Simultaneous Study of Vacancy Formation and Migration at High Temperatures inB2-Type Fe Aluminides

In order to study the vacancy formation and migration the temperature variation and the equilibration process of the thermal vacancy concentration in $B$2-type Fe aluminides ( ${\mathrm{Fe}}_{63}{\mathrm{Al}}_{37}$, ${\mathrm{Fe}}_{61}{\mathrm{Al}}_{39}$) were measured by means of the positron lifetime technique using a diffused ${}^{58}$Co positron emitter. The equilibration process occurs rather slowly, indicating a low vacancy mobility. The present values for the enthalpies of vacancy formation $H_{\mathrm{V}}^{\mathrm{F}}=1.04\mathrm{}\mathrm{eV}$ ( ${\mathrm{Fe}}_{63}{\mathrm{Al}}_{37}$) or 0.98 eV ( ${\mathrm{Fe}}_{61}{\mathrm{Al}}_{39}$) and migration $H_{\mathrm{V}}^{\mathrm{M}}=1.7\mathrm{}\mathrm{eV}$ are discussed with respect to the self-diffusion mechanisms.