Eliminating topologically closed-packed phases in deteriorated nickel-based superalloy by pulsed electric current

摘要

This work investigates the reverse thermodynamic dissolution of the topologically closed-packed (TCP) phases in the deteriorated nickel-based superalloy using the pulsed electric current. The mechanical properties cannot be restored directly by the conventional heat treatment because the dissolution temperature (1130 degrees C) of the TCP phases is higher than the initial solvation temperature (950 degrees C) of the gamma' phase. Here it was found that the TCP phases can be selectively dissolved under the pulsed electric current at a relative low temperature (800 degrees C), and the volume fraction of gamma' phase is unchanged. It means the pulsed processing is a lossless performance regeneration method. The count of TCP phases decreased from 3.49 x 10(9)/m(2) to 1.24 x 10(9)/m(2), accounting for only 35.5% of the thermal exposure sample. Correspondingly, the mechanical properties change toward the young stage. By the HRTEM, the TCP phases initially interrupted at stacking faults have been observed, and the stacking faults are basically aligned along the (111)(TCP) direction. Subsequently, the interrupted TCP phases dissolved from both ends to the middle. The solute elements can be rapidly diffused into the gamma-matrix and gamma' phase using the high current density regions that caused by conductivity discrepancies. (C) 2021 Elsevier B.V. All rights reserved.