1. Ph.D Theses
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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 Characterization of Zro2 Reinforced Al-12.5si Alloy Matrix Composite Fabricated Through Spray Forming Technique(National Institute Of Technology Karnataka Surathkal, 2023) Patil., Ishwaragouda S; Rao, Shrikantha S; Herbert, Mervin AAluminium and its alloys possess high stiffness, lightweight and high strength. They can provide solutions to optimize strength-weight ratio in aerospace and automobile industries. Among several methods to fabricate Aluminium metal matrix composites, spray deposition method is used for large-scale production due to its high deposition efficiency. In the first phase, stir cast processing route was employed to prepare the composite. Taguchi experimental plan with a set of parameters such as stir speed, stir time, ZrO2 % reinforcement, and casting temperature were studied to know their influence on the composite properties. Super ranking concept was adopted to optimize the key process parameters of stir casting. It has resulted in 25.02% and 5.64% increase in ultimate tensile strength and hardness, respectively, whereas the reduction in wear loss of composites was 37.68% compared to initial stir casting conditions. The hot-pressing technique was applied to the composites prepared according to optimized stir casting conditions. The hot-pressing parameters (pressure, temperature, and dwell time) were analysed to know the process insights on composite properties. The pressure is the most dominating factor followed by temperature on all the properties of composites. The optimal hot-pressing conditions were again obtained by Super ranking concept. The usage of these optimal conditions showed a 39.3% reduction in wear loss, 11.54% and 4.88% increase in ultimate tensile strength and hardness values, respectively, compared to initial hot-pressing condition. The comparison of properties exhibited by samples fabricated by initial, and optimal conditions of stir casting and hot-pressing technique have resulted in excellent enhancement of properties which was strongly justified with the analysis of resulted microstructures and worn surface morphologies. In second phase, the metal matrix composites were fabricated using 99.9 wt. % aluminium and silicon (the wt % 12.5Si ) is reinforced with the (5wt%, 10 wt% and 15wt%) ZrO2 powder particles by stir casting and spray deposition method. Mechanical properties, micro hardness and evolution of microstructure of AlSi alloy with three different wt. % of zirconium oxide as particulate reinforcement were studied. The microstructural results indicate that the rich interface among the metal matrix and AlSi-ZrO2 particles and depicts the agglomeration of reinforced phase resulting to poor wettability of ZrO2 and observed decohesion. The mechanical testing results indicate that the tensile strength increases with the percentage of ZrO2. Moreover, as cast composites exhibit reverse tendency in compressive and hardness values. The highest compressive values for as cast and hot-pressed composites xi` were 380 MPa and 337 MPa for the addition of 10% ZrO2. The highest tensile strength of 191.83 MPa was obtained for 5% ZrO2 as cast composite and 164 MPa for 15% ZrO2 hot pressed composite. It is to note that as cast composite method represented more homogenous data compared to the hot-pressed composites. Hot pressed samples exhibited the reduction in the porosity compared to the as cast. In the third phase, research aims to study the effect of flight distance as a potential key factor that changes the optimum percentage of AlSi-ZrO2 in terms of mechanical and microstructural properties. The alloy is sprayed at varying the flight distance from 320 mm to 480 mm. The alloys were prepared by spray deposition technique and effects on microstructural properties were investigated. The AlSi-ZrO2 alloy was subjected to hot isostatic pressing for reducing the porosity of the deposit from 14.4% to 8.2%. Series of experimental study were carried out in the laboratory by varying the flight distance from 320 mm to 480 mm for AlSi-ZrO2 alloy to characteristic loading. In this paper, an optimized artificial neural network using genetic algorithm are developed to predict the mechanical behaviour for AlSi-ZrO2 composites. Based on the experimental data, the ANN models were developed, trained and tested. The microstructure of the AlSi-ZrO2 alloy consisted of finely divided globular shaped eutectic Si uniformly distributed in the Al matrix. With addition of ZrO2 composition to AlSi alloy, the tensile strength and micro hardness increased from 123 MPa to 147 MPa and 48 HV to 72 HV. The preferred flight distance for the current study is found to be 420 mm. Microstructural images obtained at flight distance consist of co-existing primary Si phase and needle like eutectic Si. The physical properties, such as tensile strength, compressive strength, yield strength, micro hardness and porosity of sprayed AlSi-ZrO2 can hence be adjusted by setting the optimized flight distance. The developed ANN-GA method proved to be accurate, reduced time and efficient to predict the numerous samples, and it will help materials designers to design their future experiments effectively. In fourth phase, the wear behaviour and microstructural characterization of aluminium silicon alloy with a reinforced ZrO2 composite material with respect to various flight distances are investigated. The amounts of ZrO2 (5, 10 & 15 wt %) were added to Al-12.5Si alloy. The microstructural characterization of the developed composites was analysed using Scanning Electron Microscope (SEM) and Energy Dispersive Spectrum (EDS). The effect of flight distance (320 to 480 mm), applied load (30 to 50 N) and the influence of reinforced ZrO 2 (5, 10 and 15 wt %) were investigated using the design of experiment (5x3x5 mm). The findings of the study reveals that there is a remarkable improvement in wear behaviour when xii` surfactant functionalized MWCNT-in-oil is used. Finally, a wear map of the underlying wear mechanisms is also presented. This investigation showed that wear resistance of the developed Al-12.5Si alloy can be improved by the effect of optimized effect of flight distance and wt% of ZrO2. In addition, ANN-GA model were developed to predict the wear behaviour of Al-12.5Si with reinforced material of ZrO2, applied load and the effect of flight distance as inputs. The estimated values were compared with experimental tests and the results showed that a high degree of association (Correlation coefficient, R ranging from 0.91 to 0.96). Therefore, the develop model can be used to predict the behaviour of wear within the range of tests performed. Another important outcome of this research is the development of prediction model using ANN and genetic algorithm (GA) to assist in validation. This method is a combination of two soft-computing methods of ANN and GA. GA logic helps in the transformation of the human knowledge and the ANN helps in the learning process and reduces the rate of errors in the determination of rules in ANN logic.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 Experimental Studies on Friction Coefficient of Al 6061-T6 Alloy Contacts under Full Sliding(National Institute of Technology Karnataka, Surathkal, 2021) I, Srinivasula Reddy.; Kaliveeran, VadivuchezhianAim of the present research work is to study dry sliding coefficient of friction of aluminium to aluminium contacts in detail and to study evolution of coefficient of friction with change in normal load, sliding speed and temperature. Dry sliding experiments were conducted using pin on disk type tribometer. Specimens (both pin and disk) were fabricated using Al 6061-T6 alloy. The disk specimen has dimensions of 165 mm diameter and 8 mm thickness; the pin specimen dimensions are 30 mm length, 6 mm x 6 mm cross-section and 3 mm radius of curvature at cylindrical contact. Experiments were conducted with cylinder on flat contact configuration. Dry sliding experiments were conducted by applying normal loads of 1 kg, 1.5 kg and 2 kg; at different sliding speeds of 1.25 m/s, 2 m/s and 3 m/s; at different temperatures room temperature (31 ± 1 °C), 60 °C, 100 °C and 150 °C. The coefficient of friction at contact interface is influenced by both frictional heat generated and external temperature. The frictional heat at contact interface was estimated by measuring temperatures at 3 mm and 7 mm from contact interface of pin specimen during dry sliding experiments. One-dimensional inverse heat transfer model was developed using Finite Element Method and Beck’s algorithm to estimate the contact interface temperature. The inverse heat transfer model was validated by using ANSYS transient thermal analysis. Maximum bulk temperature at contact interface was observed for all the experimental conditions at room temperature. Temperature due to frictional heat at contact interface increased with increase in normal load and sliding speed. The maximum frictional heat of 100 °C was observed at 2 kg normal load and 3 m/s sliding speed condition. The frictional heat and external heat source temperatures are the reasons for formation of oxide layer at contact interface during sliding which ultimately changes the coefficient of friction of contact pair. Coefficient of fiction, after the first cycle of sliding, stabilized stage, unsteady state and steady state are reported elaborately in this study. The coefficient of friction and wear rate were more influenced by increase in normal load than by increase in sliding speed and temperature. Adhesive and abrasive wear mechanisms were observed in dry sliding of Al 6061-T6 alloy contacts from the microscopic analysis of worn contact surfaces. Under normal loads of 1 kg and 1.5 kg, Al 6061-T6 alloy showed better wear resistance at higher temperatures when compared to that at room temperatureItem 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 Investigation on Elevated Temperature Adhesive Wear Behavior of Microwave Fused Thermal Spray Tribaloy Composite Coatings(National Institute of Technology Karnataka, Surathkal, 2019) C, Durga Prasad; Joladarashi, Sharnappa; Ramesh, M. R.Metallic materials that operate under high speed, high temperature and harsh chemical environments are prone to wear and corrosion degradation. This leads to the failure of metallic components and results in huge economic loss to industries. The amorphous alloy or metallic glasses exhibit superior properties like high hardness, good wear, and corrosion resistance. Metallic glasses eliminate an ordered crystalline structure, hinders plastic deformation. The Co-based amorphous alloy is the best example of bulk metallic glassy structure alloy and presence of primary intermetallic laves phase’s exhibits good mechanical as well as chemical properties. This is mostly employed as coatings because they are too brittle to be used in bulk form. Co-based metallic glass coating depositing on metallic materials could positively eliminate the failure of the working component caused by serious wear and erosion issues. In the present study, CoMoCrSi superalloy powder (Tribaloy-T400) comprising of a primary intermetallic laves phase of Co-rich solid solution has shown better mechanical and tribological properties. Processing of CoMoCrSi feedstock powder is carried out through a high-energy ball milling (HEBM) technique to obtain a higher volume fraction of intermetallic laves phases. The hard phases of 30% Cr3C2, WC-CrC-Ni and WC-12Co are reinforced into milled CoMoCrSi feedstock. The four different feedstock powders CoMoCrSi, CoMoCrSi+30%Cr3C2, CoMoCrSi+30%WC-CrC-Ni and CoMoCrSi+30%WC- 12Co are sprayed on pure titanium grade-15 substrate using High-Velocity-Oxy-Fuel (HVOF) and flame spray methods. The as-sprayed coatings are subjected to post heat treatment to refine their metallurgical and mechanical properties using microwave hybrid heating technique. Characterization of feedstock, as-sprayed and microwave fused coatings is done by using Scanning Electron Microscopy (SEM), Energy dispersive spectroscopy (EDS) and X-ray Diffraction (XRD). Porosity, surface roughness, microhardness, and adhesion strength of as-sprayed and fused coatings are evaluated. The substrate, as-sprayed and microwave fused coatings are subjected to elevated temperature sliding wear test against alumina disc under dry conditions. The test is carried out at 200°C, 400°C, and 600°C temperatures for 10 N and 20 N normal loads. Microwave fused coatings exhibit higher wear resistance than the as-sprayed coatings and substrate. The hard intermetalliclaves phases which are amorphous (bulk metallic glass) in nature strengthen the coatings at high temperatures. Co3Mo2Si, Co7Mo6, Mo3Si, Co3Mo, and Co2Mo3 are the intermetallic laves phases generated in CoMoCrSi feedstock during HEBM process. The coatings produced from HVOF and flame spray process exhibits heterogeneous structure by showing cracks and pores, also cohesive strength between splats is low. The microhardness and adhesion strength of as-sprayed coatings is lower than fused coatings. Microwave fused coatings exhibit homogeneous structure with less porosity, and surface roughness. The posttreated coatings reveals the inter-diffusion of atoms near substrate-coating interface region, these results in formation of metallurgical bonding leads to increase in microhardness and adhesion strength. The as-sprayed coatings exhibits higher wear rate and coefficient of friction due to lower microhardness. The worn surface of as-sprayed coatings reveals detachment of splats with severe deformation results in adhesive wear mechanism. Microwave fused coatings exhibits lower wear rate and coefficient of friction due to higher microhardness obtained from intermetallic laves phases and also formation of homogeneous structure. The fused coatings exhibits tribo-oxide layers during sliding action which is the main phenomenon for improving the wear resistance of the fused composite coatings. CoMoCrSi+WC-12Co composite coating showed better mechanical and tribological properties compared to other types of coatings.Item Development and Characterization of Metal Injection Moulded Components in Improving Resistance to High Temperature Wear and Oxidation(National Institute of Technology Karnataka, Surathkal, 2019) C, Veeresh Nayak.; Ramesh, M. R.; Desai, Vijay.Metal injection moulding (MIM) is a near-net shape manufacturing technology for producing intricate parts, cost-effectively. MIM comprises combined techniques of plastic injection moulding and powder metallurgy. A wax-based binder system consisting of paraffin wax (PW), low-density polyethylene (LDPE), polyethylene glycol (PEG-600) and stearic acid is established for MIM of powder systems of Cr3C2- NiCr (30% Wt.) +NiCrSiB (70% Wt.), SS316L (70% Wt.) +WC-CrC-Ni (30% Wt.) and Tool Steel. The excellence of the MIM product depends on feedstock characteristics, process parameters of the injection moulding stage as well as debinding and sintering stage. Injection stage is most important as many defects such as phase separation, weld line, voids etc. may occur during injection stage due to improper selection of injection moulding parameters and these defects cannot be repaired in the subsequent debinding and sintering stages. The feedstock was characterized by rheological properties at different temperatures. Injection temperature was determined by the rheological investigation of the feedstock having the 56 % powder loading and 44% binder by volume. The solvent debinding temperature is optimized and defect-free MIM component is obtained at a temperature of 48°C. Sintering process was carried out with the temperature cycle in the range of 1150–1200 °C under hydrogen purged atmosphere. The sintering density achieved was 96%. The MIM components showed good and acceptable shrinkage in linear dimensions. Material behaviour at elevated temperature is becoming an increasing technological importance. Components working at higher temperatures like in land-based gas turbines, power generation boiler tubes, hot sections of aero engine, gas and steam turbine, propulsion bearings, materials processing, and internal combustion engines are subjected to surface friction, wear, oxidation conditions. Service conditions of such components in elevated temperature environments may compromise their mechanical properties resulting in a reduced life cycle. Components working in such adverse conditions demand suitable components processed through near net shape techniques. The proposed MIM compacts are investigated for their resistance to wear and oxidation under laboratory conditions.vi Three types of MIM specimens namely Cr3C2-NiCr+NiCrSiB, SS316L+WC-CrC-Ni, and Tool Steel are characterized using Scanning Electron Microscope (SEM), Energy Dispersive Spectroscopy (EDS) and X-ray diffraction (XRD). Further, microstructure and mechanical properties were characterized to evaluate their potential for hightemperature application. Dry sliding wear behaviour of MIM specimens are evaluated using a high-temperature pin on disc tribometer. The SS316L+WC-CrC-Ni and Tool Steel MIM specimens displayed a lower coefficient of friction and wear rate in comparison with Cr3C2- NiCr+NiCrSiB. Excellent wear resistance of the MIM specimens is attributed to the solid lubricants effect. Based on the wear rate data, the relative wear resistance of the MIM specimens under dry sliding conditions is arranged in the following sequence: (Tool Steel) > (SS316L+WC-CrC-Ni) > (Cr3C2-NiCr+NiCrSiB) Higher wear resistance of MIM Tool Steel specimens is attributed to the high hardness of Cr3Ni2 phase formed during the sintering process. Thermo cyclic oxidation behaviour of MIM specimens was carried out at 700 °C for 20 cycles. Each cycle consisted of heating at 700 °C for 1 hour, followed by 20 minutes of cooling in the air. The thermogravimetric technique is used to approximate the oxidation kinetics of MIM specimens. The Cr3C2-NiCr+NiCrSiB and SS316L+WCCrC-Ni MIM specimens reported lower weight gain as compared to the Tool steel. Cr3C2-NiCr+NiCrSiB MIM specimens registered less weight gain as compared to SS316L+WC-CrC-Ni which is attributed to the excellent oxidation resistance of NiCrSiB and formation of NiCrO4 along with NiO and Cr2O3 oxides on the surface of MIM specimens. In the present study, the powders of Cr3C2-NiCr+NiCrSiB, SS316L+WC-CrC-Ni, and Tool Steel are successfully metal injection moulded and sintered to achieve 96% density. Developed MIM components exhibit resistance to high-temperature wear and oxidation which is suitable for components subjected to elevated temperature service conditions.Item Development and Characterization of Functionally Graded Al-Si Alloy System and Al-Si/SiCP Composites using Centrifuge Casting(National Institute of Technology Karnataka, Surathkal, 2013) S., Kiran Aithal; Desai, Vijay; Narendranath, S.FGM is a material that shows change in magnitude of property values from one end of a specimen or component to the other end. FGM has an intermediate layer whose structure, composition and morphology vary smoothly from one end of the specimen to the other end. Fabrication of FGM and their components with gradient microstructures and properties are challenging. Most of the investigations which focus on material behavior of FGMs are limited to analytical or numerical studies. One of the major bottlenecks with experimental studies is the preparation of FGMs having large property gradation. This necessitates the development of a suitable technique to produce such FGMs with reproducibility of structure and properties. The present work aims at developing a manufacturing technique for the FGMs in order to meet the wide range of and also suitable mechanical and tribological properties for specific thermal and mechanical engineering applications. Among the processing techniques available the most commonly used is horizontal centrifugal method, but, this method is used to produce mainly hallow cylinders. In this work a centrifuge setup is fabricated and FGMs have been successfully developed to produce solid castings. The major advantage of this machine when compared to the conventional machine is that the pouring is done while the mold is stationary and machine operates about a vertical axis. The principal advantage of this is good mold filling combined with microstructural control, which usually results in improved mechanical properties. In this process, when the melt is subjected to high G forces the lighter particles segregate towards the axis of rotation, while the denser particles move away from the axis of rotation depending on the density difference between melt and the reinforcement. This segregation depends on several process parameters such as mold rotational speed (G Factor), pouring temperature, mold temperature etc. The use of aluminum, its alloys and aluminum based composites in the present day has shown many advantages through its unique combination of physical and mechanical properties. The light weight, strength, formability, corrosion resistance, ofIV aluminum, its alloys give it the potential to meet a wide range of design challenges. Taking into consideration the advantages such as high wear resistance, controlled thermal-expansion coefficient, good corrosion resistance, and improved mechanical properties over a range of temperatures that Al alloys and its composites can provide, in this work manufacturing and characterization Al-Si FG alloys and Al-Si-SiCP FG composites have been taken up. Two Al-Si alloys eutectic (12%Si) and hypereutectic (17%Si) were used for producing FG alloys. Further effect of 3 mold rotational speed 200, 300, 400rpm, 2 pouring temperatures 800oC , 900oC and 2 mold temperatures ambient and preheating the mold at 180oC temperature were studied. Similarly FG composites were also produced using Al-17%Si and Al-12% Si as matrix with SiCP as reinforcement. Three different volume fractions of SiCP were used to produce FG composites. The FG composites were produced using 900oC pouring temperature with preheating the mold at 180oC under 200, 300, 400rpm mold rotational speed. The structure and properties of the FG alloys and Composites are studied to understand the effect of different process parameters. The Al-Si FGM specimens are studied for distribution of Si along the length of the specimen (from bottom to top) using optical microscope. The hardness's is measured along the length of the specimen using Brinell hardness tester. Sliding wear tests at room temperature are conducted at normal loads of 40, 60, and 80N and at 1.466m/s sliding speed for a constant sliding distance 879.6m in order to measure the wear resistance and friction characteristics. Similar tests were carried out for FG composites. Diametral compressive strength were conducted to know the strength of the specimen along the length at bottom, middle and top regions. It is found that the FG alloy and Composites are produced successfully using centrifuge technique. In both alloy and composite the gradation occurs at higher rpm, teeming temperature and mold temperature. The experimental findings of hardness and the wear tests provide adequate proof on the gradation characterization (% volume fraction of primary Si, % volume fraction of SiCP and rim thickness) done using microstructural studies.Item Severe Plastic Deformation of Magnesium Alloys by Equal Channel Angular Pressing(National Institute of Technology Karnataka, Surathkal, 2017) K. R, Gopi; Nayaka, H ShivanandaMagnesium and its alloys possess good mechanical properties like low density, good castability, high specific strength and low cost. Requirement of magnesium alloys is more towards industrial applications, particularly in aerospace and automotive industries. The main limitation is the poor room temperature formability, with limited number of slip systems, due to their hexagonal closed packed (HCP) structure. Formability at room temperature in Mg alloys can be improved by grain refinement, as fine-grained structure improves ductility. Severe plastic deformation (SPD) is a technique where high strains are induced into the material to produce fine grained structural material. They also have few limitations, like high wear rate and low corrosion resistance, which hinders the usage of magnesium in many applications. Wear rate and corrosion resistance can be improved by subjecting the material to SPD, thereby, increase the applications of magnesium alloys. Equal channel angular pressing (ECAP) is one of the simple and most effective methods of SPD to improve the material properties. ECAP 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. ECAP process leads to ultrafine-grained microstructure in the material which may show superplastic deformation at low temperature and high strain rate. In HCP structured metals, grain refinement also leads to textural changes i.e. high strengthening in some particular directions. Magnesium alloys are available in various systems – (a) Mg-Al system where aluminum addition improves the mechanical property as well as the castability. Addition of aluminum up to 6% and more makes the alloy age-hardenable. Manganese (Mn) addition plays a vital role in grain refinement for magnesium alloys. (b) Aluminum-manganese (AM) series magnesium alloys are widely used in manufacturing of various automobile components such as seat frames, instrument panels etc., due to their better damping, better toughness, impact absorption and elongation properties compared to aluminum-zinc (AZ) series alloys.In the present study, ECAP was performed on AM70, AM80 and AM90 alloy with varying percentage of aluminum and manganese. In spite of various applications of AM series magnesium alloy, limited work has been done to improve the physical properties of AM series magnesium cast alloys. We may further improve these properties by using ECAP, so that its application can be expanded in different areas of engineering. ECAP was carried out using hot die steel (HDS) die with channel angle (Φ) as 110° and outer arc of curvature (Ψ) as 20° using route BC. Unprocessed and ECAP processed samples were subjected to microstructural studies and tested for mechanical properties. Strength and hardness values showed increasing trend for the initial 2 passes of ECAP processing and then started decreasing with further increase in the number of ECAP passes, even though the grain size continued to decrease in all the successive ECAP passes. However, the strength and hardness values still remained quite high when compared to the initial condition (as-cast and homogenized). This behavior was found to be correlated with texture modification in the material as a result of ECAP processing. Wear and corrosion tests were conducted to study tribological and corrosion behavior of ECAP processed samples. Results showed reduction in wear mass loss for the ECAP processed samples. Coefficient of friction (COF) was studied for different loads and improvement in COF values was observed for ECAP processed samples compared to initial condition. Potentiodynamic polarization and electrochemical impedance spectroscopy test showed improvement in corrosion resistance of ECAP processed samples. Immersion test showed similar trend with increased corrosion resistance of ECAP processed samples with low hydrogen evolution.