Advances in the development of corrosion and creep resistant nano-yttria dispersed ferritic/martensitic alloys using the rapid solidification processing technique

High-temperature creep and corrosion resistant nano-dispersed ferritic/martensitic (F/M) alloys (such as a T91 steel), or other 'the oxide dispersion strengthened (ODS) steels', are under consideration for nuclear applications because of their high-temperature mechanical properties. They consist typically of a high-chromium steel structure dispersed and reinforced by a dispersion of nano-sized rare-earth metal oxides, typically yttrium oxide (Y₂O₃). In this study, the production of ODS based on T91 is examined by adding a 0.3 wt% colloidal Y₂O₃ dispersion to a T91 steel melt in combination with metallic yttrium (Y_M). The production of the following systems is evaluated: T91-Y₂O ₃, T91-Y_M and T91-Y_M-Y₂O ₃. At first, it was found that when Y_M is added to a steel melt, internal oxidation occurs. Furthermore, it was shown that the T91 system with addition of Y₂O₃ in combination with rare-earth metal Y_M, creates a homogeneously dispersed ODS T91 material. Moreover, the role of Y_M as a possible surface active element lowering the surface tension at the contact interface is studied. High-temperature contact angle wetting tests between Y₂O₃ ceramic substrates in contact with an T91 and a [T91+Y_M] melt, combined with auger-electron spectroscopy (AES), indicate the influence of Y_M on the surface activity of Y₂O₃ in contact with T91. After Y_M addition, the contact angle between T91 and the Y₂O₃ substrate lowers down to angles below 90°.