Collaborative Research and Development Contract. Delivery Order 0018: Grain-Structure Evolution During Thermomechanical Processing (TMP) of Superalloys

摘要

This research in support of the Air Force Research Laboratory, Materials and Manufacturing Directorate was conducted at Wright-Patterson AFB, Ohio from 1 September 2004 through 28 February 2006. Usual models of recrystallization are based on the Avrami formulation. They induce rigidities, mostly due to the lack of physic representativeness of parameters. A meso-scale mechanism-based model was developed. It is composed of two main parts that are a geometric framework and a set of equations which are to represent driving forces. The geometric framework is based on MesoStructure Units, which can be seen as aggregates of similar grains. It accepts two kinds of inputs, grain boundary velocities and nucleation rates, from which it is able to deduce the evolution of geometric variables of the microstructure. Driving forces equations are used to calculate these grain boundary velocities and nucleation rates through three groups of equations, which aim at representing the three stages of dynamic recrystallization: energy storage, nucleation, grain growth. Equations parameters have been identified so that the model fits the recrystallization behavior of ingot and wrought initial microstructures of Waspaloy.