The effect of oxygen on ball milling of a near-equiatomic FeV sigma phase

A coarse-grained near-equiatomic tetragonal sigma phase Fe48V52 is milled in argon in a vibratory mill with a small steady air supply. The oxygen content increases regularly at a rate of about 0.25 at. %/h. Besides a classical short step, during which the sigma phase transforms into an alpha phase, two main steps occur. During the first step, from similar to 40 to similar to 140 h of milling, the bcc alpha phase is enriched in iron and heterogeneous because of a preferential oxidation of vanadium atoms. The bcc phase is partially amorphized as it is when milling in the absence of oxygen and nanocrystalline vanadium oxides do form. The second step is characterized by the coarsening of vanadium oxide particles and by the formation of ternary ferrous oxides. The results are discussed in the light of a vacancy mechanism proposed recently to account for the high stability of oxide nanoclusters in oxide dispersion strengthened Fe-based alloys processed by ball milling. c 2008 American Institute of Physics. [DOI: 10.1063/1.3005876]