Development of the peening processes micropeening and ultrasonic wet peening to work hardening

微喷丸和超声湿式喷丸工艺提供了机械表面处理的可能性，可显著提高钢的疲劳强度，与已有的喷丸等方法相比具有几个优点。这不仅包括高表面质量，几乎不受爆破介质对粗糙度的影响，而且还包括非常低的喷丸强度，允许加工薄壁部件。另一个显著的影响是表面出现了纳米晶区，这影响了边界层的力学性能。在赠款的第一阶段，使用Armco铁作为模型材料，以分离影响疲劳强度的因素，并基于改进的局部耐久概念开发和验证了细化和固结的材料模型。在该项目的第二阶段，这种对机理的理解现在将转移到42CrMo4 V450调质钢上。这带来了一个困难，即不可能像在Armco铸铁中那样通过热处理来分离参数。此外，在这种热处理条件下，边界层的各个状态不能清楚地分开。此外，在建模方法中必须考虑严重修改的变形行为，这也会影响表面层状态。在前面有限元模拟的基础上提出的概念也将通过微观组织和疲劳行为的实验表征来验证。这将最终应用于常规喷丸后微喷丸或超声波湿式喷丸的顺序机械表面处理。这将实现高渗透率和优化的近表面性能的优化组合，从而显著提高厚壁部件的寿命。

The processes micro-peening and ultrasonic wet peening offer the possibility of mechanical surface treatment to significantly increase fatigue strength of steels, with several advantages over established methods such as shot peening. This includes not only a high surface quality with little effect of blasting media impacts on the roughness but also a very low peening intensity, which allows for the processing of thin-walled components. Another notable effect is the occurrence of nanocrystalline regions on the surface, which affect the mechanical properties of the boundary layer. In the first phase of the grant Armco iron was used as the model material to separate the factors influencing the fatigue strength and are based on developed and validated a material model of grain refinement and consolidation of a modified concept of local endurance. In the second phase of the project this understanding of the mechanisms will now be transferred to the quenched and tempered steel 42CrMo4 V450. This bears the difficulty that a parameter separation by heat treatment as in the Armco iron, is not possible. Furthermore, the individual states of the boundary layer cannot be clearly separated in this heat treatment condition. In addition, the heavily modified deformation behavior, which also affects the surface layer state, must be considered in the modelling approach. The concept to be developed on the basis of previous FEM simulations will also be validated with an experimental characterization of the microstructure and the fatigue behavior. This is to be finally applied to a sequential mechanical surface treatment of conventional shot peening followed by micro-peening or ultrasonic wet peening. This should achieve an optimized combination of high penetration with optimized near-surface properties so that a significant increase in lifetime results for thick-walled components.