DEFORMATION-BEHAVIOR OF A NI-30AL-20FE-0.05ZR INTERMETALLIC ALLOY IN THE TEMPERATURE-RANGE 300-K TO 1300-K

The deformation behavior of an extruded Ni-30 (at. pct) Al-20Fe-0.05Zr intermetallic alloy was studied in the temperature range of 300 to 1300 K under initial tensile strain rates varying between about 10(-6) and 2 x 10(-3) s-1 and in constant load compression creep between 1073 and 1300 K. The deformation microstructures of the fractured specimens were characterized by transmission electron microscopy (TEM). Three deformation regimes were observed: Region I consisted of an athermal regime of low tensile ductility (less than 0.3 pct) occurring between 400 and 673 K, where the substructure consisted of slip bands in a few grains. Exponential creep was dominant in region II between 673 and 1073 K, where the substructure changed from a mixture of dislocation tangles, loops, and dipoles at 673 K to a microstructure consisting of subgrains and dislocation tangles at 973 K. The tensile ductility was generally about 2.0 to 2.5 pct below 980 K in this region. A significant improvement in tensile ductility was observed in region III, which occurred between 1073 and 1300 K. An analysis of the data suggests that viscous glide creep with a stress exponent, n, of about 3 and high-temperature dislocation climb with n almost-equal-to 4.5 where the two dominant creep mechanisms in this region depending on stress and temperature. The average activation energy for deformation in this region was about 310 +/- 30 kJ mol-1 for both processes. In this case, a transition from viscous glide creep to dislocation climb occurred when sigma/E < 1.7 x 10(-4), where sigma is the applied stress and E is the Young's modulus.