Hot hardness and creep of Fe3Al-based alloys

Hot hardness and creep studies were carried out on Fe3Al and Fe3Al containing Cr or Ti. Indentation and impression creep testing methods were employed to characterize the creep behaviour. Compared to the binary alloy, Fe3Al–Cr exhibits a lower hardness indicating solid-solution softening effect of Cr. On the other hand, solid-solution hardening effect of Ti is significant in the temperature range 300–900 K. Results from indentation creep indicates that a power-law creep behaviour (n between 6 and 8) is observed in the binary and Cr containing alloys at temperatures greater than 753 K. At lower temperatures in the above two alloys and in the Ti-containing alloy even at higher temperatures, there is a power-law break down. On the other hand at low stress levels covered in the impression creep studies, power-law creep is observed in all the alloys in the stress and temperature range of investigation. Under these conditions, all the alloys exhibit a stress exponent value of around 3 for the steady state creep rate. The activation energy for creep is estimated to be in the range 325 and 375 kJ mol. Among the alloys studied, Fe3Al–Ti exhibits the best creep resistance. The results indicate that in the B2 region, viscous glide controls the creep rate at low stresses while climb of dislocations may be rate controlling at higher stresses.