2. Thesis and Dissertations
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Item An Experimental Investigation on the Properties of Cu-Al-Be-X Shape Memory Alloys for Vibration Damping Applications(National Institute of Technology Karnataka, Surathkal, 2022) T., Kalinga; S.M., Murigendrappa; S., KattimaniSmart materials are a new class of materials that possess adaptive capabilities which include sensing, responding and regulatory in a precise manner to the change of its environment stimuli, and are of great interest in structural, robotics, biomedical, marine, aerospace, and spacecraft technologies. Fiber Optics, Piezoelectric (PE), Magnetorheological (MR), Magnetostrictive (MS), Chromogenic, Electrorheological (ER), Electrostrictive (ES), Shape Memory Polymers (SMPs), and Shape memory alloys (SMAs) are the most common smart materials. Among these, SMAs exhibit a peculiar property in that deformed material can restore its original/predefined shape either by increasing the temperature or removing the load, which is known as the shape memory effect (SME) and “pseudoelasticity (PE) or superelasticity (SE)”, respectively. In addition, certain SMAs can exhibit the magnetic shape memory effect (MSME) by undergoing magnetic-field-induced reverse martensitic transformations. The merits of these unique properties attract the use of SMAs as dampers and actuators in smart/adaptive structures to suppress unwanted vibrations and provide seismic protection with the adoption of passive, active, semi-active, or hybrid control strategies. The functional and mechanical properties of various groups of SMAs are still being progressive in the development and implementation of a novel, cost-effective, and long functional SMA for the vibration damping and isolation of mechanical and civil structures. Ni-Ti-based shape memory alloys (popularly known as Nitinol-based SMAs) are the most commonly used in many applications and already had a commercial presence due to their superior advantages, such as high strain recovery and long functional life, however, these are restricted its vast usage due to shortcomings like processing difficulties and high cost. Cu-Al-based SMAs are selected as a prime alternative to Ni-Ti-based SMAs owing to their ease of manufacture and economical, and this has motivated to develop the suitable Cu-Al- based shape memory alloys. The aim of this thesis is to design and develop Cu-Al-Be-based polycrystalline shape memory alloys with improved microstructure, enhanced mechanical properties, better pseudoelastic shape/strain recovery, and suitability for use as seismic protection material to isolate vibrations through a passive control strategy. The present investigation has been carried out on the influence of variations in the weight percentage of Copper (Cu), Aluminium (Al), Beryllium (Be) and the grain refiners, namely Boron (B), zirconium (Zr), on the alloy phases, microstructure, mechanical, and pseudoelastic hysteresis properties. Outcomes of the present investigation reveals that Al followed by Be plays a vital role in the alloy phase modifications i.e., parent austenite, martensite or mixed phase at room temperature. The minimal addition of quaternary boron and zirconium grain refiners leads to substantial grain refinement, enhanced mechanical properties, and better pseudoelastic shape recovery. Because of these improvements in properties, they are identified as suitable for the passive damper in mechanical and civil structure applications at ambient temperature.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 An Experimental Investigation on Properties of Cu-Al-Be-X Shape Memory Alloys for Smart Structure Applications(National Institute of Technology Karnataka, Surathkal, 2020) Narasimha, G Bala.; Murigendrappa, S. M.Smart materials are new class of materials, capable of sensing and responding to the change of its environment are of much interest in robotics, structural, biomedical and aerospace technologies. Shape memory alloys (SMA), Shape memory polymers (SMP), Hydrogels, Electrostrictive (ES), Electrorheological (ER), Piezoelectric (PE), and Magnetostrictive (MS), Magnetorheological (MRE) are the most common smart materials. Among these, shape memory alloys hold a peculiar property viz. deformed material can restore their actual shape either by an increase in temperature or removal of the load, known as shape memory effect and super-elasticity respectively. These two distinct properties attract the usage of SMA’s as actuators in smart structures to suppress flutter and in civil structures to isolate vibrations. Past decades, intense research has been carried out and still progressing in the development of a novel, economical and long functional SMA for the flutter suppression in the smart/adaptive structures. From 1960s to till today, Ni-Ti based SMAs are used mostly in applications because of their superior advantages i.e., high strain recovery, long functional life, however their utilization is limited due to the difficulties in processing and expensive. Cu-Al based shape memory alloys are selected as an alternative to Ni-Ti (Nitinol), because of ease of production and economical. This thesis is concerned with the design and development of Cu-Al-Be based shape memory alloys with improved microstructure, mechanical properties, and narrow thermal hysteresis with better shape/strain recovery for the actuator applications. The investigation has been carried out on the effect of variation in wt.% of Cu, Al, Be and the grain refiners viz. Boron (B), zirconium (Zr), and rare-earth elements, cerium (Ce) and gadolinium (Gd), and also manganese (Mn) on microstructure, mechanical and shape memory properties. The present investigation suggests that Al plays a vital role in the modification of martensitic fraction followed by Be. Boron and zirconium grain refiners enhance the grain refinement with minimal addition and better shape recovery. Cu-Al-Be-B shape memory alloys are chosen as suitable for the rapid response.Item Microstructure and Mechanical Properties of Cast Aluminium-Zinc-magnesium Alloys Processed by Equal Channel Angular Pressing(National Institute of Technology Karnataka, Surathkal, 2019) Manjunath, G. K.; G. V, Preetham Kumar; K, Uday BhatEqual channel angular pressing (ECAP) is one of the severe plastic deformation (SPD) techniques used to develop ultrafine-grained (UFG) materials. In this technique, large amount of shear strain is introduced in the material, without any change in the cross sectional dimensions. Al-Zn-Mg alloys are promising light weight high strength materials, wherein precipitation strengthening will be possible. In this investigation ECAP is used to enhance the strengthening in the Al-Zn-Mg alloys. The alloys studied in the present work were prepared by gravity casting method. ECAP processing was carried out in a die having an internal angle between two channels (Φ) of 120º and outer arc curvature (Ψ) of 30º. The processing was attempted at lowest possible temperature in route BC. Techniques, like optical microscopy, scanning electron microscopy, transmission electron microscopy and X-ray diffractometer were used to characterize and analyse the microstructures before and after ECAP processing. To assess the mechanical properties, microhardness measurement and tensile tests were conducted. Fracture mode and fracture surface morphologies of the tensile test samples of the processed and unprocessed materials were studied. Wear properties were evaluated before and after ECAP processing. Wear mechanisms involved in the samples were studied. Microstructural study reveals that, in as-cast condition, alloys were composed of dendritic structure. Also, with increase in the zinc content in the alloy, volume of precipitates was increased. After ECAP processing, considerable decrease in the grain size of the alloys was noted. Also, after ECAP processing, high density dislocation structures with high fraction of high angle grain boundaries were observed. It was also noticed that, ECAP processing leads to enhance the precipitation kinetics of the alloy. In all three alloys, after ECAP processing, fine size spherical shaped precipitates were noticed and these precipitates were uniformly distributed in the alloy. After ECAP processing, significant improvement in the mechanical properties of the alloys was perceived. Microhardness and strength were increased with increase in the zinc content in the alloy. At the same time, elongation to failure of the alloy decreased with increase in the zinc content. Optimum mechanical properties were perceivedwhen the alloys were processed at lowest possible temperature. Compared to as-cast alloys, microhardness increases by 109% for Al-5Zn-2Mg alloy, 67% for Al-10Zn-2Mg alloy and 58% for Al-15Zn-2Mg alloy, processed at 200 °C. Compared to as-cast alloys, ultimate tensile strength (UTS) increases by 122% for Al-5Zn-2Mg alloy, 153% for Al-10Zn-2Mg alloy and 139% for Al-15Zn-2Mg alloy, processed at 200 °C. Brittle fracture mode was observed during tensile test of as-cast and homogenized samples. The fracture mode was changed to shear fracture after ECAP processing. Large sized dendrites were observed in the fracture surfaces of the as-cast condition tensile test samples. While, narrow and shallow dimples were noticed in the fracture surfaces of the ECAP processed samples. ECAP processing leads to considerable improvement in the wear resistance of the alloys. Wear resistance of the alloys increased with increase in the zinc content. Coefficient of friction of the alloy decreased after ECAP processing. Also, coefficient of friction of the alloy decreased with increase in the zinc content. Irrespective of the applied load, abrasive wear mechanism was reported in the as-cast and homogenized condition samples. In the ECAP processed samples, wear mechanism shifts from adhesive to abrasive wear with increase in the applied load. Also, in the ECAP processed samples, at lower load; transfer of iron particles from the disc surface to the sample surface was noticed. Compared to the Al-5Zn-2Mg and Al-10Zn-2Mg alloys better wear properties were observed in Al-15Zn-2Mg alloy.Item Effect of Ageing on the Microstructure and Mechanical Properties of Al-Si Alloys with Copper Additions(National Institute of Technology Karnataka, Surathkal, 2017) Channappagoudar, Shivaprasad; S, Narendranath; Desai, VijayAluminum has a density approximately one-third that of cast-iron or steel and have proved effective alternatives for many engineering applications. The good strength to weight ratio offered by Al-Si and Al-Si-Cu alloys has made these alloys popular as they present opportunities for weight reduction in automotive applications. The mechanical properties of aluminum can be enhanced by adding alloying elements such as silicon, copper, magnesium, zinc etc. Silicon as an alloying element has the ability of to reduce density and coefficient of thermal expansion, improve hardness, mechanical properties such as modulus and strength, thermal stability, wear resistance and corrosion resistance of aluminum. Further it also improves castability of aluminum also. This has created considerable interest among the materials and manufacturing engineers to explore the Al–Si family of alloys for possible applications in automotive, electrical and aerospace industries. Based on Si content Al-Si alloys are generally classified as hypoeutectic (up to 11%), eutectic (11 to 13 %) and hypereutectic (13 to 19 %) alloys. Grain refinement and modification of the alloy using suitable refiner and modifier improves the mechanical properties further. Addition of copper to Al-Si alloys induces precipitation of CuAl2 particles and depending on cooling rate and modifier level, this phase appears as blocky CuAl2 or fine eutectic colonies at the grain boundaries. Hence, an addition of Cu to Al-Si alloys improves the tensile strength. Solution heat treatment and ageing in Al-Si-Cu alloys, forms variants of CuAl2 leading to still better hardness and mechanical properties. The present work is carried out to investigate the influence of addition of copper (4.5 wt.%), combined modification and grain refinement, effect of T6 heat treatment process on hypoeutectic (7% Si), eutectic (12% Si) and hypereutectic Al-Si (15% Si) alloys. Al-1Ti-3B is used as grain refiner while Sr and P are used as modifiers. The effect of these processes on microstructure of Al-Si alloys, mechanical properties and tribological properties are investigated.IV Al-1Ti-3B grain refiner showed a markedly positive effect on the refinement of α-Al phase. Addition of Al-10Sr modifier was responsible for the modification of Si. The micro structural changes due to modification and grain refinement led to an improvement in UTS and % elongation of all the three types of alloys considered in this work. For Al-7Si the UTS increased from 154 MPa to 171 MPa (11%) while % elongation showed marked improvement increasing from 7.6 to 11.9 (56.6%). The corresponding improvement in UTS values for Al-12Si and Al-15Si were 18% and 22% and % improvement in elongation were 57 and 28, respectively. Addition of 4.5 wt.% Cu to Al-Si alloys was responsible for improved tensile strength and also resulted in improved sliding wear properties. This is attributed to the presence of CuAl2 as particle or eutectic in the Al interdendritic region. A combined addition of Al-1Ti-3B and Al-10Sr to hypoeutectic and eutectic alloys resulted in conversion of large α-Al grains in to equiaxed grains, plate like eutectic Si in to fine particles and changed the coarse CuAl2 morphology to fine eutectic colonies of Cu + CuAl2. A combined addition of Al-1Ti-3B grain refiner and AlP and Al-10Sr modifier to Al- 15Si-4.5Cu alloy provided a favorable microstructural change that led to superior mechanical and sliding wear properties. The heat treatment schedule applied in this study consisted of solution heat treatment at a temperature of 500°C for 6h; quenching in water at room temperature; ageing at a temperature of 200°C for varying time periods. Experimental results showed that heat treatment influenced the mechanical properties to a good extent in both the as-cast as well as combined modified and refined alloy. The Al-7Si-4.5Cu alloy showed a peak hardness of 126 BHN in as-cast condition where as the modified alloy showed 138 BHN. The UTS of melt treated Al-7Si-4.5Cu alloy increased from 208 MPa to 262 MPa (26% improvement), Similar trends were also observed for the other two alloys. The refinement during solution treatment and subsequent precipitation of fine CuAl2 particles may be the main reason for this improvement. The increase in strength due to Cu addition and age hardening of the alloy is balanced out by corresponding decrease in ductility. For 7Si alloy the ductility reduced by 22%V on adding Cu and further reduced by 22% on ageing for 20 h. However, the ductility is improved to a certain extent by grain refinement and modification. During dry sliding wear test, melt treatment reduced the wear volume loss of as-cast Al-7Si alloy by 25% and with Cu addition and melt treatment, the loss reduced by 40%. The solution treatment and ageing for 20 h improved the wear resistance substantially, with wear volume loss reducing by 79% as compared to as-cast Al-7Si alloy. Similar results were also observed for 12Si and 15Si alloys.