Search

The phase change induced by MeV electron irradiation in the intermetallic compound E93-CoTi2 was investigated using high-voltage electron microscopy. Under MeV electron irradiation, CoTi2 was first transformed into an amorphous phase and, with continued irradiation, crystallite formation in the amorphous phase (i.e. formation of crystallites of a solid-solution phase within the amorphous phase) was induced. The critical temperature for amorphisation was around 250 K. The total dose (dpa) required for crystallite formation (i.e. that required for partial crystallisation) was high (i.e. 27-80 dpa) and, even after prolonged irradiation, the amorphous phase was retained in the irradiated sample. Such partial crystallisation behaviour of amorphous Co33Ti67 was clearly different from the crystallisation behaviour (i.e. amorphous-to-solid solution, polymorphous transformation) of amorphous Cr67Ti33 reported in the literature. A possible cause of the difference is discussed. [ABSTRACT FROM AUTHOR]

This study investigates equilibrium-to-nonequilibrium solid phase transitions induced by MeV-scale electron irradiation in B2-CoTi and L12-Co3Ti intermetallic compounds by means of high-voltage electron microscopy. Under MeV-scale electron irradiation, B2-CoTi transforms into a body-centered cubic solid solution through chemical disordering and eventually transforms into an amorphous phase. The critical temperature for amorphisation is found to be 110 K. L12-Co3Ti also exhibits chemical disordering at temperatures below 700 K. However, its amorphisation does not occur even at a low temperature of 20 K. The dominant factor in these solid phase transitions is discussed in terms of the Gibbs free energy. [ABSTRACT FROM PUBLISHER]

Electron irradiation effect on nanometer-sized Al2Au compound particles has been studied by using transmission electron microscopy. Particles of Al2Au compound smaller than about 10 nm in diameter were irradiated with 200-keV electrons at room temperature. Selective sputtering of Au atoms from Al2Au compound particles was so strong that particles of Al2Au with the CaF2 structure changed into particles of α-Al with the fcc structure. The same irradiation experiment was also carried out using nanometer-sized particles of AlAu with the B2 structure. However, no change in the AlAu particles could be observed after irradiation. It was revealed that the selective sputtering of Au atoms from the Al2Au compound particles under irradiation with 200-keV electrons can be attributed to both the unique CaF2- type structure and the size effect of particles. Copyright © 2012 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This review is concerned with high voltage electron microscopy (HVEM) studies on the non-equilibrium solid phases produced by MeV electron irradiation. In such studies, one can combine the strong points of electron irradiation that the primary defects are simple in their configuration and distribution, with the advantage of electron microscopy that , direct observations make it possible to analyze both the morphology and structure of the phases produced. Making full use of this merit, HVEM studies to clarify the conditions in which non-equilibrium solid phases can successfully be produced under MeV electron irradiation have been carried out. Results on such subjects as electron-irradiation-induced crystalline-to-amorphous transition in crystals, electron-irradiation-induced phase decomposition and electron-irradiation-induced foreign-atom implantation, are reviewed. [ABSTRACT FROM PUBLISHER]

Abstract: MeV electron irradiation via high voltage electron microscopy can lead to amorphous-to-crystal transition (i.e., crystallization) as well as crystal-to-amorphous transition (i.e., solid-state amorphization). Irradiation-induced crystallization can be observed in various alloy systems such as Co-, Fe-, Ni-, Pd-, and Zr-based metallic glasses, indicating that this phenomenon has wide generality in metallic materials. Irradiation-induced crystallization mechanism was discussed based on the following factors; (1) an increase in free energy for an amorphous phase, (2) the formation of crystalline clusters through modification of the atomic configuration near radiation induced defects, and (3) enhanced diffusion. The stability of an amorphous phase against irradiation-induced crystallization can be estimated from the thermal crystallization temperature (Tx), and Ni–Nb based metallic glasses have a tendency for high stability against irradiation because of high Tx. [Copyright &y& Elsevier]