THE INFLUENCE OF GRAIN-SIZE AND COMPOSITION ON 1000-K TO 1400-K SLOW PLASTIC-FLOW PROPERTIES OF NIAL

The compressive slow plastic flow behaviour of several B2 crystal structure NiAl intermetallics has been studied in air between 1000 and 1400 K. Small grain-sized Ni-48. 25 at % Al ( approximately equals 5 and 10 mu m) was found to be stronger than the previously studied 17 mu m diameter material. While grain refinement improved the strength at all test temperatures, the exact mechanism is not clear. Experiments at lower temperature revealed that composition as well as grain size can be an important factor, since Ni-49. 2 Al was weaker than Ni-48. 25 Al. Pronounced yield points were found during slow strain-rate testing at 1000 K; however, continued deformation appears to take place by the same mechanism(s) as found at high temperatures. Small changes in thermomechanical processing (TMP) schedules to fabricate Ni-49. 2 Al indicated that basic deformation characteristics (stress exponent and activation energy) are not affected; however, the pre-exponential term could be modified if TMP alters the grain structure.