Engineering Commons^™

Laser Surface Structuring Of Alumina, Sandip Pundlikrao Harimkar

Doctoral Dissertations

Alumina ceramic is an important abrasive material for grinding wheels used for rough grinding/machining of materials in manufacturing industry. Purpose of this work is to explore laser surface structuring of alumina grinding wheels for precision machining/grinding of materials by modifying surface microstructure of wheels. Major objective of this work is to study the evolution of surface microstructure and depth of modification such that microstructures/properties of modified wheels can be efficiently tailored based on fundamental understanding of physical processes taking place during laser surface structuring.

Surface structuring of alumina using a continuous wave Nd:YAG laser resulted in significant surface melting and …

Processing And Phase Formation In Zr-Based Bulk-Metallic Glass-Forming Alloys, James Joseph Wall

Doctoral Dissertations

Bulk-metallic glasses have established a formidable presence in the scientific community in recent years, due to a number of properties that are uncharacteristic of metallically-bonded materials. One of the fundamental challenges facing researchers in this field is to develop new and improved processing methods with the ultimate goal of facilitating a large-scale industrial integration of the materials.

The research described herein is directed toward the pursuit of developing and improving upon the current state-of-the art in the science of bulk-metallic glass processing. A number of research and development projects were undertaken in this pursuit. First, the technology to process bulk-metallic …

Degradation Mechanism Of Expanded Polystyrene (Eps) Foam In Lost Foam Casting, Pips Approach For Synthesis And Novel Expansion Techniques For Cellular Foam, Indraneel Sen

Doctoral Dissertations

Lost Foam Casting (LFC) is a metal casting technology that facilitates fabrication of near-net shape metal castings using expanded polystyrene (EPS) foam patterns that are coated with refractory slurry and is effective for producing aluminum or iron castings of complicated geometry. However, the LFC process can produce considerable amount of scrap due to casting defects. Removing the EPS thermal decomposition products through the ceramic coating ahead of the advancing metal front during the liquid metal pour is a key factor in obtaining a defect free casting. Developing a fundamental understanding of foam degradation mechanism is essential in improving LFC process. …

A Study Of The Secondary Electrons, Yinghong Lin

Doctoral Dissertations

Slow secondary electrons (SEs) (E<50 eV) are those emitted from a sample as the result of bombardment by energetic particles. They are the most important signal source for SEM and for other advanced microanalysis techniques. SE yield δ and spectrum N(E) are the two important parameters evaluating the capability of a sample on producing SEs and the energy distribution of SEs generated from the sample respectively. Measuring δ and N(E) is not easy since SEs are easily affected by sample surface condition and by experimental configuration. Though SE has been studied since its first find in 1902, experimental date of it are inconsistent and unsystematic. Theoretical models on the SE production are not well established.

To better understand the secondary electrons, an optimization of a scattered experimental SE yield database was carried out by fitting the data to a semi-empirical universal curve and by a Monte Carlo simulation. The profiles of SE yield versus beam energy and the values of SE excitation energyε and mean SE escape depthλ were generated for 44 elements. An atomic shell filling effect was found on the maximum SE yields and the corresponding beam energies.

To obtain more accurate and systematic SE yield data, a novel experimental method by collecting electron spectra on an AES …

A Finite Element Study Of The Contact Stiffness Of Homogenous Materials And Thin Films, Haitao Xu

Doctoral Dissertations

The applicability of the stiffness equation S=2E_ra to elastic and elastic-plastic homogeneous materials and thin films on substrates is studied by finite element techniques. It is found that the stiffness equation works well in all these materials provided that a correction factor β is included. For elastic homogenous materials, the correction factor is examined for different friction conditions, Poisson’s ratios, and indenter cone angles. In the case of elastic-plastic indentation with a 70.3° cone, the correction factor is very close to that for elastic indentation of a matching conical hole, which provides a convenient way to model the …

A Study Of Fabrication Of Ultra-High Resolution Nano Devices Through Electron Beam Lithography Process And Its Application To Electron – Optical Systems, Jihoon Kim

Doctoral Dissertations

Today’s semiconductor industry has been significantly changing in its techniques and processes for the fabrication of devices and accordingly, there has been dramatic increase in performance and a reduction in cost. To obtain still higher device performances and still further cost reduction, the dimensions of patterns in integrated circuits should be as small as possible and the 3-dimensional accuracy of multidimensional semiconductor structures should be also achieved as well. The manufacturing of smaller feature dimensions and 3-dimensional devices has been enabled by developments in lithography – the technology which transfers designed patterns onto the silicon wafer. Especially, electron beam lithography …

Plastic Deformation And Annealing Of Zr- And Cu- Based Bulk Metallic Glasses, Sujing Xie

Doctoral Dissertations

Plastic deformation in crystalline metals occurs by the motion and multiplication of lattice defects called dislocations, resulting in strain hardening. Metallic glasses, in contrast, lack long-range order; therefore, dislocation-mediated plasticity is not possible in these materials. Metallic glasses undergo plastic deformation through the nucleation and propagation of defects called shear bands, which cause strain softening.

This strain softening can be recovered after annealing, i.e., annealing makes the plastically strained metallic glasses harder, in sharp contrast to the annealing-induced softening typically observed in crystalline metals. During annealing, hardness initially recovers more rapidly in heavily deformed specimens than in lightly deformed ones, …

Elucidating The Growth Mechanisms Of Electron Beam Induced Deposition Via A Three Dimensional, Monte-Carlo Based Simulation, Daryl Allen Smith

Doctoral Dissertations

The rapid and precise direct-write growth of nanoscale features by electron-beaminduced deposition (EBID) and etching (EBIE) requires the optimization of the growth parameters to maintain nanoscale feature dimensions. The tremendous and complex EBID parameter space includes the precursor gas pressure, the primary electron beam energy, the electron beam current, surface diffusion rates of adsorbed precursor species, thermal effects on desorption, and the cascade of electron species produced by elastic and inelastic scattering processes. These variables determine the feature growth velocity and the size of the structure through a series of complex, coupled nonlinear interactions. A dynamic computer simulation based on …

Equal-Channel-Angular Processing (Ecap) Of Materials: Experiment And Theory, Grigoreta Mihaela Stoica

Doctoral Dissertations

Equal Channel-Angular Processing (ECAP), as a severe plastic deformation of metals and composites, is analyzed both theoretically - to describe the ECAP macromechanics - and experimentally - to obtain ultrafine-grained materials with new thermo-mechanical properties - with a focus on hexagonal-closed-packed (HCP) structures such as Mg alloys. Due to their obvious similarity to ECAP, the slip-line–field theories developed for orthogonal cutting are applied to the ECAP deformation for predicting the shear-strain spatial heterogeneities. A theoretical model for predicting the plastic-deformation zone in an ECAP-ed billet with a free surface is provided, and is validated experimentally. A shear-strain-mapping procedure was developed …