Development of texture, strain/stresses in oxide layers

Materials are subjected to high temperature corrosion in numerous technical processes and environments. The most obvious are turbines, engines, catalysers and power stations. The lifetime of components strongly depends on the density of the oxide layer. Both the mechanical integrity and the diffusion barrier properties depend on the composition of the layer as well as on its morphology, texture and internal strain/stress state. A determination of the internal strain/stress state resulting from the growth of the oxide layer is only possible by in-situ investigations during the oxidation process, since a cooling process superimposes cooling stresses on the layers and the substrate. This research project aims at developing models for the oxidation process and the evolution of the microstructure, texture, and especially strain/stress state of the oxide layer on iron. Systematic studies will start with oxide layers on single crystals and move on towards fine and coarse grained materials. This enables studies of internal and external oxidation effects separately. For studying the microstructure, texture and strain/stress state we focus on microscopy and diffraction methods. Novel techniques using synchrotron radiation are expected to enable in-situ investigations of the oxide layers and, thus, studying the development of the strain/stress state. In-situ studies are necessary since the additional stresses imposed by cooling the samples to room temperature often results in microcracking and delamination and hence stress relief. Since the layer microstructure, morphology, texture and strain / stress state are crucial for the oxide layer integrity, its barrier function against diffusion and its bonding to the substrate an understanding of the layer development will provide a substantial contribution towards a longer lifetime of components in high temperature environments.

Materials are subjected to high temperature corrosion in numerous technical processes and environments. The most obvious are turbines, engines, catalysers and power stations. The lifetime of components strongly depends on the density of the oxide layer. Both the mechanical integrity and the diffusion barrier properties depend on the composition of the layer as well as on its morphology, texture and internal strain/stress state. A determination of the internal strain/stress state resulting from the growth of the oxide layer is only possible by in-situ investigations during the oxidation process, since a cooling process superimposes cooling stresses on the layers and the substrate. This research project aims at developing models for the oxidation process and the evolution of the microstructure, texture, and especially strain/stress state of the oxide layer on iron. Systematic studies will start with oxide layers on single crystals and move on towards fine and coarse grained materials. This enables studies of internal and external oxidation effects separately. For studying the microstructure, texture and strain/stress state we focus on microscopy and diffraction methods. Novel techniques using synchrotron radiation are expected to enable in-situ investigations of the oxide layers and, thus, studying the development of the strain/stress state. In-situ studies are necessary since the additional stresses imposed by cooling the samples to room temperature often results in microcracking and delamination and hence stress relief. Since the layer microstructure, morphology, texture and strain / stress state are crucial for the oxide layer integrity, its barrier function against diffusion and its bonding to the substrate an understanding of the layer development will provide a substantial contribution towards a longer lifetime of components in high temperature environments.