Dissertations/Theses - Department of Materials & Metallurgical Engineering
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Item Effects of Gd on microstructure and deformation mechanisms of hot-rolled Mg-Zn-Y alloy(Department of Materials and Metallurgical Engineering (MME), BUET, 2023-09-24) Mallick, Bijoy; Al Rashed, Dr. Hossain Mohammad MamunThe microstructural evolution under various conditions (as-cast, homogenized, and hot rolled) and the deformation mechanisms at four distinct temperatures (250°C, 300°C, 350°C, and 400°C) and two strain rates (1x10-4 and 5x10-4 s-1) of the Mg-1Zn-1.5Y alloy were investigated with the addition of Gd (1%, 2%, and 6 wt%) to the alloy system. The chemical composition was analyzed using XRF, confirming the desired alloy composition with negligible deviation. Optical microscopy was employed to observe dendritic arm presence, measure grain size, assess precipitation conditions, and identify secondary phases within the matrix. Dendritic arms were evident in the as-cast condition, with density increasing due to Gd addition. Additionally, a trend of grain size reduction was observed with Gd inclusion in all conditions. Notably, hot rolling significantly reduced grain size through dynamic recrystallization (DRX). XRD, SEM, EDS, DSC, and CALPHAD analysis were utilized to determine different phases present in the alloy matrix, phase morphology, chemical composition, phase formation temperature, and phase evolution and volume fraction with temperature for the three alloys. The 14H-LPSO phase was consistently found within the α-Mg matrix of all compositions, with volume fraction increasing as Gd content rises. However, morphological variations were identified due to compositional changes, with lamellar and blocky LPSO phases forming in alloy A (1% Gd) and B (2% Gd), and blocky LPSO in alloy-C (6% Gd). Furthermore, in CALPHAD analysis Mg5(Gd,Y) was observed in alloy-A and C, while alloy-B contained the W-phase (Mg3Zn3(Y,Gd)2), which remained stable till the elevated temperatures around 600°C. However, above 450°C, the 14H-LPSO phase was found to start dissolving within the α-Mg matrix. Tensile testing at four different temperatures and two strain rates was conducted to assess changes in strength, ductility, and deformation mechanisms due to Gd addition. An optimal combination of strength and ductility was observed in alloy-B (2% Gd) at high temperature (400°C) and both strain rates, attributed to the presence of a bimodal 14H-LPSO phase (mix of lamellar and blocky LPSO) and the W-phase at elevated temperatures. Conversely, alloy-C demonstrated promising performance below 350°C, possibly due to the maximum volume fraction of the blocky LPSO phase. To determine the deformation mechanisms, activation energy, strain exponent (n) values, and strain rate sensitivity (m) of the alloys were calculated. Dispersed strengthening mechanism was predominant at lower temperatures (250°C and 300°C), transitioning to climb-controlled creep, glide-controlled creep, and grain-boundary sliding at higher temperatures (350°C and 400°C).Item Theoretical and experimental estimation of structural, electronic and optoelectronic properties of alkali metals absorbed monolayer of g-C3N4(Department of Materials and Metallurgical Engineering, BUET, 2023-08-09) Ayeman Mazdi Nahin; Ahmed Sharif, Dr.Carbon nitride of layered structure, bulk form, and its state of nano-particles bear separate characteristics. Adsorbing alkali metal in it modifies its geometrical structure. The intercalation property of C3N4allows it to adsorb ions of varied sizes, even in greater quantity. From the various allotropes of g-C3N4, the trigonal structure is the most popular as well as readily fabricable. In this work,electrical and optoelectrical properties of Li, Na, and K adsorbedg-C3N4was investigated using DFT simulation and several other properties are observed by experiment.DFT based simulation was carried out based on 3×3×1 supercell. Several different DFT functionals on Quantum Espresso and CASTEP codes were tested to choose the best option. It was found that the BLYP_US_VDW functional yielded the best performance. Simulation shows that the layers of graphitic carbon nitride mandatorily distort after ion adsorption. Angle of contact between the ions and the C3N4 layer was lowest (44.9°) for Li+ and the highest (58.2°) for K+.Simulation shows the band gap energy to benearly indirect after all the ion adsorptions. Density of states is almost identical for Li and Na doping. But it is noticeably different for K doping. Graphitic carbon nitride can find its application in various pressure and vibration sensing devices. Therefore, piezoelectric constant measurement is very important. This work estimated the values of piezoelectric constant (d33) from the simulated piezoelectric tensor data. The estimated and experimental values are comparable. In experiment it is found that the piezo-electric constant differs very slightly upon doping. The highest value is for K doping and it is 3.8 × 10-11 C/N (Pure g-C3N4shows3.3 × 10-11 C/N). So, the dopants are not a well contributor to the improvement of piezoelectricity.In this thesis, UV-vis spectroscopy was carried out for pure g-C3N4, K and Na adsorbed samples. All of them have shown notable absorbance peaks at around 200 nm wavelength (more or less) and the band gap decreased from 2.74 eV to 2.65 eV. So, the band gap suggests thatgraphitic carbon nitride can be a promising candidate in photodegradation-relatedapplications, though the effectiveness has not been justified in this work.At the end of this thesis paper, the concluding remarks are included and perspectives are made for further study.Item Machine learning-assisted approach towards finding the promising low-toxic perovskite halides for solar cell applications(Department of Materials and Metallurgical Engineering(MME), BUET, 2023-05-18) Humayun, Kabir.; Mohammad Shorowordi, Dr. KaziPredicting the bandgap of perovskite absorbers properly is vital for an effective perovskite solar cell design. According to the literature, the bandgap of perovskites is the most dominant parameter affecting solar cell performance. The primary objective of this study was to develop a suitable machine-learning (ML) model to predict the bandgap of any halide-based perovskite absorber. First, three ML algorithms, such as linear regression, random forest regression, and gradient boosting regression, were developed based on the elemental properties of each site present in the perovskites. Different error metrics such as root mean squared error (RMSE), coefficient of determination (R2), and cross-validation scores were calculated to compare their performances. Among the standalone ML models, the gradient-boosting model achieved the best performance. Then, these base models were used to construct the ensemble voting regression model utilizing weighted averages according to the base models’ performances. The voting regressor model outperformed the three baseline models, with the lowest RMSE (0.076) and highest fitting accuracy of R2 (0.95). To reduce the toxicity of lead in MAPbI3, three potential replacements of Ge, Sn, and Si were considered for bandgap prediction and Sn based MAPb1-xSnxI3 was found the best. Finally, a suitable composition of MAPb0.75Sn0.25I3 from the predicted dataset and pristine MAPbI3 was selected for SCAPS-1D analysis. It was found that pristine MAPbI3 performed well in a single junction solar cell with the highest power conversion efficiency of 21.65%. However, replacing the Pb site with 25% Sn reduced the performance showing maximum efficiency (PCE) of 18.58%. The MAPb0.75Sn0.25I3 composition needs further attention to enhance its performance. This study gives an effective tool for the experimentalists to make the task of predicting bandgap efficient, making the whole design process smooth and easier.Item Mangifera indica mediated biogenic synthesis of undoped and doped tio2 nanoparticles and evaluation of their structural, morphological, photocatalytic and antibacterial properties(Department of Materials and Metallurgical Engineering(MME), BUET, 2022-05-01) Asrafuzzaman; Gulshan, Dr. FahmidaPristine and doped TiO¬¬2 nanoparticles were synthesized utilizing mango leaf extract via a cost effective and eco-friendly biogenic route. As a precursor, titanium isopropoxide (TTIP) was used. The transition metals, Cu and Ag, were added as dopant materials in various concentration levels of 0.5%, 1%, 1.5%, and 2%. To assess the morphological, structural, photocatalytic, and antibacterial properties of the prepared samples, several characterization techniques such as SEM, EDX, XRD, UV-Vis, Kirby-Bauer disk diffusion method were implemented. The observation from SEM analysis revealed that compared to undoped TiO¬2¬, Cu- and Ag-doped TiO2 nanoparticles showed agglomeration. Evaluation of elemental analysis by EDX confirmed the doping of Cu2+ and Ag+ ions in the TiO2 lattice structure. It also ensured the absence of any kind of impurities. According to XRD analysis, pure TiO2 as well as Cu- and Ag-doped TiO¬2 nanoparticles exhibited formation of anatase phase without any rutile phase. Crystallite size and micro-strain of the prepared nanoparticles were determined from XRD results along with W-H plot. At maximum doping percentage (2%), both Cu- and Ag-doped TiO2 samples showed reduction in crystallite size compared to pure TiO2. UV-Vis spectroscopy was employed to determine the band gap and photocatalytic efficiency of the prepared samples. Both Cu- and Ag-doped TiO2 samples showed a gradual decline in band gap in comparison to undoped TiO2 with the increasing doping percentage. The result of the photo-degradation of methylene blue (MB) demonstrated that doping of TiO2, whether with Cu/Ag, greatly enhance the photocatalytic performance which is attribute to the “Red-Shift” phenomena along with the reduced photo-generated electron-hole recombination rate. Antibacterial performance of the prepared samples was examined against Gram positive and Gram negative bacteria strain utilizing Kirby-Bauer disk diffusion technique. Cu- and Ag- doped TiO2 nanoparticles of specific doping percentage showed mentionable zone of inhibition confirming their potential as bactericidal agent. Results obtained suggest that TiO2 nanoparticles (both undoped and doped) synthesized through a greener approach may have a promising future for water purification, dye remediation, medical sector and food industry owing to better photo-degradation and antibacterial activity. Keywords: TiO2 nanoparticles, Mango leaf extract, Biogenic route, Photocatalytic activity, Antibacterial activity.Item Synthesis of zirconia nanopowders from local zircon sand and study the influence of crystal structure on photocatalytic activity(Department of Materials and Metallurgical Engineering (MME), 2022-07-03) Mahbuba, Sultana; Gulshan, Dr. FahmidaIn the present study purification of natural zircon sand was performed by hydrometallurgical method and zirconia (ZrO2) nanopowders were synthesized from the purified zircon. Later influence of crystal structure on photocatalytic activity was investigated. The characterization and upgradation processes were employed on local ZrSiO4 sand collected from Cox’s Bazar Sea Beach via Beach Sand Minerals Exploitation Center (BSMEC). Traditional beneficiation methods like acid leaching and alkali leaching were performed. As received sample contained 73.8% ZrSiO4 which turned 86.3% purity after upgradation. Major impurity rutile (19.8%) was removed completely through these beneficiation processes. The particles found uniformly distributed and possessed negligible amount of moisture. Standard tetragonal phase of ZrSiO4 was found in the as received sample which didn’t show any phase transition at low temperature (up to 750oC). Through consecutive alkali-fusion, co-precipitation followed by calcination ZrO2 nanoparticle with different phases were formed from ZrSiO4nano powder. Depending on calcination temperature ZrO2 showed different crystal structure. Calcination at 800oC and 1000oC showed predomination of tetragonal ZrO2 whereas comparatively high temperatures (1100oC and 1300oC) showed mostly monoclinic structure. Zirconia samples with different crystal structures were used to decolorize Methylene Blue dye.Calcinedsample at 1100oC showed maximum decolorization (71.75%) efficiencydue to presence of combined monoclinic, cubic and tetragonal phases. The result concludes that nanoparticle of zirconia can be synthesized from local zircon sand and it can be used forphotodegradationof textile dye.Item Development and characterization of cellulose crystal reinforced biodegradable composite material(Department of Materials and Metallurgical Engineering (MME), 2022-07-04) Sharaban, Tohora; Hasan, Professor Dr. MahbubPresently, development of biodegradable materials is one of the most popular topics in the field of materials science because of the adverse effects of plastics. Cellulose crystals (CC) as fillers in bio-composites have recently gained much interest amongst researchers for its promising qualities like improving elasticity and viscosity, rheological properties, and biodegradability. In present research, cellulose crystal has been extracted from jute using two steps of pretreatment. At first the raw jute fiber was ground and alkali treated with 15% sodium hydroxide for 1.5 hours. Then the resultant fiber was washed until neutral and bleached with 50% pure hydrogen peroxide for 1.5 hours. After the pretreatment, acid hydrolysis was done using 64% pure sulfuric acid for 15 minutes to produce pure cellulose crystal. The cellulose crystal was then freeze dried and used as reinforcement in a recently developed biodegradable composite from jute. The purchased jute polymer was dissolved and reinforced with cellulose crystal at 0, 0.1, 0.2, 0.3, 0.4 wt.% loading. The characteristics of the synthesized CC was studied using Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis. The results show that pure cellulose crystal was found, and micrographs showed presence of microscale particles with tear in the surface. For characterization of the films Fourier-transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) and X-ray diffraction (XRD) analysis was used. The results showed that the reinforcement did not introduce any new functional groups and did not help increase the crystallinity of the films. The SEM micrographs showed that CC loading up to 0.2% helped reduce the pore formation, however increasing the CC loading any further caused agglomeration and pores. Thermal characteristics of the reinforced composite films was tested using thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC) and tensile properties were tested using UTM. The results show that the thermal and tensile properties increased up to 0.2% CC loading. The composites were tested for biodegradability and all the films degraded in soil after 100 days and the adding of cellulose crystal decreased degradation rate. Water absorption test revealed that the composites had a very high-water absorbance and the adding of cellulose crystal increased water absorption.Item Modelling phase transformation and tensile properties of micro-alloyed structural steels for fire resistance(Department of Materials and Metallurgical Engineering (MME), 2022-01-08) Fahim, Khan; Rashed, Dr. Hossain Mohammad Mamun AlFire is one of the most extreme situations in which structural steels can be damaged, culminating in catastrophic failure. Common structural steels incur subsequent changes in physical characteristics, stiffness, and mechanical properties because of high temperature treatment, which is irreversible after cooling. As a result, many alloy steels have been created to address these issues. Steel produces ferrite to austenite transformation temperatures of 700–750 °C and relative instability of carbide precipitates over 650 °C since it is not fire resistant. Few steel grades have been developed to prevent this, which has led to an increase in the use of certain steel grades at higher temperatures. The demand for fire-resistant high-temperature construction steels has increased as construction technology has improved, resulting in shorter construction periods and more efficient use of space. The aim of the research was to establish a common structural steel by adding a few specific alloying elements like Mo, Cr, Al, and Ti that will assist the steel to maintain its strength at high temperatures. Using thermodynamic data for phases and mobility, CALPHAD-based computational techniques provided insights of microstructure and its impact on different properties.The addition of Mo and Cr retarded the cementite growth and widened the melting range. Consequently, solidus line shifted at higher temperature. Addition of Mo passively raised the cooling rate by increasing time of formation of ferrite, pearlite, austenite and martensite. Mo and Cr enhanced the precipitation of intermetallic carbides of high melting temperatures and controlled and retarded the growth of such carbides. Thus, yield strength of fire-resistant steel was greater than that of conventional steels at elevated temperatures. Owing to low yield ratio, the alloys had a higher ductility. High temperature steels had the same workability and weldability as standard steels. Mo addition significantly modified the elevated temperature strength. To consider the economic perspective, an alternative to Mo can be Cr which is quantitatively found in the prediction. Addition of Cr over Mo might not give better high temperature mechanical properties than solely added Mo but provided superior properties than the base alloy. Combined Mo and Cr addition retarded the formation of cementite which is brittle in nature. Mo addition is exclusively responsible to increase the phase transformation time that will definitely reduce the residual stress of the sample while cooling. The predictions derived from statistical data will undoubtedly aid in the development of experiments for future research.Item Design and fabrication of biocompatible copper based shape memory alloy by spark plasma sintering(Department of Materials and Metallurgical Engineering (MME), 2022-07-03) Auditee, Majumder Momo; Gulshan, Dr. FahmidaCopper based shape memory alloys are at the forefront of R&D for biomedical applications due to their good shape recovery, ease of fabrication, excellent thermal and electrical conductivity, antibacterial properties, and corrosion resistance. Spark plasma sintering (SPS) is a consolidated powder metallurgy process, which offers biocompatibilities to the materials by controlling grain growth, forming desired phases and controlled number of porosities. In the present study, two type of shape memory alloys- CuAlNi and NiTiCu have been fabricated by the SPS method. Studying the ternary phase diagram of the alloys, the composition has been chosen. The SPS parameters have been determined through multiple trials. CuAlNi and NiTiCu alloys have been sintered respectively at 475℃and 730℃.The present study aims to find out the effectiveness oflower sintering temperature and pressure for sintering the shape memory alloys. After selecting the material and experimental parameters, the sample powders have been prepared by wet ball milling at lower ball powder ratio (BPR) and lower milling hour. DSC analysis of the powder has been done to find out the melting point of the alloy powders and the temperatures for different phase formations. XRD, SEM and EDS analysis of the sintered CuAlNi and NiTiCu samples have been carried out to identify the phases and to see the morphology of the samples. Micro hardness of the sintered alloys has been measured and static corrosion test have been done on the sample to find out the corrosion rate. The DSC analysis of the alloy powders provides evidence that successful sintering of CuAlNi and NiTiCu is possible at lower SPS and ball milling parameters. XRD, SEM and EDS results also confirm the presence of desired phases in the sintered alloys. The Vickers hardness values of CuAlNi and NiTiCu refer to the further modification of CuAlNi sample is required whereas the hardness of NiTiCu alloys already have the desired values. The corrosion rates of presently studied CuAlNi alloys are lower. But corrosion resistance of NiTiCu samples in the present study requires further improvement.Item In situ aluminium based dual matrix hybrid composite through powder metallurgy route for automotive industries(Department of Materials and Metallurgical Engineering (MME), 2023-03-22) Tasratur Reaj, Neha; Gulshan, Dr. FahmidaIn recent times, the focus of researchers worldwide has shifted from monolithic materials to composite materials, primarily due to the need for high performance and affordable materials. Amongst the various types of composite materials, aluminum metal matrix composites (AMMC) are an excellent choice for manufacturing high-specific-strength automotive components, as well as for various mechanical and tribological applications. They are preferred over other materials because of their lighter weight, which is around one-third as much as steel per cubic meter. This property not only ensures more energy-efficient automobiles but also facilitates their production at a lower cost.This study was carried out to attain a deeper understanding of the structural performance of AMMCs. For this purpose, a simple Al-H3BO3-TiO2 system was utilized for AMMC production through ball milling, cold pressing, and sintering. The ball milling process was found to have a considerable impact on particle growth, and the in situ generated reinforcements provide several benefits, including strong bonding and clean particle-metal interface. During the sintering procedure, reinforcement particles were created and uniformly distributed throughout the Aluminium matrix. AMMC's dual matrix structure was observed to perform as a desired characteristic, increasing both ductility and toughness.The percentage of added external aluminum varied from 0% to 25% to 50% to 75% of the total sample. Differential thermal analysis of the green sample was performed up to 800°C, which indicated that the particle development took place after 550°C. Consequently, the sintering temperature was chosen from 600°C to 800°C. Initial microstructural analysis was carried out using optical microscopy, while scanning electron microscopy (SEM) and X-ray diffraction (XRD) techniques were utilized to examine the morphological and structural reinforcing effects of AMMCs.The presence of various in situ reinforcements, including γAl2O3, AlB2, B2O3, TiB2, and TiAlin aluminum matrix was confirmed through X-ray diffraction (XRD) analysis.The mechanical properties were evaluated using a diametral compression tester and a Brinell hardness tester. It was observed that hardness increased with higher sintering temperatures. The sample sintered at 800°C with 0%unmilled aluminum exhibited the highest hardness of 169.2 HV. The results showed that the highest toughness, approximately 6.12 J/m-3, was found in the 75% external aluminum dual matrix compositessintered at 800°C.Item Recovery of copper nanoparticles from waste printed circuit board and its characterization(Department of Materials and Metallurgical Engineering(MME), BUET, 2021-07-01) Arifur Rahman Khan, Md.; Al Rashed, Dr. Hossain Mohammad MamunWaste PCBs were collected and shredded by a shredder in the current work. Shredded PCBs were treated by NaOH solution to remove or loosen up the polymer coating painted on the PCB. As copper was the target element in this experiment two step leaching process was adopted. In the first step, low concentration HNO3 treatment was done to leach the solders and other metals except copper and second step leaching was done by H2O2 added HCl solution for copper leaching. Copper was reclaimed as nanoparticles by electrowinning process using this copper pregnant leach liquor as the electrolyte. Concentration of various elements in the leach liquors of two step leaching process was determined by Atomic absorption spectrometry (AAS). Different characterization techniques such as particle size analysis, SEM with EDX, XRD and Rietveld refinement were applied to characterize copper nanoparticles. Final Cu rich solution found the concentration of Cu 29,437.5 ppm with the presence of few other elements. Reclaimed copper particles were in the range of around 30 to 200 nm revealed by SEM images while having the average crystallite size of 76 nm determined by Rietveld refinement. Presence of metastable cuprous oxide phase was found from the XRD analysis and elemental Cu phase percentage was 65. Macro scale EDX analysis confirmed that vacuum drying of the Cu particles dropped the O contamination from 30% to 6%.