Defect Occurrence and Modeling for the Thermomechanical Processing of Aerospace Alloys (Preprint)

摘要

Mechanism-based models for the evolution of defects during the thermomechanical processing of aerospace titanium- and nickel-base alloys are described. These defects include those comprising microstructural/metal-flow irregularities and those that are damage-related (i.e., cracks and cavities.). The development of undesirable/non-uniform microstructures and cavities during the mill processing of alpha/beta titanium alloys is addressed first. Relatively simple, diffusion-based models of spheroidization and coarsening are applied to quantify the propensity for microstructure non-uniformities. Similarly, first order micromechanical models have been formulated to estimate the effect of local crystallographic texture on non-uniform flow, the generation of triaxial stresses, and cavity growth/closure in alpha/beta titanium alloys with a colony-alpha microstructure. The occurrence of non- uniform grain structures (and so-called ALA, or 'as large as,' grains) in cast, wrought, and powder-metallurgy superalloys are also discussed. A physics-based model to treat the topology of recrystallization and the evolution of ALA grains in such materials is proposed.