Hot-dip aluminum coating of hypo-eutectoid steels containing 0.05-0.88 mass% carbon were performed, and the alloy layers formed in the coating were investigated. In the hot-dip aluminum coating at immersion temperatures ranging from 700 to 850°C, the alloy layers on the steels consisted of a single phase of the intermetallic compound Fe 2 Al 5 . The thickness of the alloy layer increased in proportion to the increasing square root of the immersion time (t 1/2 ) for immersion temperatures lower than 800°C for the whole base steel. On the other hand, for immersion temperatures higher than 800°C, the thickness of the alloy layer on the 0.05 mass% C steel and 0.45 mass% C steels exhibited a negative deviation from the linear relationship. The growth rate constant k decreased as the carbon concentration of the base steel increased up to 0.8 %, above which k had a constant value. The reaction activation energies for the base steel in this study were approximately 70-80 kJ/mol. The alloy layer/base steel interfaces were serrated, and the serration width decreased with increasing carbon concentration of the base steel. In addition, the serration width had a larger value in the immersion temperature range wherein the pro-eutectoid ferrite content in the base steel was larger.
The Lüders’ front and a previously discovered optical interferometric band structure were observed simultaneously in steel specimens under tensile loading. The observed Lüders’ front and optical band structure show the same propagation characteristics, confirming our previous interpretation that the optical band structure represents the plastic deformation front. Analysis shows that the stress at which the optical band structure begins to appear is approximately 10% lower than the corresponding Lüders’ front, indicating that the optical band structure reveals the plastic deformation front with higher sensitivity than the Lüders’ front.
The prebreakdown phenomena and the resulting transient processes from the prebreakdown phenomena to the glow discharge in low-pressure N2, O2 gases, and N2/O2 mixtures were investigated. When the applied voltage was a lower overvoltage ratio less than about 2%, nonprebreakdown phenomenon was observed, and the overvoltage ratio was independent of the gas materials. This phenomenon, however, was observed at the overvoltage ratio of higher than about 3%. The prebreakdown phenomenon in N2 gas differed from those in O2 gas, and formed pulseless components. On the other hand, those in O2 gas formed pulsed components. The prebreakdown phenomenon in N2 gas changed to a pulsed discharge by mixing it with a small amount of more than 0.3% O2 gas. These transient processes from the prebreakdown phenomena to the glow discharges were also observed by a high-speed video camera. As a result, the formation processes of the glow discharge became clear.
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