Today laser alloying/dispersing of Aluminum is a well-known technique to increase the wear resistance of parts. The alloyed/dispersed layer is typically limited in depth to about 1-1.5 mm. For Aluminum the absorptivity of near infrared wavelengths is comparably low. This makes conventional laser alloying/dispersing inefficient. In contrast, the overall absorption of the laser power using the deep penetration effect is comparatively high. The comparison of the principles of the conventional laser alloying process and the deep penetration alloying process is shown in this study. In deep penetration alloying, the track geometry and the distribution of the filler material can both be influenced by the process parameters. It is shown that a deeper alloying is possible by using the deep penetration effect caused by a highly intensive laser beam. The laser beam is scanned in a circular or other motion in order to control the shape of the track. By this manner of alloying it is possible to realize nearly rectangular and comparable deep track geometries. The dependencies of the penetration depth on the process parameters will show a way how to compromise between the optimal distribution of the filler material and the geometry of the track in order to optimize the whole process.
Thermal treatments of steel components with the goal of hardening often result in distortion by releasing the residual stresses which were brought into the specimen during the preceding processing steps. The goal of the presented work is the minimization of this distortion. By generating definite residual stress fields and investigating the resulting distortion, the distortion mechanism can be observed in detail. A flexible and reproducible way to generate such residual stress fields inside a specimen is by means of local thermal treatment with a laser beam. Computer simulations as well as experiments were carried out using an idealized tooth of a gearwheel (finger sample) as a model system. The deformation of the samples due to the laser heat treatment and the stress fields generated inside the samples were determined with respect to different process parameters.
There are quite different requirements for tribological properties of surfaces in industry. Both reduction and maximization of friction and/or wear are possible requirements. The friction and wear properties depend on the tribological system consisting of the friction partners, the medium between them and the environment around them. So for each application tailored surfaces with special tribological properties are needed. In the paper examples are presented which deal with the investigation and the implementation of laser based processes to obtain surfaces with very different tribological properties. Wavelengths, output power values, intensity distributions and beam qualities of the available lasers vary in a wide range. Also the available devices for beam formation and beam guidance enable special processes for tailoring properties for particular applications. These processes are for example the single-layered or multi-layered laser cladding generating homogeneous or graded claddings, the laser alloying or laser dispersing and the laser stimulated deposition of diamond layers at atmospheric pressure.
Kurzfassung Das Laserstrahlhärten von Stahl ist eine lokale Wärmebehandlung, bei der eine örtliche Austenitisierung mit nachfolgender Härtung stattfindet. Eine Steigerung der Dauerfestigkeit von Proben oder Bauteilen durch das Laserstrahlhärten ist möglich, wenn die Härtezone so gelegt wird, dass die hoch beanspruchten Bereiche eine Härtesteigerung erfahren, während die Anlasszone, welche die Härtezone umgibt, in wenig beanspruchten Bereichen liegt. Dieses ist bei gekerbten oder abgesetzten Proben und Bauteilen möglich, welche in der vorliegenden Arbeit untersucht wurden. Im Teil 1 der Veröffentlichung wurde das experimentelle Versuchsprogramm sowie die Simulation der Eigenspannungen beschrieben [1]. Der Einfluss des partiellen gepulsten Laserstrahlhärtens von konstruktionsbedingten Kerben in Form von Bohrungen und Kehlen auf die Dauerfestigkeit ist der Schwerpunkt des vorliegenden zweiten Teils. Die Dauerfestigkeiten wurden sowohl experimentell als auch rechnerisch bestimmt. Die Basis hierfür ist das erweiterte Fehlstellenmodell, mit dem neben der Dauerfestigkeit auch Rissbildungswahrscheinlichkeiten an der Oberfläche und im Volumen von Proben und Bauteilen berechnet werden können. Da die Rissbildung fast ausschließlich an der Oberfläche beobachtet wurde, konnte die Anwendung des erweiterten Fehlstellenmodells auf die Oberfläche beschränkt werden, wobei für die Rissbildung die Schwingfestigkeitshypothese von Dang Van angewandt wurde.
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