Fabrication and mechanical properties of oxide dispersion strengthened high entropy superalloy

Abstract

High entropy alloys, which is a new type of alloy in which 5 or more elements are mixed at a high atomic fraction, are attracting attention as new alloys with excellent mechanical properties due to their severe lattice distortion and low diffusion rate. In recent years, refractory high entropy alloys with BCC structure have been discovered to exhibit excellent mechanical properties at high temperatures, and the possibility of replacing the conventional Ni-based superalloy with refractory high entropy alloy was presented. However, refractory high entropy alloys with BCC structure have difficulties in applying to high temperature structural materials due to their limitations such as brittleness under tensile load, poor oxidation resistance and their expensive prices.

In this study, high entropy superalloys were fabricated by fusing the precipitation strengthening principle in the Ni-based superalloys to the FCC high entropy alloys that exhibit excellent ductility. In order to improve the mechanical properties at elevated temperature, dispersion strengthening was applied by dispersion of yttria particles, and a new alloy with composite of yttria and high entropy alloy was fabricated. In the manufacturing process, a powder metallurgy process which can simultaneously obtain the mechanical alloying of high entropy superalloy and the dispersion of yttria particles without any additional process is adopted. Alloy powders produced by the planetary high energy ball milling machine were sintered by spark plasma sintering method, and microstructural analysis and mechanical properties characterization were conducted. Mechanical properties were evaluated by tensile strength tests at room temperature, 600℃, 700℃, 800℃, and 1000℃. As a result, in the case of the alloy with 1% vol.% of yttria, specific yield strength value showed higher value than commercial Ni-based superalloy, Inconel 718 at temperature up to 700℃. The strengthening mechanisms of the fabricated ODS HESA was investigated by dispersion strengthening and grain boundaries strengthening effect.

This study suggests the possibility of oxide dispersion strengthening in the study of high entropy superalloys, and it is hoped that it will be the basis of research for replacing pre-existing Ni-base superalloys.