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Shoji, Mizuki*; Kurihara, Kensuke*; Lobzenko, I.; Tsuru, Tomohito; Serizawa, Ai*
Keikinzoku, 74(12), p.535 - 545, 2024/12
While Plate-like Guinier-Preston (GP) zones are formed during aging process in Al-Cu alloys, spherical nanocluster formation occurs in the early stage of aging in Al-Mg-Si alloys. Unlike well-known GP (I) zone in Al-Cu, there is no specific configurations within the nanocluster. However, the solute concentration and local configuration should play decisive role in subsequent formation of precipitations. In the present study, the first-principles calculations were performed to investigate the factors determining the stable shape during the formation process of GP zones and clusters in Al-Cu and Al-Mg-Si alloys. As a result of formation energy of three-body bonds, the Cu-Cu-Cu triplet with the bond angle of 90deg was the most stable. Monte Carlo simulations with newly developed machine-learning potential were then performed, and consequently the segregation of Cu atom formed with bond angle of 90deg are observed more frequently. In contrast, three-body triplet in Al-Mg-Si alloy was most stable without any specific directional anisotropy, when the bond angle was 60deg, resulting in the formation of spherical nanoclusters. These results suggest that the intrinsic feature of the stability of local bonding dominates the shape of GP zones and nanoclusters, in which planar- or spherical-like cluster is formed.
Tsuru, Tomohito; Mayama, Tsuyoshi*
Keikinzoku, 74(9), p.442 - 450, 2024/09
Magnesium (Mg) alloys have a wide range of expanding applications as structural materials and biomaterials. On the other hand, there is room for improvement in mechanical properties and corrosion resistance, and there are many issues related to structural design and prediction of deformation behavior due to their remarkable plastic anisotropy, and material development based on material/process design is still actively conducted. In this paper, as computational materials science research into the mechanical properties of Mg alloys, we introduce a method for non-empirical evaluation of the effect of alloying on mechanical properties using first-principles calculations, and an analysis method for polycrystalline behavior and non-uniform deformation using the crystal plasticity finite element method, together with specific analysis examples.
Higa, Ryota*; Fujihara, Hiro*; Toda, Hiroyuki*; Kobayashi, Masakazu*; Ebihara, Kenichi; Takeuchi, Akihisa*
Keikinzoku, 73(11), p.530 - 536, 2023/11
In Al-Zn-Mg alloys, suppression of hydrogen embrittlement is necessary to improve their strength. In this study, the distribution of stress, strain, and hydrogen concentration in the actual fracture region was investigated using the crystal plasticity finite element method and hydrogen diffusion analysis based on a model derived from three-dimensional polycrystalline microstructural data obtained by X-ray CT. In addition, the distributions of stress, strain, and hydrogen concentration were compared with the actual crack initiation behavior by combining in-situ observation of tensile tests using X-ray CT and simulation. The results show that stress loading perpendicular to the grain boundary due to crystal plasticity dominates grain boundary crack initiation. It was also found that internal hydrogen accumulation due to crystal plasticity has little effect on crack initiation.
Yano, Rei*; Tanaka, Masaki*; Yamasaki, Shigeto*; Morikawa, Tatsuya*; Tsuru, Tomohito
Keikinzoku, 73(10), p.497 - 503, 2023/10
Impact tests and tensile tests were conducted between 77 K and 450 K in order to elucidate the temperature dependence of absorbed-impact energy, yield stress, effective shear stress, and activation volume. The impact-absorbed energy decreased with decreasing test temperature, however, this alloy did not undergo low-temperature embrittlement although it has a bcc structure. Tensile tests showed changes in both the work-hardening rate and the temperature dependence of yield stress at approximately 120 K. This suggests a change in the mechanism behind the plastic deformation at the temperature. The temperature dependence of the activation enthalpy for dislocation glide suggests that double-kink nucleation of a screw dislocation is the dominant mechanism for the dislocation glide from 150 K to 200 K, while the interaction between a dislocation and solute atoms dominantly controls the dislocation glide above 200 K. On the other hand, superelasticity appears below 120 K, suggesting that the yielding is governed by transformation-induced plasticity below 120 K. The enhanced toughness at low temperatures in these alloys is discussed from the viewpoint of dislocation shielding theory.
Kurihara, Kensuke*; Lobzenko, I.; Tsuru, Tomohito; Serizawa, Ai*
Keikinzoku, 72(7), p.427 - 429, 2022/07
Nanoclusters formed of the Al-Mg-Si alloy affect the aging behavior of the alloy depending on the formation temperature. Since Al, Mg and Si have adjacent atomic numbers, it is difficult to analyze them using the X-ray diffraction method. Therefore, in recent years, Al-Mg-Ge alloys in which Si is replaced with the homologous element Ge have been used. Attempts have been made to analyze the structure of the precipitate. In this study, we quantitatively evaluate the interaction between solute atoms and pores in Al-Mg-Si alloys and Al-Mg-Ge alloys using first-principles calculations based on the density general function theory, and solute atoms. From the viewpoint of bond stability between pores and pores, the precipitation behavior of both alloys was compared and examined.
Kurihara, Kensuke*; Lobzenko, I.; Tsuru, Tomohito; Serizawa, Ai*
Keikinzoku, 72(2), p.47 - 53, 2022/02
Nanoclusters formed in Al-Mg-Si alloys affect the aging behavior of the alloys depending on the formation temperature. In the present study, first-principles calculations were carried out to evaluate the two- and three-body interactions between Mg, Si atoms and vacancies in the Al matrix and to estimate the effect of local bond structures on the formation of nanoclusters. Monte Carlo simulations were subsequently performed to investigate the stable structure of nanocluster formed in Al-Mg-Si alloy. We found that Mg-Si bond and Si-Vac bond were stable in Al matrix. The result showed that the solute atoms are easy to aggregate with another type of atoms and that Si atom had a strong attractive interaction with a vacancy. Mg-Si-vacancy three-body bond were more stable than Mg-Si two-body bond and Si-vacancy two-body bond in Al matrix. Therefore, vacancies were strongly trapped within the cluster region due to the stable local bonds composed of Mg and Si atoms which indicates that the nanoclusters in Al matrix were thermally stabilized by the stable bonds between solute atoms and vacancy. In addition, these results suggested that inner bonds of nanocluster played a significant role in not only the thermal stability but also the formation and growth behavior of nanoclusters during aging at low temperatures.
Tsuru, Tomohito
Keikinzoku, 70(2), p.73 - 81, 2020/02
Elements strategy becomes important to investigate alternative materials of rare metals. I have dedicated to establish a new approach based on computational methods. In the present paper, I propose two approaches based on first-principles and theory of dislocations. These methods are introduced to magnesium alloys.
Yamaguchi, Masatake; Tsuru, Tomohito; Ebihara, Kenichi; Itakura, Mitsuhiro
Keikinzoku, 68(11), p.588 - 595, 2018/11
no abstracts in English
Ebihara, Kenichi; Yamaguchi, Masatake; Tsuru, Tomohito; Itakura, Mitsuhiro
Keikinzoku, 68(11), p.596 - 602, 2018/11
Hydrogen embrittlement (HE) is considered as one cause of stress corrosion cracking. HE is a serious problem in the development of high strength aluminum alloy as with steels. For understanding HE, it is inevitable to know hydrogen trapping states in the alloys and it can be identified using thermal desorption spectrometry of H. In this study, we numerically simulated thermal desorption spectra of hydrogen in aluminum for a cylindrical and a plate specimens and interpreted the desorption peaks included in them on the basis of the trap site concentration and the trap energy. As a result, we found that the peak at the lowest-temperature side can result from grain boundaries and confirmed that the reported interpretation for other peaks is reasonable. We also obtained the result showing the possibility that the trap site concentration of defects changes during heating the specimens. This result may give a suggestion for the interpretation of temperature desorption spectra of steels.
Xu, P. G.; Akita, Koichi; Suzuki, Hiroshi; Moriai, Atsushi
Keikinzoku Gakkai Heisei-24-Nendo Dai-2-kai Kako To Netsu Shori Ni Yoru Yusen Hoi Seigyo Kenkyu Bukai Kokai Koenkai Shiryo, p.19 - 20, 2012/10
Xu, P. G.; Tomota, Yo*; Vogel, S. C.*
Keikinzoku Gakkai Heisei-24-Nendo Dai-2-kai Kako To Netsu Shori Ni Yoru Yusen Hoi Seigyo Kenkyu Bukai Kokai Koenkai Shiryo, p.21 - 22, 2012/10
no abstracts in English
Ooka, Norikazu; Ishii, Toshimitsu
Keikinzoku Yosetsu, 37(1), p.17 - 24, 1999/00
no abstracts in English
Ooka, Norikazu;
Keikinzoku Yosetsu, 36(4), p.169 - 174, 1998/00
no abstracts in English
Ooka, Norikazu;
Keikinzoku Yosetsu, 36(5), p.216 - 221, 1998/00
no abstracts in English
Si
and aluminium at high temperature in out-pileOoka, Norikazu; ; ;
Keikinzoku Yosetsu, 28(8), p.339 - 347, 1990/08
no abstracts in English
; ; ; Ooka, Norikazu
Keikinzoku Yosetsu, 28(11), p.489 - 497, 1990/00
no abstracts in English
; ; ; Ooka, Norikazu
Keikinzoku Yosetsu, 28(12), p.525 - 533, 1990/00
no abstracts in English
; ; Okamoto, Yoshizo;
Keikinzoku Yosetsu, 25(9), p.29 - 39, 1987/09
no abstracts in English
; ;
Keikinzoku Yosetsu, 24(1), p.2 - 14, 1986/00
no abstracts in English
; ;
Keikinzoku Yosetsu, 24(2), p.51 - 58, 1986/00
no abstracts in English
