Influence of heat treatment on the structure evolution and creep deformation behavior of a precipitation hardened B2-(Ni, Fe)Al alloy

Abstract The effect of quenching and aging on structural evolution of the Ni27Fe26Al32Cr10Co5 alloy hardened by coherent α-Fe(Cr) precipitates was studied by scanning electron microscopy (SEM) and high-resolution electron microscopy (HRTEM). Heat treatment of the alloy was shown to optimize the morphology and size of hardening α precipitates and give rise to particles of the intermetallic σ-FeCr phase along the grain boundaries. The mechanical properties of the alloy were measured in the temperature range of 273–1573 K. Temperature dependences for the offset yield strength at different strain rates and the Young's modulus values were obtained. Quenching followed by age hardening increased the resistance to viscoplastic strain. The strain rate sensitivity coefficient was evaluated in the temperature range of 873–1573 K. The elastic limit and yield stress values reached under external tensile stress at 973 and 1073 K were determined. The analyzed B2-(Ni, Fe)Al-based alloy was subjected to deformation at stresses of 100, 150, 200, and 300 MPa in the temperature range of 773–1200 K. The steady-state creep strain rate was approximated by the Arrhenius creep equation (stress power being 8.3 and the effective creep activation energy being 335 kJ/mol). Threshold stresses equal to 94, 70, and 33 MPa were observed at 873, 973, and 1073 K, respectively. Calculations of critical stresses for the potential mechanisms controlling creep strain showed that the threshold stresses are caused by local and general dislocation climb over coherent α precipitates. The HRTEM studies of the dislocation substructure of the alloy after high-temperature creep testing confirmed that the creep strain mechanism was controlled by dislocation climb.