Elastic constants modulus defect

The nickel aluminide NijAl - known as the y phase - crystallizes with the cubic LI2 structure (CujAu-type) which results from the fc.c. structure by ordering (see Fig. 1). Deviations from stoichiometry are accommodated primarily by antisite defects (Lin and Sun, 1993). The density of NijAl is 7.50 g/cm (see Liu et al., 1990) and thus is only slightly lower than that of the superalloys (see Table 2) which, however, is still of interest. The elastic constants have been studied experimentally and theoretically by various authors (e.g. Davies and Stoloff, 1965 Dickson et al., 1969 Kayser and Stassis, 1969 Foiles and Daw, 1987 Wallow et al., 1987 Yoo and Fu, 1991, 1993 Yasuda et al., 1991a, 1992). Young s modulus of cast polycrystalline NijAl at room temperature is about the same as that of pure Ni with a weaker temperature dependence (Stoloff, 1989),... 

As seen in Fig. 3.20, these elastic properties decrease rapidly at doses less than 0.1 MD-dpa and the decrease becomes smaller at high dose levels. Due to the dose dependence of the formation and coalescence of point defects and small clusters, it was concluded [18] that point defects and small clusters contribute much more than topological disorder to the degradation of the elastic properties of a-SiC. The elastic constants and elastic modulus showed the expected softening behavior under irradiation for the dose range of interest. 

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