Improvement of Slurry Aluminide Coating on Ferritic Stainless Steel AISI430 for High-Temperature Oxidation Resistance

摘要

One of the surface modification processes for high-temperature oxidation resistance is slurry aluminizing process, forming protective layer of alumina (Al_2O_3). However, several important parameters such as annealing times and temperatures should be intensively considered. The objective of this study is to improve the process of slurry aluminide coating of ferritic stainless steels type AISI430 (16%Cr) combat to high-temperature oxidation. The specimens were cut, then ground, and finally sprayed with slurry mixture (Al powder + polyvinyl alcohol (PVA)). They were annealed in Ar at 1100°C for 15 minutes in order to eliminate PVA and form aluminide on their surface. The protective layer Al_2O_3 was finally formed in the temperature range of 900-1100°C for 15-60 minutes. The cyclic oxidation tests were performed at 1000°C for 24 hours. The surface morphology were then examined by XRD, SEM equipped EDS. The results showed that all oxidation kinetics of coated specimens were parabolic. The oxidation rate of uncoated specimens was apparently higher than that of coated specimens. Comparing with all coated specimens, the oxidation rate decreased with the increasing temperature and annealing time. In this study, the coating process at 1100°C for 60 minutes exhibited the lowest oxidation rate due to the most complete layer of Al_2O_3. The surface morphology showed the formation of continuous layer of Fe_2Al_5 and Al_2O_3, acting as barrier layer to oxide growth. Effect of temperature and time on oxidation resistance were discussed in this study.