Volume 52, Issue 4

Kurzfassung Zugeigenspannungen, wie sie beim Schweißprozess durch inhomogene Temperaturverteilungen und Schrumpfungen hervorgerufen werden, können die Lebensdauer geschweißter Verbindungen signifikant herabsetzen. Eine neue und außerordentlich attraktive Methode, um Druckeigenspannungen bereits während des Schweißens gezielt einzustellen, gelingt mit sogenannten LTT (Low Transformation Temperature)-Legierungen. LTT-Legierungen weisen eine martensitische Phasenumwandlung bei relativ niedrigen Temperaturen auf, wobei die damit verbundene Volumenexpansion zu einer Reduktion der Schrumpfeigenspannungen bzw. Erzeugung von Druckeigenspannungen führt. Zum direkten Nachweis der Phasenumwandlungen und der damit verbundenen resultierenden Schweißeigenspannungen wurden erstmals In-situ-Schweißexperimente unter Nutzung hoch energetischer, polychromatischer Synchrotronstrahlung (Weißstrahl) realisiert, um die Umwandlungskinetik während eines realen Schweißprozesses und die daraus resultierenden Schweißeigenspannungen zu analysieren. Es wird gezeigt, dass mit LTT-Legierungen signifikante Druckeigenspannungen in der Schweißnaht erreicht werden.

Kurzfassung Hochglänzende Spritzgussteiloberflächen werden aus Design- und aus funktionellen Gründen eingesetzt. Eine hervorragende Oberflächenqualität des korrespondierenden (Stahl-)Formeinsatzes ist eine Grundvoraussetzung, welche neben der Auswahl des Kunststoffes und der Prozessführung des Spritzgießens das gewünschte Erscheinungsbild der Formteiloberfläche beeinflusst. Im Rahmen eines multilateralen Forschungsprojektes am Polymer Competence Center (PCCL), Leoben wurden 12 unterschiedliche metallische Hochglanzpoliturgüten erstellt und über Topografiemessungen mittels Weißlichtinterferometrie, dreidimensionaler Rauigkeitsauswertung und 3 daraus abgeleiteten topografischen Qualitätsparametern eindeutig beschrieben. Letztere berücksichtigen die in unterschiedlicher lateraler Ausprägung auftretenden Oberflächendefekte Orangenhaut sowie Mattigkeit (Rauheit sowie Feinstrauheit). Weiters wurde die Abformung in die Kunststoffe Polypropylen und Polycarbonat untersucht.

Desired characteristics for brake linings are stable friction, low wear rate, light weight, long life, low noise, resistance to corrosion, and acceptable cost versus performance characteristics. This paper presents a research carried out on production of five different friction composites. Hardness, wear resistance, friction coefficients, compression strength, compression elastic modulus, and density of the developed brake lining composites were determined by related test methods. The composition consisting of 10% PbS, 10% ZnS, 10% graphite, 10% steel wool, 2% aramid pulp, 12% novalak type phenolic resin, 8% friction dust, 25% BaSO 4 , 8% rubber powder, and 5% iron powder was found suitable. All components were mixed homogeneously and hot molded under 35 MPa pressure at 200 °C for 10 minutes. The prepared samples were cured in an air-circulated oven at 200 °C for 6 hours. Normal friction coefficient 0.384, hot friction coefficient 0.370, density 2.22 g/cm 3 , hardness 70–75 HRL, compression elastic modulus 775 MPa, compression strength 51.87 MPa were found. These test results were compa- tible with commercial brake lining materials.

In the study for this contribution, good mechanical properties have been obtained from Mo (and Cu) alloyed PM-steels after suitable heat treatment. The influence of two to four weight percent nickel additions in these Mo (and Cu) alloyed PM-steels on the mechanical properties have been studied. The influence of such an alloying modification on the defect characteristics has also been investigated. The heat treatment of the steel material has been realized via a novel way, i.e. with the sinter-hardening method. The mechanical properties like tensile strength, matrix microhardness, and toughness have been measured. Transverse rupture tests have been implemented for toughness measurement while the transverse rupture strength data has been obtained by using the Weibull statistics. Microstructural studies have been performed with various microscopy techniques, where the general steel matrix was observed to exist of tempered martensite, bainite, residual austenite, and micropores. The amount of pores was measured with image analysis technique, while the amount of retained austenite was measured with the magnetic saturation method. The results show that the values of the transverse rupture test are determined primarily by pores/pore agglomerates that fit big size defect criteria. On the other hand, a positive effect of increasing Nickel content has been observed on the resistance against fracture.

Ceramics are attractive dental materials as a result of their supe- rior aesthetics and biocompatibility. However, they are brittle and prone to premature failure, especially at repeated contact strain and in moist environments. The chemical stability of dental ceramics is important, because it directly affects mechanical properties and aesthetic value of restorations. The aim of this study was to investigate the effects of a corrosive agent, i.e. 4% acetic acid, on the surface of glazed and unglazed feldspathic ceramics. Metal-ceramic plates (9.0 × 9.0 × 1.2 mm) composed of a Ni-Cr alloy (Wiron 99, Bego Germany) and glazed or unglazed feldspathic ceramics (IPS Classic, Ivoclar-Vivadent, Schaan, Liechtenstein) were prepared according to the manufacturer‧s instructions. The samples were immersed in the solution at 80 °C and kept there for 16 h (ISO 6872). The surfaces of the samples before and after immersion in the corrosive medium were examined by atomic force microscopy (AFM). The pre- and post- corrosion AFM images of the surfaces of the feldspathic ceramics samples clearly show that the glazed surfaces are much less prone to deterioration by corrosion than the unglazed ones.

Kurzfassung Für den vorliegenden Beitrag wurde der Einfluss der Wärmebehandlung auf das Gefüge eines hochlegierten austenitisch-ferritischen Duplexstahles untersucht. Außerdem wurde der Einfluss des Homogenisierens und des Alterns auf das Werkstoffverhalten ermittelt. Die Proben wurden entsprechend ASME 1883 vorbereitet. Sie enthielten neben einem niedrigen Molybdängehalt höhere Kohlenstoff-, Chrom- und Nickelanteile. Nach dem Homogenisieren bei 1060 °C wurden die Proben der Reihe nach auf 475, 650 und 850°C erwärmt, bei diesen Temperaturen jeweils 80 h gealtert und danach in einem Eiswasserbad mit 3,5% NaCl rasch abgekühlt. Danach wurden das Gefüge und die mechanischen Eigenschaften des Werkstoffes untersucht. Bei den mechanischen Eigenschaften des Werkstoffes wurden viele und wichtige Unterschiede gefunden. Außerdem wurden alle Proben zur Bestimmung der intermetallischen Phasen und der Karbide lichtmikroskopisch, röntgenografisch und elektronenmikroskopisch untersucht. Aus den DTA-Kurven geht hervor, dass zwischen den Temperaturen von 1100 und 1221°C nur ein Umwandlungspeak existiert. Die ferritische und die austenitische Phase lösten sich in diesem Temperaturbereich auf und wandelten sich ausschließlich in Ferrit um.

In this study, the surface of AA2024-T4 Al alloy substrate was coated by Al 2 O 3 + TiO 2 powders without and with NiAl bond coat by using a plasma spray process. The TiO 2 content was added at different concentrations (3, 13 and 40 wt.-%) to the Al 2 O 3 content. The coated samples were characterized by means of an optical microscope, scanning electron microscope (SEM), energy dispersive X-ray spectroscopy (EDX), and the hardness as well as the bond strength were tested. These results showed that the hardness and porosity decreased with the increasing of the TiO 2 content of the Al 2 O 3 + TiO 2 coatings. The bonding strength of the coated specimens was increased by using the NiAl bond coat.

Joining of NiO-YSZ cermet with 316 stainless steel was carried out using B-Ni2 brazing alloy (7 wt.-% Cr, 4.5 wt.-% Si, 3 wt.-% Fe, 3 wt.-% B, 0.06 wt.-% C, 0.02 wt.-% P, Ni-balance, m. p. 972–999 °C), and moderate loading was applied during brazing normal to the joint surface to realize a reliable sealing of the NiO-YSZ cermet anode/316 stainless steel interconnect structure in a SOFC. In the present research, interfacial (chemical) reactions during brazing at the NiO-YSZ/316 stainless steel interconnect were also promoted by addition of an electroless nickel plate to NiO-YSZ cermet as a coating with relevant process variables and procedures optimized during the electroless nickel plating. A special fixture for static loading was designed for filler metal alloy strips to be pre-placed at the joint surface so that during melting of the brazing filler alloy the liquid alloy layer would be perpendicular to the static load direction during brazing. Brazing was performed in a cold-wall vacuum furnace at 1080 °C. Post-brazing examination of interfacial morphologies between NiO-YSZ cermet and 316 stainless steel was performed using the SEM and EDS procedures. The results indicate that the B-Ni2 brazing filler alloy was fused fully during brazing and a continuous interfacial layer formation and the joint integrity were significantly affected by applied static loading during brazing. The positive loading effect was possibly attributed to the rectification of the joints under load by enhanced diffusion of Fe and Ni atoms from 316 stainless steel to B-Ni2 brazing filler alloy and the consequent increase in the fraction of Fe- and Ni-rich intermetallic phases in the joint. The thickness of the interfacial area, however, remained almost constant at 100 ¼m before and after brazing.