Microstructure-Based High Temperature Processing and Failure Analyses of Engineering Alloys under Complex Conditions

From traditional petrochemical applications to contemporary manufacturing techniques, advanced structural materials are subjected to intricate thermomechanical and environmental conditions. In these engineering domains, high-temperature deformation plays a pivotal role, profoundly influencing the ultimate outcomes of industrial applications. Nevertheless, the underlying mechanisms of this deformation remain elusive, largely due to the absence of a microstructure-based mechanistic understanding of high-temperature processing and failure of materials.

This dissertation endeavors to comprehensively examine these mechanisms through computational methodologies, focusing on three quintessential topics: grain boundary cavitation failures (2 examples: stress relaxation cracking (SRC) and grain size dependence), high-temperature hydrogen attack (HTHA), and additive friction stir deposition (AFSD). Firstly, a micromechanical finite element framework incorporating precipitate-free zones is proposed to investigate SRC. This framework enhances our comprehension of residual stress evolution, the impact of material constitutive parameters on lifetime predictions. Secondly, a microstructure-informed and micromechanics-based model is developed, integrating the interplay between hydrogen transport and intergranular cavity-based fracture processes. This model offers a robust methodology for computing Nelson curves, providing novel insights into their mechanisms and elucidating the roles of two critical parameters: pipe thickness and applied stresses. Finally, a numerical model utilizing the Coupled Eulerian Lagrangian (CEL) method is implemented to validate our theoretical analysis of the effects of processing parameters during AFSD. This simulation not only replicates but also explicates the experimental results.