Fundamentals of Radiation Materials Science by GARY S. WAS

Author:GARY S. WAS
Language: eng
Format: epub
Publisher: Springer New York, New York, NY

crystal structure transformation: A → B,

crystal structure A → quasicrystal structure, and

crystal structure A → amorphous structure.

The first three transformations will be briefly discussed and amorphization will be discussed in Sect. 9.8. For a more complete discussion of metastable phase formation, the reader is referred to [33].

9.7.1 Order–Disorder Transformations

The order–disorder transformation and its role in phase stability were discussed in Sect. 9.3. However, radiation-induced disorder has been linked to metastable phase formation. In fact, many compounds are believed to undergo chemical disordering prior to amorphization under electron irradiation. Luzzi and Meshii [34] showed that of 32 compounds irradiated, all underwent chemical disordering and 15 amorphized. They concluded that irradiation-induced chemical disordering provided the driving force for amorphization and cited the difficulty in forming the amorphous structure in pure metals as support for this argument. The linkage between disordering and amorphization also depends on the irradiation conditions, in particular the mass of the particle and whether damage is introduced via Frenkel pairs (electron irradiation) or in cascades (heavy ion irradiation). Comparison of the enthalpy for the order–disorder transformation to that for the crystalline-to-amorphous transformation shows that ΔH O-D ~ 5ΔH c-a [16]. So in fact, the enthalpy change for disordering may be sufficient to induce amorphization. The role of disordering in the onset of amorphization will be discussed in Sect. 9.8.

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