The Effect of Zr Incorporation Caused by Ball Abrasion in a Milled Fe-Y 2 O 3 Model Alloy
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TRODUCTION
IN the last few years, mechanical alloying became quite popular as it is a method to distribute fine yttria powders in steel powders in order to improve the thermal properties of steels.[1–5] Especially for fuel claddings in fast breeding reactors mechanically alloyed steel is a promising candidate. It is known that milling causes a metastable dissolution of yttria in Fe and, subsequently, a formation of Y-O particles in nanometer scale.[6] However, besides yttria also other alloying elements have a very strong effect on the thermal properties of ODS steels. Ukai et al.[7,8] found out that the addition of a small amount of Ti can enhance the effect of the Y-O clusters and further improve the mechanical properties at elevated temperatures. Transmission electron microscopy (TEM) investigations on such alloys were employed for example by Klimiankou[9] and Hirata et al.[10] Klimiankou found an orientation correlation of a nanometer-sized particle with a 9Cr ferritic alloy lattice. Using energy-filtered (EF)-TEM, he verified Y-Ti-O particles with a stoichiometry of Y2Ti2O7. Hirata made 3D structure modeling of a (Ti, Y, Fe, Cr)O nanocluster by Cs corrected TEM. He concluded that these clusters have a defective NaCl structure and a high degree of lattice coherency with the bcc steel matrix. Furthermore, Nomura et al.[11] investigated the effect of other alloying GERALD RESSEL, Doctoral Student, is with the Department of Physical Metallurgy and Materials Testing, Montanuniversita¨t Leoben, 8700 Leoben, Austria. Contact e-mail: [email protected] SOPHIE PRIMIG, Head of the Steel Group, is with the Department of Physical Metallurgy and Materials Testing, Montanuniversita¨t Leoben, and also Scientist, with the Christian Doppler Laboratory for Early Stages of Precipitation, Montanuniversita¨t Leoben. HARALD LEITNER, formerly Head of the Steel Group with the Department of Physical Metallurgy and Materials Testing, Montanuniversita¨t Leoben, is now Employee with the Bo¨hler Edelstahl GmbH and Co KG Company, Mariazellerstraße 25, Kapfenberg, Austria. Manuscript submitted July 12, 2013. Article published online October 22, 2013 1552—VOLUME 45A, MARCH 2014
elements such as Zr besides Ti. In the case of Ti as alloying element, they detected fine complex oxides as Y2TiO5 and Y2Ti2O7 besides the original Y2O3. They suggested that Ti can decompose Y2O3 to produce such fine complex oxides. They concluded that also Zr, Nb, and V are effective in strengthening the ODS 12Cr ferritic steel. This strength improvement is mainly attributed to the refinement of the particles. Uchida et al.[12] investigated the effect of minor alloying elements on dispersed nanoparticles in ODS steels. They reported that Ti, Zr as well as Hf have a strong effect of cluster refinement. By the formation of an oxide with the stoichiometry YxMyOz with the minor alloying element M (e.g., Ti), the enthalpy of formation should decrease compared to common yttria. They assumed that the lower the diffusivity of the alloying element M is the higher is the stabilit
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