Engineering Commons^™

Fundamentals Of Cavity Formation In Α-Fe And Fe-Cr Alloys, Yan-Ru Lin

Doctoral Dissertations

Ferritic-martensitic steels are attractive candidate materials for fusion and advanced fission reactors primarily due to their low swelling characteristic, attractive thermo-mechanical properties, and the potential for development of nanostructured ferritic alloys. However, significant discrepancies exist regarding the effect of solutes and irradiation temperature on cavity swelling under ion versus neutron irradiation conditions. Several mechanisms have been proposed that may affect cavity swelling, but no general theory or model has received complete acceptance to explain these phenomena.

To better understand the formation of cavities in ferritic steels, we have performed multi-temperature (400-550°C) single-beam and simultaneous dual-beam irradiations (ex-situ and in-situ) on …

Assessing Mechanical Performance Of Dissimilar Steel Systems Made Via Wire-Arc Additive Manufacturing, Obed Daniel Acevedo

Masters Theses

Hot stamping is part of a specific type of metalworking procedure widely used in the automotive industry. This research seeks to help make hot stamp tooling component production more cost-effective by using large-scale additive manufacturing. Additive manufacturing can produce dissimilar steel components that can be more cost-effective and time-efficient and allow for complex geometries to be made. A dissimilar steel system consisting of 410 martensitic stainless steel and AWS ER70S-6 mild steel is proposed to make hot stamps, making them more cost-efficient. However, the material interface's mechanical behavior in 410SS-mild steel additively manufactured material systems is not well understood. This …

Studies Of Creep Damage In The Heat-Affected Zone Of 9cr-1mo-Vnb Steel Weldments, John William Bohling

Doctoral Dissertations

Creep strength enhanced ferritic (CSEF) steels are used in power plants for high temperature, pressure-containing welded components such as steam headers. One CSEF steel, 9Cr-1Mo-VNb or Grade 91, often exhibits localized creep deformation and cavitation in the weld heat-affected zone (HAZ), identified as Type IV creep damage. Three Grade 91 weldments were evaluated by creep testing and microstructural characterization using optical and scanning electron microscopy, combined with image analysis, to investigate microstructure evolution and creep damage. Two weldments fabricated from dissimilar base metals were used for direct comparison of creep damage in two materials simultaneously during cross-weld testing. Longitudinal creep …

Transients In Plastic Instabilities During Thermo-Mechanical Reversals In An Additively Manufactured Ti6al4v, Sabina C. Kumar

Doctoral Dissertations

A complex interaction of process variables in an evolving geometry during Additive Manufacturing (AM), can bring about spatial and temporal transients of temperature and stress within each layer in a part. Although AM shares commonalities with conventional processing techniques such as casting, welding, and thermo-mechanical process, published literature has shown that the steady-state conditions are not strictly valid during AM process. Macro-scale fluctuations of thermal gradients (dT/dx: 10³ to 10⁷ K/m) combined with local changes in thermal expansion coefficients, crystallographic strains and localized stress-strain constitutive properties in conjunction with thermal cycles, can bring about a plastic strain gradient …

Microstructural Characterization And Analysis Of Laser-Powder Bed Fusion Grcop-84 By Metallurgical And Neutron Scattering Methods, Robert Minneci

Doctoral Dissertations

GRCop-84 or Cu-8Cr-4Nb (atomic %) is a structural high-heat-flux Cu alloy that is dispersion strengthened by C15 Laves Cr₂Nb [Niobium Chromide] that has seen significant development with laser additive manufacturing (AM), specifically laser-powder bed fusion (L-PBF) in recent years. A review of the development, properties, and performance of GRCop alloys has been conducted and provides pertinent background. The body of research provides fundamental understanding regarding microstructure evolution and phase interaction of GRCop-84 through characterization by neutron and X-ray scattering and metallographic techniques. This research is intended to bridge fundamental research of L-PBF, Cu alloys, structural thermal conductors, and …

Local Dynamics And Atomic-Level Structures In Metallic Liquids And Glasses, Zengquan Wang

Doctoral Dissertations

Structure and dynamics at the atomic level in metallic glasses and liquids are poorly understood when compared to the crystalline solids. For instance, even though viscosity is the basic property of liquids, its atomistic origin is not well elucidated. Also, the physics of the fragility of liquids and the crossover phenomenon is far from full understanding. Earlier, through molecular dynamics (MD) simulations a direct connection was found between the timescale describing the macroscopic viscous behavior, the Maxwell relaxation time (t_M = h/G_∞, h is the shear viscosity and G_∞ is the high-frequency shear modulus) and …