Pressure infiltration of molten aluminum for densification of environmental barrier coatings

Environmental barrier coatings (EBCs) effectively protect the ceramic matrix composites (CMCs) from harsh engine environments, especially steam and molten salts. However, open pores inevitably formed during the deposition process provide the transport channels for oxidants and corrosives, and lead to premature failure of EBCs. This research work proposed a method of pressure infiltration densification which blocked these open pores in the coatings. These results showed that it was difficult for aluminum to infiltrate spontaneously, but with the increase of external gas pressure and internal vacuum simultaneously, the molten aluminum obviously moved forward, and finally stopped infiltrating at a depth of a specific geometry. Based on the wrinkled zigzag pore model, a mathematical relationship between the critical pressure with the infiltration depth and the pore intrinsic geometry was established. The infiltration results confirmed this relationship, indicating that for a given coating, a dense thick film can be obtained by adjusting the internal and external gas pressures to drive a melt infiltration. [Figure not available: see fulltext.]