Scale structure of aluminised Manet steel after HIP treatment

Coatings on low activation steels are required in fusion technology in order to reduce the tritium permeation rate through the steel into the cooling water system by a factor of at least 100. Alumina seems to be a promising coating material. However, an appropriate coating system must also have the potential for self-healing since the ceramic alumina scale tends to fail if mechanical stress is applied. A technology is introduced here to form a ductile Al enriched surface scale on Manet II steel (Fe-10.3%Cr) with an alumina overlayer. This technology consists of two main process steps. Hot dip aluminising has been performed at 700 degreesC for 30 s in order to introduce Al to the near surface zone. The very hard intermetallic scale Fe2Al5 which forms during the immersion process gets completely transformed into FeAl2, FeAl and alpha -Fe(Al) phases during a subsequent hot isostatic press (HIP) process step at high pressure at 1040 degreesC for 30 min. The pressures chosen for the HIPing were 1000 and 2000 bar. Without HIPing pores form due to the Kirkendall effect. The influence of the high pressure on the heat treatment (1040 degreesC, 30 min) will be discussed in this paper. (C) 2000 Elsevier Science B.V. All rights reserved.