Faculty Publications
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Item Effect of retrogression and re-ageing heat treatment on microstructure and microhardness of aluminium 7010 alloy(EDP Sciences edps@edpsciences.com, 2018) Nandana, M.S.; Udaya Bhat, K.; Manjunatha, C.M.Aluminium alloy 7010 is subjected to retrogression and re-ageing (RRA) heat treatment to study the influence of microstructural changes on hardness. Retrogression is performed at 190 °C for different time intervals ranging from 10 to 60 minutes. Optimum time for retrogression treatment is estimated based on the retrogression time that result with equivalent mechanical properties as that of peak aged (T6) condition. Retrogression performed for 30 minutes resulted with micro hardness of 203 HV, which is equivalent to that obtained by following T6 treatment. Microstructural characterization done with the help of transmission electron microscope (TEM) indicates RRA treatment results with the coarsened and discontinuous precipitates along the grain boundary which is similar to over aged (T7) condition, where as fine and densely populated precipitates in the matrix similar to T6 condition. Coarse and discontinuous grain boundary precipitates (GBP's) improves resistance to stress corrosion cracking. Fine and dense precipitates in the matrix ensures hardness equivalent to that of T6. © The Authors, published by EDP Sciences, 2018.Item Effect of wire feed rate on microstructure development during bead on plate welding of microalloyed steel using P-GMAW(Elsevier Ltd, 2020) John, M.; Kumar, P.A.; Udaya Bhat, K.Welding of advanced high strength steel has been challenging because of difficulties associated with retaining high strength and toughness in the weldment. In this investigation, Ti-Nb microalloyed 800 MPa steel was subjected to bead on plate welding trials using ER70S-6 filler wire. Synergic pulsed mode was used for welding. Here the system could optimize the welding current and voltage once the selection of wire feed rate was done. Analysis of weld bead was done by measuring the weld bead parameters, observing microstructural details and calculating microhardness values. The investigation indicates that 6 m/min wire feed rate produces good weld bead, minimum reinforcement and optimum dilution. The microstructure is predominantly acicular in nature and microhardness in weld and HAZ is higher compared to the beads produced using other wire feed rates. © 2020 Elsevier Ltd. All rights reserved.Item A study on HAZ behaviour in 800 MPa cold rolled and hot rolled steel weld(Elsevier Ltd, 2021) John, M.; Perka, P.; Udaya Bhat, K.; Bhat Panemangalore, D.In the automotive sector, the demand for advanced high strength steels (AHSS) is increasing day by day. Based on the application, cold rolled and hot rolled steels are used for various components in a vehicle body. Typically, cold-rolled grades with dual-phase, DP780 steel is used in the form of welded blanks. Hot rolled grades with Ti-Nb microalloy content, like HS800 steel are used in as long members. Welding is an important step to be considered in the design of materials for mass production as required in the automobile sector. In this investigation, Pulsed Gas Metal Arc Welding (P-GMAW) is carried out on both steels with a solid filler wire of strength 800 MPa. Static tensile tests indicated that failure in both steels welds occurred in the heat-affected zone region. The crack initiation and propagation behaviour were compared in both steels. In DP780 steels, the presence of the acicular ferrite and acicular martensite resisted the crack initiation and propagation in the weld region whereas, the chaotic nature of the acicular ferrite in HS800 steel. Microstructural studies revealed that the reason for heat affected zone (HAZ) failure in HS800 steel is due to the presence of hard TiN particles with a size of more than 1 µm which causes decohesion in the matrix. In DP780 steel failure is due to the presence of tempered martensite in the subcritical heat affected zone (SCHAZ). This study divulges the influence of filler wire chemistry, dilution, and welding parameters on cold rolled and hot rolled AHSS steels used in the automotive industry. © 2021 Elsevier Ltd. All rights reserved.Item Compositionally modulated multilayer Cu-Zn alloy coatings fabricated using eco-friendly non-cyanide pulse electrochemical deposition(Elsevier Ltd, 2023) Bharadishettar, N.; Kumar, K.; Udaya Bhat, K.Pulse electrodeposition of Cu-Zn compositional modulated multilayer alloy (CMA) coatings was carried out onto AISI 304 stainless steel substrate using an environmentally friendly alkaline non-cyanide electrolytic bath. Cu-Zn alloy multilayer coating was co-electrodeposited using a trapezoidal pulse current. Multilayer coatings can have two different metals in layers or two-phase mixtures. Different sets of multilayers of 10, 20, 50, and 100 were done using a trapezoidal pulse current. In the trapezoidal pulse current module, during the higher current stage (0.1 A) Zn was deposited as compared to the lower current module (0.02 A) where Cu was deposited. Microstructural and structural analysis of the coatings confirmed nanocrystalline morphology with peaks corresponding to crystallographic planes of (002), (111), (020), and (022). Deposited coatings are hydrophilic in nature. The microhardness of the coatings is decreased with an increase in the number of layers deposited. © © 2023 Elsevier Ltd. All rights reserved.Item Influence of milling parameters on Al-Li alloy surface characteristics(Elsevier Ltd, 2023) Marakini, V.; Srinivasa Pai, P.; Udaya Bhat, K.; Thakur, D.S.; Achar, B.P.Lightweight alloys attract the aerospace industries due to their high specific strength. Al-Li alloy has been investigated in the present study to identify their functional performance in terms of surface characteristics namely surface roughness and hardness. Dry face milling was performed using uncoated carbide inserts for the experimental conditions obtained from Taguchi L27 design of experiments. The effect of milling parameters, such as feed rate, cutting speed and depth of cut on surface roughness and hardness have been investigated and presented. Further, the optimal milling conditions are identified using statistical techniques – Grey Relational Analysis (GRA) and Technique for Order of Preference by Similarity to Ideal Solution (TOPSIS). The study showed that feed rate is the most influential parameter on both surface characteristics. Both GRA and TOPSIS showed similarity in identifying the same condition as optimal for milling Al-Li alloy under dry condition. © © 2023 Elsevier Ltd. All rights reserved.Item Microstructure Evolution in Cast Al-Zn-Mg Alloys Processed by Equal Channel Angular Pressing(Springer New York LLC barbara.b.bertram@gsk.com, 2018) Manjunath, G.K.; Udaya Bhat, K.; Preetham Kumar, G.V.In the present work, microstructure development and enhancement in the microhardness of Al-Zn-Mg alloys (with 5, 10, and 15% zinc) during equal channel angular pressing (ECAP) were investigated. Dendritic morphology was observed in the cast condition of all three alloys, and precipitates were situated along the inter-dendritic regions. After homogenization, precipitates in the inter-dendritic regions were uniformly distributed in the aluminum matrix and grain boundaries were developed. After 4 passes in route BC, large reduction in the grain size was observed. X-ray diffractometry showed that MgZn2 precipitate was developed in the ECAP-processed samples. Increase in the intensity of MgZn2 peaks was observed when the quantity of zinc is increased in the material. Also, changes in the intensity of XRD peaks were observed in ECAP-processed samples due to shear deformation. After ECAP, substantial increase in the microhardness was perceived. After four passes, microhardness increased to 109, 67, and 58% from the initial condition in A1, A2, and A3 alloys, respectively. Also, improvement in the microhardness was also observed when the quantity of zinc is increased in the material. © 2017, Springer Science+Business Media, LLC, part of Springer Nature and ASM International.Item Effect of zinc content on the microstructure and mechanical properties of Al-Zn-Mg alloy(Elsevier Ltd, 2022) Manjunath, G.K.; Udaya Bhat, K.; Preetham Kumar, G.V.In the present work, Aluminium-Zinc-Magnesium alloys (5 wt%, 10 wt% and 15 wt% Zinc and 2 wt% Magnesium) were prepared by casting process in a metal die. After casting process, heat treatment was conducted to the prepared alloys. To study the consequence of Zinc on the prepared alloys microstructure and mechanical properties were investigated. In as-cast state, in all three compositions, dendrite formation was noticed. While, after homogenization heat treatment, grain boundaries were noticed. Rise in the Zinc in the material leads to enhance the secondary particles. Microhardness and tension experiments were conducted to investigate the mechanical properties. Rise in the Zinc in the material leads to enhance the microhardness and tension strength. But ductility of the material declined with rise in the Zinc in the material. © 2021Item Enhancing the surface integrity characteristics of Al-Li alloy using face milling(Elsevier B.V., 2022) Marakini, V.; Srinivasa Pai, P.; Udaya Bhat, K.; Thakur, D.S.; Achar, B.P.This work presents the milling induced surface integrity investigation of Al-Li alloy. The effect of milling on the surface roughness, microhardness, microstructure, and residual stress is studied. Uncoated carbide inserts are used for milling due their superior hardness and greater life, when machining softer materials such as aluminium and its alloys. Results show that the minimum surface roughness (Ra = 0.043 µm) and maximum microhardness (216 HV) are achievable from the milling process, when compared with the roughness (Ra = 0.528 µm) and microhardness (180 HV) of the as-received material. Results indicate limited harm to alloy microstructure from the milling process and the presence of compressive residual stress induced from milling. The work finds scope for aerospace applications. © 2022 Elsevier B.V.Item Microstructural Features Intimated in Automotive Grade IF Steel Subjected to Conventional and Severe Shot Peening(Springer, 2024) Sahoo, B.; Udaya Bhat, K.A significant amount of interstitial-free or IF steel is used to manufacture automotive body parts due to its high ductility, high formability, and low yield strength. But, the major drawback of this steel is the lower surface hardness. The current investigation intended to enhance the surface hardness by employing shot peening at different coverages. The work also studied the microstructural features intimated after the treatment and its effect on the surface hardness. The optical and transmission electron microscopy (TEM) results showed a prominent grain refinement and dislocation hardening, which improved the micro-hardness to 2.5 times. Tri-junctions, sub-grains, twins, nanocrystalline regions, and several dislocation-induced microstructural features, like dislocation bands, dislocation forests, dislocation walls, dislocation cell structure, etc., were detected in the samples after peening. These features bear a beneficial impact on the surface hardness of the substrate. A spatial filter (Sobel filter) was used to refine the image and detect the presence of NbC precipitates near the grain boundary. Using Gatan DigitalMicrograph software, the thermal imaging technique effectively identified thinner grain boundaries near the segregation zone. © ASM International 2024.Item Tailoring the surface characteristics and mechanical behavior of Ti-Nb stabilized IF steel through controlled shot peening coverage(Elsevier Ltd, 2025) Sahoo, B.; Udaya Bhat, K.; Kumar, D.S.The rising demand for a qualitative surface opens a new window of research in the domain of mechanical surface treatment, known as severe shot peening, especially in the automotive industry. The effectiveness of this method is usually affiliated with various process parameters, of which peening coverage is the most sought-after. It is anticipated to elevate the surface characteristics by proficiently optimizing the peening coverage. On this ground, the current investigation tries to gather the beneficial effect of peening coverage on the surface properties of Ti-Nb stabilized interstitial-free steel subjected to severe shot peening by considering four different coverages (100 %, 500 %, 1000 %, and 2000 %). The work attempts to interpret the impact of peening coverage on grain refinement and dislocation-induced microstructures at different depths of the as-treated sample. The crossectional microscopy unveiled a prominent grain refinement hardening and dislocation hardening in 2000 % peening coverage up to a depth of 90–120 µm, firmly agreeing with the microhardness depth profile. The optical microscopy identified four zones of deformation (severe deformation, deformation, transition, and undeformed zone) in the sample treated with the highest coverage. The transmission electron microscopy demonstrated the dominance of certain dislocation-derived features like dislocation forest, dislocation cells, tangled dislocations, dislocation bands, nanocrystalline region, stress concentration region, etc., at the deformed zone of the treated samples. Interestingly, the trace of these features was detected at a greater depth for the highest-peened sample than the lowest-peened sample, affirming the beneficial aspect of higher peening coverage. The stored energy and thermal stability assessment in the as-received and as-treated sample was done in the differential scanning calorimeter, revealing the favorable impact of severe peening on the substrate. The surface topographical study in a 3D profilometer also unveils the variation in the surface roughness and functional volume parameters. The present investigation also analyzed the maximum depth and mean density of furrows to verify the severe plastic deformation in the as-treated sample. © 2024