PREPARATION AND OXIDATION OF A CeO CeO2-DISPERSEDCHROMIZING COATING BY PACK-CEMENTATION AT 700℃

摘要

Chromizing coatings can improve the high temperature corrosion resistance of carbon orrnlow-alloys steels in oxidizing, sulphidizing and carburizing environments encountered in coal gasificationrnplants and petrochemical industries. Pack-cementation is one of the easiest and cheapest processes tornobtain the chromizing coatings. Unfortunately, the pack-cementation chromizing was normally performedrnat temperatures above 1000 ℃. The temperatures significantly damaged their mechanical properties.rnTherefore, reducing pack-cementation temperature is required for the widespread application of thisrnchromizing coatings to the steels. In this work, chromizing by low-temperature pack-cementation wasrnexplored using a two-step process. First, to deposit a thin nano-grained Ni-CeO2 nanocomposite film ontorna carbon steel. Second, to chromize the Ni-CeO2 nanocomposite film by pack-cementation at 700 ℃.rnOxidation at 800 ℃ indicated that the CeO2-dispersed chromizing coating had a lower oxidation rate. Thernmicrostructures of the CeO2-dispersed chromizing coating before and after oxidation were investigatedrnusing SEM/EDAX and OM. The effect of CeO2 on the formation and oxidation of the chromizing coatingrnis also discussed in detail.