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
The NiAl phase prepared by pack cementation （PC） on a nickel base superalloy was investigated by X-ray photoelectron spectroscopy （XPS） and positron annihilation technique （PAT）. The focus was on the effect of t...The NiAl phase prepared by pack cementation （PC） on a nickel base superalloy was investigated by X-ray photoelectron spectroscopy （XPS） and positron annihilation technique （PAT）. The focus was on the effect of the solid solution of the alloying element from substrate on the binding energy of Ni （Al） 2p peaks and vacancy concentration of the NiAI phase formed in a superalloy. The results showed that the binding energy of Ni 2p peak of the NiAI phase grown in a superalloy was shifted by up to 0.55 eV at the temperature from 850 to 1050℃ towards higher energies and the binding energy of Al 2p peak by up to 1.09 eV in comparison with the NiAl phase formed in pure Ni. The positron lifetimes obtained from the NiAl phase formed in a superalloy were found to be markedly lower than the theoretical values, indicating the decrease in vacancy concentration. The variation of binding energies and vacancy concentration are possibly due to the solid solution of the alloying atoms from the substrate into the NiAI lattice.展开更多
目的通过机械合金化与热压烧结相结合的方法制备含有B2结构纳米NiAl相的铁基合金,研究不同含量(质量分数为30%、40%、50%、60%)的纳米NiAl相,对合金显微组织及力学性能的影响。方法以Ni粉和Al粉为原材料,通过高能球磨法制备B2结构纳米N...目的通过机械合金化与热压烧结相结合的方法制备含有B2结构纳米NiAl相的铁基合金,研究不同含量(质量分数为30%、40%、50%、60%)的纳米NiAl相,对合金显微组织及力学性能的影响。方法以Ni粉和Al粉为原材料,通过高能球磨法制备B2结构纳米NiAl粉体,采用真空热压烧结炉将NiAl粉体与Fe粉混合烧结,得到块体试样。采用扫描电镜(Scanning electron microscopy,SEM)进行微观组织观察,采用能谱仪(Energy dispersive spectroscopy,EDS)、X射线衍射仪(X-ray diffraction,XRD)以及透射电子显微镜(Transmission electron microscopy,TEM)进行物相分析,并测试不同NiAl含量的铁基合金的硬度、密度、室温压缩性能以及600℃的抗氧化性能。结果合金的硬度、抗压强度随NiAl含量先增后降。当NiAl的质量分数为50%时,合金硬度为35.2HRC,抗压强度为2530MPa,密度为6.68g/cm^3,较未添加NiAl时,合金的抗压强度提升了239.6%,密度降低了14.5%。θ=600℃、t=1200min时,其表面氧化增重较纯铁降低了37.9%,此时NiAl相的尺寸约为100~200nm,组织最为均匀,致密度较高。结论纳米NiAl相在降低铁基合金密度的同时,能有效提升其力学性能与抗氧化性能,但由于B2结构的纳米NiAl相为一种硬脆相,当其含量过高时,会极大程度地降低合金的力学性能。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
A β--NiAI alloy with normal purity, a S-doped and a Dy and S co-doped （Y-NiAI alloys were prepared by arc-melting and their corresponding S contents were less than 20 ×10-6, 33 ×10-6 and 22 × 10-6, re...A β--NiAI alloy with normal purity, a S-doped and a Dy and S co-doped （Y-NiAI alloys were prepared by arc-melting and their corresponding S contents were less than 20 ×10-6, 33 ×10-6 and 22 × 10-6, respectively. The isothermal oxidation behavior of the alloys at 1200 ℃ was investigated and the extent of S segregation at the scale-alloy interface was determined by scanning Auger microscopy. S-doping had no significant effect on the phase transformation rate from e- to β-Al2O3, while the addition of Dy retarded this process. For the S- doped alloy, scale rumpling occurred only after 2 h thermal exposure and numerous large voids were observed at the scale-alloy interface where S segregated. In contrast to this, the oxide scale formed on the Dy and S co-doped alloy still remained flat even after 50 h isothermal oxidation and only small voids existed at the interface where S segregation was not detected.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Financial support from the National Natural Science Foundation of China under grant Nos. 50501024 and 50671102 is gratefully acknowledged.
文摘The NiAl phase prepared by pack cementation （PC） on a nickel base superalloy was investigated by X-ray photoelectron spectroscopy （XPS） and positron annihilation technique （PAT）. The focus was on the effect of the solid solution of the alloying element from substrate on the binding energy of Ni （Al） 2p peaks and vacancy concentration of the NiAI phase formed in a superalloy. The results showed that the binding energy of Ni 2p peak of the NiAI phase grown in a superalloy was shifted by up to 0.55 eV at the temperature from 850 to 1050℃ towards higher energies and the binding energy of Al 2p peak by up to 1.09 eV in comparison with the NiAl phase formed in pure Ni. The positron lifetimes obtained from the NiAl phase formed in a superalloy were found to be markedly lower than the theoretical values, indicating the decrease in vacancy concentration. The variation of binding energies and vacancy concentration are possibly due to the solid solution of the alloying atoms from the substrate into the NiAI lattice.
文摘目的通过机械合金化与热压烧结相结合的方法制备含有B2结构纳米NiAl相的铁基合金,研究不同含量(质量分数为30%、40%、50%、60%)的纳米NiAl相,对合金显微组织及力学性能的影响。方法以Ni粉和Al粉为原材料,通过高能球磨法制备B2结构纳米NiAl粉体,采用真空热压烧结炉将NiAl粉体与Fe粉混合烧结,得到块体试样。采用扫描电镜(Scanning electron microscopy,SEM)进行微观组织观察,采用能谱仪(Energy dispersive spectroscopy,EDS)、X射线衍射仪(X-ray diffraction,XRD)以及透射电子显微镜(Transmission electron microscopy,TEM)进行物相分析,并测试不同NiAl含量的铁基合金的硬度、密度、室温压缩性能以及600℃的抗氧化性能。结果合金的硬度、抗压强度随NiAl含量先增后降。当NiAl的质量分数为50%时,合金硬度为35.2HRC,抗压强度为2530MPa,密度为6.68g/cm^3,较未添加NiAl时,合金的抗压强度提升了239.6%,密度降低了14.5%。θ=600℃、t=1200min时,其表面氧化增重较纯铁降低了37.9%,此时NiAl相的尺寸约为100~200nm,组织最为均匀,致密度较高。结论纳米NiAl相在降低铁基合金密度的同时,能有效提升其力学性能与抗氧化性能,但由于B2结构的纳米NiAl相为一种硬脆相,当其含量过高时,会极大程度地降低合金的力学性能。
基金Supported by the National Natural Science Foundation of China(10972190)Scientific and Technological Project of Hunan Science and Technology Commission(2010FJ3132)
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supported by the National Natural Science Foundation of China (NSFC) under Grant Nos. 51071013 and 51231001the National Basic Research Program (973 Program) of China under Grant Nos. 2010CB631200 and 2012CB625100
文摘A β--NiAI alloy with normal purity, a S-doped and a Dy and S co-doped （Y-NiAI alloys were prepared by arc-melting and their corresponding S contents were less than 20 ×10-6, 33 ×10-6 and 22 × 10-6, respectively. The isothermal oxidation behavior of the alloys at 1200 ℃ was investigated and the extent of S segregation at the scale-alloy interface was determined by scanning Auger microscopy. S-doping had no significant effect on the phase transformation rate from e- to β-Al2O3, while the addition of Dy retarded this process. For the S- doped alloy, scale rumpling occurred only after 2 h thermal exposure and numerous large voids were observed at the scale-alloy interface where S segregated. In contrast to this, the oxide scale formed on the Dy and S co-doped alloy still remained flat even after 50 h isothermal oxidation and only small voids existed at the interface where S segregation was not detected.
