Metallurgy Commons^™

The Characterization And Nanomechanical Properties Of Microstructurally Complex Systems, Kerry Ann Baker

Theses and Dissertations--Chemical and Materials Engineering

Since the dawn of civilization, the use of metals has played an integral role in the evolution of human society. Over the years, and with the introduction of new engineering and science, we have learned how to combine metals to create new metallic systems. We have expanded our understanding of dealloying and chemical reactions, and, in doing so, we created nanoporous metals. Our use of metals has evolved from basic alloys such as bronze and steel to more complex alloys such as multi-principal element alloys. Nanoporous gold is an advanced metallic system that can be created through the dealloying process. …

Thermomechanical Process Simulation And Quantification Of Nanoscale Precipitation Influencing Ductility And Strength During Alloy Processing, Alyssa Stubbers

Theses and Dissertations--Chemical and Materials Engineering

Experimental process simulation and quantification of microstructure development during processing are challenging due to limitations with machinery temperature capability, inadequate resolution and sampling volume of currently available characterization techniques, and difficulty characterizing material microstructures as close to processing-relevant conditions as possible. This dissertation addresses how process simulation can be performed using Gleeble thermomechanical technologies and how microstructure development during these processing simulations can be quantified both in-situ and ex-situ.

The first portion of this dissertation demonstrates how Gleeble technologies can be applied to simulate complex material processing conditions in order to produce process-property profiles that can be used to inform …

Application Of Multi-Scale Computational Techniques To Complex Materials Systems, Mujan N. Seif

Theses and Dissertations--Chemical and Materials Engineering

The applications of computational materials science are ever-increasing, connecting fields far beyond traditional subfields in materials science. This dissertation demonstrates the broad scope of multi-scale computational techniques by investigating multiple unrelated complex material systems, namely scandate thermionic cathodes and the metallic foam component of micrometeoroid and orbital debris (MMOD) shielding. Sc-containing "scandate" cathodes have been widely reported to exhibit superior properties compared to previous thermionic cathodes; however, knowledge of their precise operating mechanism remains elusive. Here, quantum mechanical calculations were utilized to map the phase space of stable, highly-faceted and chemically-complex W nanoparticles, accounting for both finite temperature and chemical …

Derivation, Exploration And Evaluation Of Non-Equiatomic High Entropy Alloys, Artashes Ter-Isahakyan

Theses and Dissertations--Chemical and Materials Engineering

High-entropy alloys (HEAs) are a class of multicomponent alloys based on an innovative alloying strategy that employs multi-principle elements in relatively high concentrations. Commonly defined as alloys that contain at least five principal elements, each with a concentration between 5 and 35 at %. The term entropy refers to the excess configurational entropy associated with HEAs, which is thought to facilitate the formation of solid solutions. The design strategy results in vast compositional space for exploration and innovative potential triggering a renaissance in physical metallurgy. These alloys may have favorable properties compared to conventional dilute solid solutions, but their preeminent …

Laptop Recycling Case Study: Estimating The Contained Value And Value Recovery Process Feasibility Of End-Of-Life Consumer Electronics, Zebulon Hart

Theses and Dissertations--Mining Engineering

Work has been done to establish, through the development and use of novel assay techniques and analysis metrics, the contained value of a sampling of laptop computers (as an analog for myriad e-waste sources). This work has conceptualized e-waste as an alternative to geologic-origin complex metallic ores and has likewise evaluated the feasibility of value recovery from e-waste sources in a similar manner to an ore. The application of conventional and novel mineral separation techniques to e-waste recycling processes has been evaluated and positive results are demonstrated. Further, this work has demonstrated the ability to identify the presence of base …

Modeling Of Rare Earth Solvent Extraction Process For Flowsheet Design And Optimization, Vaibhav Kumar Srivastava

Theses and Dissertations--Mining Engineering

The separation and purification of rare earth elements (REEs) into individual products has been a topic of significant interest for researchers and engineers for many decades. The prime reason for such sustained interest is due to REEs’ demand and application in modern technology, as well as the challenges associated with their separation and purification. The chemical similarity of rare earth group elements is responsible for difficult separability which makes purification of individual elements challenging. Despite associated complications, processes such as solvent extraction (SX) and ion-exchange have been successfully utilized in the separation and production of REEs on pilot and commercial …

Enhanced Surface Integrity With Thermally Stable Residual Stress Fields And Nanostructures In Cryogenic Processing Of Titanium Alloy Ti-6al-4v, James R. Caudill

Theses and Dissertations--Mechanical Engineering

Burnishing is a chipless finishing process used to improve surface integrity by severe plastic deformation (SPD) of surface asperities. As surface integrity in large measure defines the functional performance and fatigue life of aerospace alloys, burnishing is thus a means of increasing the fatigue life of critical components, such as turbine and compressor blades in gas turbine engines. Therefore, the primary objective of this dissertation is to characterize the burnishing-induced surface integrity of Ti-6Al-4V alloy in terms of the implemented processing parameters. As the impact of cooling mechanisms on surface integrity from SPD processing is largely unexplored, a particular emphasis …

Leaching Characteristics Of Rare Earth Elements From Bituminous Coal-Based Sources, Xinbo Yang

Theses and Dissertations--Mining Engineering

The demand for rare earth elements (REEs) has increased over the last decade due to applications in high technology devices including those in the defense industry. The recovery of REEs from primary sources such as rare earth minerals are viable using physical separations followed by chemical processing. However, weak market values and environmental concerns have limited the viability of such operations. On the other hand, REE recovery from secondary sources such as apatite ore, bauxite waste, and waste recycling, provides an opportunity to take advantage of a resource that does not require mining costs as well as other associated costs …

Synthesis And Characterization Of Magnesium - Titanium Composites By Severe Plastic Deformation, Baleegh Alobaid

Theses and Dissertations--Chemical and Materials Engineering

Magnesium alloys are widely used in engineering applications, including aerospace and automobile industries, due to their desirable properties, such as lower density, high damping capacity, relatively high thermal conductivity, good machinability, and recyclability. Researchers have, therefore, been developing new magnesium materials. However, mechanical and corrosion properties are still limiting many commercial applications of magnesium alloys. In this Ph.D. thesis research, I developed Mg-Ti composite materials to offer some solutions to further improve the mechanical behavior of magnesium, such as titanium-magnesium (Ti-Mg) claddings, Mg-Ti multilayers, and Ti particle enforced Mg alloys. Low cost manufacturing processes, such as hot roll-bonding (RB) and …

Combinatorial Screening Approach In Developing Non-Equiatomic High Entropy Alloys, Azin Akbari

Theses and Dissertations--Chemical and Materials Engineering

High entropy alloys (HEA) are a relatively new group of alloys first introduced in 2004. They usually contain 5 to 6 different principle elements. Each of these elements comprise 5-35 at. % of the chemical composition of the alloy. There is a growing interest in the research community about the development of these alloys as well as their engineering applications. Some HEAs have interesting properties that have made them well suited for higher temperature applications, particularly refractory uses, while some have been shown to maintain their mechanical properties even at cryogenic temperatures.

Initially, the HEA research was focused on developing …

The Formation Mechanism Of Α-Phase Dispersoids And Quantification Of Fatigue Crack Initiation By Experiments And Theoretical Modeling In Modified Aa6061 (Al-Mg-Si-Cu) Alloys, Gongwang Zhang

Theses and Dissertations--Chemical and Materials Engineering

AA6061 Al alloys modified with addition of Mn, Cr and Cu were homogenized at temperatures between 350 ^ºC and 550 ^ºC after casting. STEM experiments revealed that the formation of α-Al(MnFeCr)Si dispersoids during homogenization were strongly affected by various factors such as heating rate, concentration of Mn, low temperature pre-nucleation treatment and homogenization temperature. Through analysis of the STEM results using an image software Image-Pro, the size distributions and number densities of the dispersoids formed during different annealing treatments were quantitatively measured. It was revealed that increasing the heating rate or homogenization temperature led to a reduction of …

A Microstructure-Based Model Validated Experimentally For Quantification Of Short Fatigue Crack Growth In Three-Dimensions, Pei Cai

Theses and Dissertations--Chemical and Materials Engineering

Built on the recent successes in understanding the crystallographic mechanism for short fatigue crack (SFC) growth across a grain boundary (GB) and developing an experimental method to quantify the GB resistance against short crack growth, a microstructure-based model was developed in this study to simulate the growth behaviors of SFCs in 3-D, by taking into account both the driving force and resistance along at each point along the crack front in an alloy. It was found that the GB resistance was a Weibull function of the minimum twist angle of crack deflection at the boundary in AA2024-T3 Al alloys. In …

Shape Memory Behavior Of Dense And Porous Niti Alloys Fabricated By Selective Laser Melting, Soheil Saedi

Theses and Dissertations--Mechanical Engineering

Selective Laser Melting (SLM) of Additive Manufacturing is an attractive fabrication method that employs CAD data to selectively melt the metal powder layer by layer via a laser beam and produce a 3D part. This method not only opens a new window in overcoming traditional NiTi fabrication problems but also for producing porous or complex shaped structures. The combination of SLM fabrication advantages with the unique properties of NiTi alloys, such as shape memory effect, superelasticity, high ductility, work output, corrosion, biocompatibility, etc. makes SLM NiTi alloys extremely promising for numerous applications.

The SLM process parameters such as laser power, …

Effects Of Temperature, Orientation, Load Level And Indenter Shape On The Indentation Response Of Niti-Based Shape Memory Alloys, Peizhen Li

Theses and Dissertations--Mechanical Engineering

Owing the capability of recovering large deformations through reversible phase transformation, shape memory alloys (SMAs) are well-known for their unique behaviors such as shape memory effect (SME) and superelasticity (SE), which can also be characterized by instrumented indentation techniques. Nickel titanium (NiTi) SMAs have been extensively used for nano/micro-indentation studies and widely applied to biomedical and other elaborate medical devices.

In this study, indentation responses of NiTi, NiTiHf, NiTiHfPd and NiTiHfCu alloys were investigated using spherical and Berkovich indenters at room temperature. Spherical and Berkovich indentation hardness, modulus, and work/depth recoverable ratio of these NiTi-based alloys were revealed as a …

Cryogenic Processing Of Al 7050-T7451 Alloy For Improved Surface Integrity, Bo Huang

Theses and Dissertations--Mechanical Engineering

Al 7050-T7451 alloy with good combinations of strength, stress corrosion cracking resistance and toughness, is used broadly in the aerospace/aviation industry for fatigue-critical airframe structural components. However, it is also considered as a highly anisotropic alloy as the crack growth behavior along the short transverse direction is very different from the one in the long transverse direction, due to the inhomogeneous microstructure with the elongated grains distributed in the work material used in the sheet/plate applications. Further processes on these materials are needed to improve its mechanical and material properties and broaden its applications.

The material with ultra-fine or nano …

Nanomechanical And Scaling Behavior Of Nanoporous Gold, Nicolas J. Briot

Theses and Dissertations--Chemical and Materials Engineering

Nanoporous metals have recently been drawn significant interest in various fields of research. Their high surface-to-volume ratio present a strong potential for applications in sensing, catalysis, micro-electromechanical systems (MEMS) and even in the medical field. However, the mechanical properties of nanoporous metals have not yet been well determined, as conducting mechanical tests was found to be challenging. Scaling relations linking the mechanical properties of porous materials to those of their dense counterparts are successfully and widely used for many porous metals. However, their applicability to nanoporous metals have recently been questioned, as estimations from the classic scaling relations were found …

Sustainable Disposal Of Coal Processing Waste Streams, Mohammad Rezaee

Theses and Dissertations--Mining Engineering

Modern coal preparation facilities incorporate a wide array of solid-solid and solid-liquid separation processes for rejecting mineral matter to meet market specifications. The coarse mineral matter is typically placed into engineered refuse piles whereas the fine refuse is either stored in impoundments or co-disposed with the coarse refuse. The discharge water from the refuse material represents an environmental concern due to the potential release of trace elements, and the subsequent elevation of total dissolved solids and conductivity. The research findings reported in this dissertation addresses sustainable coal processing waste disposal through using strategies aimed at minimizing the environmental impacts. To …

Engineered Surface Properties Of Porous Tungsten From Cryogenic Machining, Julius M. Schoop

Theses and Dissertations--Chemical and Materials Engineering

Porous tungsten is used to manufacture dispenser cathodes due to it refractory properties. Surface porosity is critical to functional performance of dispenser cathodes because it allows for an impregnated ceramic compound to migrate to the emitting surface, lowering its work function. Likewise, surface roughness is important because it is necessary to ensure uniform wetting of the molten impregnate during high temperature service. Current industry practice to achieve surface roughness and surface porosity requirements involves the use of a plastic infiltrant during machining. After machining, the infiltrant is baked and the cathode pellet is impregnated. In this context, cryogenic machining is …

Shape Memory Behavior Of Single And Polycrystalline Nickel Rich Nickel Titanium Alloys, Irfan Kaya

Theses and Dissertations--Mechanical Engineering

NiTi is the most commonly used shape memory alloy (SMA) and has been widely used for bio-medical, electrical and mechanical applications. Nickel rich NiTi shape memory alloys are coming into prominence due to their distinct superelasticity and shape memory properties as compared to near equi-atomic NiTi shape memory alloys. Besides, their lower density and higher work output than steels makes these alloys an excellent candidate for aerospace and automotive industry. Shape memory properties and phase transformation behavior of high Ni-rich Ni₅₄Ti₄₆ (at.%) polycrystals and Ni-rich Ni₅₁Ti₄₉ (at.%) single-crystals are determined. Their properties are sensitive …

Magnesium-Titanium Alloys For Biomedical Applications, Ilona Hoffmann

Theses and Dissertations--Chemical and Materials Engineering

Magnesium has been identified as a promising biodegradable implant material because it does not cause systemic toxicity and can reduce stress shielding. However, it corrodes too quickly in the body. Titanium, which is already used ubiquitously for implants, was chosen as the alloying element because of its proven biocompatibility and corrosion resistance in physiological environments. Thus, alloying magnesium with titanium is expected to improve the corrosion resistance of magnesium.

Mg-Ti alloys with a titanium content ranging from 5 to 35 at.-% were successfully synthesized by mechanical alloying. Spark plasma sintering was identified as a processing route to consolidate the alloy …

Precipitation, Orientation And Composition Effects On The Shape Memory Properties Of High Strength Nitihfpd Alloys, Emre Acar

Theses and Dissertations--Mechanical Engineering

NiTiHf high temperature shape memory alloys are attractive due to their high operating temperatures (>100 ^oC) and acceptable transformation strain compared to NiTi. However, NiTiHf has limitations due to their lack of ductility and low strength, resulting in poor shape memory properties. In this study, Pd has been added to NiTiHf alloys in an attempt to improve their shape memory behavior. A combined approach of quaternary alloying and precipitation strengthening was used.

The characterization of a Ni_45.3Ti_29.7Hf₂₀Pd₅ (at. %) polycrystalline alloy was performed in compression after selected aging treatments. Transmission electron …

Linking The Structure And Mechanical Behavior Of Nanoporous Gold, Ye Sun

University of Kentucky Doctoral Dissertations

The structure of nanoporous gold (np-Au) provides a very limited volume for deformation to occur, and thus offers an opportunity to study the role of defects such as dislocations in nanoscale metal volumes. A practical goal is to understand mechanical properties of np-Au so that it can be can produced in stable form, for use in applications that require some mechanical integrity. Bulk and thin film np-Au have been fabricated and studied here.

Bulk np-Au was prepared by electrochemically dealloying Au-Ag alloys with 25 and 30 at.% Au. In the lower Au content material, cracks always formed during dealloying. When …