Grain refinement in the edge zone of metallic materials by mechanical surface hammering (FinePeening)

 

Metals with a fine-grained structure have better mechanical properties than metals with a coarse-grained structure. An increase in strength, fatigue strength, wear and corrosion resistance of metallic materials with a fine-grained microstructure has already been demonstrated experimentally. Therefore, grain refinement of metallic materials is a promising approach to significantly improve their mechanical properties.

The edge zone of technical components is often the most heavily stressed area. Therefore already a local grain refinement in the peripheral zone can significantly improve the overall component function. Grain refinement in the peripheral zone can be achieved by local high plastic deformation using surface treatment processes. Mechanical surface hammering (MOH) is an innovative industrial process for the surface treatment of highly stressed components.

The MOH smoothes the surface, induces residual compressive stresses and strainens the workpiece edge zone. In addition, the MOH can be used to create structures that improve the tribological properties of the surfaces. These aspects have so far been the focus of research activities to investigate the MOH process. The MOH is potentially suitable for producing grain refinement in the peripheral zone of metallic components. However, there are no explanatory models for the interactions between the process parameters of the MOH and the resulting grain refinement in the boundary zone.

In order to enable a target-oriented industrial design of the MOH process for grain refinement, the basic cause-effect relationships between the MOH process parameters and the resulting grain refinement in the marginal zone are first explained using the example of the steels 42CrMo4 and X5CrNi18-10 using experimental test series as well as numerical finite element simulations. Furthermore, the effect of the fine-grained peripheral zone of MOH treated components on wear and fatigue behaviour is described by pin-on-cylinder tribometer tests and rotating bending investigations.