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 Department: Department of Materials Science and Engineering
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A Study of Mechanisms to Engineer Fine Scale Alpha Phase Precipitation in Beta Titanium Alloy, Beta 21S

A Study of Mechanisms to Engineer Fine Scale Alpha Phase Precipitation in Beta Titanium Alloy, Beta 21S

Date: August 2013
Creator: Behera, Amit Kishan
Description: Metastable b-Ti alloys are titanium alloys with sufficient b stabilizer alloying additions such that it's possible to retain single b phase at room temperature. These alloys are of great advantage compared to a/b alloys since they are easily cold rolled, strip produced and can attain excellent mechanical properties upon age hardening. Beta 21S, a relatively new b titanium alloy in addition to these general advantages is known to possess excellent oxidation and corrosion resistance at elevated temperatures. A homogeneous distribution of fine sized a precipitates in the parent b matrix is known to provide good combination of strength, ductility and fracture toughness. The current work focuses on a study of different mechanisms to engineer homogeneously distributed fine sized a precipitates in the b matrix. The precipitation of metastable phases upon low temperature aging and their influence on a precipitation is studied in detail. The precipitation sequence on direct aging above the w solvus temperature is also assessed. The structural and compositional evolution of precipitate phase is determined using multiple characterization tools. The possibility of occurrence of other non-classical precipitation mechanisms that do not require heterogeneous nucleation sites are also analyzed. Lastly, the influence of interstitial element, oxygen on a precipitation ...
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Corrosion Protection of Aerospace Grade Magnesium Alloy Elektron 43™ for Use in Aircraft Cabin Interiors

Corrosion Protection of Aerospace Grade Magnesium Alloy Elektron 43™ for Use in Aircraft Cabin Interiors

Date: August 2013
Creator: Baillio, Sarah S.
Description: Magnesium alloys exhibit desirable properties for use in transportation technology. In particular, the low density and high specific strength of these alloys is of interest to the aerospace community. However, the concerns of flammability and susceptibility to corrosion have limited the use of magnesium alloys within the aircraft cabin. This work studies a magnesium alloy containing rare earth elements designed to increase resistance to ignition while lowering rate of corrosion. The microstructure of the alloy was documented using scanning electron microscopy. Specimens underwent salt spray testing and the corrosion products were examined using energy dispersive spectroscopy.
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Mist and Microstructure Characterization in End Milling Aisi 1018 Steel Using Microlubrication

Mist and Microstructure Characterization in End Milling Aisi 1018 Steel Using Microlubrication

Date: August 2013
Creator: Shaikh, Vasim
Description: Flood cooling is primarily used to cool and lubricate the cutting tool and workpiece interface during a machining process. But the adverse health effects caused by the use of flood coolants are drawing manufacturers' attention to develop methods for controlling occupational exposure to cutting fluids. Microlubrication serves as an alternative to flood cooling by reducing the volume of cutting fluid used in the machining process. Microlubrication minimizes the exposure of metal working fluids to the machining operators leading to an economical, safer and healthy workplace environment. In this dissertation, a vegetable based lubricant is used to conduct mist, microstructure and wear analyses during end milling AISI 1018 steel using microlubrication. A two-flute solid carbide cutting tool was used with varying cutting speed and feed rate levels with a constant depth of cut. A full factorial experiment with Multivariate Analysis of Variance (MANOVA) was conducted and regression models were generated along with parameter optimization for the flank wear, aerosol mass concentration and the aerosol particle size. MANOVA indicated that the speed and feed variables main effects are significant, but the interaction of (speed*feed) was not significant at 95% confidence level. The model was able to predict 69.44%, 68.06% and 42.90% of ...
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Mechanics and Mechanisms of Creep and Ductile Fracture

Mechanics and Mechanisms of Creep and Ductile Fracture

Date: August 2013
Creator: Srivastava, Ankit
Description: The main aim of this dissertation is to relate measurable and hopefully controllable features of a material's microstructure to its observed failure modes to provide a basis for designing better materials. The understanding of creep in materials used at high temperatures is of prime engineering importance. Single crystal Ni-based superalloys used in turbine aerofoils of jet engines are exposed to long dwell times at very high temperatures. In contrast to current theories, creep tests on Ni-based superalloy specimens have shown size dependent creep response termed as the thickness debit effect. To investigate the mechanism of the thickness debit effect, isothermal creep tests were performed on uncoated Ni-based single crystal superalloy sheet specimens with two thicknesses and under two test conditions: a low temperature high stress condition and a high temperature low stress condition. At the high temperature, surface oxidation induced microstructural changes near the free surface forming a layered microstructure. Finite element calculations showed that this layered microstructure gave rise to local changes in the stress state. The specimens also contained nonuniform distribution of initial voids formed during the solidification and homogenization processes. The experiments showed that porosity evolution could play a significant role in the thickness debit effect. This ...
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Interspecimen Study of Bone to Relate Macromechanical, Nanomechanical and Compositional Changes Across the Femoral Cortex of Bone

Interspecimen Study of Bone to Relate Macromechanical, Nanomechanical and Compositional Changes Across the Femoral Cortex of Bone

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Date: May 2013
Creator: Nar, Mangesh
Description: Mechanics of bone is widely studied and researched, mainly for the study of fracture. This has been done mostly on a macro scale. In this work hierarchical nature of bone has been explored to investigate bone mechanics in more detail. Flexural test were done to classify the bones according to their strength and deflection. Raman spectroscopy analysis was done to map the mineralization, collagen crosslinking changes across the thickness of the bone. Nanoindentation was done to map indentation hardness and indentation modulus across femoral cortex of the bone. The results indicate that the composition of the bone changes across the thickness of the femoral cortex. The hypothesis is confirmed as increase in mineralization, carbonate to phosphate ratio and collagen crosslinking shows the effect as increased indentation hardness and modulus and decreased deflection.
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Effect of Retting on Surface Chemistry and Mechanical Performance Interactions in Natural Fibers for High Performance Polymer Composites

Effect of Retting on Surface Chemistry and Mechanical Performance Interactions in Natural Fibers for High Performance Polymer Composites

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Date: May 2013
Creator: Ramesh, Dinesh
Description: Sustainability through replacement of non-renewable fibers with renewable fibers is an ecological need. Impact of transportation costs from South-east Asia on the life cycle analysis of the composite is detrimental. Kenaf is an easily grown crop in America. Farm based processing involves placing the harvested crop in rivers and ponds, where retting of the fibers from the plant (separation into fibers) can take 2 weeks or more. The objective of this thesis is to analyze industrially viable processes for generating fibers and examine their synergistic impact on mechanical performance, surface topography and chemistry for functional composites. Comparison has been made with commercial and conventional retting process, including alkali retting, enzymatic retting, retting in river and pond water (retting occurs by natural microbial population) with controlled microbial retting. The resulting kenaf fibers were characterized by dynamic mechanical analysis (DMA), Raman spectroscopy (FT-Raman), Fourier transform infrared spectroscopy (FT-IR), polarized optical microscopy (POM), X-ray photoelectron spectroscopy (XPS), Scanning electron microscopy (SEM) optical fluorescence microscopy, atomic force microscopy (AFM) and carbohydrate analysis. DMA results showed that pectinase and microbe treated fibers have superior viscoelastic properties compared to alkali retting. XPS, Raman, FT-IR and biochemical analysis indicated that the controlled microbial and pectinase retting was ...
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An Integrated Approach to Determine Phenomenological Equations in Metallic Systems

An Integrated Approach to Determine Phenomenological Equations in Metallic Systems

Date: December 2012
Creator: Ghamarian, Iman
Description: It is highly desirable to be able to make predictions of properties in metallic materials based upon the composition of the material and the microstructure. Unfortunately, the complexity of real, multi-component, multi-phase engineering alloys makes the provision of constituent-based (i.e., composition or microstructure) phenomenological equations extremely difficult. Due to these difficulties, qualitative predictions are frequently used to study the influence of microstructure or composition on the properties. Neural networks were used as a tool to get a quantitative model from a database. However, the developed model is not a phenomenological model. In this study, a new method based upon the integration of three separate modeling approaches, specifically artificial neural networks, genetic algorithms, and monte carlo was proposed. These three methods, when coupled in the manner described in this study, allows for the extraction of phenomenological equations with a concurrent analysis of uncertainty. This approach has been applied to a multi-component, multi-phase microstructure exhibiting phases with varying spatial and morphological distributions. Specifically, this approach has been applied to derive a phenomenological equation for the prediction of yield strength in a+b processed Ti-6-4. The equation is consistent with not only the current dataset but also, where available, the limited information regarding certain ...
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Laser Modified Alumina: a Computational and Experimental Analysis

Laser Modified Alumina: a Computational and Experimental Analysis

Date: December 2012
Creator: Moncayo, Marco Antonio
Description: Laser surface modification involves rapid melting and solidification is an elegant technique used for locally tailoring the surface morphology of alumina in order to enhance its abrasive characteristics. COMSOL Multiphysics® based heat transfer modeling and experimental approaches were designed and used in this study for single and multiple laser tracks to achieve densely-packed multi-facet grains via temperature history, cooling rate, solidification, scanning electron micrographs, and wear rate. Multi-facet grains were produced at the center of laser track with primary dendrites extending toward the edge of single laser track. The multiple laser tracks study indicates the grain/dendrite size increases as the laser energy density increases resulting in multiplying the abrasive edges which in turn enhance the abrasive qualities.
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Molecular Dynamics Simulations of the Structures of Europium Containing Silicate and Cerium Containing Aluminophosphate Glasses

Molecular Dynamics Simulations of the Structures of Europium Containing Silicate and Cerium Containing Aluminophosphate Glasses

Date: August 2012
Creator: Kokou, Leopold Lambert Yaovi
Description: Rare earth ion doped glasses find applications in optical and photonic devices such as optical windows, laser, and optical amplifiers, and as model systems for immobilization of nuclear waste. Macroscopic properties of these materials, such as luminescence efficiency and phase stability, depend strongly on the atomic structure of these glasses. In this thesis, I have studied the atomic level structure of rare earth doped silicate and aluminophosphate glasses by using molecular dynamics simulations. Extensive comparisons with experimental diffraction and NMR data were made to validate the structure models. Insights on the local environments of rare earth ions and their clustering behaviors and their dependence on glass compositions have been obtained. In this thesis, MD simulations have been used to investigate the structure of Eu2O3-doped silica and sodium silicate glasses to understand the glass composition effect on the rare earth ions local environment and their clustering behaviors in the glass matrix, for compositions with low rare earth oxide concentration (~1mol%). It was found that Eu–O distances and coordination numbers were different in silica (2.19-2.22 Å and 4.6-4.8) from those in sodium silicate (2.32 Å and 5.8). High tendencies of Eu clustering and short Eu-Eu distances in the range 3.40-3.90 Å were ...
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Scratch Modeling of Polymeric Materials with Molecular Dynamics

Scratch Modeling of Polymeric Materials with Molecular Dynamics

Date: August 2012
Creator: Hilbig, Travis
Description: It is impossible to determine the amount of money that is spent every replacing products damaged from wear, but it is safe to assume that it is in the millions of dollars. With metallic materials, liquid lubricants are often used to prevent wear from materials rubbing against one another. However, with polymeric materials, liquid lubricants cause swelling, creating an increase in friction and therefore increasing the wear. Therefore, a different method or methods to mitigate wear in polymers should be developed. For better understanding of the phenomenon of wear, scratch resistance testing can be used. For this project, classic molecular dynamics is used to study the mechanics of nanometer scale scratching on amorphous polymeric materials. As a first approach, a model was created for polyethylene, considering intramolecular and intermolecular interactions as well as mass and volume of the CH2 monomers in a polymer chain. The obtained results include analysis of penetration depth and recovery percentage related to indenter force and size.
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