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

具有细晶组织的金属材料在粗晶状态下具有更好的力学性能。细晶金属材料的强度、疲劳强度、耐磨性和耐腐蚀性的提高已经被实验证明。因此，金属材料的晶粒细化是显著提高其力学性能的一条很有前途的途径。由于这一事实，表面层中的局部颗粒细化提高了整个部件的性能。通过机械表面处理，可以通过严重塑性变形(SPD)实现表层的晶粒细化。机械锤击强化(MHP)是一种工业上使用的高载荷零件的机械表面处理工艺。利用MHP可使表面粗糙度变得光滑，应变硬化，并在表层产生残余压应力。此外，可以制造改善表面摩擦学特性的MHP结构。上述两个方面都是以往MHP领域研究的重点。此外，MHP是一种潜在的适合于产生细晶表面层的技术。然而，目前还没有关于MHP工艺参数和由此产生的表层晶粒细化的解释模型。为了使MHP工艺参数能够面向目标地在工业上实施以实现晶粒细化，必须解释MHP工艺参数与所产生的表层晶粒细化之间的基本因果关系。此外，还研究了经MHP处理的零件的细晶表层对磨损和疲劳强度的影响。

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.