Effect of Mo addition on laves phase precipitation behavior in Fe-20%Cr-x%Nb alloys

Abstract

The precipitation behavior of the C14 Laves phase in the BCC-Fe matrix during aging treatment at 1073 K was investigated using alloys with compositions of Fe-20at.%Cr-xat.%Nb (x = 0.2, 0.5) additionally containing 0 to 2 at% Mo. Electron microscopy, chemical analysis and electrical resistivity measurements confirmed that the onset of Laves phase precipitation and its growth are accelerated with increasing Mo contents. This behavior is considered to be due to the increase in the driving force for nucleation of the Laves phase and the increase in the supersaturation of Nb in the matrix phase by the addition of Mo. Furthermore, the compositional ratio Mo/Nb of the Laves phase increased with aging time in the alloys containing 2 at.% Mo. This phenomenon can be explained by the fact that the composition at the Laves phase/matrix phase interface in the early stage of precipitation shifts from the equilibrium composition to the high Nb direction because the diffusion rate of Nb in the matrix phase is higher than that of Mo.