Reduction of residual stresses in CVD diamond layers on steel parts through creation of hierarchically structured surface topographies by applying cutting processes

在钢材料上应用CVD金刚石涂层能够实现各种性能改进，例如减少摩擦机械高负载系统中的摩擦和磨损，或降低热机械应用中功能表面的粘附趋势。钢和金刚石的不同热膨胀系数导致在从涂层温度冷却到室温期间和之后金刚石层中的强残余压应力。因此，CVD金刚石涂层被限制在非常小的厚度，因为较厚的层倾向于剥落。有限元分析的金刚石涂层的钢衬底的冷却特性和残余应力测量的拉曼光谱的沉积CVD金刚石层的衬底上的钢X46 Cr 13有助于增强的理解的粘附机制。可以确定的是，由超声振动叠加端面铣削产生的预定义的衬底表面微观结构显着影响层固有残余应力的分布。结合TiNB中间层，实现了定制的界面。这使得能够应用厚度高达16 µm的封闭、均匀以及粘附的CVD金刚石层。金刚石层的相对良好的粘附强度主要归因于冷却残余应力的降低，这是由于在低于400 °C的温度下在贝氏体-贝氏体转变期间钢体积显著增加。总之，在该项目的第一阶段，成功地开发了科学基础，作为通过适当的相变提高钢基体上CVD金刚石层附着强度的先决条件。在此基础上，研究了具有较高热质量的CVD金刚石涂层试样的功能特性，该试样由导致较强冷却残余应力的“不利（较高贝氏体开始温度）转变”钢（X40 CrMoV 5 -1）组成。由于金刚石层中应力降低的转变行为不太吉祥，因此该钢有资格证明和分析表面微观结构对金刚石层粘附力的影响。这将拓宽对粘附机制的基本理解以及潜在的应用，因为这种钢也具有很高的技术相关性。由于其特殊的振动特性，它可以用作超声波发生器材料，例如。G.用于铝部件的超声波焊接。

The application of CVD diamond coatings on steel materials enables various improvements of the performance, such as a reduction of friction and wear in tribomechanically highly loaded systems or a decrease of the adhesion tendency of functional surfaces in thermomechanical applications. The different coefficients of thermal expansion of steel and diamond result in strong residual compressive stresses in the diamond layer during and after cooling down from the coating temperature to room temperature. Consequently, CVD diamond coatings were limited to a very small thickness, since thicker layers tend to flake off. FE analyses of the cooling characteristics of the diamond coated steel substrate and residual stress measurements by RAMAN spectroscopy of the deposited CVD diamond layers on substrates of the steel X46Cr13 contributed to an enhanced understanding of the adhesion mechanisms. It could be determined that a predefined substrate surface microstructure generated by ultrasonic vibration superimposed face milling significantly influences the distribution of the layer-inherent residual stresses. Combined with the TiNB intermediate layer, a tailored interface was realised. This enabled the application of a closed and homogeneous as well asadherent CVD diamond layer with a thickness of up to 16 µm. The relatively good adhesion strength of the diamond layers is mainly attributed to a reduction of the cooling residual stresses due to the significant steel volume increase during the austenite-bainite transformation at temperatures below 400 °C. Summing up, in the first periode of the project, the scientific fundamentals were successfully developed as a prerequisite for increasing the adhesion strength of CVD diamond layers on a steel substrate with an appropriate phase transformation. Based on this, the functional properties of CVD diamond coated specimens with a higher thermal mass and comprising of a "less favourably (higher bainite starting temperature) transforming” steel (X40CrMoV5-1) resulting in stronger cooling residual stresses is investigated. Due to the transformation behaviour which is less auspicious for a stress reduction in the diamond layer, this steel qualifies to demonstrate and analyse the influence of surface microstructures on the adhesion of the diamond layer. This will broaden the basic understanding of the adhesion mechanisms as well as the potential applications, since this steel is also of high technical relevance. Due to its special vibrational properties, it can be used, as a sonotrode material, e. g. for ultrasonic welding of aluminium components.