Interface interaction of additively manufactured composite systems coated by PVD - Correlation of surface hardening, residual stresses, roughness, and fatigue strength

激光束熔化（LBM）等增材制造工艺已成为原型制造领域的常见制造工艺，并在机械和汽车工程的金属部件设计自由度方面为用户开辟了新的可能性，同时具有高成本效率。这些部件经常承受动态载荷。为了保护摩擦应力功能表面免受过早磨损，氮化物PVD硬质涂层的应用已成为表面技术中的一种既定方法。然而，没有研究LBM钢基PVD涂层复合材料在循环载荷下的疲劳行为。第一个初步工作表明，涂层316 L基板制造的LBM与CrAlN PVD硬质涂层导致低周疲劳强度的增加。涂层生长以及所得的粘附强度受LBM基底表面的微观结构和残余应力状态的影响，所述残余应力状态是由于构建过程以及机械预处理过程，然而，其中直接相关性是不确定的。此外，它们对疲劳强度的影响尚不清楚。本研究项目的目的是调查采用激光束加工处理的钢表面的不同界面改性的影响，即机械性能的调整（界面硬化、残余应力状态）和结晶微结构，对PVD硬质涂层的形核和生长相以及它们对LBM基体- PVD涂层复合材料疲劳强度的影响。为此，LBM制造的奥氏体钢1.4404（X2 CrNiMo 17 -12-2和316L）和回火钢1.6773（36 NiCrMo 16）经过不同的处理，如抛光、等离子渗氮和应力消除退火，以提供不同的表面（界面）性能。所得的显微组织和机械性能进行了分析，使用射线照相检查以及机械技术测试方法。根据不同的预处理LBM基板，不同的PVD Cr 1-xAlXN化学计量的结合强度和涂层生长的影响。通过疲劳试验（高周疲劳）评估LBM基材PVD涂层复合材料的长期性能。所获得的知识将与微观结构分析的结果相关联，以确定由于（涂层）LBM部件的机械、热和热化学处理程序而导致的材料机械过程，以增加疲劳强度。

Additive manufacturing processes such as laser beam melting (LBM) have become a common manufacturing process in the field of prototyping and open up new possibilities for the user in terms of design freedom of metallic components for the mechanical and automotive engineering with high-cost efficiency at the same time. Such components are very often subject to dynamic loads. To protect tribologically stressed functional surfaces from premature wear, the application of nitride PVD hard coatings has become an established approach in surface technology. However, the fatigue behavior of LBM steel substrate PVD coating composites under cyclic loading were not investigated. First preliminary work shows that coating 316L substrates manufactured by LBM with CrAlN PVD hard coatings lead to an increase in low-cycle fatigue strength. The coating growth as well as the resulting adhesion strength are influenced by the microstructure and the residual stress state of the LBM substrate surface as a result of the building process as well as mechanical pretreatment procedures, whereby the direct correlations however are unsettled. Furthermore, their influence on fatigue strength is unclear. The aim of this research project is to investigate the influence of different interface modifications of steel surfaces processed employing LBM, i.e. an adjustment of the mechanical properties (interface hardening, residual stress state) and crystalline microstructure by means of mechanical, thermal and thermochemical substrate pretreatments, on the nucleation and growth phase of PVD hard coatings as well as their effect on the fatigue strength of LBM substrate — PVD coating composites. For this purpose, the austenitic steel 1.4404 (X2CrNiMo17-12-2 respectively 316L) and the tempered steel 1.6773 (36NiCrMo16) manufactured by LBM are subjected to different processes like polishing, plasma nitriding and stress relief annealing to provide different surfaces (-interfaces) properties. The resulting microstructural and mechanical properties are analyzed using radiographic examinations as well as mechanical technological test methods. Depending on the differently pretreated LBM substrates, the adhesion strength and coating growth of different PVD Cr1-xAlXN stoichiometries are investigated. The long-term behavior of the LBM substrate PVD coating composites is evaluated by means of fatigue tests (high cycle fatigue). The knowledge gained will be correlated with the results of microstructure analysis to determine the material mechanical processes due to mechanical, thermal, and thermochemical processing procedures of (coated) LBM components to increase fatigue strength.