Formation of Inter-Diffusion Layer between NiCrAlY Coating and Nb Substrate during Vacuum Heat-Treatment

摘要

The formation of the inter-diffusion layer between NiCrAlY coating and Nb substrate during vacuum heat treatment was investigated. A NiCrAlY coating was applied on Nb substrate by cathode arc deposition. Vacuum heat treatments were carried out at 800, 900, and 1000 degrees C for 2 h. SEM, EPMA, EDS, and XRD were performed to analyze the microstructure of the inter-diffusion layer and the results were interpreted using the 1002 degrees C isothermal ternary Nb-Ni-Cr phase diagram. It was found that at 800 degrees C the inter-diffusion layer has a single NbNi3 layer; at 900 degrees C the inter-diffusion layer consists of an outer NbNi3 layer, a thin intermediate NbCr2(HT) layer, and an inner Nb7Ni6 layer; at 1000 degrees C the inter-diffusion layer has three well-developed layers of an outer NbNi3 layer, an inner Nb7Ni6 layer, and an intermediate layers comprising NbCr2(HT) and NbNi3. A small amount of Cr exists in both the NbNi3 and the Nb7Ni6 phases as solid solution, and a large amount of Ni in the NbCr2(HT) phase as solid solution.