Bond coat composition formed by spark plasma sintering for gradient material with thermal barrier properties

Abstract

High-temperature materials for thermal barrier coatings (TBC) have important prospects for application in the aircraft engine industry. To increase the service life and reliability of superalloy parts, the bond coat (BC) in the structure of the TBC is of great importance. In this study, the architecture of the BC material between the superalloy and the external ceramics is proposed. It is shown that the BC layer can consist of a sublayer of intermetallic NiAl (VKNA) and a mixture of VKNA with 15 or 30 wt.% zirconium dioxide (8YSZ). This architecture allows us to form by spark plasma sintering (SPS) technique. In the work, samples of a gradient BC VKNA/VKNA+(15% or 30%)YSZ/YSZ were obtained using SPS at 1070 oC, a pressure of 30 MPa and an isothermal exposure of 5 min. In all sintered compositions the porosity did not exceed 2%. The structure of the BC material is characterized by scanning electron microscopy, energy-dispersion spectroscopy, and micro-durometry. It is shown that the SPS provides an adhesive connection of the sublayers in the BC layer and with the external ceramics. The microhardness increases li nearly during the transition from the VKNA layer to the YSZ layer through a BC with different YSZ content in the sublayer. The BC samples demonstrated a thermal conductivity gradient from the Inconel 625 substrate to YSZ and the influence of the YSZ content in the sublayers on the decrease in the coefficient of linear thermal expansion in the temperature range of 800–1000 oC was also determined. Damage to the ceramic surface during thermal cycling in air at 1100 oC, i.e. the appearance and development of cracks, is not more than 10% at 45 cycles.This research was carried out under Basic Scientific Research Assignment No. FSNM-2020-0026 of the Ministry of Education and Science of Russia and was funded by the Russian Foundation for Basic Research, Grant No. 19-48-590007.