Grain refinement in the surface layer of metallic materials by means ofmachine hammer peening (FinePeening)

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Metallic materials with a fine-grained microstructure have better mechanical properties as in a coarse-grained state. An increase of strength, fatigue strength, wear, and corrosion resistance of fine grained metallic materials has already been proven experimentally. Therefore, the grain refinement of metallic materials is a promising approach to significantly improve their mechanical properties.The surface layer is often the most loaded zone of technical components. Due to this fact a local grain refinement in the surface layer improves the performance of the complete component. A grain refinement in the surface layer can be achieved through severe plastic deformation (SPD) by means of mechanical surface treatment. Machine hammer peening (MHP) is an industrially used process for mechanical surface treatment of highly loaded technical components.A smoothening oft the surface asperities, strain hardening, and induction of compressive residual stresses in the surface layer are achiever by means of MHP. Furthermore, MHP structures to improve the tribological characteristics of the surfaces can be produced. Both mentioned aspects were in the focus of previous research in the field of MHP. Furthermore, MHP is a potentially suitable technology for a generation of a fine-grained surface layer. However, there exist no explanation models with regard to the process parameters of MHP and the resulting grain refinement in the surface layer.In order to enable a goal-oriented industrial implementation of MHP for the grain refinement, basic cause-and-effect relationships between the MHP process parameters and the resulting grain refinement in the surface layer must be explained. Furthermore, the influence of the fine-grained surface layer of MHP treated components on the wear and fatigue strength is to be characterized.