Influence Of Alloying Elements Of Bond Coat Of Thermal Barrier Coatings On Its Interface Conjunction Factors

Thermal barrier coatings (TBCs) are commonly used to the surface of thermo-parts. TBCs can improve the work efficency and longevity of parts by covering top coat on the surface of alloy substrate. Bond coat is a kind of coating that improved the interface conjunction between the bond coat and the top coat. Some elements of bond coat are oxidized and forms thermally grown oxide (TGO) between bond coat and ceramic top coat during the application of the thermal barrier coatings. It is proved by experiments that the failure of TBCs typically occurs at the interface between the bond coat and the TGO.Based on the Empirical electron theory in solid and molecule (EET) and improved Thomas-Fermi-Dirac (TFD) theory in this thesis, the valence electron structure ofα-Al₂O₃ in the thermally grown oxide (TGO) are analyzed, and that is in view of the valence electron structure and interface electron structure of the crystals. The interface conjunction factor between the bonding layer and ceramic layer of the thermal barrier coatings of different content of Al,Co,Cr,Y,Hf are calculated. The results are as following. Considering the electron density parameters ofρ,△ρ_min,σ,σ_super,σ_equal on the bond-coat/TGO interface, the following conclusion can be obtained:1. Considering the cohesion force of the interface, the most favorable aluminium content of the bond-coat is 2-wt%. The aluminium content beneath 10-wt% is favorable, and the aluminium content over 10-wt% is harmful in this case. The aluminium content of the bond-coat being not more than 8-wt% is considered to decrease the interface stress.2. When the orientation of the bonding layer is (100) or (111), the addition of Y can improve the interface conjunction. When the orientation is (110), the electron density parameters of△ρ_min is lower than the one without Y when the Y content is more than 0.7-wt%; Furthermore,△ρ_min is the lowest when the Y content is 0.7-wt%. The electron density with Y content of 0.7-wt% of its (110) crystal plane is higher than without Y, and the interface electron density slightly decreases with the increase of the yttrium content when the yttrium content is higher than 0.7-wt%. Comprehensive analysis indicates that the bond-coat yttrium content of 0.7-wt%-0.9-wt% or a little higher is also suitable for the stability of the interface cohesion of the bond coat.3. No matter what orientation of the bonding layer in, the addition of Co can be in favor of the release of interface stress and keep the continuity of the interface electron density. At the same time, the Co content of 10-wt% -14-wt% is the optimal. While the orientation of the bonding layer is (110), the increasing of Co content can enhance the interface conjunction. However, when the orientation is (100) or (111), the content of Co almost has no effect.4. When the orientation of the bonding layer is (100) or (111), the addition of Cr can improve the interface conjunction of the interface. If the factors of techniques can be controlled and formed orientation of being (111), (100) in the bonding layer, the addition of Cr can improve the interface conjunction between the bond coat and the TGO. Therefore, in the situation when the texture in the bonding layer is controlled with difficulty, considering the interface conjunction, the content of Cr of Ni-based bonding layer should be reduced as low as possible.5. The additional of Hf is beneficial for the interface conjunction. Furthermore, these interface conjunction factors tend to the better estate beneath the Hf content of 1.3-at% (3.9-wt%). It is thought that the suitability Hf content can improve the interface conjunction between the bond coat and the TGO at the condition of meeting the intensity, toughness and anti-thermo -causticity of Ni-based bond coat.