12th International Conference on Magnesium Alloys and their Applications (Mg 2021): LPSO & MFS Structures II
Program Organizers: Alan Luo, Ohio State University; Mihriban Pekguleryuz, McGill University; Sean Agnew, University of Virginia; John Allison, University of Michigan; Karl Kainer; Eric Nyberg, Kaiser Aluminum Trentwood; Warren Poole, University of British Columbia; Kumar Sadayappan, CanmetMATERIALS; Bruce Williams, Canmetmaterials Natural Resources Canada; Stephen Yue, Mcgill University
Thursday 10:50 AM
June 17, 2021
Room: Contributed II
Location: Virtual
Session Chair: Mitsuhiro Itakura, Jaea
Atomic-resolution Characterizations of Deformation Twins in Mg-Gd Alloys: Kai Guan1; Daisuke Egusa1; Gerardo Garces2; Eiji Abe1; 1The University of Tokyo; 2National Centre for Metallurgical Research (CENIM-CSIC)
As one of the important deformation mechanisms, twinning plays a crucial role in plastic deformation and eventually in controlling the formability and mechanical properties of Mg alloys. In this work, extruded Mg-Gd alloys were compressed at 150 °C and 200 °C, and the corresponding compression curves exhibit obvious serrations. We investigated twin boundaries in the samples compressed to 4 % plastic strain by atomic-resolution high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The results indicate that numerous Gd atoms distinctly segregated at the interface between {10-12} twin and matrix, and the Gd-rich plane is always separated by steps. It is interesting to note that the average step height in samples with large serrations is greater than that in those with small serrations. Therefore, we deduce that the strong interaction between solute atoms and twin boundary leads to stress drops in serrated stress-strain curves.
Direct Observation of Solute Segregations at Kink Boundaries in LPSO-type Mg Alloys: Daisuke Egusa1; Koji Inoue2; Yasuyoshi Nagai2; Eiji Abe1; 1The University of Tokyo; 2Tohoku University
Mg alloys containing long period stacking/order (LPSO) phase have gathering wide attention because of their excellent mechanical properties, which are believed to be derived from their unique deformation modes, “kinking”. In the present study, we have investigated atomic structure of kink boundary (KB) in a hot-extruded Mg-Zn-Y alloy, based on scanning transmission electron microscopy (STEM) and atom-probe tomography (APT). STEM observations show that KBs are composed of arrays of extended basal dislocations that selectively locates on solute-enriched stacking faults (SESF) in the LPSO structure. Introduction of such dislocations on SESF causes structural reconstruction, forming local hexagonal close-packed Mg region within SESF. Atomic-scale STEM/APT observations reveal that a composition of such local hcp regions becomes as dilute as that of Mg matrix in this alloy. This significant reconstruction should enhance a thermal stability of kink microstructure, which is essential for understanding mechanical properties of the Mg-Zn-Y alloys at elevated temperature.
Attempt to Apply X-ray Fluorescence Holography to a Grain of Mille-Feuille Structure Mg Alloys: Koji Kimura1; Daisuke Egusa2; Hidetoshi Miyazaki1; Artoni Ang1; Seiji Kashima1; Yuta Yamamoto1; Naohisa Happo3; Tomohiro Matsushita4; Eiji Abe2; Kouichi Hayashi1; 1Nagoya Institute of Technology; 2The University of Tokyo; 3Hiroshima City University; 4Nara Institute of Science and Technology
Mg alloys containing Zn and rare earths (RE) have been received increasing attention owing to their superior mechanical properties. It has been reported that Zn and RE form clusters, which should play an important role in strengthening these alloys. X-ray fluorescence holography (XFH) is a powerful tool to visualize a three dimensional atomic arrangement around a selected element. XFH has been applied to Mg-Zn-Y alloys to characterize the L12-type Zn6Y8 clusters. However, XFH requires mm size single crystals, which has been restricted the range of application of this technique. In particular, almost all Mg-Zn-RE alloys can not be obtained in the single crystal form. In this study, we attempt to apply XFH technique to a grain of polycrystalline Mg97Zn1Gd2 using a micro beam X-ray and a two dimensional detector to record Zn-Kα holograms. We will discuss the pattern of the obtained hologram in comparison with the calculated results.
Analysis of Local Elasticity in Mille-feuille Structured Magnesium Alloys: Yutaka Urakawa1; Daisuke Egusa1; Mitsuhiro Itakura2; Eiji Abe1; 1The University of Tokyo; 2Japan Atomic Energy Agency
Mille-feuille structured (MFS) materials, in which hard layers and soft layers are alternately laminated, exhibit high strengths by hot working. Although their strengthening mechanisms are still unclear, the inhomogeneous properties between the hard layers and the soft layers is accepted to be playing a large part. In the LPSO structure, the elastic properties of hard/soft layers can be estimated by macroscopic investigations of nearly single crystalline specimens, however it is difficult for MFS owing to their low degree of order. In the present study, we have investigated the elastic property of solute enriched layers in the MFS of Mg-Zn-Y alloy, based on STEM direct observations, the linear elastic model and first-principles calculations. We estimated Young's Modulus of Zn/Y enriched layers, based on the linear elastic model, resulting to suggest that Zn/Y enriched layers are indeed behave as hard layers in MFS Mg alloys.
Evaluation of Residual Strain Distributions around Ridge-type Kinks in a Single-phase Mg-6at%Zn-9at%Y Alloy by Synchrotron X-ray Radiation: Tomotaka Miyazawa1; Ryota Namba1; Toshiyuki Fujii1; Shigeto Yamasaki2; Masatoshi Mitsuhara2; Hideharu Nakashima2; 1Tokyo Institute of Technology; 2Kyushu University
Mg-Zn-Y alloys have a typical mille-feuille structure which is named long-period stacking ordered (LPSO) phase consisted of alternative stacking of hard and soft layers. It has been known that the LPSO phase can be plastically deformed with forming kinks during compressive deformation. In this study, to investigate the kink formation mechanism, residual strain distributions around ridge-type kinks in a compressively deformed LPSO single phase specimen were measured by the energy-dispersive X-ray diffraction microscopy with synchrotron white X-ray. Tensile strain remained locally near by the tips of ridge-type kinks after unloading. This is caused that grain boundaries inhibit bending of basal planes due to the formation of kinks. There were local residual strain distributions which were asymmetric with respect to the ridge-type kinks. This result is consistent with the asymmetric pre-kink formation mechanism before development of the ridge-type kinks.
In-situ Analysis on LPSO Formation from Amorphous Mg85Y9Cu6 Alloys: Hiroshi Okuda1; Shan Lin1; Michiaki Yamasaki2; Yoshihito Kawamura2; Shigeru Kimura3; 1Kyoto University; 2Kumamoto University; 3JASRI
Effect of substitution of transition elements from Zn to other 3d elements on the formation and stability of LPSO structures is an interesting subject to understand microstructure control of the alloys. In the present work, phase transformation process in amorphous Mg85Y9Cu6 alloys during heating the sample at a constant rate of 10 K/min. has been analyzed by in-situ small- and wide- angle scattering/diffraction measurements. Results were compared with those previously obtained for Mg85Y9Zn6 alloys, which we have examined in detail[1]. Present results suggest that the tendency to form solute clusters in supersaturated hcp matrix is far less remarkable when compared with that for MgYZn alloys. Nucleation sites of the LPSO crystallites were found to be different when compare the path with the MgYZn alloy under the same heat treatments.[1] H.Okuda et al., Acta Mater. 194(2020)587.
Developments of Resonant Small-angle Scattering Mearuements for Contrast Control at the Mg K Absorption Edge: Hiroshi Okuda1; Shan LIN1; Rei Sakohata1; Shigeru KIMURA2; Yusuke TEMENORI2; Yoshinori KITAJIMA3; 1Kyoto University; 2JASRI; 3KEK-PF
Small-angle scattering is a useful approach for examining quantitative analysis of precipitation nanostructures, and also of compositional fluctuations in alloys. We would like to present our recent developments on resonant small-angle scattering measurements made at the K absorption edge of light metals, in particular, at Mg. Since the photon energy of such absorption edge are in the so-called tender X-ray region, i.e., around 1 keV, there are several experimental difficulties to overcome. By using the resonant scattering, control of contrast for Al3Mg nano precipitates in Al-Mg alloys and MgO nanoparticles supported on polymer membranes were confirmed.Present approach is expected to be useful in examining not only the precipitation nanostructures or Mg nanostructures such as nanoparticles and pillars, but also the average structure in multilayered microstructures having large distribution.
Kink Deformation Dynamics of LPSO Alloy in the Experimental View Point of Multilayer Structure Deformation: Kazuya Aizawa1; Wu Gong2; Stefanus Harjo1; Takuro Kawasaki1; 1Japan Atomic Energy Agency; 2Kyoto University
We discuss a dynamics of kink deformation for Mg-based LPSO alloy, using neutron diffraction data and AE data. We treat the kink deformation of LPSO alloy as an example for multilayer structure deformation with large deflection, namely kink structure, chevron structure, etc. and try to characterize its dynamics features.