Fig. 8-1 Stress-strain curves of Ti-47Al alloy before and after neutron irradiation Unexpected irradiation induced ductilization is observed.

Irradiation is known to cause embrittlement in metallic and ceramic materials. This degradation may occur during irradiation, after irradiation, or both. For example, austenitic stainless steels, which are widely used as engineering materials (including nuclear applications), change from ductile to very brittle after irradiation. Advanced materials with superior irradiation resistance have been strongly searched for to develop safer and more efficient future nuclear reactor systems. Intermetallic compounds are one of the leading materials being examined. Among them, Ti-Al alloys have received attention for development; although they have as yet to mature as steels and there is no nuclear application experience. However, they have the inherently attractive properties of high-temperature strength, large specific strength, and low induced activation. Furthermore, recent tensile data indicates good irradiation resistance, shown in Fig. 8-1, where stress-strain curves of Ti-47Al alloys before and after neutron-irradiation are compared. The 6% elongation of an unirradiated specimen increases to about 10% after irradiation, without the increase in yield stress generally observed in irradiated materials. Such irradiation induced ductility has (never before) observed in ordinary alloys. This offers the expectation of development of nuclear materials having strong irradiation resistance and moreover, self-repairability.

Reference A. Hishinuma et al., Ductilization of TiAl Intermetallic Alloys by Neutron-Irradiation, Intermetallics 4(3), 179 (1996).

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