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 …

High Energy Synchrotron X-Ray Study Of Fatigue Damage In Amorphous And Polycrystalline Engineering Alloys, Chih-Pin Chuang

Doctoral Dissertations

The dissertation summarizes a series of studies on the fatigue damage of both amorphous and crystalline engineering alloys. The attention focuses on the utilization of synchrotron x-ray scattering related techniques for advanced material characterizations. In the first part of the research, critical issues regarding the mechanical response and structural evolution of Bulk-Metallic Glasses (BMGs) in the elastic region are addressed. The effects of cyclic-loading on the microstructures of an amorphous alloy are investigated, aiming to provide better mechanistic understandings of fatigue damage in BMGs. The second part of the research focuses on the characterization method based on two-dimensional X-ray diffraction …