Elektronenstrahlbehandlung von PVD‐Hartstoffschichten

Electron beam treatment of PVD – hard coatings Coatings of the type CrN_x, (Ti, Cr)N, (Ti, Al)N, Ti(C, N) and Ti(B,N) were deposited on the quenched and tempered steel C45 to investigate the effect of electron beam treatment on the structure and the properties of hard coated steels. A controlled energy input by electron beams was used to investigate the thermal behaviour of hard coatings with fixing the transformation levels by self‐quenching. Simultaneously a different case hardening of the substrate was caused providing a different effect of supporting the hard layer. There are big differences in the thermal stability of the investigated coatings. The surface hardness, adhesion and wear resistance of the composit hard coating/steel was improved in dependence on the energy input. The use of electron beam technologies enables the generation of support layers which locally increase the working behaviour of hard coated steel.     

Potenziale von ausgewählten Randschichtbehandlungsverfahren sowie deren Kombinationen zur Verbesserung des Verschleiß‐ und Korrosionsverhaltens von Gusseisenwerkstoffen

Die typischen hohen C‐ und Si‐Gehalte von Gusseisenwerkstoffen und der weiche Graphit limitieren die Behandel‐ und Beanspruchbarkeit nach dem Nitrieren und der Hartstoffbeschichtung. Wenn die Gusseisenoberfläche vor den genannten Randschichtbehandlungen mittels Elektronstrahls umgeschmolzen wird (Kombinationsbehandlung) und eine harte, graphitfreie ledeburitische Randschicht gebildet wird, dient diese als Stützschicht für die harte und dünne Verbindungs‐ bzw. Hartstoffschicht. Vergleichende Verschleißtests (Stift‐Scheibe) zeigten, dass bei geringen Lasten die Verschleißrate aller Einzel‐ und Kombinationsbehandlungen auf einem vergleichbar niedrigen Niveau wie der unbehandelte und beschichtete Grundwerkstoff liegen. Bei höheren Lasten kommt das überragende Verschleißverhalten der Kombinationsbehandlungen gegenüber den Einzelbehandlungen voll zum Tragen. Die Bildung defektfreier Randschichten nach der Kombinationsbehandlung resultiert außerdem in einer deutlichen Verbesserung der Korrosionsbeständigkeit in chloridhaltiger Lösung. Im Vergleich zum Grundwerkstoff und den Einzelbehandlungen wurden die relevanten Potenziale zu deutlich positiveren Werten verschoben.     

Elektronenstrahl‐Randschichtbehandlung für die Herstellung verschleißbeständiger Auftragschichten auf nichtrostenden Stählen

Stainless steel components exposed to mechanical stresses are subjected not only to corrosion, but to abrasive wear. There are several possibilities for enhancing the wear resistance of stainless steels; however, such processes are very often associated with a reduction in corrosion resistance. This paper presents an electron beam surface treatment technology to significantly improve the wear resistance of austenitic steels (e.g. X6CrNiMoTi17‐12‐2) and duplex steels (e.g. X2CrNiMoN22‐5‐3), without a negative influence on the corrosion behavior. Fe‐ and Co‐additive wires were deposited thermally by electron beam cladding. The cladding layers produced were free of defects such as cracks and pores, and were well metallurgical bonded to the base materials. Microstructural analysis, hardness measurements, wear tests and corrosion tests were carried out. The wear rate k was reduced by a factor of 100 compared to the base materials for electron beam cladding with Fe‐based wire and by a factor of 10 with Co‐based wire. Corrosion resistance was preserved for the Fe‐based cladding layers and slightly increased (by a factor of 3) for the Co‐based cladding layers.     

Influence of electron beam deflection techniques used during the cladding process on the wear and corrosion behaviour of cobalt‐based protective coatings on austenitic stainless steel

The present work aims to improve the wear resistance of the austenitic stainless steel X6CrNiMoTi17‐12‐2. In view of the potential use of this alloy, however, corrosion resistance should be maintained where possible. An electron beam surface treatment (cladding) was performed, and the cobalt‐based alloy Stellite® 12 was used as the wear‐resistant material. The presented results show the effects of several electron beam oscillation figures during the cladding process with regard to layer bonding, microstructure formation and hardness. The surface hardness achieved was 576±18 HV 0.3, almost three times higher than that of the base material (203±3 HV 0.3). The scratch energy density – which represents the resistance to abrasive wear – could be increased by a factor of 1.5. Under abrasive‐adhesive stress loading conditions, the determined wear volume decreased by a factor of almost 5. Based on the corrosion investigations carried out, it was possible to prove that in comparison to the base material, the tendency towards pitting corrosion could be almost completely suppressed.     

Untersuchungen zum Elektronenstrahl‐Randschichtumschmelzen einer sprühkompaktierten übereutektischen eisenhaltigen Al‐Si‐Legierung

The present study shows the influence of two different electron beam deflection techniques on surface deformation, microstructure and hardness after an electron beam surface remelting of a spray‐formed hypereutectic aluminium alloy (AlSi17Fe5Cu4Mg). Due to the specific rapid heating and cooling rates on the one hand and the high content of alloying elements on the other hand, the surface microstructure was modified by phase formation, grain refinement and an oversaturation of aluminium solid solution. As a result the hardness was threefold increased (284 HV 0.1) compared to the untreated base material (104 HV 0.1). This hardness increase was significantly higher than the level of the conventional heat treatment (e. g. age hardening approx. 170 HV 0.1). The remelting process largely influenced the wear behaviour under abrasive (scratch test) and abrasive‐adhesive (pin‐on‐disc test) load conditions. Remelted surface layers generated by meander deflection technique showed the most improvement regarding their wear performance.