Due to coming emission legislations, the temperature is expected to increase in heavy-duty diesel engines, specifically in the hot-end of the exhaust system affecting components, such as exhaust- and turbo manifolds. Since the current material in the turbo manifold, a ductile cast iron named SiMo51, is operating close to its limits there is a need for material development in order to maintain a high durability of these components. When designing for increased life, many material properties need to be considered, for example, creep-, corrosion- and fatigue resistance. Among these, the present work focuses on the latter two up to 800°C improving the current material by additions of Cr, for corrosion resistance, and Ni, for mechanical properties. The results show improved high-temperature corrosion resistance in air from 0.5 and 1wt% Cr additions resulting in improved barrier layer at the oxide/metal interface. However, during oxidation in exhaust-gases, which is a much more demanding environment compared to air, such improvement could not be observed. Addition of 1wt% Ni was found to increase the fatigue life up to 250°C, resulting from solution strengthening of the ferritic matrix. However, Ni was also found to increase the oxidation rates, as no continuous SiO2-barrier layers were formed in the presence of Ni. Since none of the tested alloys showed improved material properties in exhaust gases at high temperature, it is suggested that the way of improving performance of exhaust manifolds is to move towards austenitic ductile cast irons or cast stainless steels. One alloy showing good high-temperature oxidation properties in exhaust atmospheres is an austenitic cast stainless steel named HK30. This alloy formed adherent oxide scales during oxidation at 900°C in gas mixtures of 5%O2-10%H2O-85%N2 and 5%CO2-10%H2O-85%N2 and in air. In the two latter atmospheres, compact scales of (Cr, Mn)-spinel and Cr2O3 were formed whereas in the atmosphere containing 5%O2 and 10%H2O, the scales were more porous due to increased Fe-oxide formation. Despite the formation of a protective, i.e. compact and adherent, oxide scale on HK30, exposure to exhaust-gas condensate showed a detrimental effect in form of oxide spallation and metal release. Thus, proving the importance of taking exhaust-gas condensation, which may occur during cold-start or upon cooling of the engine, into account when selecting a new material for exhaust manifolds. / <p>QC 20130508</p>

Internal Combustion Engine (ICE) exhaust components are exposed to extreme operating temperatures. Thus, it is necessary that they are designed with materials that can sustain thermal and vibrational stresses. This study investigates the wear mechanisms and tribological performance of the exhaust manifold joint in Scania CV diesel trucks, focusing on the lip seal ring between the exhaust and turbo manifolds. The joint is prone to wear due to thermal and vibrational stresses, impacting its service life and raising environmental concerns. The manifold material, ductile cast iron SiMo51, offers good thermal resistance, while the lip seal ring, made of Inconel 718c, provides excellent thermal fatigue and corrosion resistance, coated with AlTiN for wear and oxidation resistance. However, the tribological performance of this joint and material combination remains unknown, necessitating further research.  This work aims to understand wear initiation mechanisms and their relationship with temperature. Test setups were established using an oscillating cylinder on disc configuration in the SRV 3 tribometer. SiMo51 uncoated/coated with Tribaloy 400 and Inconel 718c uncoated/coated with AlTiN were tested against each other to identify the best material pair. Analysis involved coefficient of friction, visual inspection, wear volume measurements, SEM micrographs, and EDS for surface chemical composition. Results indicated that friction behaviour is temperature-dependent, with oxide layer formation reducing the coefficient of friction when the manifold is uncoated, while the opposite occurs when coated with Tribaloy 400. Wear behaviour varied based on material combinations and temperature. Uncoated manifold exhibited dominant adhesion (galling) accompanied by tribo-oxidation at higher temperatures, with maximum wear volumes at room temperature. Introduction of T-400 on the manifold initiated galling on the lip seal, leading to abrasion on the manifold surface, accompanied by tribo-oxidation at elevated temperatures. Wear increased until 500°C, followed by a decrease at 700°C. Further explanations of T-400 wear behaviour are lacking in the literature.