Papers by Keyword: Metastable Phase

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Authors: F. Lourdjane, Z. Chaieb, A. Raho, M. Kadi-Hanifi
Abstract: The development of the transition metastable phases and the accompanying hardening of these transformations are studied for Al-20wt%Ag and Al-3wt%Cu-1wt%Mg supersaturated solid solutions. During the precipitation the GP and GPB zones form by a process of negative diffusion. The metastable phases are characterized by their hardness isotherms and their temperature range determined on the hardness isochronal.
Authors: Hai Yan Wang, Hui Ping Ren, Zong Chang Liu
Abstract: Microstructure evolution of Fe-1.18%Cu high purity steels during solution and aging was investigated under high-resolution electron microscope (HREM). In addition, the aging strengthening mechanisms were discussed based on the microstructure observation. The results show that there were lots of Cu atom clusters in ferrite matrix during solid solution and aging initial stages, subsequently, Cu-rich metastable Fe-Cu particles precipitate at the aging strength peak. It is found that the intense strengthening is controlled by the coherency relationship of Fe-Cu metastable phase with matrix that forms the obstacle of the dislocation motion, while the decrease of strength after the peak is attributed to the loss of coherency, which should highly likely be the dominant reason of aging strengthening in Cu bearing high purity steels Thus our TEM observation results are in reasonably agreement with some previous assume.
Authors: Kenji Matsuda, Susumu Ikeno, Tatsuo Sato, Akihiko Kamio
Authors: Kenji Matsuda, Junya Nakamura, Yoshio Nakamura, Tatsuo Sato, Susumu Ikeno
Abstract: The crystal structure of metastable phase in Ag added Al-Mg-Si alloy was investigated by comparing the β’-phases in Al-Mg-Si alloy without Ag, using images of high resolution transmission electron microscope (HRTEM), selected area electron diffraction patterns (SADPs) and an energy dispersive X-ray spectroscopy (EDS). SADPs and HRTEM images obtained from metastable phase in the Ag added Al-Mg-Si alloy showed similar to those of β’-phase in Al-Mg-Si alloy without Ag and had different lattice spacings because of the effect of Ag. According to our careful analysis on obtained HRTEM images and SADPs, it includes more complicated crystal lattice of distorted hexagons.
Authors: Kenji Matsuda, Teruyoshi Munekata, Susumu Ikeno
Abstract: Rod-shaped precipitates in Al -1.1 mass% Mg2Ge (balanced) and Al -1.0 mass% Mg2Ge – 0.5 mass% Mg (excess Mg) alloys aged at 523 K were observed by high-resolution transmission electron microscope (HRTEM) to understand their crystal lattices and chemical compositions. Rod-shaped precipitates were parallel to <100> directions of the matrix. There were 2 groups for rod-shaped precipitates in the base alloy, namely, small cross sections about 10 nm and large ones over 20nm in diameter. Small precipitates showed a hexagonal network of bright dots in their HRTEM images, and its crystal lattice was estimated as a hexagonal having a= 0.72 and c= 0.405 nm based on analysis of HRTEM images and selected area electron diffraction (SAED) patterns. This lattice parameter was slight larger than that of the β’-phase in Al-Mg-Si alloy.
Authors: Wei Li, Hai Bo Yang, Ai Dang Shan, Jian Sheng Wu
Abstract: Nb/Nb5Si3 in-situ composites are very attractive structural materials for these materials perform a good balance in mechanical properties, including a high strength at high temperature (>1373K) and reasonably high fracture toughness at room temperature. Metastable phase Nb3Si plays an important role in the properties of Nb/Nb5Si3 composites by affecting microstructure and volume fracture of ductile phase. In this paper, Nb-10Si-xMo and Nb-18Si-xMo (x=0,5,15) are prepared by arc melting and annealed at 1473K for 100h. Single edge-notched bending (SENB) test was used to study the fracture toughness of Nb-Si-Mo alloys. The stability of metastable phase is analyzed by XRD. The room temperature fracture toughness of Nb-10Si is 10.47MPa(m)1/2 and higher than that of binary Nb-18Si alloys at near-eutectic compositions. The addition of Mo improves the fracture toughness of as cast Nb-Si alloys from 4.1 MPa(m)1/2 to 9.9MPa(m)1/2 at near-eutectic compositions and decreases it from 10.47 MPa(m)1/2 to 8.8MPa(m)1/2 at hypoeutectic compositions.
Authors: Kenji Matsuda, Daisuke Teguri, Tatsuo Sato, Susumu Ikeno
Authors: Zi Qian Huang, Qing Lian Xie, Guo Hua Huang, Pei Lan Li
Abstract: Coating and gradient structure can improve the quality of products, but growth-induced stress generates in the forming process of the coating and the gradient structure due to the existence of the defects and metastable phase. The existence of growth-induced stress can conversely affect the quality of the product, even lead to cracking and product failure. This paper shows the model of stress calculation according to the crystal structure’s defect theory.
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