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In the present study the fatigue strength of austempered ductile irons with dual matrix structures (ADI with DMS) has been studied for an unalloyed ductile cast iron. For this purpose, specimens were intercritically austenitized (partially austenitized) in two phase region (α + γ ) at various temperatures (810°C, 820°C and 830°C) for 20 minutes and then quenched into salt bath held at austempering temperature of 315°C and 375°C for 120 minutes and then air cooled to room temperature to obtain various ausferrite volume fractions and their morphologies. Conventionally austempered specimens (austempered from 900°C) with fully ausferritic matrix and unalloyed as cast specimens having ferrit + pearlite structures were also tested for a comparison. Rotating bending fatigue test were carried out an the experimental results showed that, in ADI with DMS, volume fraction of ausferrite and continuity of ausferritic structure along intercellular boundaries play important role in determining fatigue strength. The fatigue strength of these specimens increases with increasing ausferrite volume fraction. The fatigue strength was correlated with the ausferrite volume fraction and high carbon austenite and its carbon content. Conventionally austempered specimens exhibited much greater fatigue strength than ADI with DMS specimens.KEY WORDS: austempered ductile iron; dual matrix structure; fatigue; ausferrite volume fraction.

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In this article, effects of traditional surface machining processes and a newly used surface finishing process called burnishing process on a brass material are compared on the basis of microstructure, circularity, cylindricity, and surface roughness. For this reason, test samples made of brass material which is a non-ferrous metal were prepared to be widely used in many fields of machining industry as it accurately reveals deformation effects of surface finishing processes, and those samples were subjected to drilling, lathing, reaming, grinding, honing, and burnishing. After these processes, hole surface roughness, cylindricity, and change in microstructure were analyzed. All surface machining processes were performed under constant depth of cut, cutting speed, and feed rate. Data collected after experimental research indicates that the best combination of surface characteristics is obtained by burnishing process, in comparison to all other different methods of finishing. Also the highest hardness and best surface quality of machined surface are provided with burnishing. All results show that burnishing should be preferred to provide the optimum characteristics in hole surfaces subjected to continuous deformation and corrosion.

The effects of various reinforcements (boron carbide -silicon carbide-alumina) with constant volume fraction (20 %) on the abrasive wear properties of AA6061 matrix composites produced with hot pressing process were investigated. The wear tests were carried out using a pin-on-disk wear tester by sliding at sliding speeds of 1.2 m/s against silicon carbide paper. Applied normal loads have 5, 10 and 15 N magnitude at room temperature. The wear morphologies of the worn surfaces were analyzed using a scanning electron microscope in order to examine the wear characteristics and to investigate the wear mechanisms. The effects of reinforcement type on the wear behavior of AA6061 matrix composites were observed. Results exhibited that the optimum wear resistance obtained with the boron carbide reinforced composite parts. All reinforced samples showed better wear resistance compared to as-received samples in all the studied conditions. Scanning electron microscope characterization showed that test specimens have complex combination of wear mechanisms on the worn surface. Keywords: Composite, wear / AA6061 / boron carbide / silicon carbide / alumina Die Wirkungen verschiedener Verstä rkungen (Borcarbid -Siliziumkarbid -Aluminiumoxid) mit konstantem Volumenanteil (20 %) auf das Abriebverhalten von durch Heißpressen hergestellten AA6061 Matrixverbundwerkstoffen wurden untersucht. Die Verschleißuntersuchungen wurden bei einer Gleitgeschwindigkeit von 1,2 m/s gegen Siliziumkarbid mit einem Stift-Scheibe-Verschleißtester durchgefü hrt bei Normalbelastungen von 5, 10 und 15 N bei Raumtemperatur. Die Verschleiß-Morphologien der verschlissenen Oberflä chen wurden unter Verwendung eines Rasterelektronenmikroskops auf die Verschleißmechanismen untersucht. Die Auswirkungen der Verstä rkung auf das Verschleißverhalten von AA6061 Matrix-Verbundmaterialien wurden beobachtet. Die Ergebnisse zeigen, dass die optimale Verschleißfestigkeit durch mit Borcarbid verstä rkte Verbundteile erhalten wird. Alle Proben wiesen eine bessere Verschleißfestigkeit im Vergleich zu Proben ohne Verstä rkung in allen untersuchten Bedingungen auf. Die Charakterisierung durch das Rasterelektronenmikroskops zeigte, dass die Prü flinge eine komplexe Kombination von Verschleißmechanismen auf der geschä digten Oberflä che haben.