Papers by Keyword: Twinning

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Authors: Vasile Danut Cojocaru, Ion Cinca, Nicolae Serban, Doina Margareta Gordin, Mariana Lucia Angelescu, Elisabeta Mirela Cojocaru, Doina Raducanu
Abstract: In the present days titanium and titanium alloys are extensively studied and used as biomaterials due to their biological, mechanical and physical properties. During last year’s special attention was paid to β-Titanium alloys due to their low elastic modulus. The present study investigates the twinning deformation features occurred during multi-pass cold-rolling processing of a biocompatible Ti-Nb-Zr-Fe alloy. Twinning deformation features were investigated using EBDS analysis by means of Inverse Pole Figures (IPF’s), Pole Figures (IP’s) and computed Schmid factor (SF’s) for the possible {332}<113> twinning variants.
Authors: Jens Gibmeier, Manuela Klaus, Berthold Scholtes
Abstract: The deformation behavior of the magnesium base alloy AZ31 was studied by means of energy dispersive diffraction using high energy synchrotron radiation. The investigations were performed at the EDDI-beamline operated by the Hahn-Meitner-Institute at Bessy II, Berlin. In-situ stress analyses were carried out for samples subjected to purely elastic as well as elasto-plastic 4- point-bending. In addition reversely loaded states were investigated. The results impressively illustrate the potential of the energy dispersive diffraction analysis processed in transmission mode for residual stress analysis of challenging material states. Inhomogeneous loading and residual stress distributions with respect to the bending height of the prestressed bars were determined for the highly textured material state indicating different predominant deformation mechanisms during tensile loading and compressive loading, respectively. After load inversion also the predominant deformation mechanisms reverse.
Authors: Ondrej Muránsky, David G. Carr, Petr Šittner, E.C. Oliver, P. Dobroň
Abstract: In-situ neutron diffraction has been used to study the pseudoelastic-like behaviour of hydrostatically extruded AZ31 magnesium alloy during stress-strain cycles in compression and tension along the extrusion direction. It has been confirmed that the activation of reversal twinning processes during unloading is responsible for the macroscopically observed hysteresis effect. Moreover, neutron diffraction data reveals the existence of high tensile stresses in grains which have just experienced significant twinning activity prior to the start of the unload cycle. It is thus proposed that this tensile stresses provides the necessary driving force for the activation of untwinning in already twinned grains.
Authors: Harald Rösner, Gerhard Wilde
Abstract: In this study we show that in-situ tensile tests performed in a transmission electron microscope (TEM) in combination with high-resolution TEM are feasible, and, that this method is appropriate to elucidate the deformation processes in nanocrystalline materials directly. First results on nanocrystalline Pd produced by repeated cold-rolling with intermediate folding of metal sheets are presented revealing that the material ruptured during the in-situ tensile tests along grain boundaries. Deformation twinning was observed in grains next to the crack indicating that the deformation processes must have originated from the grain boundaries.
Authors: Igor Matko, Bernard Chenevier, M. Audier, Roland Madar, M. Diani, L. Simon, L. Kubler, D. Aubel
Authors: Valerie Randle, Gregory Owen
Abstract: Grain boundary engineering (GBE) has been carried out on copper and brass. A comparison of the resulting microstructure and grain boundary characteristics from the two specimens revealed that the brass specimen had approximately the same number fraction of Σ3s as the copper specimen (38%), but a lower number fraction of Σ9s and Σ27s and a markedly different microstructure. In the brass specimen twins were not incorporated into the grain boundary network, whereas in the copper specimen Σ3s replaced portions of the grain boundary network. These two mechanisms are discussed in detail.
Authors: A. Jaworski, Sreeramamurthy Ankem
Abstract: In recent years, significant advances have been made in regard to the creep deformation behavior of two phase titanium alloys. It has been shown that the creep resistance depends on a number of factors, including the shape of the component phases, the strength difference between the phases, and the stability of the beta phase. For example, in two-phase materials with a similar volume fraction and morphology of phases, if the beta phase is less stable, then the creep resistance is lower. These developments will be reviewed and the reasons for such effects will be suggested.
Authors: Jian Yu Huang, Yuntian T. Zhu
Authors: Natalya Frolova, Vitaly Zel'dovich, Vitaly Pilyugin, Vyacheslav Gundyrev, Alexander Patselov
Abstract: Transmission electron microscopy and X-ray diffraction were used to study structural changes in the Ti-50.5 at. % Ni alloy upon severe plastic deformation by shear under pressure and subsequent heating. An increase in the degree of deformation leads sequentially to a martensite transformation, twinning of martensite crystals, formation of reorientation bands, development of rotational modes of deformation, formation of a nanocrystalline structure, and finally amorphization. A scheme of the formation of amorphous structure of the alloy during deformation is suggested based on the observed structural changes. It has been found that a reverse martensitic transformation might be one of mechanisms of plastic deformation of the alloy. Therefore, as the degree of deformation increases, first forward and subsequently reverse martensitic transformations can occur. The formation of an amorphous structure starts as the degree of deformation reaches 4.2 (one revolution of Bridgman anvils); at a degree of deformation of 6.8 (5 revolutions of the anvils), the process is virtually completed. The crystallization of the amorphous alloy upon heating starts even at 200°C. However, upon heating up to 300°C (for 0.5-h holdings), the kinetics of crystallization is slow. After annealing at 350°C, the complete crystallization with the formation of a nanocrystalline structure with a grain size of 20-70 nm takes place
Authors: Guang Sheng Song, Shi Hong Zhang, Ming Cheng, Bin Wang
Abstract: For the technology of EBSD, the twinning of metals was described in the form of rotation angle combined with rotation axis, while the twinning of metals was usually described in the form of twinning plane combined with twinning direction. In this report, the corresponding relationship between the two description forms of twinning of face-centered cubic (FCC) metals has been built, based on this relationship, the twinning plane and twinning direction of FCC metals can be determined by EBSD. As the practical application of this relationship above, the twinning variants of two kinds of Ni based superalloys were analyzed.
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