Faculty Publications
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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 Microstructure and tribological characteristics of APS sprayed NiCrBSi/flyash cenosphere/Cr2O3 and NiCrBSi/flyash cenosphere/Mo composite coatings at elevated temperatures(Institute of Physics Publishing helen.craven@iop.org, 2019) Nagabhushana, N.; Rajanna, S.; Mathapati, M.; Ramesh, M.R.; Koppad, P.G.; Reddy, N.C.In the present investigation NiCrBSi/flyash/Cr2O3 and NiCrBSi/flyash/Mo composite coatings are developed using atmospheric plasma spray technique on superni 76 alloy. Coatings are characterized in terms of microstructure, phase analysis, and microhardness. Tribological properties of the coatings are evaluated using a pin on disc tribometer. Test is conducted under dry sliding conditions at room temperature, 200 °C, 400 °C, and 600 °C respectively. Microstructure and worn surfaces of the coatings are analyzed by utilizing Scanning Electron Microscope (SEM) where in phase analysis is carried out using x-ray diffractometer (XRD). XRD results revealed the presence of ?-Ni as primary phase along with Ni3B, Cr7C3, SiO2 and Al2O3 as minor phases in both the NiCrBSi/flyash/Cr2O3 and NiCrBSi/flyash/Mo coatings. Among the two coatings, Mo composite coating exhibited lower porosity and higher microhardness. The friction coefficient of both the coatings decreased with increasing temperature. The wear rate is found to decrease at lower temperatures but increased at a higher temperature (>400 °C) for Cr2O3 composite coating wherein Friction coefficient is decreased with increase in the temperature for Mo composite coatings. The worn surface analysis conducted revealed abrasive wear at lower temperatures while the transition from abrasive to adhesive is observed at higher temperatures. © 2019 IOP Publishing Ltd.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 Microstructure, mechanical and wear properties of the A357 composites reinforced with dual sized SiC particles(Elsevier Ltd, 2019) Avinash, A.; Bontha, S.; Krishna, M.; Koppad, P.G.; Ramprabhu, T.Current work reports on the development of A357 alloy composite which is reinforced with dual size SiC particles by stir casting route. Influence of different weight fractions (3% coarse+ 3% fine, 4% coarse + 2% fine, and 2% coarse + 4% fine) of dual size SiC particles on mechanical properties and wear resistance of A357 composites is the focus of this work. Hardness and tensile properties were studied for dual size composites and then were compared with A357 alloy. Microstructural study, fractured surface and worn surface investigation were carried out using optical and scanning electron microscopes respectively. Microstructural analysis showed fairly uniform dispersion of dual size SiC particles in A357 matrix with good interfacial bonding. Compared to A357 alloy, the composites showed improvement in hardness, yield, and tensile strength. In particular, composite with 4 wt. % of fine and 2 wt. % of large SiC particles displayed the highest tensile strength while composite with 4 wt. % of large and 2 wt. % of fine SiC particles exhibited high hardness and wear resistance among A357 alloy and dual particle size composites. The strengthening mechanisms that contributed to improvement in strength values were effective load transfer and dislocation strengthening due to thermal mismatch. © 2019 Elsevier B.V.Item The effect of heat treatment on the mechanical and tribological properties of dual size SiC reinforced A357 matrix composites(Elsevier Editora Ltda, 2020) Avinash, A.; Prabhu, T.R.; Babu, U.S.; Koppad, P.G.; Gupta, M.; Krishna, M.; Bontha, S.In the present work, the effect of aging temperature and particle size ratio of SiC particles on the mechanical and tribological properties of A357 composites reinforced with dual particle size SiC were investigated. The composites were prepared by melt-stirring assisted permanent mold casting technique with different weight fractions (3% coarse +3% fine, 4% coarse +2% fine, and 2% coarse +4% fine) of large and small size SiC particles. These three prepared composites are referred as DPS1, DPS2 and DPS3 composites. The solutionizing temperature was maintained constant at 540 ?C for 9 h while the aging was done at 160 ?C, 180 ?C and 200 ?C (T6 treatment) for 6 h. Optical and scanning electron microscopy studies showed fairly uniform dispersion of dual size SiC particles in A357 matrix with good interfacial bonding. High-resolution transmission electron microscopy images showed formation of uniformly dispersed needle-like phase and spherical shaped -Mg2Si precipitates under peak aging conditions. Compared to T6 treated A357 alloy, the T6 treated DPS A357 composites showed improved yield strength, tensile strength, hardness and wear resistance. Among the three composites, hardness and wear resistance of T6 treated DPS2 composite was found to be significantly higher when compared to the other two composites (DPS1 and DPS3). Ratio of large particles to small particles also seems to effect the mechanical and tribological properties. Presence of more small particles was found to be good for strength and ductility whereas more large particles were found to be good for hardness and wear resistance. © 2020 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND licenseItem Microstructure, microhardness, and tensile properties of hot-rolled Al6061/TiB2/CeO2 hybrid composites(South African Institute of Mining and Metallurgy, 2021) Iyengar, S.; Sethuram, D.; Shobha, R.; Koppad, P.G.TiB2 and CeO2 particle-reinforced Al6061 hybrid composites were manufactured using stir casting and hot rolling techniques. The base alloy and composites were hot-rolled at 500ºC and a 50% reduction was achieved through 12 passes. The effect of varying TiB2 and CeO2 particle additions on the microstructure and mechanical properties of the Al6061 matrix was studied. Scanning electron microscopy showed uniform dispersion of both the reinforcements, with good interfacial bonding. Microhardness and tensile properties like yield and tensile strength were found to be higher for hybrid composite with 2.5% TiB2 and 2.5% CeO2 compared to Al6061 alloy and other hybrid composites. The increased tensile strength is attributed to good dispersion and interfacial bonding between the particles and Al6061 matrix. Fracture analysis using a scanning electron microscope revealed ductile fracture for the Al6061 alloy and mixed characteristics of ductile-brittle fracture for hybrid composites. © 2021 South African Institute of Mining and Metallurgy. All rights reserved.Item Effect of carbon nanotubes on microhardness and adhesion strength of high-velocity oxy-fuel sprayed NiCr–Cr3C2 coatings(SAGE Publications Ltd, 2022) Manjunatha, M.; Gaikwad, G.; Natarajan, J.; Koppad, P.G.NiCr–Cr3C2 coatings are widely used for high temperature and tribological applications due to their high hardness, oxidation, and wear resistance properties. In the present investigation, an attempt is made to further enhance the hardness and adhesion strength of NiCr–Cr3C2 coatings by reinforcing them with multi-walled carbon nanotubes. The carbon nanotubes (3–7 wt%) with varying weight percentages were mixed with NiCr–Cr3C2 using a planetary ball rolling mill and sprayed on SA213 T12 (T12 alloy steel tube) using a high-velocity oxy-fuel spraying process. The microstructures of mixed powder, coating cross-section, and fractured coating surface were characterized using a scanning electron microscope while X-ray diffraction was used for phase identification in the fractured coating surface. The coated samples were subjected to microhardness and adhesion strength tests according to ASTM E384 and ASTM D4541-09 standards. Out of all coatings, NiCr–Cr3C2/7% carbon nanotube composite coating showed the lowest porosity of 1.17%, highest microhardness, and adhesion strength of 563.8 HV and 55.8 MPa, respectively. A fracture analysis after a pull-off adhesion test revealed adhesion failure for NiCr–Cr3C2 coating and combined adhesion/cohesion failure for NiCr–Cr3C2/7% carbon nanotube composite coating. © IMechE 2021.Item Hardness and electrical conductivity of uncoated and silver coated carbon nanotubes reinforced copper nanocomposites(Springer, 2022) Koti, V.; Mahesh, n.; Murthy, K.V.S.; Koppad, P.G.; Sethuram, D.In the present study, carbon nanotube reinforced copper nanocomposites were fabricated using the powder metallurgy technique which includes ball milling and hot pressing. The carbon nanotube weight percentage in the nanocomposite was varied from 0.25 to 1.50% in the steps of 0.25%. Further, to improve the interfacial bonding between the carbon nanotubes and copper matrix, the carbon nanotubes were coated with silver using the electroless deposition method. The sintered and hot pressed copper nanocomposites with uncoated and silver-coated carbon nanotubes were subjected to optical and scanning electron microscope studies to understand the dispersion of nanotubes. The density, microhardness and electrical conductivity of developed nanocomposites were studied. The dispersion of nanotubes was found to be uniform throughout the copper matrix resulting in the improvement in microhardness. Especially when compared with sintered samples, the hot-pressed nanocomposites with silver-coated carbon nanotubes showed significant improvement in microhardness however beyond 0.75% content the microhardness for samples was found to drop. The electrical conductivity of nanocomposites was found to decrease with the increase in the MWCNT content which was attributed to the clustering of MWCNTs due to strong van der Waal forces and the increase in the number of interfaces between MWCNTs and copper matrix. © 2022, Indian Academy of Sciences.Item Optimization of Wear Properties of B4C Nanoparticle-Reinforced Al7075 Nanocomposites Using Taguchi Approach(Springer, 2023) Kumar, G.A.; Satheesh, J.; Murthy, K.V.S.; Mallikarjuna, H.M.; Puneeth, N.; Koppad, P.G.In the present work, Al7075 nanocomposites with varying B4C contents were produced using powder metallurgy technique. The developed nanocomposites were subjected to microstructure, grain size and wear behaviour analysis. Dry sliding wear test of nanocomposites was conducted as per ASTM G99 standard using pin on disc test ring using Taguchi L9 approach with varying B4C nanoparticles (2.5, 5 and 10%), load (10, 20 and 30 N), speed (200, 250 and 300 rpm) and sintering temperature (500, 550 and 600 °C). Scanning electron microscopy (SEM) analysis showed uniform dispersion and good bonding between B4C nanoparticles and Al7075 matrix. Grain size analysis conducted according to ASTM E112-96 showed that irrespective of sintering temperature the average grain diameter of nanocomposites decreased as the B4C nanoparticle content increased. According to response table for S/N ratio, the most influential parameter on wear volume was B4C nanoparticles content. Worn surface analysis showed delamination and abrasion as dominant mechanisms for nanocomposites with lower B4C nanoparticle content and abrasion for nanocomposites with higher B4C nanoparticle content. © 2022, The Institution of Engineers (India).