Thermal barrier coatings(TBCs) consisting ofLa_(2)Ce_(2)O_(7)(LCO) and Y_(2)O_(3)-stabilized-ZrO_(2)(YSZ) doubleceramic layer and Dy/Pt co-doped NiAl bond coat were produced by electron beam physical vapor deposition(EBPVD). Thermal cyclic performance of the TBCs was evaluated by flame shock testing at 1300 ℃. For comparison, the TBCs with a undoped NiAl bond coat were also studied. The microstructural evolution and failure mechanisms of the above TBCs during thermal cycling were investigated. Spallation failure of the TBCs with the undoped bond coat occurs after around 500 cycles by cracking at the interface between YSZ ceramic layer and thermally grown oxides(TGO) layer. The TBCs with Pt/Dy modified bond coat reveal improved interface bonding even after 1200 thermal cycles, whereas some delamination cracks are presented in the LCO layer. On the other hand,the Pt/Dy modified bond coat effectively suppresses the formation of the needle-like topologically closed packed phases(TCP) in the single crystal superalloy.
Zi-Min ZhouHui PengLei ZhengHong-Bo GuoSheng-Kai Gong
γ’+β Binary-phase Ni-Al coatings were prepared on second-generation single-crystal superalloy Rene N5(N5) substrates by electron beam physical vapor deposition.Inter-diffusion behavior between coatings and substrates at 1100℃ and its effects on microstructure stability of the substrates were investigated.A 3-μm-thick substrate diffusion zone(SDZ) layer forms beneath the coating/substrate interface after 5-h heat treatment.The SDZ layer is composed of γ’-Ni_(3) Al phases and needle-like precipitates growing along(100)(110) or(100) <■> direction.After100-h annealing,the thickness of the SDZ layer increases to~17 μm,much lower than that of the single β-NiAl-coated substrate,while keeping single-crystal microstructure.
The Cr-/Si-modified Ni Al Hf coatings were produced on single-crystal(SC) superalloy N5 by electron beam physical vapor deposition(EB-PVD). The cyclic oxidation behavior of the coatings at 1100 °C was investigated. The microstructures of the oxide scales grown on the coatings were characterized by scanning electron microscope(SEM) with energy-dispersive X-ray spectrum(EDX),electron probe micro-analyzer(EPMA) and X-ray diffraction(XRD). The effects of Cr and Si on the cyclic oxidation behavior of the Ni Al Hf coatings were discussed. The addition of Si to the Ni Al Hf Cr coating not only reduces the oxidation rate but also enhances the oxide scale adherence.Owing to the addition of Si in the coating, the segregation of Cr and Mo beneath the oxide scale is effectively avoided,which contributes to enhancing oxide scale adherence.
As potential thermal barrier coating(TBC)materials,Ruddlesden—Popper structured BaLn_2Ti_3O_(10)(Ln=rare earth)compounds possess excellent phase stability and desirable thermo-physical properties as well as interesting anisotropic structure.In this paper,the effects of pressure during BaLa_2Ti_30_(10)(BLT)bulk preparation on the grain orientation were investigated.BLT grains exhibited lamellar structure,but the grain orientation depended strongly on the existence of pressure during bulk preparation.When pressure was applied,BLT grains preferentially grew along pressing direction,leading to formation of the texture parallel to pressing direction,but BLT grain orientation became relatively random when pressure was absent.However,in the small scale area,BLT grains grew preferentially along c-axis with independence on pressure during preparation.Pressure affected BLT grain orientation at the rapid growth stage according to the grain growth model of BLT.
Xizhong WangLei GuoHongbo GuoGuohui MaShengkai Gong
Plasma-activated electron beam-physical vapor deposition(EB-PVD)was used for depositing nitride multilayer coatings in this work.Different from the conventional coating methods,the multilayers were obtained by manipulating electron beam(EB)to jump between two different evaporation sources alternately with variable frequencies(jumping beam technology).The plasma activation was generated by a hollow cathode plasma unit.The deposition process was demonstrated by means of tailoring TiN/TiAlN multilayers with different modulation periods(M1:26.5 nm,M2:80.0 nm,M3:6.0 nm,M4:4.0 nm).The microstructure and hardness of the multilayer coatings were comparatively studied with TiN and TiAlN singlelayer coatings.The columnar structure of the coatings(TiN,TiAlN,M1,M2)is replaced by a glassy-like microstructure when the modulation period decreases to less than 10 nm(M3,M4).Simultaneously,superlattice growth occurs.With the decrease of modulation period,both the hardness and the plastic deformation resistance(H^3/E^2,H-hardness and E-elastic modulus)increase.M4coating exhibits the maximum hardness of(49.6±2.7)GPa and the maximum plastic deformation resistance of^0.74 GPa.
