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Y.V. Shan, R. Sowa, J. Svoboda, F.D. Fischer, E. Kozeschnik:
"Influence of stress relaxation on the coarsening kinetics of incoherent precipitates";
Talk: Euromat 2019, Stockholm; 2019-09-01 - 2019-09-05.

Introduction
Incoherent pPrecipitates in a solid-state material can cause a stress field around the particles during nucleation,if due to the higha volumetric misfit exists between precipitate and matrix, i.e., precipitate and matrix phases have different molar volumes. However, this stress can relax by diffusion creep. Given enough time, the stress can be equalized between the matrix, which also leads to a stabilization of smaller precipitates towards coarsening. In this work the coarsening kinetics of these precipitates is investigated, since the well-established LSW theory fails to describe this effect.

Methods
A pressure, following the theory of elasticity, is applied to the newly nucleated precipitates. Power-law creep in the matrix reduces this pressure. In the case of coarsening, the pressure can turn negative in the course of dissolving dissolution of the smaller particles and, thus, significantly slow impact the process of coarsening. Case studies are applied to study the interaction of nucleation, growth and coarsening of an ensemble of precipitates within the framework ofon a multi-class precipitation model as implemented in the thermokinetic software package MatCalc.

Results
Experiments on the coarsening of delta phase precipitates in Ni-base superalloy indicated that the growth kinetics of delta phase can be well described by the nucleation and growth (SFFK) mean-field model of MatCalc. With all parameters left identical for simulation of the coarsening process of delta phase precipitates, the a slower coarsening rate of ?-precipitates in the ? system (Roman Sowa?)these particles is substantially overestimated, indicating that the coarsening process is slowed down by some mechanism than should be expected from the conventional models. This issue is discussed and it is shown that The the coarsening kinetics of model presented in this study is compareds to well with the experiments.

Conclusions
A new model, describing the coarsening kinetics of incoherent precipitates with different molar volume compared to the matrix, , based on the new stress relaxation concept developed by some of the authors, is introduced briefly reviewed in this work. It provides a good supplement to the LSW theory, which lacks a formulation to take strong misfits between precipitate and matrix into accountis shown that this approach can reasonably well describe the retarded coarsening kinetics, which is observed experimentally these systems.