Advanced Materials Design by Irradiation of High Energy Particles

Abstract

The MeV electron irradiation by high-voltage electron microscopy (HVEM) can introduce the simplest type of irradiation defects in materials, and sometimes leads to a phase transition with negligible temperature change and contamination. This technique makes it possible to continuously observe the phase transition process using electron microscopy simultaneously as defects are introduced. Therefore, HVEM can provide a unique opportunity to carry out in-depth studies on the phase transition introduced by the accumulation of defects under a significantly simplified condition. In this paper, the following phase transitions related to non-equilibrium phases under MeV electron irradiation are discussed: (1) solid state amorphization (SSA) in metallic compounds, (2) crystallization of metallic glasses, and (3) crystal-to-amorphous-to-crystal (C–A–C) transition.

Appendix: Technical Terms

• (1) Anti-free volume-like defect [6, 13–15]

  • In an amorphous phase, not only vacancy-type defects but also interstitial-type defects can be considered, as shown in Fig. 12.1a. Anti-free volume-like defects correspond to interstitial-type defects. Petrusenko et al. reported MeV electron irradiation damage and suggested the existence of vacancy-type defects and interstitial-type defects in metallic glasses based on the experimental results. The recovery of introduced defects in metallic glasses has two threshold temperatures because of the changes in the relaxation mechanism under 298 K: the first was related to with complexes containing interstitial-type defects in metallic glass, while the second was a result of the relaxation of vacancy-containing complexes [14].

• (2) High-entropy materials (HE materials) [16–18]

  • This class of alloys consists of multi-component materials with an approximately equiatomic ratio of components. Thus, these alloys have a high entropy of mixing, which distinguishes them from conventional alloys. Solid solutions with multi-principal elements have generally been found to be more stable than intermetallic compounds at elevated temperatures because of their large entropies of mixing. Some researchers have defined a high-entropy material as one that has at least five principal elements, each of which has an atomic concentration between 5 % and 35 %; for example, the Fe₂₀Ni₂₀Cu₂₀Co₂₀Cr₂₀ alloy.