Worse Corrosion Resistance Research Articles

N<SUB>2</SUB>-NH<SUB>3</SUB>-CO<SUB>2</SUB>ガス雰囲気における低炭素鋼の酸窒化

Low crabon steel (S15CK) specimens were oxy-nitrided in nitrogen-ammonia-carbon dioxide mixed gas atmosphere. The microstructures of oxy-nitrided surface layers were examined by optical microscope, X-ray microanalysis and X-ray diffraction. Corrosion-resistance and wear-resistance of oxy-nitrided layers were also studied. The gas composition greatly affects the microstructure of oxy-nitrided surface layers, which is classified into white layer, gray layer with white layer and gray layer. The white nitride layer is composed of an ε phase, Fe3N and γ′ phase. The main constituent of the white layer containing higher nitrogen is ε, and that with lower nitrogen is γ′. The main constituent of the gray layer is found to be Fe3O4. The thickness of oxide layer increases as the premixed ammonia ratio decreases or the premixed carbon dioxide ratio increases through activated oxidation. With less than 45 vol% ammonia ratio and high carbon dioxide atmosphere, the oxy-nitrided layer is composed of only Fe3O4. The white nitride layer, ε, Fe3N and γ′ shows good corrosion resistance. The thickness of nitrided layer decreases as the premixed carbon dioxide ratio increases and the thin gray Fe3O4 layer formed on the nitride layer. These layers show bad corrosion resistance. But the thick gray Fe3O4 layer shows good corrosion resistance. Wear-resistance of oxy-nitrided steels is improved about fourfold compared with untreated specimens. The nitride layer shows good wear resistance and it slightly decreases as the thin gray Fe3O4 layer formed on the nitride layer.

Production of Porous Sintered Co–Cr–Mo Alloys for Possible Surgical Implant Applications: Part 2: Corrosion Behaviour

Abstract In the first part of this study, data were presented for the compaction, sintering, and mechanical properties of a water atomised cobalt based alloy and a bimodal mixture of ball milled ASTM F75 plasma rotating electrode process powder blended with the cobalt based alloy powder. In the present study, the corrosion of these two powders was compared for a range of compacts of varying porosity between 6 and 35% total porosity and between 0·5 and 26% interconnected porosity under conditions which simulated in vitro body fluid conditions. Differences in microstructure and surface composition caused by reactions with three different sintering atmospheres, e.g. loss of chromium, decarburisation, or Cr2N formation, altered the corrosion behaviour. The worst corrosion resistance occurred in compacts sintered in molecular 75H2–25N2 (by volume) gas, while argon atmosphere sintered compacts were the most resistant to corrosion. Pore size and pore geometry also had a considerable influence on the corrosion be...

Dynamic mechanical analysis of a two-dimensional carbon-carbon composite

A two-dimensional carbon-carbon composite material consisting of stacked carbon cloths densified with a carbon matrix has been characterized with respect to its dynamic mechanical properties. Unprotected specimens and some protected against oxidizing conditions were investigated over the temperature range of subambient (−100°C) to 500°C. The reproducibility of the calculated storage modulus as well as the loss factor was within 5% at any one temperature over the entire temperature range. Results concerning protected and unprotected specimens were compared analytically and the difference of the relative plots above 400°C reflects the bad corrosion resistance of the unprotected samples under oxidizing conditions, where the carbon matrix material is more sensitive to oxidation than the fibre. The transition regions which appeared on the loss factor plots are strongly connected with the relevant secondary transition regions of the antioxidation protected material used. This technique, which has been demonstrated to be non-destructive for the sample analysed, proved that no differences exist in the dynamic mechanical properties of the specimens with respect to fibre orientation (warp or weft direction). Details of the experimental technique and assumptions made are also presented.

Effect of Beta Heat Treatment on Microstructure and Nodular Corrosion of Zircaloy-4

Abstract The effect of β-heat treatment on microstructure and nodular corrosion of Zircaloy-4 were investigated for the specimens which were β-heat treated and then cooled in various cooling process, such as, iced brine, water, oil, air, and furnace cooling. It was observed that the martensitic structure with substructures of dislocations as well as twins is formed at the cooling rate of 2,100°C/s, whereas at the cooling rate of l,200°C/s the classical Widmanstatten structure appears with dense dislocations in a lath and precipitates along the lath boundary. The transformation in the water quenched specimens was suggested to take place by both diffusion- and diffusionless transformation process. The nodular corrosion behavior was investigated at steam of 500°C and 10.3 MPa. The corrosion resistance of the β quenched specimens decreased with the decrease in the cooling rate so that the furnace cooled specimens exhibit the worst corrosion resistance, resulting in nodular corrosion. The corrosion of the furn...

The effect of V or W additives to microstructure and coercivity of Nd-Fe-B based magnets

Co-substituted Nd-Fe-B magnets show an increased Curie temperature. The coercivity of these magnets is reduced due to the formation of Co-rich phases. In addition to the hard magnetic phase the Nd-rich intergranular phase exists, which results in bad corrosion resistance. In (Nd,Dy)-(Fe,Co)-B:Al type magnets doped with V, (V/sub 1-x/Fe/sub x/)/sub 3/B/sub 2/ intergranular phases and precipitates with Si/sub 2/U/sub 3/ structure and a Nd-rich Co-containing phase partly replacing the Nd-rich phase were found. X-ray microanalysis shows that in (Nd,Dy)-(Fe,Co)-B:(Al,V) magnets Dy is mainly dissolved in the hard magnetic phase. Comparison with W-doped Nd-Fe-B magnets shows that W also forms an intergranular WFeB phase with Co/sub 2/Si-structure and precipitates within the hard magnetic phase with presumably the same composition. >