Metallurgy Commons^™

Atomistic Calculations Characterizing Thermodynamic And Mechanical Properties Of High Entropy Alloys, Sarah O'Brien

Theses and Dissertations--Chemical and Materials Engineering

High entropy alloys (HEAs) are an exciting new class of materials. HEAs combine multiple elements in concentrations ranging from 5% to 35%. The large variation in concentrations increases the alloy’s entropy, stabilizing it. The stabilization is due to both an increased configurational entropy and increases the vibrational entropy when the alloy is at higher temperatures. This was seen for both MoNbTaW and FeNiMoW by combining the atomistic techniques: density functional theory (DFT) and density functional perturbation theory (DFPT). For MoNbTaW, the composition plays a large role in stabilizing the alloy over the configuration of elements. For the three-phase alloy, FeNiMoW, …

Characterization Of The Solid-State Bonding For Simulated Charge And Seam Welds In The Porthole Die Extrusion Process, Randall L. Bowers

Theses and Dissertations--Chemical and Materials Engineering

The isothermal (ISO-T) compression configuration is ideal for utilizing as a material input of flow stress at temperature and strain rate in models of the porthole die extrusion process due to the isothermal nature of the test. Micro-tensile testing was conducted to validate the solid-state welding integrity of the ISO-T samples at various temperatures and strain rates. Results of the mechanical testing were correlated with fractography and microstructural evaluations of the welds to confirm bonding behavior. Both clean interface conditions and oxidation and lubrication layers were evaluated to simulate the difference of seam and charge welds in the process. Results …

Combinatorial Thin Film Approach To Accelerate Materials Discovery: Development Of Nanoporous And Bulk Multi-Principal Element Alloys, Tibra Das Gupta

Theses and Dissertations--Chemical and Materials Engineering

Multi-principal element alloys (MPEAs) have garnered significant attention in materials science due to their potential for exhibiting a combination of desirable properties stemming from their unique configurational entropy. While early research focused on equiatomic compositions, recent studies have indicated that non-equiatomic MPEAs may offer superior mechanical performance. However, the identification of optimal non-equiatomic compositions remains challenging due to the vast compositional space and the reliance on time-consuming and computationally expensive methods. This dissertation presents a combinatorial thin film approach as a rapid and efficient strategy for discovering two types of materials: nanoporous and bulk MPEAs.

The first study explores the …

Microstructural Characterization Of Complex Metal Alloy Systems With A Focus On Electron Microscopy, Alexandra Allamon

Theses and Dissertations--Chemical and Materials Engineering

Multi-principal element alloys (MPEAs)/high-entropy alloys (HEAs) are a class of materials that provide novel and superior combinations of properties, with promise for use in challenging application areas that many of the current established materials cannot fit. With a higher number of constituent elements, many of the newly created alloys are compositionally complex in nature, known to contain combinations of relatively soft FCC phases, hard BCC phases, and, in some cases, even harder intermetallic phases. Microstructural study of these new materials is essential to understanding the enhanced properties they may possess, but their complexity can make this study much more challenging …

Pulsing-Induced Healing Of A Surface Crack Of A Nickel-Based Alloy, Liwei Wang, Mingming Quan, Zhen Tan, Ming Liu, Dianlong Wang, Xiao Yang, Ying Liu, Yaning Mao, Zhimin Liang, Fuqian Yang

Chemical and Materials Engineering Faculty Publications

In this work, we demonstrate the feasibility of applying electric pulses to heal surface cracks on nickel-based alloy GH4169 under compressive load. There exists an incubation time for the onset of the healing of a crack, which is associated with local temperature at the crack tip. The crack size decreases with increasing the pulsing time at a constant healing rate prior to complete healing of the crack. Increasing compressive load accelerates the healing process. The electric pulsing leads to the formation of an influential zone surrounding the crack with the finest grain sizes in the healed crack and the coarsest …

Inhibited Surface Diffusion In Nanoporous Multi-Principal Element Alloy Thin Films Prepared By Vacuum Thermal Dealloying, Tibra Das Gupta, Thomas John Balk

Chemical and Materials Engineering Faculty Publications

Nanoporous structures with 3D interconnected networks are traditionally made by dealloy- ing a binary precursor. Certain approaches for fabricating these materials have been applied to refrac- tory multi-principal element alloys (RMPEAs), which can be suitable candidates for high-temperature applications. In this study, nanoporous refractory multi-principal element alloys (np-RMPEAs) were fabricated from magnesium-based thin films (VMoNbTaMg) that had been prepared by magnetron sputtering. Vacuum thermal dealloying (VTD), which involves sublimation of a higher vapor pres- sure element, is a novel technique for synthesizing nanoporous refractory elements that are prone to oxidation. When VMoNbTaMg was heated under vacuum, a nanoporous structure was …

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. …

Advancing Combinatorial Screening Of Refractory High Entropy Alloys Through Intrinsic Ductility Assessment Via Thin Film Fragmentation Testing, Taohid Bin Nur Tuhser

Theses and Dissertations--Chemical and Materials Engineering

High Entropy Alloys (HEAs), also known as Multiprincipal Element Alloys (MPEAs), represent a paradigm shift in alloy design. Unlike traditional practices that limit compositions to the edges of phase diagrams, HEAs exploit equiatomic mixing of five or more elements at the center of phase diagrams to maximize configurational entropy. This unconventional approach exponentially expands the spectrum of potential alloy compositions, rendering conventional experimental methods inadequate for exploring this extensive compositional space.

In response to these challenges, the scientific community has shown a growing interest in high-throughput techniques, encompassing both computational and experimental domains. Particularly, Refractory High Entropy Alloys (RHEAs) have …

Microstructural Investigation Of The Influence Of Geometry On The Mechanical Reliability Of Additively Manufactured Metals, Tracy Connor Varney

Theses and Dissertations--Chemical and Materials Engineering

The adoption of additive manufacturing across a wide range of fields is ever-increasing, allowing for solutions that were previously impossible to achieve. This dissertation demonstrates the wide range of macro- and micro- characterization techniques used to investigate several precipitation strengthened AM alloy systems. While AM allows for nearly unlimited design freedom, this brings along its own issues as the interplay between scan strategy and part geometry is less well known. In this work, a novel thin-wall dogbone geometry was utilized to study one type of complex geometry observed in a large portion of AM focused designs. The mechanical behavior of …

Calculation Of Elastic Constants Of Bulk Metallic Glasses From Indentation Tests, Zhitong Xu, Ming Liu, Fuqian Yang

Chemical and Materials Engineering Faculty Publications

One of the challenges in the applications of instrumented indentation is to simultaneously measure elastic modulus and Poisson’s ratio of homogeneous, isotropic materials. This work proposes empirical equations for simultaneous calculation of elastic modulus and Poisson’s ratio of bulk metallic glasses (BMGs) from the ratio of the short diagonal length to the long diagonal length and the area of the Knoop imprint. The parameters pre- sented in the empirical equations are determined first by Knoop microhardness tests of 24 BMGs, whose elastic moduli and Poisson’s ratios are measured by resonant ultrasound spectroscopy. These empirical equations are further validated by the …

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 …

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 …

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 …

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 …

Optimization Of Induction Quenching Processes For Hss Roll Based On Mmpt Model, Ligang Liu, Hui Yu, Zhiqiang Yang, Chunmei Zhao, Tongguang Zhai

Chemical and Materials Engineering Faculty Publications

To improve the comprehensive performance of high speed steel (HSS) cold rolls, the induction hardening processes were analyzed by numerical simulation and experimental research. Firstly, a modified martensitic phase transformation (MMPT) model of the tested steel under stress constraints was established. Then, the MMPT model was fed into DEFORM to simulate the induction quenching processes of working rolls based on an orthogonal test design and the optimal dual frequency of the induction quenching process was obtained. The results indicate that the depth of the roll’s hardened layer increases by 32.5% and the axial residual tensile stress also becomes acceptable under …

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 …

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 and Aerospace 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 …

Research And Development Of Powder Brazing Filler Metals For Diamond Tools: A Review, Fei Long, Peng He, Dusan P. Sekulic

Mechanical Engineering Faculty Publications

Powder brazing filler metals (PBFMs) feature a number of comparative advantages. Among others, these include a low energy consumption, an accurate dosage, a good brazeability, a short production time, and a high production efficiency. These filler metals have been used in the aerospace, automobile, and electric appliances industries. The PBFMs are especially suitable for diamond tools bonding, which involves complex workpiece shapes and requires accurate dosage. The recent research of PBFMs for diamond tools is reviewed in this paper. The current applications are discussed. The CuSnTi and Ni-Cr-based PBFMs have been the two commonly used monolayer PBFMs. Thus, the bonding …

Analysis Of Surface Integrity In Machining Of Aisi 304 Stainless Steel Under Various Cooling And Cutting Conditions, F. Klocke, B. Döbbeler, S. Lung, S. Seelbach, Ibrahim S. Jawahir

Institute for Sustainable Manufacturing Faculty Publications

Recent studies have shown that machining under specific cooling and cutting conditions can be used to induce a nanocrystalline surface layer in the workspiece. This layer has beneficial properties, such as improved fatigue strength, wear resistance and tribological behavior. In machining, a promising approach for achieving grain refinement in the surface layer is the application of cryogenic cooling. The aim is to use the last step of the machining operation to induce the desired surface quality to save time-consuming and expensive post machining surface treatments. The material used in this study was AISI 304 stainless steel. This austenitic steel suffers …

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 …

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 …

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 …

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 …

Note On The Rate And Energy Efficiency Limits For Additive Manufacturing, Timothy Gutowski, Sheng Jiang, Daniel Cooper, Gero Corman, Michael Hausmann, Jan-Anders Manson, Timo Schudeleit, Konrad Wegener, Matias Sabelle, Jorge Ramos-Grez, Dusan P. Sekulic

Mechanical Engineering Faculty Publications

We review the process rates and energy intensities of various additive processing technologies and focus on recent progress in improving these metrics for laser powder bed fusion processing of metals, and filament and pellet extrusion processing of polymers and composites. Over the last decade, observed progress in raw build rates has been quite substantial, with laser metal processes improving by about 1 order of magnitude, and polymer extrusion processes by more than 2 orders of magnitude. We develop simple heat transfer models that explain these improvements, point to other possible strategies for improvement, and highlight rate limits. We observe a …

Analysis And Modeling Of The Growth Of Intermetallic Compounds In Aluminum–Steel Joints, Gang Zhang, Manjiao Chen, Yu Shi, Jiankang Huang, Fuqian Yang

Chemical and Materials Engineering Faculty Publications

In this work, we experimentally and numerically studied the microstructures and growth of intermetallic compounds (IMCs) formed in Al–Fe (aluminum–steel) joints welded by a pulsed double electrode gas metal arc welding (DE-GMAW)-brazing method. The IMCs consist of Fe₂Al₅ and FeAl₃, with Fe₂Al₅ being the main compound in the joints. The thickness of an IMC layer increases with an increase of the welding current (heat input) into the base metal. EBSD measurement suggests that the preferred crystal orientation of the Fe₂Al₅ IMC likely provides the necessary path for Al atoms …

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

Theses and Dissertations--Mechanical and Aerospace 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 and Aerospace 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 and Aerospace 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 …

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 …