High temperature creep transitions in single crystalline Ni₃Al(Ta, B)

Abstract

The high temperature (T = 1083–1388 K, 0.65–0.84 T_m) creep behavior of single crystalline Ni₃Al(Ta, B) was investigated. A change in the creep characteristics as a function of applied stress was observed at the uppermost testing temperatures of 1288 and 1388 K. At low applied stress levels the Norton law stress exponent is equal to 4.3; for higher stresses the stress exponent is equal to 3.2. Different creep curves were observed, depending on the value of the stress exponent. The change in stress exponent and nature of the creep curve correspond to a change in the controlling deformation mechanism from dislocation climb to viscous dislocation glide for Ni₃Al(Ta, B). The experimentally observed transition stress values between climb and viscous glide are in good agreement with values predicted from theory, assuming that the major force retarding viscous dislocation glide in Ni₃Al(Ta, B) is the antiphase boundary interaction.