Abstract
The existence of a sharp transition of high-temperature creep behavior in bcc solid solutions has been confirmed by studying steady-state creep characteristics of an Fe-2.1mol% (3.56mass%)Mo alloy in the temperature range T from 1 100 to 1200K under the tensile stress range a from 4 to 50MPa. In the lower stress region, the creep characteristics are those typical in creep controlled by viscously-gliding dislocations which drag the solute (Cottrell) atmosphere. Steady-state creep-rates εs can be represented by the equation, sMs=1.21×10-2 (Gb/kT) DMo (σ/G)3.45 (G: the shear modulus, b: Burgers vector, DMo: the diffusion coefficient of Mo). In the higher stress region, the creep characteristics are different from those observed in the lower stress region and εHs=5.7×107(Gb/kT). DFe (σ/G)5.3 (DFe: the diffusion coefficient of Fe). Results obtained in conventional tensile test at 1 100K with strain-rates ranging from 3× 10-5 s-1 to 3×10-3s-1 coincide well with creep behavior. The solute atmosphere seems to be broken at some locations under high stresses and a part of dislocations can move as a bare dislocation in the matrix where immobile solute atoms are distributed randomly. The transition observed in this investigation is essentially the same as the upper transition, i.e., the transition between regions M and H, observed in Al-Mg (fcc) alloys and α-Ti-Al (hcp) alloys.
