The Research Of ZrB₂ Disperse Strengthened ZrO₂ Active Diffusion Barrier

Aging at high temperature, the elements inter-diffusion behavior will occurs between the bond-coat of thermal barrier coating and the turbine blade of Nickel based super-alloy, which will lead to a performance degradation of the bond-coat and the substrate.By introducing an active ZrO2 diffusion barrier between the bond-coat and the nickel base alloy, which will react with Al element from the bond-coat and the nickel based alloy to form a "sandwich" structure of Al2O3/ Zr rich layer /Al2O3, so as to effectively prevent the mutual diffusion of elements.Moreover, the in-situ reaction can also improve the binding force between the coatings. But because of the brittle nature of ZrO2 ceramic and formed "sandwich" structure, once cracks formed it will expand rapidly and finally cause brittle fracture.This paper aims at improving the lifetime of the ZrO2 active diffusion barrier via the ZrB2 dispersion-strengthened ZrO2 active diffusion barrier(BDSZ) to enhance the fracture toughness. By using EB-PVD preparation technology, two systems of N5/ BDSZ/NiCrAl and N5/ZrO2/NiCrAl were made.Vivtorinox hardness?X ray diffraction(XRD)?scanning electron microscopy(SEM) and energy dispersive spectroscopy(EDS) were used to measure the toughness of these two coating systems, the evolution process in the interface of two systems under different temperature,and thermodynamcs and dynamics of the generation of Al2O3 in two systems under different heat treatment conditions. Finally the failure behavior and mechanism of these two systems at high temperature for a long time were analyzed and the lifetime of the two system were compared. The experimental results are as follows:1. The preparation state of BDSZ coating and the ZrO2 coating were analyzed by XRD, the results show that the ZrB2 performs stable, it does not react with ZrO2 and has no effect on the phase structure of ZrO2. Also it did not affect the deposition rate of the coating.2. Through the preparation state of BDSZ coating and the ZrO2 coating surface indentation test, it was found that the toughness of the BDSZ coatingis higher than that of the ZrO2 coating3. At 800 ?,the N5/BDSZ/NiCrAl system has not formed the Al2O3 activity diffusion barrier at BDSZ/NiCrAl interface,but the Al2O3 diffusion barrier has been formed at ZrO2/NiCrAl interface in N5/ZrO2/NiCrAl system. The reason is that the addition of ZrB2 affects the diffusion rate and the dynamics of ZrO2 reaction with Al. Both of these two systems had no Al2O3 activity diffusion barrier near the Ni based side. By analysising, it was found that the difference of composition and content of each element with bond-coat, resulting in the diffusion rate of matrix elements slower than the NiCrAl layer and NiCrAl layer diffusion rate of elements is DNi>DAl>DCr.4. After 1000 ? /250 h oxidation treatment, the fracture behavior was found inN5/ZrO2/NiCrAl system and the fracture position is located inside the Al2O3/Zr richlayer/Al2O3 “sandwich” structure. Because of the existence of the mixed phase atAl2O3/Zr rich layer/Al2O3 interface, they made stress increased in duced crack, causedthe fracture behavior.5. After 1000?/300 h oxidation treatment, cracks occurred in N5/BDSZ/NiCrAl system and after 1000 ?/350 h oxidation treatment, fracture occurred in this system. The fracture position is located at the interface of matrix/active diffusion barrier and active diffusion barrier /NiCrAl. This is mainly because of the interface roughening by creep from bond-coat and the substrate, ceramic and metal mismatch of thermal expansion coefficient, which caused the interface stress increase.