Effect of surface precipitation of titanium carbide on adherence of alumina film on steels

Abstract

Alumina (Al 2O 3) was deposited on two types of iron-based alloy, type 14C and type 47C, with an r.f. magnetron sputtering method. Type 14C contains 0.14% carbon and 0.7% titanium. Type 47C contains 0.47% carbon and 0.7% titanium. Samples were annealed at 900 or 1100 K in a high vacuum. Al 2O 3 films on type 47C blistered or exfoliated. However, Al 2O 3 films on tyoe 14C exhibited neither of these behaviours at these two temperatures. Therefore the adherence of Al 2O 3 films on type 14C was better than that of Al 2O 3 on type 47C. Depth profile analyses with Auger electron spectroscopy and X-ray photoelectron spectroscopy showed that titanium carbide (TiC) precipitated at the interface between type 14C and Al 2O 3, and that graphite precipitated or sulphur segregated at the interface between type 47C and Al 2O 3. Precipitated TiC could relax thermal stress, had an anchoring effect and reacted with Al 2O 3. Therefore Al 2O 3 films on surfaces where TiC precipitated had good adherence. However, graphite precipitation at the interface between type 47C alloy and Al 2O 3 film was accompanied by volume expansion and the distribution of precipitated graphite was not uniform. The sulphur segregation at the interface made the Al 2O 3 film sensitive to thermal stress. Therefore Al 2O 3 films on the surfaces where graphite precipitated or sulphur segregated did not adhere well.