Article ID Journal Published Year Pages File Type
9781813 Journal of Physics and Chemistry of Solids 2005 5 Pages PDF
Abstract
Internal nitrides form in two ductile cast irons (SiMo and Ni-Resist) intended for exhaust systems in vehicles. Samples oxidised at 650-1050 °C for 50 h in modified synthetic exhaust gases were analysed by using AES and FEG-SEM. No nitrides formed in absence of NOx. In dry petrol gas coarse nitrides (<20 μm) precipitated heterogeneously deep (600 μm at 950 °C) into SiMo. It is argued that the accommodation of volume change, preferential diffusion paths and increased N solubility as Si was depleted contribute to a self-accelerating process. The Si depletion around the coarse nitrides lowered the microhardness and the corrosion resistance of the alloy. In diesel and in normal petrol gases μ-sized MgSiN2 form in SiMo in cell boundaries where Mg segregates. This also occurs in Ni-Resist in both dry and normal petrol whereas no nitrides were observed in Ni-Resist exposed to diesel gases.
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Physical Sciences and Engineering Materials Science Electronic, Optical and Magnetic Materials
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