The Microstructure Evolution Mechanism of Hot Isostatically Pressed High-Nb Tial Alloy with Fe Microalloying

Abstract

Ti-45Al-8Nb-0.5Fe alloy(TiAl-Fe) was ball milled by adding 0.5wt%Fe to Ti-45Al-8Nb pre-alloyed powder to prepare Fe microalloyed high niobium TiAl alloy by hot isostatic pressing(HIP) process. The microstructure and compressive properties of the TiAl-Fe alloy were systematacially studied. After the addition of trace Fe element, compared with the traditional casting process, the compositions of this alloy are detcted to be uniform without element segregation. The addition of Fe element promotes the transformation of α→α2, resulting in more α2 phase and the formation of (α2 + B2 + γ) phase region. As a strong β-stabilizing element, more stable B2 could cause stress concentration in the interface and hinder the growth of γ-TiAl grains, resulting in obvious grain refinement of the prepared samples compared with Ti-45Al-8Nb alloy. In addition, due to the radius difference between Fe and Al atom, Fe occupies the position of Al (2e) atom in γ-TiAl and B2, causing lattice distortion, which increases the compressive strength of TiAl-Fe by about 3.0%. The strengthening mechanism of introducing trace Fe element into high niobium TiAl alloy is mainly grain refinement strengthening and solid solution strengthening.

Keywords: TiAl, Alloying elements, Microstructure, Compression property