Characterization of interfaces of alumina – high alloyed steels by SST and AES depth profiling

Thin alumina films, deposited at 280°?C on several high alloyed steels by low pressure metal-organic chemical vapour deposition (LP-MOCVD), were annealed at 0.17 kPa in a nitrogen atmosphere for 2, 4 and 17 h at 600 and 800°?C. The effect of the annealing process on the adhesion of the thin alumina films was studied using a scanning scratch tester (SST) and Auger electron spectroscopy (AES). The best adhesion properties were obtained with commercial oxide dispersion strengthened (ODS) high temperature alloys, especially type PM 3030. From the “normally” high alloyed stainless steels, type AISI-321 showed the best properties. The other stainless steel – alumina combinations showed after a thermal treatment a decrease of the critical load, L_c. Using ODS alloys as the substrate resulted in an increased L_c. AES-studies revealed that the increased L_c can be explained by 1) the presence of sulphur trapping elements, avoiding segregation of sulphur near the interface which could have a detrimental effect on scale adherence, and 2) titanium and carbon enrichment at the interface resulting in a beneficial effect on the adherence between the oxide and the substrate.