Precipitation phases in the nickel-based superalloy DZ 125 with YSZ/CoCrAlY thermal barrier coating

Interdiffusion behavior of the thermal barrier coating (TBC) with the CoCrAlY bond coat (BC) and directionally solidified Ni-based superalloy DZ 125 was investigated. Severe inward-diffusion of Al, Co and Cr from the BC to the superalloy and outward diffusion of Ni and refractory elements such as W from the superalloy occur during annealing at 1050 degrees C in air. After 100 h annealing, a similar to 30 mu m thick inter-diffusion zone (IDZ) forms between the BC and superalloy, and a similar to 35 mu m thick secondary reaction zone (SRZ) forms beneath the IDZ. The IDZ mainly consists of beta phase and gamma matrix. Besides, small amount of Ta and Hf containing carbides are also observed in the IDZ. Needle and fine granular topologically close-packed (TCP) phases, characterized as rhombohedral mu phases, are abundant in the SRZ. The formation of SRZ is mainly due to the precipitation of refractory elements such as W and Mo from the gamma matrix and beta phase. The formation mechanism of SRZ and mu-TCP phase is discussed. (C) 2011 Elsevier B.V. All rights reserved.