Thermodynamic guidance for implantation treatments to improve coating–substrate adhesion

Abstract

A novel ‘‘seeding’’ method is disclosed, in which ion implanted Al atoms promote bonding between SiC and a subsequently deposited Al2O3 coating. Al+ ions were implanted in SiC substrates near room temperature to a fluence of 4×1017 Al/cm2 at an energy of 110 keV. The substrates were coated with 100–200 nm of aluminum oxide and then heated in air (i.e., oxidized) for 4 hours at temperatures from 500 to 1000 °C. Scratch tests demonstrated that coatings spalled from nonimplanted substrates but not from Al+-implanted substrates. Auger sputter depth profiles of substrates oxidized at 850 °C showed that Al diffused out of the implanted layer and an Al-Si-O layer formed at the coating-substrate interface. Cross-section and plan TEM of a substrate oxidized at 1000 °C identified the interface phase as mullite and found fine-grained SiC and mullite (Al6Si2O13) in the implanted layer. The composition and phase changes were explained in terms of the thermochemical reactions expected of the Al-Al2O3-SiC-O2 system.