Ni and Fe tracer diffusion in the B2-ordered Ni 40Fe 10Al 50 ternary alloy

Abstract

Ni and Fe bulk diffusion in the B2-ordered Ni 40Fe 10Al 50 ternary alloy is investigated by means of radiotracer measurements ( 63Ni and 59Fe tracers) and SIMS analysis ( 64Ni tracer) in an extended temperature interval from 1150 to 1550 K. Almost linear Arrhenius behavior was observed for both, Ni (pre-exponential factor D 0 ∗ Ni =1.3·10 −5 m 2/s and activation enthalpy Q Ni=270 kJ/mol) and Fe ( D 0 ∗ Fe =1.2·10 −4 m 2/s and Q Fe=279 kJ/mol) diffusion. The Fe diffusivity was found to be by a factor of three to five larger than that of Ni. Furthermore, Ni diffuses in Ni 40Fe 10Al 50 faster than in stoichiometric NiAl and the activation enthalpy of Ni diffusion in Ni 40Fe 10Al 50 is significantly smaller as compared to the stoichiometric binary NiAl alloy (by about 35 kJ/mol). The activation enthalpy of Ni diffusion in the Ni 50− x Fe x Al 50 ternary alloys was found to reveal a minimum for ternary compositions with about 10% of Fe addition. The apparent controversial behavior of creep resistance and self-diffusivity in the NiFeAl ternary alloys is discussed. The analysis of experimental data favors nearest-neighbor jumps (most likely the triple defect mechanism) as a dominant diffusion mechanism in the alloy.