| Summary: | 碩士 === 國立海洋大學 === 材料工程研究所 === 88 === Abstract
The corrosion behavior of Ti-Al alloys (containing various amounts 0, 10, 20, 30, and 40 wt.%Al) and Y-Al (containing various amounts 0, 5, and 10 wt.%Al)alloys were studied over the temperature range of 800~1000℃ in a H2/H2S/H2O gas mixture. The result indicated that the corrosion kinetics of Ti-Al alloys followed the parabolic rate law at all temperatures. The corrosion rate constants increased with increasing temperature, but decreased with increasing Al content. The of scale formed on pure Ti is exclusively TiO2, and some amounts of Ti1-xS are observed near the substrate regardless of temperature, while the scales formed on Ti-Al were duplex and always spalled after cooling, consisting of the outer-layer of most TiO2 and the inner-layer of most TiO2, Al2O3, and minor Ti1-xS. The amount of Al2O3 increased with increasing Al content. The formation of Al2O3 is responsible for the reduction in the corrosion rates of Ti-Al alloys as compared to those of pure Ti.
The results indicated that the corrosion kinetics of Y-Al alloy studied followed the parabolic law. But the corrosion kinetics of Y-10wt.﹪Al alloy at 800℃ happened kinetics inversion, the corrosion rates were much higher than pure Y and Y-5wt.﹪Al alloy, and in the same alloy the corrosion rates were much higher than those in the high temperature. The reason of the kinetics inversion might transformate Y2Al to Al2Y to cause the crack of the scales at 800℃ and induced the increasing corrosion. Moreover, the corrosion rates of the other Y-Al alloys increased with increasing temperature, but decreased with increasing Al content at T>800℃. X-ray diffraction results show that the scale formed on pure Y is mostly Y2O3 and minor Y2O2S regardless of temperature, while Y-Al alloy formed scales that consisted of mostly Y2O3 and very little Y2O2S whose amount is much less than that formed on pure Y.
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