Metallurgy Commons^™

Stress Relaxation Cracking In 347h Austenitic Steel Weldments Under Various Heat Treatments: Experiments And Modeling, Yi Yang

Doctoral Dissertations

347H austenitic stainless steel exhibits exceptional creep and corrosion resistance, rendering it an exemplary candidate for pipeline materials, particularly in mid- to high-temperature working conditions. However, due to constraints in component dimensions, welding has been chosen as the preferred method for joining pipeline systems extensively employed in nuclear power plants, fossil fuel plants, and petrochemical companies. The welding process entails the accumulation of residual stress during the cooling stage, along with the introduction of microstructure evolution. Moreover, the residual stress field and microstructure continuously evolve under service conditions, thereby intensifying the susceptibility of crack initiation and propagation. The initial residual …

Characterization Of Residual Stress And Precipitate Evolution In Aluminum 2xxx Self-Reacting Friction Stir Welds, Benjamin Joe Wing

Doctoral Dissertations

2xxx series aluminum alloys possess attractive properties for structural aerospace applications including high strength to weight ratio, corrosion resistance, and stable cryogenic performance. Solid state joining processes are often employed to reduce weld defects and improve weld performance/consistency as many alloys of this range have poor weldability for traditional fusion based joining techniques. One such process, self-reacting friction stir welding (SRFSW) allows for consistent high-quality, welding of large and curved articles is often used in the construction of large structures such as launch vehicle liquid propellant tanks.

Despite the merits of this process, joint softening (a decrease in mechanical properties …

Investigation Of Microstructure And Mechanical Behavior Of Novel Powder-Extruded Al-Ce-Mg Alloys, Mairym Vazquez

Doctoral Dissertations

Pursuing advanced structural materials with enhanced performance, reduced weight, and lower costs is a constant endeavor in the aerospace and automotive industries. Conventional structural alloys, such as cast irons, carbon steels, and titanium alloys, have strength, weight, and cost limitations. Aluminum-based alloys, known for their lightweight and high strength, have gained popularity in these industries. This dissertation focuses on investigating microstructure and mechanical behavior of novel powder-extruded Al-Ce-Mg alloys as potential candidates for high-performance structural materials.

This research explores using powder extrusion, a well-established forging methodology in the steel industry, to produce Al-Ce-Mg alloys with improved properties and aims to …

Refractory High-Entropy Alloys: Design, Fabrication, Characterization, And Nanoparticle Synthesis, John Hutson Whitlow

Masters Theses

High-Entropy Alloys have been a highly researched area of metals ever since their introduction in 2004 by Brian Cantor and Jien-Weh Yeh. In the continued research of High-Entropy Alloys (HEAs), a specific area concerning Refractory High-Entropy Alloys (RHEAs) has emerged for their high-temperature applications. Although RHEAs have maintained high strength and toughness at high temperatures, their low ductility still needs to be addressed. A dataset was created to find correlations between various characteristics of RHEAs and their composition. A set of seven compositions were selected and fabricated. Mechanical tests were run on the seven compositions, and a proposal was written …

A Study Of The Effect Of Machine Parameters On Defects Produced In Eos Additive Manufacturing Builds, Tina White Malone

Doctoral Dissertations

⁵Additive Manufacturing (AM) is defined in the American Society for Testing and Materials (ASTM) standard F2792 as “a process of joining materials to make objects from 3D model data, usually layer upon layer, as opposed to subtractive manufacturing methodologies. It provides an advanced method for building complex geometries and parts for high performance with a significant cost savings. ⁵⁵It’s advantages include the reduced need for tools and molds commonly used in manufacturing, a large reduction in wasted material, much shorter manufacturing cycles for the building of hardware, and its uniquely inherent ability to produce much more complex shapes. …

Al-Ce-Mn Solidification Phase Selection And Solid-State Phase Transformations, Kevin Dean Sisco

Doctoral Dissertations

The design of Al alloys has become an important topic in Additive Manufacturing (AM). The adoption of Al alloys to AM has been difficult because traditional alloys are prone to processing related defects such as solidification cracking. The Al-10Si-Mg alloy was initially adopted because of its resistance to solidification cracking. However, the Al-10Si-Mg alloy has reduced tensile properties especially at high temperatures, where the silicon phase coarsens readily. Therefore, efforts have been made to design new Al alloys that can take advantage of the AM processing. The goal of new alloys is to optimize based on rapid solidification conditions, while …

Surface Corrosion Response Of Al Alloys A383 And Aural 2 With Ce Additions In Aqueous Nacl And Salt-Fog Environments, Michael James Thompson

Masters Theses

Copper is commonly used in aluminum alloys to increase its strength by solid solution and precipitation strengthening, however, the corrosion resistance is inversely related to the amount of copper in the alloy. Over 70 percent of material used to produce aluminum alloys in the US come from recycled (secondary) alloys, many of which have a copper content of more than one percent by weight. Alloys with tightly controlled tolerances, where copper is seen as an impurity, are unable to utilize many of the recycling feedstock without adding newly processed (primary) aluminum to dilute impurities to within specifications. Primary aluminum is …

Kinetics And Phase Stability Of Nano-Scale Precipitates In Fe-Based Binary Alloys During Ion Irradiations, Yajie Zhao

Doctoral Dissertations

Due to the high void-swelling resistance and good mechanical, thermal and chemical properties, FeCr based ferritic-martensitic steels are promising structural materials in future nuclear reactors. However, they suffer from the well-known “475 °C embrittlement” phenomenon due to formation of Cr-rich alpha prime (α’) precipitates. Despite the extensive observation of α’ after neutron irradiations, α’ formation was seldom reported after high dose rate ion irradiations.

In this study, high purity FeCr alloys with Cr concentrations of 5-18% were irradiated by 8 MeV Fe ions at -123 °C to 450 °C, 10^-5 – 10^-3 dpa/s to mid-range doses of 0.37-3.7 …