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1.
《Intermetallics》2015
Fine-grained fully-lamellar (FL) microstructure is desired for TiAl components to serve as compressor/turbine blades and turbocharger turbine wheels. This study deals with the process and phase transformation to produce FL microstructure for Mo stabilized beta-gamma TiAl alloys without single α-phase field. Unlike the α + γ two-phased TiAl or beta-gamma TiAl with single α-phase field, the wrought multi-phase TiAl–4/6Nb–2Mo–B/Y alloys exhibit special annealing process to obtain FL microstructure. Short-term annealing at temperatures slightly above β-transus is recommended to produce the desired FL microstructure. The related mechanism is to guarantee the sufficient diffusion homogenization of β stabilizers during single β-phase annealing, and further avoid α decomposition by α → γ + β when cooling through α + β + γ phase field. The colony boundary β phase contributes to fine-grained nearly FL microstructure, by retarding the coarsening of the α phase grains. 相似文献
2.
H. L. Du S. R. Rose Z. D. Xiang P. K. Datta X. Y. Li 《Materialwissenschaft und Werkstofftechnik》2003,34(4):421-426
The oxidation/sulphidation behaviour of a Ti‐46.7Al‐1.9W‐0.5Si alloy with a TiAl3 diffusion coating was studied in an environment of H2/H2S/H2O at 850oC. The kinetic results demonstrate that the TiAl3 coating significantly increased the high temperature corrosion resistance of Ti‐46.7Al‐1.9W‐0.5Si. The SEM, EDX, XRD and TEM analysis reveals that the formation of an Al2O3 scale on the surface of the TiAl3‐coated sample was responsible for the enhancement of the corroison resistance. The Ti‐46.7Al‐1.9W‐0.5Si alloy was also modified by Nb ion implantation. The Nb ion implanted and as received sampels were subjected to cyclic oxidation in an open air at 800oC. The Nb ion implantation not only increased the oxidation resistance but also substantially improved the adhesion of scale to the substrate. 相似文献
3.
In the oxidation of TiAl alloys, the role of scale-growth stresses formed during oxidation has, thus far, been unknown. In the present paper the oxide-growth stresses were investigated by the deflection-test method in monofacial oxidation (DTMO) accompanied by acoustic-emission measurements. On unmodified surfaces the growth stresses are compressive and reach levels of around –100 MPa. At the same time, significant acoustic emission occurs indicating that even under isothermal conditions, stresses are relieved by a scale-cracking mechanism. For oxide scales on TiAl surfaces, which had been ion implanted with chlorine before oxidation, a very thin protective alumina layer is formed which, however, develops growth stresses in the range of several GPa, accompanied by intensive acoustic emission. In all stress–time curves, a dynamic situation is observed. This consists of phases of stress relief by scale microcracking and phases of stresses increase due to crack healing and further oxide growth. As a result, the level of stress as a function of oxidation time, is characterized by an oscillating course. 相似文献
4.
5.
Ag-BaO thin films doped with lanthanum were prepared by vacuum deposition. Compared with the normal Ag-BaO thin film, there is almost no change with the shape and the peak site of the fluorescence spectrum; however, fluores-cence emission strength of the whole observation band(325 -600 nm)increases about 40%, and the increase of short wavelength range is more remarkable than that of long wavelength range, which we named “blue-stronger“ phenomenon. Analytic results show that, with the forming of intermetallic compounds between silver and lanthanum, the 4f-state energy levels lie just below the Fermi level within 5 eV. It is the energy exchange between the 4f energy levels and the conduction band that causes the increase effect of fluorescence emission, and it is the optical absorption cross section of 4f electron, which increases with the increase of energy of incidence photon, that gives rise to the “blue-stronger“ phenomenon. 相似文献
6.
The microstructure and thermal behavior of the Sn-Zn-Ag solder were investigated for 8.73–9% Zn and 0–3.0% Ag. The scanning
electron microscopy (SEM) analysis shows the Ag-Zn compound when the solder contains 0.1% Ag. X-ray diffraction (XRD) analysis
results indicate that Ag5Zn8 and AgZn3 become prominent when the Ag content is 0.3% and above. Meanwhile, the Zn-rich phase is refined, and the Zn orientations
gradually diminish upon increase in Ag content. The morphology of the Ag-Zn compound varies from nodular to dendrite structure
when the Ag content increases. The growth of the Ag-Zn compounds is accompanied by the diminishing of the eutectic structure
of the Sn-9Zn solder. Differential scanning calorimetry (DSC) investigation reveals that the solidus temperature of these
solders exists at around 198°C. A single, sharp exothermic peak was found for the solders with Ag content less than 0.5%.
Liquidus temperatures were identified with the DSC analysis to vary from 206°C to 215°C when the Ag content ranges from 1.0%
to 3.0% 相似文献
7.
Morphology of intermetallic compounds formed between lead-free Sn-Zn based solders and Cu substrates
The morphologies of intermetallic compounds formed between Sn-Zn based solders and Cu substrates were investigated in this
study. The investigated solders were Sn-9Zn, Sn-8.55Zn-0.45Al, and Sn-8.55Zn-0.45Al-0.5Ag. The experimental results indicated
that the Sn-9Zn solder formed Cu5Zn8 and CuZn5 compounds on the Cu substrate, while the Al-containing solders formed the Al4.2Cu3.2Zn0.7 compound. The addition of Ag to the Sn-8.55Zn-0.45Al solder resulted in the formation of the AgZn3 compound at the interface between the Al4.2Cu3.2Zn0.7 compound and the solder. Furthermore, it was found that the cooling rate of the specimen after soldering had an effect on
the quantity of AgZn3 compound formed at the interface. The AgZn3 compound formed with an air-cooling condition exhibited a rougher surface and larger size than with a water-quenched condition.
It was believed that the formation of the AgZn3 compound at the interface occurs through heterogenous nucleation during solidification. 相似文献
8.
Excessive intermetallic compound (IMC) growth in solder joints will significantly decrease the reliability of the joints.
IMC growth is known to be influenced by numerous factors during the component fabrication process and in service. It is reported
that, other than temperature and holding time, stress can also influence the IMC growth behavior. However, no existing method
can be used to study the effect of stress state on IMC growth in a controlled manner. This paper presents a novel method to
study the effect of stress on interfacial IMC growth between Sn-Ag-Cu solder and a Cu substrate coated with electroless Ni
immersion Au (ENIG). A C-ring was used and in-plane bending induced tensile and compressive stresses were applied by tightening
the C-ring. Results revealed that in-plane compressive stress led to faster IMC growth as compared with in-plane tensile stress. 相似文献
9.
研究了在700℃盐和水蒸气协同作用下TiAlNb合金的腐蚀行为以及溅射涂层对TiAlNb合金的防护作用。结果表明,在盐和水蒸气协同作用下,溅射TiAlCrAg涂层对TiAlNb合金具有一定的保护作用。盐和水蒸气协同作用加速了合金以及涂层的腐蚀。挥发性气体氯化物对α2相的循环作用是TiALNb合金腐蚀的主要原因。涂层中较少的α2相以及Laves相中较高的Cr含量是腐蚀有所减缓的主要原因。 相似文献
10.
运用XD工艺制备了颗粒增强TiAl基复合材料。增强颗粒均匀分布于TiAl基体中并细化TiAl合金。通过在TiB_2/TiAl、TiC/TiAl复合材料中加入适量的Si,颗粒增强TiAl基复合材料的室温延性得到了改善。 相似文献