Interdiffusion coefficients at 950℃ and 1050℃ are calculated by Wagner analysis method as a function of composition of β-NiAI phase. The β-NiAI phase is formed by pack cementation on surface of superalloy. Results...Interdiffusion coefficients at 950℃ and 1050℃ are calculated by Wagner analysis method as a function of composition of β-NiAI phase. The β-NiAI phase is formed by pack cementation on surface of superalloy. Results of the calculation show that interdiffusion coefficients in β-NiAI phase strongly depend on the compositions and vary over several orders of magnitude. Compared with the interdiffusion coefficients in the stoichiometric β-NiAI phase, the interdiffusion coefficients in β-NiAI phase formed on superalloy is obviously small, probably due to the composition, complicated microstructure and precipitates. However, it could be seen clearly that the shapes of the diffusivity curves are very similar to each other. The similarity of the diffusion curves and the difference between interdiffusion coefficients imply that the compositions, microstructures and precipitates of superalloy have a distinctly adverse effect on the interdiffusion of Ni and Al atoms during aluminization, but do not change the essential characteristics of β-NiAI phase.展开更多
β-NiAl is a potential oxidation-resistant coating material to be operated at temperatures above 1 150 ℃. In this paper,β-NiAl coatings with 0-0.5 at% Dy are prepared by electron beam physical vapor deposition （EB-...β-NiAl is a potential oxidation-resistant coating material to be operated at temperatures above 1 150 ℃. In this paper,β-NiAl coatings with 0-0.5 at% Dy are prepared by electron beam physical vapor deposition （EB-PVD）. Transient oxidation behavior of the coatings is investigated. At 1 200 ℃, only stable α-Al2O3 phase is observed on the 0.05 at% doped coating, whereas the phase transfomlation from θ-Al2O3 to α-Al2O3 occurs in the 0.5 at% Dy doped coating during 1 h oxidation. At 1 100 ℃, all the coatings reveal the transient transformation of θ-α in the early 15 min and the transformation for the 0.05 at% Dy doped coating is completed within 45 min, much earlier than that for the 0.5 at% Dy doped coating. Overdoping of Dy retards the transformation of θ-α. The undoped and overdoped coatings reveal the whisker structure of θ-Al2O3 even after 20 h oxidation at 1 100 ℃, while the 0.05 at% Dy coating reveals typical granulated structure of α-Al2O3.展开更多
Oxidation behaviour of undopedβ-NiAl andβ-NiAl-0.05Hf single crystals were investigated at 1100℃in 20 vol%O_(2)+Ar and 15 vol%H2O+Ar,respectively.On contrary to the well-known beneficial effect of Hf additions on t...Oxidation behaviour of undopedβ-NiAl andβ-NiAl-0.05Hf single crystals were investigated at 1100℃in 20 vol%O_(2)+Ar and 15 vol%H2O+Ar,respectively.On contrary to the well-known beneficial effect of Hf additions on the oxidation behaviour of polycrystallineβ-NiAl,severe-scale spallation is observed forβ-NiAl-0.05Hf single-crystal alloy,especially in dry atmosphere.It is proposed that the presence of the grain boundaries in the polycrystalline substrate enables proper content of Hf segregating at the grain boundaries of the oxide scale and at the scale-substrate interface,which promotes the conditions required for reactive element effect.Once the reactive element effect of Hf does not work,its strong affinity with oxygen will accelerate the process of high-temperature oxidation.However,the absence of the grain boundaries as fast diffusion paths partially compromises the adverse influence of water vapour on cyclic oxidation resistance ofβ-NiAl single crystal,resulting in considerable suppression of the oxidation rate and less loss of protection compared with that in dry atmosphere.In addition,interfacial cavities are observed in dry and humid atmospheres,which may eventually result in the spallation of the oxide scale.展开更多
文摘Interdiffusion coefficients at 950℃ and 1050℃ are calculated by Wagner analysis method as a function of composition of β-NiAI phase. The β-NiAI phase is formed by pack cementation on surface of superalloy. Results of the calculation show that interdiffusion coefficients in β-NiAI phase strongly depend on the compositions and vary over several orders of magnitude. Compared with the interdiffusion coefficients in the stoichiometric β-NiAI phase, the interdiffusion coefficients in β-NiAI phase formed on superalloy is obviously small, probably due to the composition, complicated microstructure and precipitates. However, it could be seen clearly that the shapes of the diffusivity curves are very similar to each other. The similarity of the diffusion curves and the difference between interdiffusion coefficients imply that the compositions, microstructures and precipitates of superalloy have a distinctly adverse effect on the interdiffusion of Ni and Al atoms during aluminization, but do not change the essential characteristics of β-NiAI phase.
基金National Natural Science Foundation of China （50771009, 50731001） National Basic Research Program of China （2010CB631200） Research Fund for the Doctoral Program of Higher Education of China （20070006017）
文摘β-NiAl is a potential oxidation-resistant coating material to be operated at temperatures above 1 150 ℃. In this paper,β-NiAl coatings with 0-0.5 at% Dy are prepared by electron beam physical vapor deposition （EB-PVD）. Transient oxidation behavior of the coatings is investigated. At 1 200 ℃, only stable α-Al2O3 phase is observed on the 0.05 at% doped coating, whereas the phase transfomlation from θ-Al2O3 to α-Al2O3 occurs in the 0.5 at% Dy doped coating during 1 h oxidation. At 1 100 ℃, all the coatings reveal the transient transformation of θ-α in the early 15 min and the transformation for the 0.05 at% Dy doped coating is completed within 45 min, much earlier than that for the 0.5 at% Dy doped coating. Overdoping of Dy retards the transformation of θ-α. The undoped and overdoped coatings reveal the whisker structure of θ-Al2O3 even after 20 h oxidation at 1 100 ℃, while the 0.05 at% Dy coating reveals typical granulated structure of α-Al2O3.
基金financially supported by the China Postdoctoral Science Foundation(Nos.2016M600028,2017T100023)。
文摘Oxidation behaviour of undopedβ-NiAl andβ-NiAl-0.05Hf single crystals were investigated at 1100℃in 20 vol%O_(2)+Ar and 15 vol%H2O+Ar,respectively.On contrary to the well-known beneficial effect of Hf additions on the oxidation behaviour of polycrystallineβ-NiAl,severe-scale spallation is observed forβ-NiAl-0.05Hf single-crystal alloy,especially in dry atmosphere.It is proposed that the presence of the grain boundaries in the polycrystalline substrate enables proper content of Hf segregating at the grain boundaries of the oxide scale and at the scale-substrate interface,which promotes the conditions required for reactive element effect.Once the reactive element effect of Hf does not work,its strong affinity with oxygen will accelerate the process of high-temperature oxidation.However,the absence of the grain boundaries as fast diffusion paths partially compromises the adverse influence of water vapour on cyclic oxidation resistance ofβ-NiAl single crystal,resulting in considerable suppression of the oxidation rate and less loss of protection compared with that in dry atmosphere.In addition,interfacial cavities are observed in dry and humid atmospheres,which may eventually result in the spallation of the oxide scale.
