1. Ph.D Theses
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Item Microstructure and Mechanical Properties of Al-Si Alloy Processed by Multi-Directional Forging(National Institute of Technology Karnataka, Surathkal., 2023) B., Kumara; G.V., Preetham KumarIn this present work, the effect of multi-directional room temperature forging on the mechanical and wear characteristics of Al-7.3Si and Al-12.1Si alloys with varying cumulative strains was investigated. Severe plastic deformation via multidirectional forging technique can be used to modify the mechanical properties. MDF can be applied to a relatively large sample that can be used for industrial applications. In the MDF process, strain per pass can be controlled by maintaining the height-to-width ratio, and thus, a wide range of metals and alloys can be deformed at room temperature. The Al Si alloy ingots were melted in a furnace and then poured into a preheated metallic die to produce a cast sample of desired shape and dimension. Al-7.3Si alloys were machined to dimensions of 30 mm x 30 mm x 24 mm for MDF processing with an equivalent strain of 0.22. Similarly, Al-12.1Si alloys were machined to dimensions of 30 mm x 30 mm x 23 mm for MDF processing with an equivalent strain of 0.27. The machined samples were then subjected to solution heat treatment before being forged in order to change the morphology of shape-edged eutectic silicon of the as-cast sample. MDF successfully processed the Al-7.3Si and Al-12.1Si alloys for two and three cycles, respectively, with cumulative strains of 1.3 and 2.43 at room temperature. Optical microscopy, field emission scanning electron microscopy, and X-ray diffractometer were used to characterise the effect of MDF processing on Al-7.3Si and Al-12.1Si alloys. Microstructural observations showed that the coarse eutectic silicon particles were effectively broken into finer particles and uniformly redistributed. With increasing MDF cycles, the silicon particles fragmented into finer particles. According to XRD results, the peak broadening in the XRD pattern of MDF-processed sample is due to the combined effect of crystallite size and micro-strain. The hardness and tensile strength of MDF samples have significantly increased. The hardness and tensile strength of the as-cast Al-7.3Si alloy increased to 60% and 149%, respectively, after two cycles of MDF. Similarly, the hardness and tensile strength of the as-cast Al-12.1Si alloy increased to 50% and 98%, respectively, after three cycles. Scratch test was conducted to measure the scratch resistance of unprocessed and MDF-processed samples. Tests were performed at ambient temperature under a progressive load of 2 15 N over a 5 mm scratch distance at a speed of 1 mm/min. Dry sliding wear tests were iii performed on a tribometer (pin-on-disc) under varying sliding speeds and loads at ambient temperatures. MDF-processed materials exhibited better scratch and wear resistance compared to as-cast materials. Furthermore, scratch and wear resistance increased with an increasing number of MDF cycles. Al-7.3Si alloy with two cycles and Al-12.1Si alloy with two and three cycles have shown maximum wear and scratch resistance. After MDF process, the wear mechanisms in both alloys shifted from adhesive and delamination wear to a combination of abrasive and a lesser amount of adhesion wear. Moreover, the degree of delamination significantly decreased after MDF process. Improvements in the mechanical and wear properties of MDF-processed samples can be attributed to the refinement and uniform distribution of eutectic silicon particles, as well as strain hardening of the aluminium phase.Item Elevated Temperature Sliding Wear Behavior Of Cocrnitimox And Cocrnitiwx High Entropy Alloys Processed Using Mechanical Alloying and High-Velocity Oxy-Fuel Spray(National Institute Of Technology Karnataka, Surathkal., 2024) Addepalli, Syam Narayana; Joladarashi, Sharnappa; M.R., RameshMaraging steels, widely used in the aircraft landing gear components were subjected to wear due to the harsh working conditions. Surface modification of these components by the deposition of advanced coating materials prolong their life. High entropy alloys (HEA) are a contemporary class of materials with multiple primary elements having applications in different fields, owing to their exceptional mechanical and physical properties. Therefore the curent research is aimed at enhancing the wear performance of maraging steels, by the deposition of HEA coatings. CoCrNiTiMox and CoCrNiTiWx (x: molar ratio; x= 0.5, 1, 1.5) HEAs were processed by mechanical alloying of pure metal powders for further application as feedstock in the High velocity oxy-fuel (HVOF) technique. The phase and microstructural transformation of the ball milled powders is investigated in detail by optimizing the milling time and speeds. The milling process is extended for 50 h and milled powder samples were collected at regular intervals of 10, 20, 30, 40 and 50 h to characterize the samples for their suitability to deposit using thermal spray techniques. The milled powders were characterized with respect to the phases, particle morphology, chemical homogeneity, particle size and crystallite sizes. Based on the characterization studies, the powders milled at a speed of 200 rpm for 10 h were selected as feedstock for HVOF deposition. After the deposition of coatings, the microstructural and mechanical characterization of coatings were performed. The phases and microstructure of the deposited HEA coatings were determined by X-ray diffraction (XRD) and scanning electron microscope (SEM). The microhardness of the coating was determined by using a vickers indenter on the coatings cross-section, with a load of 300 g and a dwell time of 15 s. The deposited coatings fracture toughness was determined by using the Evans and Wilshaw’s approach. The tribological behaviour of CoCrNiTiMox and CoCrNiTiWx HEA coatings at elevated temperatures was studied extensively using a Pin-on-Disc tribometer. The deposited coatings exhibited a lamellar structure and good mechanical bonding with the substrate. The porosities of CoCrNiTiMox and CoCrNiTiWx HEA coatings, as calculated using ImageJ software, were found to be in the range of 1-2%. i The mechanical performance of the CoCrNiTiMox and CoCrNiTiWx HEA coatings revealed superior values, when compared to other HEA coatings. The microhardness of CoCrNiTiMo0.5, CoCrNiTiMo, and CoCrNiTiMo1.5 HEA coatings were found to be 841±62 HV0.3, 927 ± 45 HV0.3 and 952±23 HV0.3, respectively. On the other hand, the microhardness of CoCrNiTiW0.5, CoCrNiTiW, and CoCrNiTiW1.5 HEA coatings were found to be 863±52 HV0.3, 951 ± 38 HV0.3 and 1025±39 HV0.3, respectively. The fracture toughness of CoCrNiTiMo0.5, CoCrNiTiMo, and CoCrNiTiMo1.5 HEA coatings were found to be 2.89 ± 0.31 (Mpa m1/2), 3.26 ± 0.25 (Mpa m1/2) and 3.79 ± 0.35 (Mpa m1/2) respectively. Likewise, the fracture toughness of CoCrNiTiW0.5, CoCrNiTiW, and CoCrNiTiW1.5 HEA coatings, were found to be 3.22 ± 0.26 (Mpa m1/2), 3.54 ± 0.32 (Mpa m1/2) and 3.87 ± 0.3 (Mpa m1/2) respectively. Further, it can be witnessed that the as-sprayed HEA coatings exhibited a steady increment in the mechanical properties with an increment in the molar fraction of Molybdenum and Tungsten. The specific wear rate of CoCrNiTiMo HEA coating dropped by 70.5%, declining from 17.34 ± 2.8 x10-6 mm3/N-m to 5.1 ± 1.6 x10-6 mm3/N-m, while CoCrNiTiW dropped by 76.3%, decreasing from 15.8 ± 3.7 x10-6 mm3/N-m to 3.73 ± 2.1 x10-6 mm3/N-m, with an increase in the temperature from RT to 600 °C. The wear rates of coatings exhibited a significant reduction at elevated temperatures, owing to the formation of TiO2, CoMoO4, NiO tribofilms for CoCrNiTiMo, and TiO2, CoWO4, WO3 oxides for CoCrNiTiW. Further, the CoCrNiTiMo1.5 HEA coatings offered better wear resistance, as compared to CoCrNiTiMo0.5 HEA coatings, at any temperature and loading condition, due to the increment in the molar fraction of Molybdenum. Additionally, the CoCrNiTiW1.5 HEA coatings exhibited superior wear performance, when compared to all the six compositions in the current research. The investigation of worn surfaces showed a transformation in wear mechanisms from adhesive and abrasive wear at room temperature to oxidative wear at elevated temperatures.Item Development oTungsten Inert Gas and Microwave Treated Claddings In Improving Resistance to Wear at Elevated Temperatures(National Institute of Technology Karnataka, Surathkal, 2022) Suresh, Gudala; M R, RameshThe remanufacturing of high-value engineering components is becoming a mainstream practice to reduce the environmental impact. The components such as cams, gears, and bearings rely on the integrity of their interacting surfaces where loads act over a small surface area, leading to high contact stresses, which may further influence the grater region of the surface. Especially at elevated temperatures, components used in the aero engine, gas and steam turbines, and bearings lose their efficiency due to the deterioration of material properties. The components used in such adverse conditions are important to adapt suitable surface modification techniques to increase the service life. Cladding emerged as an effective surface modification technology and is widely used in many industries to protect the components against surface failures like wear, corrosion, and oxidation. Among many materials, titanium has numerous applications in a rocket motor, structural forgings and fasteners, pressure vessels, chemical gas pumps, marine components, and steam turbine blades, etc. Even though titanium alloy has a high specific strength and elevated melting temperature, it has low hardness and poor wear resistance. Hence the improvement of surface mechanical properties of titanium is essential to extend its application in an abrasive environment. The present work explores the TIG cladding technique and microwave hybrid heating (MHH) technique to enhance the surface properties of the titanium 31 alloy against wear at elevated temperatures. Commercially available materials such as NiCrSiB/WC, Ag, BaF2, MoS2, and hBN are used as the cladding powders. Four types of composite coatings were prepared, namely NiCrSiB/WC/Ag/BaF2, NiCrSiB/WC/Ag/hBN, NiCrSiB/WC/MoS2/BaF2, and NiCrSiB/WC/MoS2/hBN, and deposited on Titanium 31 grade alloy substrate by TIG cladding and microwave cladding techniques at optimized parameters. The claddings were characterized using Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS), Electron Backscatter Diffraction (EBSD), and X-ray diffraction (XRD). Further, claddings are characterized for microstructural and mechanical properties (porosity, dilution, microhardness, fracture toughness) and evaluated their potential for high temperature environments in sliding wear conditions. At optimized TIG and microwave hybrid techniques, less porosity (< 2%) and dilution were obtained. The influence of solid lubricants, namely Ag, BaF2, MoS2, and hBN, on NiCrSiB/WC claddings is dealt with for tribological performance at elevated temperatures. Dry sliding wear behavior of titanium 31 substrate, NiCrSiB/WC/Ag/BaF2, NiCrSiB/WC/Ag/hBN, NiCrSiB/WC/MoS2/BaF2, and NiCrSiB/WC/MoS2/hBN is evaluated using high temperature pin on disc tribometer. All four coatings showed a synergistic lubrication effect at low and high temperatures. Due to the reduction of surface contact against the alumina counter body, claddings displayed a lower friction coefficient and wear rate than the substrate. Based on the weight loss data, the relative wear resistance of the both TIG and microwave claddings under dry sliding conditions is arranged in the following sequence: NiCrSiB/WC/Ag/BaF2 > NiCrSiB/WC/Ag/hBN > NiCrSiB/WC/MoS2/hBN > NiCrSiB/WC/MoS2/BaF2. The combined lubricating effect of Ag and BaF2 solid lubricants incorporated in the claddings was adequate to reduce material loss than other composite claddings. Comparatively, TIG processed clads showed lower wear rates than the MHH clads at all wear testing conditions. Developed claddings in the present study exhibit higher temperature resistance than titanium 31 alloy substrate making them suitable for components subjected to elevated temperature service conditions.Item Multi Directional Forging Of Zinc Aluminium (Za27) Based Composites Reinforced With Sic and Al2O3 Particles(National Institute of Technology Karnataka, Surathkal, 2021) N, Anjan B.; V, Preetham Kumar G.Selection of materials with the expected characteristics is a very important for any industrial application. In the engineering and automotive industries, the current tendency is to use metal matrix composite for production of various components for high performance application. The aim of this study was to investigate the effect of SiC and Al2O3 (5 and 10 wt %) reinforcement in ZA27 matrix alloy. Further to investigate and develop the application of the MDF techniques, which may lead to an improvement in mechanical and tribological properties of these composite for industrial application. To analyse the influence of parameters such as applied load, sliding distance and sliding speed on dry sliding wear behavior of solutionized and MDF processed material using pin on disc test rig was conducted. In this study, the composite were prepared by stir casting technique followed by squeezing process. Multi directional forging (MDF) is one of the severe plastic deformation (SPD) techniques used to develop ultrafine-grained (UFG) materials. Multi directional forging technique was used to process the ZA27/SiC/Al2O3 /SiC + Al2O3 composites to produce refined microstructure in order to study the relationship between the microstructure and mechanical properties. The effects of the MDF processes have been studied on ZA27 based composite at 100 °C and 200 °C of processing temperature with a total equivalent strain of 0.54 and 1.08 respectively. Before MDF process, base alloy and prepared composites were homogenized at 365°C for 5 hours by using muffle furnace and quenched in water to room temperature. The standard metallographic technique was used to analyse the microstructural features of the ZA27 based composite. MDF processed composite were characterized by analyzing the X-Ray diffraction (XRD) profiles and studying microstructures using optical microscopy, scanning electron microscopy (SEM) attached with energy dispersive spectroscopy (EDS) and transmission electron microscopy (TEM). Density was measured using standard density measurement kit and both theoretical and experimental densities were compared. Mechanical properties such as hardness, tensile strength and ductility from tensile test and fracture surface morphologies of the tensile test samples of both MDF processed and unprocessed composites were studied. Wear behavior of composites before and after MDF process were studied with their wear mechanisms. iv Results revealed that, density of ZA27 alloy decreased by incorporation of SiC and Al2O3 particles. Some Clusters and fair dispersion of SiC and Al2O3 particles in ZA27 matrix were observed in microstructure and confirmed by EDX. SiC reinforced composites performs better when compared with Al2O3 reinforced, mixture of SiC+Al2O3 particles reinforced and ZA27 base matrix material. As the percentage of reinforcement increased from 5 wt% to 10 wt% the properties of the material also increased. Porosity level decreased with an increase in the number of MDF passes when compared with unreinforced materials. Composites reinforced with SiC particles in 5 and 10 wt % were MDF processed at different temperature. The average grain size was reduced from 25-30 µm to 0.2-0.35 µm, 0.45-0.5 µm respectively in the case of samples MDF processed at 100 °C up to three passes and for 200 °C up to six passes it shows 0.8-1.0 µm, 0.9-1.2 µm respectively. The initial lamellar Al-rich and Zn-rich phase was gradually refined to a spherical shape and distributed more uniformly with an increasing number of passes. Ultimate tensile strength of the composite material was increased with that addition of SiC particles and also by MDF process. The highest ductility was obtained when the sample forged at 100 °C 3 passes. Initial ascast condition showed a brittle type of fracture. Brittle mode of fracture was transformed into ductility mode by MDF processing. Wear results showed that samples tested with lower load and sliding distance were showing abrasive type of wear mechanism but as the applied load and sliding distance increased, mechanism changed to adhesion type. This is due to the rise in temperature between the interface of pin and disc, material detached from the pin as debris gets adhered to the surface of pin which influences the mode of mechanism to switch from abrasion to adhesion. MDF processed ZA27/SiCp for 3 passes at 100 °C showed better wear resistance with ultra-fine grains and higher hardness. Composites reinforced with Al2O3 particles in 5 and 10 wt % were MDF processed at 100 °C up to three passes reduced the grain size from 20-30 µm to 0.4-0.45 µm, 0.5- 0.6 µm respectively with the dual type of microstructure having both lamellar to the cellular structure. On further MDF processing at 200 °C upto 6 passes showed the grain size of 1.2-1.4, 1.5 µm with equiaxed grain structure. Small cracks were seen at the edges of the Al2O3 particle because of load applied during MDF process upto 3 v passes at 100 °C and with a higher number of passes the Al2O3 particle broken into several pieces and forms a cluster of Al2O3 particle. Addition of Al2O3 particle increased the UTS and hardness values in both 5 and 10 wt % reinforced composites and further improvement in UTS and hardness value is due to MDF process upto three passes at 100 °C and upto six passes at 200 °C. The ductility of Al2O3 particle reinforced composites was low when compared with other composites. Wear rate of Al2O3 reinforced composite was more when compared with SiC reinforced ones. Results of wear test showed that Al2O3 reinforced composites MDF processed for 3 passes at 100 °C gives higher wear resistance, with abrasion type of wear mechanism. For ZA27/SiC +Al2O3 composites with the average grain size reduced from 15-20 µm to 0.2-0.25 µm, 0.3-0.4 µm when processed at 100 °C upto three passes and 0.8-0.9 µm, 0.9-1.1 µm when processed at 200 °C upto Six passes. Hardness, ultimate tensile strength and ductility of the composites were improved by MDF processing. Substantial improvement in ductility of the present composites after several MDF passes can be attributed to the elimination of as-cast morphology as well as grain refinement, reduction in micro porosity (or micro-voids), redistribution of reinforcing particles, and also the change in the composition of the phases. In an overall, the results of wear test shows, SiC reinforced composite performed better as compared with Al2O3 reinforced and Mixture of SiC+Al2O3 reinforced material. Wear study of composites indicated that the specific wear rate was highly influenced by applied load and sliding distance. As an application, a Cylinder Roller Bearing is fabricated by best performing ZA27/SiC/ Al2O3/SiC+Al2O3 composite material.Item The Effect of Dual Particle Size SIC Reinforcements and Heat Treatment on Microstructure, Mechanical and Tribological Properties of A357 Composites(National Institute of Technology Karnataka, Surathkal, 2021) L, Avinash.; Bontha, Srikanth.The demand for light-weight materials is increasing in the automobile industry due to the increasing cost of fuel. In particular, there is a huge demand for high-strength and wear-resistant materials for engine cylinder applications. Al-Si-Mg series alloys such as A357 alloy would be an ideal choice for such applications owing to their low density, excellent castability, high strength and wear resistance. Enhancing the strength of any material can be achieved by work hardening, heat treatment, or reinforcing with a hard phase. The present work focused on development of A357 composites wherein the A357 alloy was reinforced with dual-size SiC particles. In the current work, two different sizes of SiC particles (coarse (140 ± 10μm)) and (fine (30 ± 5 μm)) were used to reinforce A357 alloy. Stir casting was used to develop A357 composites, with different weight ratios of the two sizes of SiC powders, keeping the total weight fraction at 6%. Three composites were cast in finger moulds; DPS1 (coarse: fine;1:1), DPS2 (coarse: fine;2:1), and DPS3 (coarse: fine; 1:2). The cast A357 alloy as well as the composites were subjected to heat treatment as per T6 temper conditions. The effect of varying solution temperature (500ºC to 540ºC in steps of 20°C for 9h and keeping aging temperature constant at 150 ºC for 6 h) and aging temperature (160°C to 200°C in steps of 20°C for 6h and keeping solution temperature constant at 540 ºC for 9h) were studied for both A357 alloy and the developed composites. Both A357 alloy and dual-size SiC reinforced composites were subjected to microstructural analysis using optical, scanning, and transmission electron microscopy techniques. Hardness and tensile testing were carried on the A357 alloy and its DPS composites before and after heat treatment. Tribological properties namely wear rate was assessed by conducting dry-sliding wear test using a pin-on-disc machine. In the wear test, the effect of varying load on wear rate was studied by keeping sliding velocity and sliding distance constant. Worn surface analysis was carried out using SEM to study the wear mechanisms operating in both untreated and heat-treated alloy and composites. Mechanical testing results showed improved hardness, yield, and tensile strength values for DPS composites when compared with that of A357 alloy. The strengthening of A357 composites is based on the addition of hard phase like SiC particles to the A357 alloy. The strengthening mechanisms that contributed to improvement in properties were effective load transfer, precipitation hardening and dislocation strengthening due to thermal mismatch. Precipitation hardening occurs for the A357 alloy and its composites because of T6 heat treatment. Formation of βʺ phase and Mg2Si precipitates were primarily responsible for strengthening after heat treatment. Wear rate of composites was found to be less than that of A357 alloy. Prohibition of direct contact between the two mating surfaces by presence of dual-size SiC particles was one of the primary reasons for low wear rate in composites. The key conclusions from this work include: Among the three developed composites, hardness, and wear resistance of DPS2 composite before and after heat treatment was found to be significantly higher than the other two composites (DPS1 and DPS3). Also, the tensile and yield strength values of DPS3 composite before and after heat treatment was found to be significantly higher when compared to the other two composites (DPS1 and DPS2). Lastly, the ratio of coarse particles to fine particles has an effect on the mechanical and tribological properties. Presence of more fine particles was found to be good for strength and ductility whereas more coarse particles were found to be good for hardness and wear resistance.Item Development and Characterization of Biomedical Porous Ti - Nb - Ag Alloy through Powder Metallurgy Method(National Institute of Technology Karnataka, Surathkal, 2021) J, Shivaram M.; Arya, Shashi Bhushan.; Nayak, Jagannatha.One of the major concerns in biomedical implants is the mismatch in the elastic modulus of the implant material and the bones leading to stress shield effect. The present investigation focuses on the development of low elastic modulus, porous Ti−Nb−Ag alloy through powder metallurgy (PM) space holder method. Elemental powders of Ti, Nb and Ag with varying amounts were mixed with the powders of space holder (NH4HCO3). These powders are blended using ball milling for 1h, 5h, 10 h, 15 h, and 20 h. The powders were compacted by applying a load of 500 MPa. These compacts were initially calcinated at 200ºC for 2 h to remove the space holder and then finally sintered at 1200ºC for 3 h under ultrahigh vacuum sintering furnace. Microstructure of the porous alloys exhibited micropores, macropores and interconnected pore structures. It was found that with increasing ball milling time, the porosity and pore size decreased while the mechanical properties and electrochemical corrosion properties [in simulated body fluid (SBF)] were improved. XRD results indicated formation of small amount martensite phase and intermetallic compound of Ti2Ag along with the α and β phases. Role of Nb was studied with various Nb content (x = 25, 30 and 35 wt%) in Porous Ti−xNb−5Ag alloys. Increase in Nb content led to decrease in porosity, reduction in both the elastic modulus and compression strength but improved corrosion resistance in SBF. Samples with different porosity levels (22% to 68%) with pore size ranging from 98 μm to 130 μm were fabricated by varying the amount of space holder. Increase in porosity further leads to the reduction in the compression strength, elastic modulus and also corrosion resistance in SBF. Tribocorrosion behaviour of porous Ti−20Nb−5Ag alloys were evaluated in SBF solution by applying various loads (0 N, 1N, 5N, 10N). The results indicate that increasing the applied loads lead to a material degradation and corrosion. The porous Ti−20Nb−5Ag samples are alkali-heat treated using 5 M NaOH, to aid the hydroxyapatite formation in SBF. Alkali treated samples were immersed in SBF for 7, 14 and 21 days at 37 ºC to examine the hydroxyapatite formation. The Ca/P ratio confirmed the formation of adequate hydroxyapatite coating. Further, the electrochemical corrosion test was conducted on hydroxyapatite coated porous alloy in SBF. The hydroxyapatite coated porous alloy after 21 days of immersion in SBF shows excellent corrosion resistance. The cytotoxicity test was conducted on the porous Ti−20Nb−5Ag alloy using MG-63 human osteoblast cells by incubating for 1, 4, and 7 days. The results indicated excellent cell growth and proliferation on porous alloy surface. Cytotoxicity test confirms that developed porous sample has non-toxic in nature and highly suitable for implant application.Item Welding of Dissimilar A5754-A5083 and A6061- A6082 Aluminium Alloys for Automotive Applications(National Institute of Technology Karnataka, Surathkal, 2021) Rajeshkumar, R.; Banerjee, Kumkum.; Devakumaran, K.In the present study, dissimilar aluminium alloy combinations A6061 T6-A6082 T6 and A5754 H111-A5083 H111 were welded using the cold metal transfer (CMT), tungsten inert gas (TIG) welding and friction stir welding (FSW) processes. Each dissimilar combination was welded by two different fillers, such as ER4043 and ER5356, in CMT and TIG. Since FSW is a solid-state welding process, no filler materials were used. The miniature tensile samples were extracted from the interface regions of the TIG and CMT welded joints and the stir zone (SZ) of the FSWed joint. The TIG and CMT welded alloys' individual interface microstructure has been correlated with mechanical properties. The SZ of FSWed parts is of prime importance because this zone primarily decides the resulting property of the welded joint. Therefore, the microstructural features and mechanical properties of the SZ in the FSWed joints have been investigated in detail. The tensile properties of the overall weld region samples have been determined using macro-tensile testing samples. The dissimilar A6061-T6 and A6082-T6 joints welded by CMT and TIG welding processes using two different fillers (ER5356 and ER4043) exhibited higher strength in the A6082 interface in comparison to the A6061 interface. When the dissimilar A5754 and A5083 alloys were welded by CMT and TIG welding processes using two different fillers (ER5356 and ER4043) fillers, the interface region of the A5083 side exhibited higher strength than the interface region of the A5754. In the FSWed joints, the refined grain structure in SZ increased the hardness and strength. The overall joint tensile properties of the dissimilar joints are essential for identifying a suitable welding process to join A6061-A6082 and A5754-A5083 dissimilar alloys. Among the A6061-A6082 dissimilar joints, the CMT joint produced by ER5356 filler and the FSW joint exhibited higher tensile properties than the other joints. The tensile properties of the A6061-A6082 dissimilar CMT joint produced by ER5356 filler and the FSW joint are nearly the same. However, the FSW process does not use any shielding gas, filler materials, and the surface preparation is also not critical for the process. These factors can play a vital role to reduce the cost of welding effectively. Also, the FSW process is environment friendly, due to the absence of fumes and shielding gases. In the case of A5754-A5083 dissimilar joints, the FSW joint shows higher tensile properties than the other joints. Therefore, the FSW process can be recommended as the preferable joining method among all the investigated processes.Item Severe Plastic Deformation of Copper-Titanium Alloys Using Multi Axial Cryo-forging(National Institute of Technology Karnataka, Surathkal, 2020) S, Ramesh.; Nayaka, H Shivananda.Severe plastic deformation (SPD) is a technique where high strains are induced into the material to produce fine-grained structural materials, thereby improving the wear resistance and corrosion resistance. There is an increase in scientific and industrial interest in the development of bulk ultra-fine-grained (UFG) alloys, intended for structural applications. UFG materials offer vastly improved mechanical and physical properties. They also exhibits superplastic properties at elevated temperatures. SPD is done using Equal Channel Angular Pressing (ECAP), High-Pressure Torsion (HPT), Repetitive Corrugation and Straightening (RCS), Accumulative Roll Bonding (ARB) and Multi Axial Forging (MAF). In MAF, materials are forged repeatedly in a closed die along three orthogonal directions, sequentially. It allows processing of relatively ductile material, because it can be performed at cryogenic temperature. Literature review shows that by using MAF technique, grain refinement phenomena can be observed in some ferrous and non-ferrous metals. MAF is one of the simple and most effective methods of SPD to improve material properties. MAF is a process in which the workpiece is subjected to shear deformation and thus, severe plastic strain is induced into the material without any change in the cross-sectional dimension of the sample. Microstructure has major effect on mechanical properties. MAF process leads to ultrafine-grained microstructure in the material which may show superplastic deformation at low temperature and high strain rate. In FCC structured metals, grain refinement also leads to textural changes i.e. high strengthening at cryogenic condition deformation. Copper-Titanium (Cu-Ti) alloy is the nontoxic substitute for Cu-Be and it showed good mechanical and electrical properties and can be used for the production of high strength spring, corrosion-resistant elements, and electrical connections like contact, relay, gears and electrical wires. Hence, in the present study, three alloys of Cu-Ti, namely, Cu-1.5%Ti, Cu-3%Ti and Cu-4.5%Ti, have been processed by MAF. Microstructural evolution in different MAF cycles is studied and it is correlated to the mechanical properties observed. As UFG materials have much higher hardness, they are expected to have higher wear resistance. MAF processed material exhibits higher wear and corrosion resistance, than the asreceived material. Hence MAF processed samples find wider engineering applications.viii Literature review consists of features of various SPD Techniques, advantages, and limitations. MAF process, parameters which influence MAF process, advantages and applications of MAF processed Cu-Ti alloys are discussed in details. Works of different researchers on MAF processed Copper alloys, with respect to, mechanical properties, wear and corrosion behavior are reported. Motivation from literature survey and objectives of the present work are highlighted. Details of the experimentation performed, right from the process adopted for the development of the UFG Cu-Ti to their characterization, are given in chapter three. Microstructural analyses were performed using optical microscopy (OM), scanning electron microscopy (SEM), transmission electron microscopy (TEM) and electron backscatter diffraction (EBSD). Tensile tests were performed on both as-received and MAF processed samples. Dry sliding wear testing was performed using Pin on disc testing machine for both unprocessed and MAF processed samples. For the study of corrosion behavior, electrochemical polarization studies were performed and tofel extrapolation technique was used to obtain the corrosion rates. Chapter 4, Chapter 5 and Chapter 6, explain the results and discussion of various experiments carried out on three alloys Cu-1.5%Ti, Cu-3%Ti and Cu-4.5%Ti Microstructural characterization by OM, SEM, TEM, EBSD and XRD analysis has been discussed. Mechanical properties which includes hardness, tensile followed by fractography has been analyzed. Wear test with different loading conditions and sliding distances has been explained. Corrosion studies by electrochemical measurements test method has been highlighted.Item Effect of Process Variables on Residual Stress and Microstructure in Laser Additive Manufacturing of γ-TiAl Alloy(National Institute of Technology Karnataka, Surathkal, 2020) Mallikarjuna; Bontha, Srikanth.; Krishna, Prasad.Laser Metal Deposition (LMD) is used to fabricate intricate three-dimensional parts from metal powder by fusing material in a layer-by-layer manner of a digital Computer Aided Drawing (CAD) model. LMD process employed for processing of various materials such as metals, alloys, functionally graded materials, and repairing purpose. The LMD process involved numerous process conditions, mainly laser power, travel speed, and the powder flow rate. Effect on a layerwise variation of melt pool size, thermal cycle, the cooling rate is required to understand for producing a successful sound part. Experimentally determination of the effect of these process conditions on melt pool, thermal cycle, the cooling rate is extremely difficult. A remedy is to achieve a quantitative understanding of the process through computational modeling approaches. In this work, Laser Engineered Net Shaping (LENS), one of the LMD techniques is used to fabricate inherently brittle γ-TiAl alloy thin-wall structures at various processing conditions. These deposits are expected to develop residual stresses due to the rapid heating and cooling cycles involved in the LMD process. Towards this end, a 3-D nonlinear thermomechanical finite element analysis is performed to simulate the process under various process conditions. A commercially available ANSYS software utilized in conducting a sequentially coupled thermomechanical analysis. The melt pool, thermal gradients, and residual stresses are predicted from the developed FE models. Results indicate that laser absorption coefficient (αA) of γ-TiAl is obtained by a laser surface melting study, and an αA value is 0.13. The simulated thin-wall results show that thermal gradients increased with an increase in the number of deposited layers i.e., from the substrate to the last layer. Cooling rates decreased with increase in the number of deposited layers i.e., from the substrate to the last layer. Along the build direction, tensile stresses are generated at the edges and compressive stresses are generated at the centre region of the thin-wall which increase with increase in distance from the substrate. Along the laser travel direction maximum compressive stresses are observed at the centre of the wall and these stresses decreasein magnitude with increase in distance from the centre. Higher laser power input yields higher residual stresses due to high-thermal gradients, and hence, laser power has a significant impact on the development of residual stresses in the thin-walls. Residual stresses in the deposited thin-wall samples are measured using the X-ray diffraction technique. Reasonable agreement observed between the predicted and measured values of residual stresses. The microstructure, phases, and hardness of the LMD γ-TiAl alloy thin-walls are also analyzed. The microstructure analysis shows fine lamellar structure comprised of γ and α2 phases, which are matches with the existing studies. Microhardness in the bottom area is found higher than the middle and top areas of the thin-wall. The hardness values increased marginally (5%) with the increase in travel speed. Further, melt pool dimensions (length, width, and depth) increased with increase in laser power and decreased with increase in travel speed. During deposition of a layer (which consists of six tracks) the maximum temperature in the melt pool is observed in track 1. Maximum tensile residual stresses are observed in track 1 and these are lower than the yield strength of the material. The magnitude of these stresses decreased from track 2 to 6. Trends of residual stress are found to be independent of the scan strategy (Unidirectional and bidirectional) considered in this study. The state and magnitude of residual stress distribution in the thin-walls and plate are attributes to the transient thermal gradients encountered during deposition.Item Effect of Equal Channel Angular Extrusion on Microstructure Mechanical Properties and Corrosion Behavior of Wrought AZ-Magnesium Alloys(National Institute of Technology Karnataka, Surathkal, 2020) Naik, Gajanan M.; S, Narendranath.Wrought magnesium alloys are lightest engineering material and it has quite special properties which lead to particular applications. In specific, their highest strength to weight ratio, good machinability and high damping capability makes magnesium alloys tremendously attractive in aerospace, electronics, marine and automobile industries. Indeed, Magnesium alloys have poor tensile strength, ductility and corrosion resistance properties associated with other engineering materials like aluminium alloys, steels and super alloys etc. Therefore, many researchers worked on equal channel angular pressing of magnesium alloys to improve the mechanical properties and corrosion resistance. In this work, the effect of channel angles on material properties were investigated during equal channel angular pressing of AZ80/91 magnesium alloy using processing route-R at 523K, 598K and 663K processing temperature. Channel angles of 90⁰ and 110⁰, common corner angle of 30⁰ have been considered for the study. It has been revealed that the channel angle has a significant influence on deformation homogeneity, microhardness, ultimate tensile strength, ductility and corrosion behaviour of AZ80/91 magnesium alloys. Specifically, AZ80/91 Mg alloys processed through 90⁰ channel angle i.e die A is considered as optimal die parameter to improve above-said material properties. Investigation showing with reference to as-received AZ80 and AZ91 Mg alloy indicates 11 %, 14 % improvement of UTS and 69 %, 59 % enhancement in ductility after processing through 4P through die A (90º) at 598K respectively. Also, the corrosion rate reduces to 97 % and 99 % after processing the sample with 4P-ECAP die A (90º) at the same processing temperature for AZ80 and AZ91 Mg alloys respectively. This is mainly due to grain refinement and distribution of Mg17Al12 secondary phase during ECAP. Further, this work investigates the effect of annealing and aging treatment on microstructure and corrosion behaviour of as-received and ECAPed AZ80/91 Magnesium alloys. Here, annealing at 523K, 623K, and 723K were accomplished, meanwhile samples were cooled in the furnace after 6 h and 12 h of diffusion annealing treatment. In this study, samples were characterized by using optical microscopy (OM) and scanning electron microscopy (SEM) and electrochemical corrosion behavior of annealed AZ80/91 Mg alloy has beeninvestigated. With this, an attempt has been made to enhance the corrosion resistance of the AZ80/91 Mg alloy by changing its microstructure and re-distribution of secondary phase during annealing and aging treatment. It was found that corrosion rates are minimum at higher annealing temperature and aging time because of uniform distribution of secondary β-phases in Mg matrix, evidently shown in the microstructure of the heat-treated AZ80/91 Mg alloy. As a result, the annealing treatment at 723K for 12 h aging is desirable to enhance the corrosion resistance. Further enhancement of asreceived and ECAPed AZ80/91 Mg alloys were observed after High Velocity Oxy-Fuel (HVOF) coating of 316 stainless steel powder. Our results revealed that 316 stainless steel coating on ECAP-4P AZ80/91 Mg alloys were uniform and compact on substrate with a thickness of 80±5 µm. Furthermore, HVOF-coating process of 4P-ECAP significantly reduce corrosion rate at 3.5wt.% NaCl solution making it promising for industrial applications. The corrosion behaviour and effect of the ECAPed fine-grained magnesium alloy and coarse-grained as-received AZ80/91 Mg alloy was investigated in a 2.5wt.% NaCl, 3.5wt.% NaCl solution and Natural Sea Water (NSW) in order to explore the corrosion performance of ECAPed magnesium alloys in various environments. From, electrochemical corrosion experiments and surface morphology observations evidently shown that grain refinement exhibited improved corrosion resistance of the AZ80/91 alloy in all environments, also which shown a protective passive film on the surface to shield corrosion