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
Effects of Ti, Hf, Nb and W alloying elements addition on the microstructure and the mechanical behaviors of NiAl-Cr(Mo) intermetallic alloy were investigated by means of XRD, SEM, EDX and compression tests. The resul...Effects of Ti, Hf, Nb and W alloying elements addition on the microstructure and the mechanical behaviors of NiAl-Cr(Mo) intermetallic alloy were investigated by means of XRD, SEM, EDX and compression tests. The results show that Ni-31Al-30Cr-4Mo-2(Ti, Hf, Nb, W) alloy consists of four phases: NiAl, α-Cr solid solution, Cr2Nb and Ni2Al(Ti, Hf). The mechanical properties are improved significantly compared with the base alloy. The compression yield strength at 1 373 K is 467 MPa and the room temperature compression ductility is 17.87% under the strain rate of 5.56×10-3 s-1, due to the existence of Cr2Nb and Ni2Al(Ti, Hf) phases for strengthening and Ti solid solution in NiAl matrix and coarse Cr(Mo, W) solid solution phase at cellular boundaries for ductility. The elevated temperature compression deformation behavior of the alloy can be properly described by power-law equation: ε =0.898 σ8.47exp[-615/(RT)].展开更多
The microstructure and mechanical behaviors of NiAl-28Cr-5Mo-1Nb eutectic alloy were investigated by using scanning electron microscopy, X-ray diffraction, transmission electron microscopy and compression tests, respe...The microstructure and mechanical behaviors of NiAl-28Cr-5Mo-1Nb eutectic alloy were investigated by using scanning electron microscopy, X-ray diffraction, transmission electron microscopy and compression tests, respectively. The alloy is mainly composed of three phases, which are the gray lamellar Cr（Mo） plate, black NiAI matrix and semicontinuously distributed Cr2Nb-type Laves phase. Through Nb addition, NiAl-Cr（Mo）/Nb alloy exhibits a reasonable balance of high temperature strength and room temperature compression ductility and its mechanical behaviors are superior to the NiAl-28Cr-6Mo eutectic alloy at all temperature. The elevated temperature compression deformation behavior of NiAl-Cr（Mo）/Nb alloy can be properly described by power-law equation.the National High Technology Committee of China （No. 863-715-005-0030） for financial supports.展开更多
Intermetallics for structural applications at high temperatures must show a sufficient high temperature strength which is controlled by creep processes. In the first section the creep behaviour of single-phase interme...Intermetallics for structural applications at high temperatures must show a sufficient high temperature strength which is controlled by creep processes. In the first section the creep behaviour of single-phase intermetallic alloys is overviewed with respect to stress and temperature dependence and effects of composition and microstructure. It is shown in particular that creep deformation is controlled by diffusion. The second section refers to multiphase intermetallic alloys, and both particulate and non-particulate alloys are regarded. Data are presented for single-phase and multiphase alloys based on B2 phases and lesscommon phases and the consequences of diffusion control for alloy design are discussed.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Project supported by Aerospace Science and Technology Innovation Fund of China
文摘Effects of Ti, Hf, Nb and W alloying elements addition on the microstructure and the mechanical behaviors of NiAl-Cr(Mo) intermetallic alloy were investigated by means of XRD, SEM, EDX and compression tests. The results show that Ni-31Al-30Cr-4Mo-2(Ti, Hf, Nb, W) alloy consists of four phases: NiAl, α-Cr solid solution, Cr2Nb and Ni2Al(Ti, Hf). The mechanical properties are improved significantly compared with the base alloy. The compression yield strength at 1 373 K is 467 MPa and the room temperature compression ductility is 17.87% under the strain rate of 5.56×10-3 s-1, due to the existence of Cr2Nb and Ni2Al(Ti, Hf) phases for strengthening and Ti solid solution in NiAl matrix and coarse Cr(Mo, W) solid solution phase at cellular boundaries for ductility. The elevated temperature compression deformation behavior of the alloy can be properly described by power-law equation: ε =0.898 σ8.47exp[-615/(RT)].
基金The authors would like to acknowledge the National Natural Science Foundation of China(No.59895152)the National High Technology Committee of China(No.863-715-005-0030)for financial supports.
文摘The microstructure and mechanical behaviors of NiAl-28Cr-5Mo-1Nb eutectic alloy were investigated by using scanning electron microscopy, X-ray diffraction, transmission electron microscopy and compression tests, respectively. The alloy is mainly composed of three phases, which are the gray lamellar Cr（Mo） plate, black NiAI matrix and semicontinuously distributed Cr2Nb-type Laves phase. Through Nb addition, NiAl-Cr（Mo）/Nb alloy exhibits a reasonable balance of high temperature strength and room temperature compression ductility and its mechanical behaviors are superior to the NiAl-28Cr-6Mo eutectic alloy at all temperature. The elevated temperature compression deformation behavior of NiAl-Cr（Mo）/Nb alloy can be properly described by power-law equation.the National High Technology Committee of China （No. 863-715-005-0030） for financial supports.
文摘Intermetallics for structural applications at high temperatures must show a sufficient high temperature strength which is controlled by creep processes. In the first section the creep behaviour of single-phase intermetallic alloys is overviewed with respect to stress and temperature dependence and effects of composition and microstructure. It is shown in particular that creep deformation is controlled by diffusion. The second section refers to multiphase intermetallic alloys, and both particulate and non-particulate alloys are regarded. Data are presented for single-phase and multiphase alloys based on B2 phases and lesscommon phases and the consequences of diffusion control for alloy design are discussed.
