KurzfassungLegierungs- und gießtechnische Neu- und Weiterentwicklungen von Gusseisen haben zur Erweiterung der Einsatzgebiete dieser Werkstoffe für Bauteile und Werkzeuge auch unter dem Aspekt des Leichtbaus geführt. Zur zusätzlichen lokalen Verbesserung der tribologischen und korrosiven Beanspruchbarkeit wurde eine Technologie zur kombinierten Randschichtbehandlung entwickelt. Dabei wird das Gusseisen lokal mittels Elektronenstrahl umgeschmolzen, sodass eine harte (650 HV 0,3), graphitfreie ledeburitische Schicht entsteht. Diese thermisch gut beständige Schicht (bis ca. 1100 °C) dient als Stützschicht für eine nachfolgend durch Plasmanitrieren erzeugte relativ dünne (< 10 μm), harte Verbindungsschicht. Es werden sowohl die werkstoffspezifischen Einflussfaktoren, wie Graphitmorphologie, chemische Zusammensetzung etc., als auch die Auswirkungen der Prozessparameter auf das Ergebnis der Einzel- und Kombinationsbehandlungen erörtert. Vergleichende Untersuchungen zum Verschleißverhalten (Kugel-Scheibe) haben gezeigt, dass insbesondere bei höheren Lasten (> 100 N) der Mehrwert der Kombinationsbehandlung gegenüber den Einzelbehandlungen voll zum Tragen kommt. Die deutliche Verbesserung des Korrosionsverhaltens nach der Kombinationsbehandlung resultiert aus der defektfreien Ausbildung der Nitrierschicht auf der graphitfreien Umschmelzschicht.
The present study reports on the impact of abnormal grain growth (AGG) on the microstructural evolution following electron beam (EB) welding of Fe-Mn-Al-Ni shape memory alloy (SMA). Polycrystalline sheet-like material was EB-welded and a cyclic heat treatment, studied in previous work, was conducted for inducing AGG and a bamboo-like microstructure, respectively. Optical and electron microscopy were carried out to characterize the prevailing microstructure upon cyclic heat treatment. For characterization of the functional properties following AGG, a load increase test was conducted. The current results clearly show that good shape memory response can be obtained in Fe-Mn-Al-Ni SMA upon EB welding and subsequent post-heat treatment. These results further substantiate the potential use of conventional processing routes for Fe-Mn-Al-Ni SMA.
The results of joining investigations, especially for low alloy TRIP steels, [1][2][3][4] depend on the class of material studied. A range of joining conditions are produced in the weld area, and these differ greatly in their mechanical properties [4] depending on the alloy compositions that are needed for the TRIP effect, such as Si or Al. The welding of such steels is linked mainly to a loss of ductility in the welding zone. [3,4] Welding of low alloy TRIP steels is already used in the joining of tailored blanks. [5] With the aid of a high-energy source such as a laser beam (LB) or an electron beam (EB), it was shown that the specific characteristics of the process, like the energy density, the narrow seam produced, the small heat-affected zone (HAZ), and the high heating rate, have a positive effect on the welding result.High alloy austenitic steels, like the metastable steel 1.4301, which exhibits the TRIP effect, are characterized by their excellent weldability. [6,7] The dendritic solidified fusion zone showed no hardness increase resulting from the welding process.Up to now only low alloy TRIP steels have been the focus of detailed studies of thermal joining. Moreover, welding of high Mn steels with the TWIP effect has very rarely been studied. [8] Results with respect to the welding of newly developed high alloy CrMnNi cast steels with TRIP/TWIP effect were not yet known. In particular, the Ni content has a significant influence on the deformation mechanisms of the steel variants studied. Thus, in this work, initial results on the welding of these new cast steels using electron beam techniques are presented in order to show their general weldability. Moreover, the present studies are focused on the influence of EB welding on the specific deformation mechanisms, i.e., martensitic transformations (TRIP) or twinning (TWIP), respectively.
Within the last years, considerable progress was achieved in the research field of plasma nitriding of Al alloys. However, due to large property differences between the very hard AlN layer and the soft Al matrix material the load capacity of the nitride layer is limited. Electron beam (EB) surface alloying modifies the chemical composition of the area near the surface up to a certain depth. This, for instance, results in high hardness levels, and therefore this layer acts as support for the hard and wear-resistant thin AlN layer generated by plasma nitriding. In the present study, surface modifications produced by a combination of EB alloying with Fe based additives and plasma nitriding of wrought, cast and spray-formed Al alloys were investigated. After the EB treatment the layers were examined regarding their influence on the structure, the nitride layer growth mechanism, the effect of the EB layer for the support of the AlN layer and the resulting duplex layer properties, e.g. hardness and wear behaviour.
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