| Summary: | 碩士 === 國立臺北科技大學 === 材料及資源工程系研究所 === 98 === In this study, pack cementation process is employed to simultaneously aluminize and chromize the Ni-Cr-Mo alloy steels at temperatures below 750°C. Different treatment temperature and time, concentration of activator, and Cr/Al ratio in the powder pack are controlled to avoid the formation of high Al containing Fe-Al intermetallic compounds which are brittle at room temperature.
This study successfully deposited low Al content Fe-Al intermetallic compounds, FeAl or Fe3Al, on Ni-Cr-Mo alloy steel surface. The coatings also contain 1-5 wt.% of Cr. The thickness of coatings range from 7.5 to 43 μm which depend on treatment temperature and time. In cases when treatment time lasts over six hours, pores and chromium carbides form in the coatings which also reduce the growth rate significantly.
Aluminum concentrations in the coatings increase with the aluminum content of the powder packs. No more than 3 wt.% of NH4Cl activator should be used, as the activator can compete with the steels to react with aluminum on steel surface in later stage of pack cementation process. In this study, combinations of good corrosion resistance and wear properties are obtained in samples deposited using powder packs of 3 wt.% NH4Cl and 12 wt.% Cr/Al=85/15 for treatment at 750°C.
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