Metallurgy Commons^™

Improving Cast Steel Rail Coupler Fatigue Resistance Through Local Wire-Arc Additive Manufacturing, Andrew M. Bunge

Dissertations, Master's Theses and Master's Reports

Every year, thousands of cast-steel railcar couplers suffer from corrosion-initiated fatigue cracking in similar areas of the coupler’s knuckle; between 2015 and 2018 about 90,000 knuckles were replaced, otherwise these couplers would have been at risk for unexpected failures. These types of couplers have been common in industrial use as early as 1932, hence it is desirable for a countermeasure to the fatigue cracking that does not involve significantly altering the geometry or casting process. Wire arc additive manufacturing (WAM) is a developing technology which boasts the ability to produce complex near-net-shape components; however, less attention has been paid to …

Nickel Superalloy Composition And Process Optimization For Weldability, Cost, And Strength, Sophie A. Mehl

Dissertations, Master's Theses and Master's Reports

To advance sustainability efforts, electric power plants have reduced specific carbon dioxide emissions by increasing operating temperatures and pressures to improve power generation efficiency. The latest improvements are utilized in advanced ultra-supercritical power generation. To meet these operating conditions, nickel superalloys are used in the highest temperature components; however, they are expensive and present weldability challenges. This project aims to experimentally optimize a nickel superalloy to improve material weldability and decrease cost without compromising strength. Three optimized compositions were developed, and their microstructures and mechanical properties were compared to Nimonic 263, a common nickel superalloy in electric power plants. The …

Effect Of Sc On Recrystallization Resistance Of Aa7050, Keaton Schmidt

Dissertations, Master's Theses and Master's Reports

The extrusion process involves high temperatures and strains that can result in undesirable microstructures, especially along the surface. Extruded alloys tend to exhibit surface recrystallization during heat treating at regions of higher strains, which can lead to reduced fatigue strength and corrosion resistance. By adding Sc to AA7050, nano-sized dispersoids are formed with Sc cores and Zr shells that restrict recrystallization more than the base alloy that only utilizes Zr. Billets with varying Sc content and a control with only Zr were cast, and extrusions were made in order to compare surface microstructures at varying strains in the as-extruded and …

Optimizing The Extrudability Of 6082 Aluminum By Varying The Magnesium And Silicon Concentration, Eli A. Harma

Dissertations, Master's Theses and Master's Reports

Alloy 6082 aluminum is used for high-volume manufacturing in the automotive industry due to its high strength, impact performance, and corrosion resistance. However, given these improved properties, the alloy has decreased formability compared to other 6xxx series alloys, especially in the extrusion process. Controlling the dynamic recovery and recrystallization properties by changing the additions of Mg and Si can improve the hot deformation properties. Five alloys of varying Mg and Si concentrations between 0.6 to 1.2wt% Mg and 0.7 to 1.3wt% Si were made with constant concentrations of Cr, Fe, and Mn and the same homogenization heat treatment. The proposed …

Thermomechanical Mechanisms That Cause Adhesion Of Aluminum High Pressure Die Castings To The Die, Alex Monroe

Dissertations, Master's Theses and Master's Reports

In high pressure die casting (HPDC) of aluminum, cast material adhering to die is a significant defect. Adhesion occurs in two primary ways. The casting may stick preventing its removal from the die. Aluminum can also adhere to the die and buildup in local areas on the die surface with additional casting cycles. This second form of adhesion is called soldering. Lubricant is the best technology to control all forms of adhesion, but it comes at the cost of casting porosity, blisters, reduced die life, and increased die casting machine wear. New strategies to prevent adhesion are desired to eliminate …

The Effects Of Molybdenum, Chromium, And Niobium On Gray Iron For Brake Rotor Applications, Matthew Hasbrouck

Dissertations, Master's Theses and Master's Reports

Brake rotor composition and microstructure must be optimized for thermal and mechanical performance to avoid thermal-mechanical cracking, excessive wear, and to reduce noise. Niobium is an element that increases the strength and wear resistance of gray iron; however, the interaction of niobium with other common alloying elements (chromium and molybdenum) is not well understood. Thirteen gray cast iron alloys were produced with varying levels of carbon equivalent (CE), Cr, Mo, and Nb. Bars with four different diameters (8, 14, 22, and 30 mm) were cast from each alloy and microstructural and physical properties such as graphite flake morphology, pearlite spacing, …

Atomistic Monte Carlo Simulation Study Of Phase Transitions In Metal Alloys, Xiaoxu Guo

Dissertations, Master's Theses and Master's Reports

The atomic-scale Monte Carlo simulation study focuses on the intrinsic behaviors of a defect-free crystal that undergoes a cubic-to-tetragonal martensitic transformation. The quasi-spin variable associated with the lattice sites characterizes the local unit cells of the orientation variants of the ground-state martensite phase, which interact with each other through long-range elastic interactions. It is shown that the diffuse scattering in the premartensitic austenite state results from the spatial correlation of the atomic-scale heterogeneous lattice displacements and manifests the displacement short-range ordering. The effects of temperature, elastic anisotropy, and shear modulus softening on the diffuse scattering and displacement short-range ordering are …

Analyzing Variation In Dispersoid Formation In Aluminum Alloys By Minor Changes In Homogenization Temperature, Brendan Treanore

Dissertations, Master's Theses and Master's Reports

The homogenization of billets in the aluminum extrusion industry is a critical step that removes chemical segregation from casting, dissolves low melting point phases, forms nanoscale dispersoid phases, and promotes the beta to alpha transformation of iron particles in the matrix. With ever increasing use of aluminum extrusion in the automotive industry there is a constant need for increased efficiency and consistency in processing of extruded aluminum. The work in this thesis explores the effects of 10°C differences in the homogenization temperature on the formation of dispersoids in 6082 alloys used in the automotive industry. The role of dispersoids is …

New Horizons For Processing And Utilizing Red Mud, M. Archambo

Dissertations, Master's Theses and Master's Reports

Red mud is an industrial slurry waste that is produced as a byproduct of the Bayer process for alumina. The waste is generated in large quantities, up to a ratio of 2:1 against the valued product alumina. Red mud exhibits many chemical and physical properties that categorize it as a hazardous material. Due to the addition of sodium hydroxide in processing, the pH is typically at values close to 13. Small particle size discourages separation from water for disposal, so drying red mud happens over many years.

The pH of red mud can be reduced with inexpensive reagents. Carbon dioxide …

Role Of Eta Phase Evolution On Creep Properties Of Nickel Base Superalloys Used In Advanced Electric Power Generation Plants, Ninad Mohale

Dissertations, Master's Theses and Master's Reports

Advanced fossil energy power generation plants require materials that withstand high temperatures and corrosive environments. One such material that is used in steam turbines is Nimonic 263. It is a nickel-base superalloy that is principally strengthened by gamma primephase (Ni₃(Ti, Al)) and has an L1₂structure. At extended times and at turbine operating temperatures however, eta (Ni₃Ti) phase is known to form at the expense of gamma prime. Eta has a complex DO₂₄structure and is the stable phase between 750°C and 900°C, but with slow kinetics of formation. Little is understood about eta …

Exploring Rapid Solidification And Equal Channel Angular Pressing In The Fabrication Of Mg-Based Alloys For Medical Applications, Emily Tom

Dissertations, Master's Theses and Master's Reports

The development of magnesium bioresorbable implants has become increasingly popular due to the increased need for temporary implants and magnesium’s excellent biocompatibility and suitable elastic modulus. Even though magnesium is an excellent candidate, when alloyed with other metals magnesium’s corrosion rate becomes too rapid for bioresorbable medical applications. The investigation into novel processing techniques to control the formation of precipitates to improve mechanical strength and ductility as well as corrosion rates has become of interest. This work investigates the combination of two nonequilibrium processing techniques, rapid solidification (RS) and equal channel angular pressing (ECAP), and the effects it has on …

Anaerobic Reductive Bioleaching Of Manganese Ores, Neha Sharma

Dissertations, Master's Theses and Master's Reports

The increasing demand of manganese in the industries and various hindrances in its production from low grade ores by conventional method has made it imperative for researchers around the world to develop a method of manganese extraction from low grade ores that is both environment friendly and economical. Bioleaching has shown significant potential in manganese extraction and efficiencies of extraction have been found to be 70-98% with the help of various bacteria and fungi.

This study focuses on extraction of manganese with the help of mixed bacterial strains that have been collected from their natural anaerobic environment. The extraction of …

The Effects Of Carbon Equivalent, Return Ratios, Mold Preparation, Riser Feed And Casting Temperature On The Microstructural And Mechanical Properties Of 100-70-03 Pearlitic Ductile Iron, Erin Vandusen

Dissertations, Master's Theses and Master's Reports

The most common and costly detriments to ductile iron foundries are casting defects, particularly in new and complex components. The ability to understand the factors and processes that create microstructures and the associated properties would allow accurate virtual predictions of casting outcomes. An experimental study of standard foundry variables, carbon equivalent, return ratio, mold preparation, riser feed, and casting temperature on a target of 100-70-03 pearlitic, hypereutectic ductile iron provided the groundwork for an ICME database. Density decreased when the fraction of graphite nodules was greater due to the low density of graphite. A greater percentage of return scrap and …

Effect Of Cerium And Magnesium Additions On The Strength And Morphology Of The Intermetallic Compound Layers In Aluminum-Steel Dissimilar Castings, Matt Thomas

Dissertations, Master's Theses and Master's Reports

Dissimilar castings are under investigation due to their light-weighting opportunities within the automotive industry. In this case, dissimilar castings consist of a solid steel core and a poured aluminum component. The strength and integrity of the casting relies on the coherency of the bond between the two components; by optimizing the metallurgical component of the bonding phenomena, the weight and complexity of the insert can be reduced, further increasing the light-weighting opportunities. An interface comprised of intermetallics, generally Fe₄Al₁₃ and Fe₂Al₅, forms between the two components with the latter forming nearest the steel. …

Influence Of Rapid Solidification And Wrought Processing On Precipitation Strengthening And Deformation Mechanisms In Al-Sc-Zr Alloys, Yang Yang

Dissertations, Master's Theses and Master's Reports

Al-Sc-Zr alloys have drawn increasing attention in the last several decades due to their strengthening and coarsening resistance. In this study, solute concentrations of Sc and Zr were increased beyond their equilibrium solubilities without primary precipitate formation using melt-spinning. The melt-spun ribbon was metallurgically bonded into bulk shape using extrusion. With the proper aging treatment, the mechanical properties of the supersaturated melt-spun ribbon and extruded rod were found to be significantly higher than a baseline dilute alloy. Increased mechanical properties include microhardness, tensile strength at ambient-temperature, and compressive strength and threshold stress at and elevated-temperature. These increases were related to …

Integrated Computational Materials Engineering (Icme) Investigation Of Electrical Conductivity And Thermodynamic Stability For Precipitation Strengthened Al-Zn-Zr And Al-Zn-Ni Ternary Alloys, Oladeji Fadayomi

Dissertations, Master's Theses and Master's Reports

High electrical conductivity Al-Zn-TM (TM=Transition metals) alloys with improved mechanical properties and thermal resistance are developed with an integrated computational material engineering (ICME) strategy. From a series of ab initio density functional theory (DFT) simulations assessing combinations of ternary alloys, Al-Zn-Ni and Al-Zn-Zr are determined as alloys with relatively high electrical conductivity compared to several other ternary Al alloy combinations. The zero-temperature stable structure of precipitates formed in these alloys are determined from computed enthalpy of formation as L1₂, with particular focus of examining the influence of Zn on stabilizing the desired L1₂ precipitate phase.

Scanning transmission …

Effect Of Development Of Scandium Trialuminide Precipitates On Corrosion And Mechanical Behavior In Aluminum-Magnesium Alloys, Carson Williams

Dissertations, Master's Theses and Master's Reports

Development of aluminum alloys has seen an increase in attention in recent years. The 5xxx series of Al-Mg alloys has the potential to provide strong, lightweight materials in various industry applications, however issues with strain formability and corrosion hinder the development of these alloys. The addition of Sc for developing Al₃Sc precipitates provides considerable precipitation strengthening as well as grain refinement characteristics that can help mitigate these issues. Alloys with varied Mg content were analyzed for heat treatment aging responses and precipitate formation, changes in mechanical behavior related to the Portevin-le Chatelier effect, and effects on intergranular corrosion …

Investigating Microalloying Elements To Accelerate Zirconium Trialuminide Precipitation In Aluminum Alloys, Philip D. Staublin

Dissertations, Master's Theses and Master's Reports

Precipitation of the L1₂-structured coherent Al₃Zr trialuminide phase in aluminum-zirconium alloys increases the alloy strength. Precipitation of a more refined dispersion of Al₃Zr can further increase the strength of these alloys. The addition of microalloying elements which bind to zirconium may accelerate the precipitation kinetics, allowing for nucleation of a greater number of precipitates and faster precipitate growth. Zirconium binding energies are computed for a wide range of elements, based on which the elements tin, antimony, and tellurium were selected for investigation. Ternary Al-Zr-X alloys (X = Sn, Sb, Te) were cast and heat …

Measurement Of Planar Fault Probabilities In Austempered Ductile Iron And 304l Stainless Steel, Nathan Peterson

Dissertations, Master's Theses and Master's Reports

During plastic deformation both stacking and twin faults can be generated in face-centered cubic materials, including iron-based metals that contain thermally stable austenite. These planar faults are a critical component of the austenite to martensite transformation, forming shear bands that can act as nucleation sites. The measurement of these faults via x-ray diffraction has been long established, however it has not been applied widely to austempered ductile irons. The ability to measure these faulting probabilities could give insights into the transformation as a function of deformation. In this work both planar fault densities were measured in austempered ductile iron to …

Effects And Limitations Of Residual Alloying Elements In Silicon Solid Solution Strengthened Ferritic Ductile Iron, Julia Scruton

Dissertations, Master's Theses and Master's Reports

Transitioning from traditional grades of ductile iron to solution strengthened ferritic ductile iron (SSFDI) grades can be difficult because of the need to reduce the amount of pearlite promoting elements, particularly copper and manganese, which are used in traditional grades. Knowing the acceptable threshold of residual alloying elements will allow for more cost-effective tailoring of the charge stream. Data were generated from a series of casting trials with the target grade of EN-GJS-500-14 where the levels of copper and manganese were varied from 0.05% to 0.3% and 0.15% to 0.4% respectively while maintaining silicon in the 3.8%-4.3% range. The pearlite …

Evaluation Of Thermal Stability Of Ausferrite In Austempered Ductile Iron Using Differential Scanning Calorimetry, Karl Warsinski

Dissertations, Master's Theses and Master's Reports

Austempered Ductile Iron (ADI) is prone to changes in microstructure and mechanical properties when exposed to elevated service temperatures. Differential Scanning Calorimetry has been used to evaluate the stabilizing effects of copper, nickel, molybdenum, and cobalt on the ausferrite structure. Previous studies have conflated the effects of various alloy additions, and little effort has been made to systematically catalog the effects of individual elements. The focus of the current research has been to identify alloying elements that more strongly stabilize the ausferrite structure in order to improve service life of ADI at elevated temperatures. Nickel has been shown to have …

Structural Characteristics And Corrosion Behavior Of Bio-Degradable Zn-Li Alloys In Stent Application, Shan Zhao

Dissertations, Master's Theses and Master's Reports

Zinc has begun to be studied as a bio-degradable material in recent years due to its excellent corrosion rate and optimal biocompatibility. Unfortunately, pure Zn’s intrinsic ultimate tensile strength (UTS; below 120 MPa) is lower than the benchmark (about 300 MPa) for cardiovascular stent materials, raising concerns about sufficient strength to support the blood vessel. Thus, modifying pure Zn to improve its mechanical properties is an important research topic.

In this dissertation project, a new Zn-Li alloy has been developed to retain the outstanding corrosion behavior from Zn while improving the mechanical characteristics and uniform biodegradation once it is implanted …

Microstructural Evolution And Mechanical Properties Of Zn-Ti Alloys For Biodegradable Stent Applications, Zhiyong Yin

Dissertations, Master's Theses and Master's Reports

Stents made of biodegradable metallic materials are increasingly gaining interest within the biomaterials field because of their superior mechanical properties and biodegradation rates as compared to polymeric materials. Zinc and its alloys have been developed and investigated as possible candidates for biodegradable stent applications in the last five years. This study intended to formulate and characterize a new series of Zn-Ti alloys, with titanium additions of less than 1-3 wt%, with the primary objective to develop and select an alloy that meets benchmark values of mechanical properties for biodegradable stents. A series of Zn-Ti alloys was formulated through vacuum induction …

Controlling Properties Of Agglomerates For Chemical Processes, Joseph A. Halt

Dissertations, Master's Theses and Master's Reports

Iron ore pellets are hard spheres made from powdered ore and binders. Pellets are used to make iron, mainly in blast furnaces. Around the time that the pelletizing process was developed, starch was proposed as a binder because it’s viscous, adheres well to iron oxides, does not contaminate pellets and is relatively cheap. In practice, however, starch leads to weak pellets with rough surfaces – these increase the amount of dust generated within process equipment and during pellet shipping and handling. Thus, even though the usual binder (bentonite clay) contaminates pellets, pelletizers prefer it to starch or other organics.

This …

Thermomechanical Processing Of Aluminum Micro-Alloyed With Sc, Zr, Ti, B, And C, Cameron Mcnamara

Dissertations, Master's Theses and Master's Reports

Critical exploration of the minimalistic high strength low alloy aluminum (HSLA-Al) paradigm is necessary for the continued development of advanced aluminum alloys. In this study, scandium (Sc) and zirconium (Zr) are examined as the main precipitation strengthening additions, while magnesium (Mg) is added to probe the synergistic effects of solution and precipitation hardening, as well as the grain refinement during solidification afforded by a moderate growth restriction factor. Further, pathways of recrystallization are explored in several potential HSLA-Al systems sans Sc. Aluminum-titanium-boron (Al-Ti-B) and aluminum-titanium-carbon (Al-Ti-C) grain refining master alloys are added to a series of Al-Zr alloys to examine …

Investigation And Modeling Of Al3(Sc, Zr) Precipitation Strengthening In The Presence Of Enhanced Supersaturation And Within Al-Cu Binary Alloys, Kyle Deane

Dissertations, Master's Theses and Master's Reports

Diffuse Al-Sc and Al-Zr alloys have been demonstrated in literature to be relatively coarsening resistant at higher temperatures when compared with commonly used precipitation strengthening alloys (e.g. 2000 series, 6000 series). However, because of a limited strengthening due to the low solubility of scandium and zirconium in aluminum, and owing to the scarcity and therefore sizeable price tag attached to scandium, little research has been done in the way of optimizing these alloys for commercial applications.

With this in mind, this dissertation describes research which aims to tackle several important areas of Al-Sc-Zr research that have been yet unresolved. In …

Nd2fe14b: (Nd1-X Dyx)2 Fe14b Core-Shell Structure Formation By Hot Press Liquid Phase Sintering, Li Chen

Dissertations, Master's Theses and Master's Reports

The purpose of this project is to produce Nd rich core-Dy rich shell grain structure in liquid phase sintered alloys by consolidating Dy rich powder mixed with powder. The technical barrier to producing the core-shell microstructure is that the Dy composition variations will homogenize during the consolidation process. This dissertation is based on the hypothesis that compositional homogenization of the core-shell structure can be minimized if consolidation occurs under applied pressure (hot press liquid phase sintering). The hypothesis is tested by comparing the homogenization of the Dy composition to the degree of consolidation with and without applied pressure. It is …

The Effect Of Solidification Rate And Solutionizing Quench Rate On The Mechanical Properties And Hardening Response Of Aluminum Alloys: A Quantitative Comparison, Rafael Gil-Figueroa

Dissertations, Master's Theses and Master's Reports

A comparative study of five aluminum alloys was performed to characterize the effect of solidification rate and quench rate on casting microstructure and properties. The alloys were cast in the geometry for Jominy End Quench (JEQ) testing, so as to take advantage of the JEQ test’s ability to give data on multiple quench rates in a single sample and illustrate the quench sensitivity of an alloy. While the Jominy End Quench test has been used in aluminum alloys, the effects of solidification rates have not been assessed in depth. The work done by other studies has either focused on a …

Investigation Of The Resistance To Demagnetization In Bulk Rare-Earth Magnets Comprised Of Crystallographically-Aligned, Single-Domain Crystallites With Modified Intergranular Phase, Jie Li

Dissertations, Master's Theses and Master's Reports

The research presented in this dissertation investigates whether an increased coercivity of Neodymium-Iron-Boron (Nd2Fe14B) based bulk magnets at elevated temperature (160°C), which is now only obtainable by substituting ~7wt% dysprosium (Dy) for a portion of neodymium (Nd), can be achieved through specific microstructural modifications with decreased Dy concentrations. The approach is to reduce the size of individual crystallographically-aligned grains in the magnet so that each grain can only support a single magnetic domain and to simultaneously dilute the Nd-Fe inter-granular phase present in conventional magnets with a non-Fe-containing, Nd-rich phase (Nd-Cu alloy) in an attempt to partially magnetically isolate the …