Herstellung und Eigenschaften nanopartikulär verstärkter Beschichtungen durch Laserauftragschweißen zum Verschleißschutz von Schmiedegesenken
Ocylok, Sörn; Reisgen, Uwe (Thesis advisor); Poprawe, Reinhart (Thesis advisor)
Aachen / Apprimus Verlag (2016) [Book, Dissertation / PhD Thesis]
Page(s): III, 205 Seiten : Illustrationen
Forging dies are exposed to high thermal load and mechanical stresses which lead to wear and fatigue on the tool surface. To fulfil the demand of prolonging the lifetime of such high value parts new material designs are necessary. Laser cladding represents an established process to build up tailored layers on complex shaped surfaces. The present work investigates a new approach by the addition of nano-sized particles to laser cladded layers. The main idea is to reduce the grain size of the cladded layers by adding nano-sized nuclei. A fine grain structure improves strength as well as ductility and fatigue resistance. Furthermore hard particles are able to increase abrasive wear resistance. In the experimental studies nano-scaled aluminum and yttrium oxides, titanium and tungsten carbides are added in small contents from 0.1 up to 2.5 wt.-% to cladded layers of conventional used hot working tool steel X32CrMoV12-28. Therefore a homogeneous powder mixture of nano- and micro-scaled materials is produced by high energy ball milling. The produced cladded layers of almost 100 % density are free from cracks. Depending on the added nano-material and the processing parameters a fine-grained orientation-free microstructure can be produced in contrast to cladded layers without nanoparticles. Superior mechanical properties like a high hardness of more than 800 HV and an increased tensile strength are achieved by adding tungsten carbides nanoparticles without affecting properties like the breaking elongation. In addition to the investigations on the tribological behavior of the layers by the calotte-wear-test the friction coefficient is analyzed by forging-test of a ring specimen. The performance of the layers is tested in a specific forging rig regarding wear at the tool surface and compared to the conventional tool steel.For demonstration purposes are cladded and tested afterwards under industrial forging conditions. Compared with the refurbished forging dies without nanoparticular addition the WC-reinforced layers show improved properties regarding an increase of lifetime of 44 %.