Fabrication of Oxide‐Dispersion‐Strengthened Ferritic Alloys by Mechanical Alloying Using Pre‐Alloyed Powder

Abstract

Progress toward controllable nuclear fusion operations largely relies on the high performance of advanced nuclear structural materials. [1][2][3][4][5][6] Attributed to the extremely harsh environments where fusion reactors work, the components suffer from both high level of heat flux and high dose of neutron radiation. Oxide-dispersion-strengthened (ODS) steel is one of the most promising candidate structural materials for the next-generation fusion reactors due to its excellent resistance to high-temperature creep, corrosion, and neutron radiation. [7][8][9][10][11][12] ODS steels are mainly based on the reduced activated alloys such as Fe-Cr-W system. These alloys can be divided as reduced activated ferritic martensitic (RAFM) steels with a lower Cr (9-12 wt%) content and reduced activated ferritic (RAF) ones with a higher Cr (>12 wt%) content. Unlike RAFM steels, the RAF steels do not experience a γ-α transformation at elevated temperatures. Therefore, they can be operated at a higher temperature and have a better resistance to radiation swelling. [13][14][15] ODS steels possess a huge number of nano-oxides that are thermally stabilized in the matrix. These nanoparticles can not only hinder the movement of dislocations, but also absorb the point defects induced by irradiation, enhancing the pore expansion resistance and preventing void swelling of the materials under neutron irradiation. [16][17][18][19][20][21] For these reasons, a higher number density, a finer size, and a better distribution of the oxides are always pursued.Mechanical alloying (MA) is one of the most widely used methods to prepare ODS steels, where Y 2 O 3 powder is often added to the steel powder for long-term high-energy ball-milling. During MA, a large amount of lattice defects (e.g., vacancies and dislocations), along with the supersaturated dissolved Y and O atoms that are decomposed from the Y 2 O 3 powder, can be gradually restored in the powders. Then, powder metallurgy is conducted to this non-equilibrious MA powders to build the components with proper sizes and shapes. [22] In this step, one of the following densification strategies, that is, hot extrusion (HE), hot isostatic pressing (HIP), or spark plasma sintering (SPS), is usually carried out. [23][24][25] Assisted by the subsequent heat treatment, a huge number of Y 2 O 3 nanoparticles win the chance to simultaneously precipitate from the supersaturated matrix. In the earlier procedures, MA is definitely a timeconsuming stage. It takes an extremely long period, usually longer than 50 h, for the complete decomposition and dissolution of Y 2 O 3 through ball-milling since it has the highest bonding energy among most of the common oxides. [24][25][26] If MA process can be accelerated by a faster decomposition of the oxide