Phase Transformation-Assisted Sintering for the Fabrication of a Bulk Nanocrystalline Fe–5 at.% Zr Alloy

Abstract

The powder metallurgy route of high-energy ball milling followed by sintering is a common method used to fabricate nanocrystalline (NC) metals. However, the poor thermal stability of NC metals limits the use of high temperatures during sintering, which can result in insufficient densification. In order to achieve a higher relative density at low sintering temperatures, phase transformation-induced volume expansion during sintering is taken advantage of. To prove this hypothesis, NC Fe–5 at.% Zr alloy is sintered at a temperature above A3 (1073 K), which is then decreased below A1 (873 K) to introduce volume expansion caused by phase transformation from austenite to ferrite. For comparison, it is also sintered at a constant temperature above A3 (1073 K). Results show that the proposed strategy can not only enhance the relative density of as-sintered NC Fe–5 at.% Zr alloy, but also ensure a relatively smaller grain size. This study is beneficial for the fabrication of high-performance NC metals.