Papers by Keyword: Optical Microscopy

Abstract: This work explores the application of gallium nitride (GaN)-based solid-state devices for high-power, high-frequency, and high-temperature technologies. It presents an in-depth study of GaN on semi-insulating SiC substrates. The study demonstrates, through bow range investigation, optical microscopy, and X-ray diffraction (XRD), that by adapting growth parameters from those used for Si substrates to those suitable for SiC substrates, it is possible to achieve high-quality crystalline MOCVD growth both under on-axis and 4°off-axis substrate orientations.

Abstract: Sn-Cu-Ni-Ge (SN100C®) is a high-performance Pb-free solder alloy widely used in the electronics manufacturing industry due to its excellent soldering performance and lower cost. SN100C has a huge potential to replace the commonly used Sn-Ag-Cu solders. This work investigates the effect of different strain rates (10^-3 to 8×10^-1s^-1) on tensile performance for bulk SN100C samples at room temperature. The tensile properties, e.g., elastic modulus (E), yield strength (σ_y) and tensile strength (σ_T) are determined from the stress-stress curves. The value of σ_y and σ_T increases with increasing strain rates and this increase becomes less prominent at higher strain rates. Necking and ductile fracture are observed for all samples with a significant number of dimples, voids and tongues formed. The level of ductility of the samples decreases with increasing strain rates, which is further confirmed by the stress-strain behaviour. The microstructural evolution of the samples is evaluated by optical microscope (OM), scanning electron microscope (SEM) and energy dispersive X-ray (EDX) to reveal the generation of recrystallisation and fracture of the intermetallic compounds (IMCs) at the fracture tips and identify the embedded of IMCs within the sample matrix.

Abstract: Additive Manufacturing (AM) is a product creation method done layer-by-layer. This process tends to create an unwanted feature known as staircase effect. Vapor smoothing is considered a viable solution for polymer-based AM products to minimized surface roughness. Research literature concerning vapor smoothing of polylactic acid (PLA) parts generally limited unlike its ABS counterpart. This research aims to identify optimum level for both chamber temperature and exposure time of the AM product. Two methods were used to compare their outputs with one another. The two methods are surface roughness tester and optical microscopy. The results provided an impressive 50.88 and 62.72% improvement based on the two test methods. Lastly, a contour-plot was generated to provide future users a guideline if they want to conduct research similar study.

Abstract: Bidriware is an ancient metal-based object of Art from South India dating back to 14th Century A.D. The base casting in a Bidriware work is made of a Zn-Cu alloy in the ratio of 16:1 while the inlay work is hemmed with pure silver. The black patination obtained on the surface of Bidriware has been a source of mystery and intrigue for a long time. In this work, this black patination has been investigated to understand the chemistry behind it. The patination in Bidriware is actually a combination of Cupric oxide, Cupric chloride and other minute quantities of cuprous oxide, cupric nitrate and Zinc oxide, which are the results obtained from XRD, SEM, Optical microscopy and XRF analysis. We have further found that similar black patination can be obtained on the surfaces of pure copper and yellow brass. Since black oxide layers have multiple applications in many fields for the property of black body, a novel method, based on ancient knowledge, has been suggested here to obtain similar surfaces on pure copper and yellow brass samples.

Abstract: The reduction of harmful greenhouse gas (GHG) emissions can be realized by utilizing lightweight structural metals, such as magnesium. Magnesium alloys have the potential to replace higher-density aluminum and ferrous components in automotive and aerospace industries, thereby decreasing vehicle weight and the associated fuel requirements. However, their strength and ductility must be improved to ensure widespread application. This goal can be achieved through ultrasonic processing in the molten state, a technique that is gaining popularity in the manufacturing of light alloys. In this study, the effects of high-intensity ultrasonic vibration on the microstructure and hardness of AZ91E Mg alloy was investigated. The molten alloys were subjected to sonication of varying durations, and the resulting castings were characterized using optical microscopy, scanning electron microscopy and hardness testing. Sonication was found to successfully increase the hardness of the alloy relative to the base condition. This improvement was attributed to the refinement of the magnesium grain structure as well as the Mg₁₇Al₁₂ and Mn-Al secondary phases in the sonicated alloys. The competitiveness of magnesium alloys can be significantly enhanced via ultrasonic processing, offering important opportunities for the production of greener, light metal components.

Abstract: The photoelastic effect was used to visualize and quantify stresses at the end of fibers embedded in birefringent epoxy resin. A method was proposed allowing not to only quantify the differences in main principal stress for a single loading state, but to allow monitoring the evolution of local stress throughout the micro-mechanical experiment. It was found that the ends of fibers foster the formation of shear stresses which influence the principal stress distribution. Typically, star-shaped principal stress distributions were found at the ends of fibers. Finite Element simulations of the tests were in good agreement with the experimental evidence.

Abstract: The microstructure and corrosion properties of weld fusion zone and the heat affected zones of gas tungsten arc (GTA) welded AA2014 alloy, welded at varying speeds of 1.5mm/s, 2.5 mm/s and 3.5 mm/s were examined for gaining knowledge on the effect of welding speed on corrosion behavior at localized regions of the weldment. The macrostructure and microstructure of the welds were evaluated with optical microscope. The corrosion properties were examined with potentiodynamic polarization in aqueous 3.5% NaCl solution. The GTA welding has resulted in grain refinement fusion zone and dispersion of coarse Al₂Cu phases within the grains and along the grain boundaries of heat affected zones. With increase in welding speed the grain size of AA2014 at the fusion zone reduces significantly and also the corrosion resistance of the fusion zone and heat affected zone could decrease as it shows higher negative corrosion potential.

Abstract: AA2014 is a heat treatable aluminium alloy found its application in light weight structures owing to its superior strength to weight ratio. The alloy was welded with automatic gas tungsten arc welding. The microstructure and mechanical properties of each zone such as parent metal (PM), heat affected zone (HAZ) and fusion zone (FZ) of the weldment were studied using optical microscopy, microhardness survey and micro-tensile testing. The PM with elongated grains with evenly distributed Al₂Cu phases showed a tensile strength of 456 MPa and 24% elongation; the HAZ and FZ offered a reduction in strength and ductility. The grain coarsening with segregation of continuous string of Al₂Cu along grain boundaries in HAZ and the formation of coarse dendritic grains with continuous network of brittle Al₂Cu and a minor fraction of porosity at interdendrite in FZ were attribured to the observed strength reduction in these regions. Keywords: AA2014 alloy; gas tungsten arc welding; optical microscopy; microhardness; micro-tensile testing.

Abstract: Using optical and atomic-force microscopy methods, it has been established that exposure to electron radiation causes a change in the supramolecular structure of polypropylene – in films obtained by recrystallization of irradiated polypropylene, spherulites have a less perfect shape than films obtained from unirradiated polypropylene. Also, the films obtained by recrystallization of irradiated polypropylene surface roughness is greater.

Abstract: Electromagnetic techniques such as Magnetic Hysteresis Loop and Barkhausen Emission are applied to determine recovery and recrystallization in low carbon IF steel. Isothermal annealing at 450 and 620°C are carried to promote recovery and recrystallization. In present study, the magnetic non-destructive parameters such as coercivity and magnetic Barkhausen noise signal measurements, recovery and onset of recrystallization are monitored for annealing treatments. Mechanical softening is very small changes than magnetic softening at 450°C, while at 620°C, both the parameters are sensitive. Microstructure analysis examined through Optical microscopy at each annealing temperature in order to determine recovery and recrystallization. Keywords: IF steel, Recrystallization, MHL, MBE, Hardness, Optical microscopy