The effect of thermal annealing on the adherence of Al2O3 films deposited by LP-MOCVD on several high alloy steels

Thin alumina films, deposited at 280°C on several high alloy steels by low-pressure metal-organic chemical vapor deposition (LP-MOCVD), were annealed at 0.17 kPa in a nitrogen atmosphere for 2, 4, and 17 h at 600 and 800°C. Film adhesion was studied by scanning scratch testing (SST) and Auger electron spectroscopy (AES). The best adhesion properties were obtained with commercial oxide dispersion-strengthened (ODS) high-temperature alloys, especially PM 3030. Among the 'normally' high alloy stainless steels, type AISI-321 showed the best adhesion. The other stainless steel-alumina combinations exhibited a reduced critical load, Lc, after thermal treatment. Alumina on ODS alloys exhibited an increased adhesion. AES studies revealed that this increase could be explained by: (1) the presence of sulfur-trapping elements, preventing segregation of sulfur at the interface; and (2) titanium and carbon enrichment at the interface, resulting in an anchoring effect between the oxide and the substrate.