.; Koppad, P.G.; Reddappa, H.N.; Ramesh, M.R.; Babu, E.R.; Varol, T.Ni3Ti and Ni3Ti + (Cr3C2 + 20NiCr) coatings were deposited on gas turbine based ASTM B265 titanium (Ti-15) and AISI 420 stainless steel (MDN-420) substrate materials using HVOF technique. Thermocyclic hot corrosion tests were carried out at 650 °C in molten salt environment of Na2SO4-40%V2O5 for about 50 cycles. Thermogravimetric analysis was carried out to study the hot corrosion kinetics of uncoated and coated titanium and stainless steel substrates. The weight gain per unit area showed that the coated substrate materials displayed better resistance to hot corrosion when compared with that of uncoated substrate materials. The surface morphology of uncoated and coated substrate materials were analysed using scanning electron microscopy and elemental analysis. The formation of different types of oxides and compounds were analysed using x-ray diffraction. The uncoated substrates surface showed microspalling at several regions while coated substrates surface were composed of protective oxide layers. The presence of ternary NiCr2O4 protective oxides on the surface of Ni3Ti + (Cr3C2 + 20NiCr) coated substrates leads to reduction in the diffusion of corrosive species inside the coating. © 2019 IOP Publishing Ltd.Item Effect of microwave heating on microstructure and elevated temperature adhesive wear behavior of HVOF deposited CoMoCrSi-Cr3C2 coating(Elsevier B.V., 2019) Prasad, C.D.; Joladarashi, S.; Ramesh, M.R.; Srinath, M.S.; Channabasappa, B.H.This research reports the improvement of high-temperature sliding wear resistance of a grade 15 titanium alloy protected by an HVOF sprayed CoMoCrSi-Cr3C2 coating. The coatings have been tested in as-sprayed condition and after a post-deposition microwave heating step. The powder feedstock has been manufactured by high energy ball milling. X-ray diffraction (XRD) and Scanning Electron Microscopy (SEM) equipped with the Energy Dispersive Spectroscopy (EDS) methods were used for coatings characterization. Surface roughness, microhardness, adhesion strength, and porosity of coatings were also measured. The wear test was conducted at an applied load of l0 N and 20 N with varying temperatures of 200 °C, 400 °C, and 600 °C under dry sliding conditions. Co3Mo2Si, Co7Mo6, Mo3Si, Co3Mo, and Co2Mo3 were the intermetallic laves phases generated in the CoMoCrSi feedstock during HEBM process. The microwave-fused coating exhibited metallurgical bonding, homogeneous structure, less porosity, and greater hardness as compared to as-sprayed coating. Microwave-treated coating revealed better wear property than an as-sprayed coating. This was mainly due to the intermetallic formation and metallurgical bonding in coatings. The fused coatings exhibit tribo-oxide layers during sliding action which was the main phenomenon of improving the wear resistance of the fused composite coatings. © 2019 Elsevier B.V.