Strengthening Hardening in Ceramics by Point Defects

Radiation more effectively increases the concentration of point defects than an increase in temperature. To study the effect of point defects on mechanical properties, such as strength or hardness-related features, large amounts of point defects are preferable. Therefore, radiation is useful for studying the effects of point defects in crystals and studies on the effects of point defects are done on irradiated materials. 

TEM images have revealed the following. Irradiation at 100 °C (lluence 8.3 X 10 n/m ) did not induce observable dislocation loops and the defects produced are isolated point defects or small clusters. This means that irradiation-induced hardening in a sample irradiated at 100 °C, which had no clear dislocation loops, is due mainly to point defects, i.e., interstitials and vacancies. Probably Frenkel pairs are formed in this manner. At 470 °C with a fluence of 2.4 x lO, dislocation loops were also found by TEM observations 

In general, an increase in hardness (or strength) is the result of retarded dislocation movement due to point defects introduced by the irradiation. This is 

Radiation-induced point defects are usually preferred over thermal point defects (obtained by quench-in from some higher temperature and freeze-in these point defects) for studying their effects on the physical and mechanical behavior of ceramics. Radiation affects mechanical properties by way of changes in strength. 

In Fig. 3.14, the changes in several ceramics are shown at the same fluence and at an irradiation temperature of 300 K. The radiation hardening at stage I in AI2O3 is attributed to both plastic and elastic hardening. This interpretation by Izumi et al. [11] is based on the dissipation of the elastic and plastic energies. We and Wp, respectively during the indentation process. 

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