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Feng Z.,Northwestern Polytechnical University | Yang Y.,Northwestern Polytechnical University | Huang B.,Northwestern Polytechnical University | Han M.,Northwestern Polytechnical University | And 2 more authors.
Materials Science and Engineering A | Year: 2010

The heterogeneous nucleation and growth of precipitates at dislocations in Al-Cu-Mg alloy were investigated by examining sample aged at 195°C for various times from 10min to 9h. High resolution transmission electron microscopy (HRTEM) observations and electron energy loss spectrometers (EELS) analysis show that the precipitation sequence of the S (Al2CuMg) phase along dislocations should be SSS→GPB zones→S (Type I)→S (Type I)+S (Type II). Type II S precipitate can nucleate and grow separately at some dislocation parts which are unfavorable for Type I S precipitate formation, or can transit from Type I S precipitate during lateral growth along dislocations by means of continuous or stepped changing in lattice orientations. Both of these modes are accomplished under the action of dislocation strain field. The deviation extent of Type II S precipitate is considered not changing with time but closely related with the interactions between the transformation strain during nucleation and the dislocation strain field. © 2010 Elsevier B.V.


Feng Z.Q.,Northwestern Polytechnical University | Yang Y.Q.,Northwestern Polytechnical University | Huang B.,Northwestern Polytechnical University | Luo X.,Northwestern Polytechnical University | And 5 more authors.
Materials Letters | Year: 2011

The high angle annular dark field scanning transmission electron microscopy (STEM-HAADF) tomography technique was applied to understand the three dimensional (3D) morphology and distribution characteristic of grain boundary precipitate (GBP) in peak-aged Al-Cu-Mg alloy. The results indicate that GBPs show both spherical and lenticular shapes and triangularly distribute along grain boundary (GB). Based on 3D observations from various directions, the values of GBP relevant parameters such as GBP size, center to center distance, number of GBPs per unit GB area and area fraction of GB covered by GBPs are further determined. The 3D method for GBP relevant parameter determination seems an effective way to avoid misunderstandings in the conventional two dimensional (2D) methods induced by GBP overlapping and projection effect as well as curved GB surface. © 2011 Elsevier B.V. All rights reserved.


Gao J.,IHEP | Zhai J.Y.,IHEP | Li Z.Q.,IHEP | Zhao T.X.,IHEP | And 11 more authors.
IPAC 2010 - 1st International Particle Accelerator Conference | Year: 2010

The combination of the low-loss shape and large grain niobium material is expected to be the possible way to achieve higher gradient and lower cost for ILC 9-cell cavities. As the key component of the "IHEP 1.3 GHz SRF Accelerating Unit and Horizontal Test Stand Project", a low-loss shape 9-cell cavity using Ningxia large grain niobium has been fabricated and surface treated at IHEP and will be tested at KEK. The fabrication procedure, surface treatment recipes as well as the SRF facilities are presented in this paper.


Wang X.,Beijing Institute of Aviation Materials | Cao J.-X.,Beijing Institute of Aviation Materials | Huang X.,Beijing Institute of Aviation Materials
Hangkong Cailiao Xuebao/Journal of Aeronautical Materials | Year: 2012

Superplastic deformation behavior and microstructure evolution of two hot-rolled Ti 3Al base alloy sheets with different strain and atypical equiaxed grains were studied in this paper. The results show that, microstructure of the alloy transformed from the initial non-equiaxed microstructure to fine equiaxed microstructure, which is regarded as beneficial for superplastic deformation. The alloy exhibited good superplasticity when deformed at the temperature range of 940~1020°C, with the strain rate of 2×10 -4~2×10 -3s -1, the maximum elongation can be reached 859.5% and the strain rate sensitivity index is high at 0.43. The superplastic deformation mechanism of this alloy is mainly for boundary sliding. The effects of deformation inside the grains and dislocation creep during the superplastic deformation are more significant in this atypical equiaxed microstructure condition than those in the typical fine-equiaxed conditions. Hot-rolled Ti 3Al base alloy sheets with atypical equiaxed grains have excellent superplasticity and do not need complex heat treatments, which represents good commercial value.

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