Oxidation Resistant Ce-modified Silicide Coatings Prepared on Ti-6Al-4V Alloy by Pack Cementation Process

摘要

Cerium-modified silicide coatings were prepared on Ti-6Al-4V by pack cementation. The effects of different kinds of activators (NaCl, AlF3, AlCl3, and NH4Cl) and pack CeO2 concentrations (1, 3, and 5 wt%) on the coating structures were studied. The results show that the coatings were mainly composed of a TiSi2 outer layer, a TiSi middle layer, a Ti5Si4 inner layer and a 1-2 mu m thick Ti5Si3 interdiffusion zone. NH4Cl was a more suitable activator for preparing the Ce-modified silicide coating on Ti-6Al-4V, based on the coating microstructure and growth rate. The coating thickness decreased with increasing CeO2 concentration in the pack. Oxidation tests at 800 A degrees C in air showed that the Ce-modified silicide coating showed improved oxidation resistance compared to both the uncoated alloy and the pure silicide coating. A dense, but thick oxide scale formed that was composed of a TiO2 outer layer and a SiO2 inner layer.