Papers by Author: Giuseppe Carlo Abbruzzese

Abstract: Grain growth processes in real polycrystalline materials are mostly characterized by the presence of restraining forces, originating, among others, from second phase particles dispersion (Zener drag) or solute atoms segregating at the grain boundaries (solute drag). Both the restraining mechanisms were introduced in the framework of the statistical theory of grain growth, showing their peculiar effects on kinetics and on grain size distribution evolution [1,2,. The present work moves from the previous results and gives a further clarification of pseudo-steady state kinetics occurring under particular solute drag inhibition intensity and will discuss it in comparison with grain growth stagnation conditions produced by Zener drag. In case of second phase particle inhibiting grain growth, the normal case in real systems is the time and temperature dependence of the inhibition intensity due to the evolution of precipitates (e.g. Ostwald ripening. Such evolutions of inhibition, which typically drops with increasing temperature, can cause microstructure instabilities like abnormal grain growth or secondary recrystallization. It is thus introduced in the model a time-temperature depending inhibition drop, which influences both kinetics and grain size distribution evolution. Conditions for the onset of particular effects like abnormal grain growth are assessed and discussed.

Abstract: The derivation of an equivalent 3-D Von Neumann equation and the corresponding kinetics equation in terms of geometrical characteristics of a grain is shown and the formulation is provided in the framework of the statistical theory of grain growth. The topological relationships between number of grain faces, grain size, number of corners and edges and how these can be calculated in a real microstructure with a statistical approach are discussed. A quadratic law for the linkage between number of faces and grain size is found and compared with available experimental results. Inside the above description a basic formulation of the statistical theory will be derived based on simple geometrical and statistical principles without any independent assumption

Abstract: The controversy about the start up of the abnormal growth as heterogeneously engendered in the microstructure or produced by peculiar continuous incubation process has still not been solved. In this work the statistical theory of grain growth has been applied to treat the case of grain growth in the presence of an homogeneously unstable Zener drag. By the simulations presented it will be shown as abnormal grain growth is a result out of a continuous and homogeneous process without requiring any heterogeneity in the microstructure presumed to give local advantages to some grains. The mechanism by which during an incubation period the preconditions for the unstable growth are built up in the microstructure is clarified and discussed. Moreover the peculiar shape of Grain Size Distribution (GSD) approaching the “structural instability” will be also analytically defined and compared with experimental results obtained in a grain oriented Silicon Iron just before the onset of abnormal grain growth.

Abstract: The statistical model of grain growth is able to predict the effect of Zener drag on the grain size distribution evolution and on grain growth kinetics [1, 2]. This paper, in the same framework, will treat the case of atoms drag on grain boundary movement. The mechanism by which atoms drag operates is significantly different by that of Zener. The corresponding peculiar features will result in a specific grain size distribution evolution with considerable change of grain growth kinetics and distribution shape from that of normal grain growth case as a function of the intensity of the pinning conditions.