Papers by Keyword: Martensitic Phase Transformation

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Authors: Petr Šittner, J. Pilch, P. Lukas, Michal Landa, H. Seiner, P. Sedlak, B. Malard, Ludek Heller
Abstract: In order to better understand the unique functional responses of shape memory alloys, improve the currently existing SMA modeling tools and used them beneficially in smart structure applications, it is desirable to investigate the deformation/transformation processes in these materials in action – i.e. under stress and temperature variation. In this work, an overview is presented on the applications of various recently developed or originally employed in-situ experimental methods and approaches to martensitic transformations in SMAs.
Authors: V.G. Kouznetsova, M.G.D. Geers
Abstract: A physically-based multi-scale model for martensitic transformation induced plasticity is presented. At the fine scale, a model for one transforming martensitic variant is established based on the concept of a lamellae composed of a martensitic plate and an austenitic layer. Next, the behaviour of 24 potentially transforming variants is homogenized towards the behaviour of an austenitic grain. As a simple example, the model is applied to deformation and transformation of a single austenitic grain under different deformation modes.
Authors: Andreas Seupel, Meinhard Kuna
Abstract: Aim of this study is to describe the ductile damage of metastable austenitic steels which show TRansformation Induced Plasticity (TRIP). Therefore, a criterion for the austenite to martensite transformation, the caused additional hardening and evolution equations for the TRIP-strain are incorporated into the damage model of Rousselier. As a first approach, the model is calibrated against unit cell simulations of the porous material for different stress triaxialities.
Authors: Fan Sun, Jing Yong Zhang, Matthieu Marteleur, Thierry Gloriant, Philippe Vermaut, Philippe Castany, Caroline Curfs, Pascal J. Jacques, Frédéric Prima
Abstract: Titanium alloys typically exhibit a limited ductility (typically 20%) and little strain-hardening. An alloy design with new concept was conducted aiming at improving both ductility and strain hardening while keeping the mechanical resistance at an excellent level. An experimental validation was illustrated with the Ti-12(wt.%)Mo alloy, exhibiting true stress - true strain values at necking, of about 1000MPa and 0.38, respectively, with a large strain hardening rate close to the theoretical limit. In order to clarify the origin of this outstanding combination of mechanical properties, detailed microstructural investigation and phase evolution analysis were conducted by means of in-situ synchrotron XRD, in-situ light microscopy, EBSD mapping and TEM microstructural analysis. In the deformed material, combined Twinning Induced Plasticity (TWIP) and Transformation Induced Plasticity (TRIP) effects are observed. Primary strain/stress induced phase transformations (β->ω and β->α’’) and primary mechanical twinning ({332}<113> and {112}<111>) are simultaneously activated in the β matrix. Secondary martensitic phase transformation and secondary mechanical twinning are then triggered in the twinned β zones. The {332}<113> twinning and the subsequent secondary mechanisms are shown to be dominant at the early stage deformation process. The evolution of the deformation microstructure results in a high strain hardening rate (~2GPa) bringing both a high tensile strength and a large uniform elongation.
Authors: Suresh Neelakantan, Pedro E.J. Rivera-Díaz-del-Castillo, Sybrand van der Zwaag
Abstract: Due to Plasticity induced Transformation in metastable β-Ti-10V-2Fe-3Al (wt.%) alloy (PiTTi) upon deformation, a noticeable improvement in mechanical properties is observed. Among the main factors controlling such effect are the β grain size and its composition. Such phase transforms into martensite upon quenching. Its martensite start temperature (Ms) varies in accordance with its composition. Following Ghosh and Olson’s theory, a thermodynamics based model to predict the compositional dependence of the Ms temperature is developed, and successfully validated for Ti-X (X = Fe, Cr, Mo, V, Nb, Zr and Al) binary alloys. The model has been used to design new alloys displaying a tailored PiTTi effect.
Authors: Hiroshi Matsuda, Hisata Noro, Yasunobu Nagataki, Yoshihiro Hosoya
Abstract: Industrial low alloy TRIP sheet steels contain blocky and lath-shaped retained austenite. In the present study, transformation behaviour of blocky and lath-shaped retained austenite during straining was investigated to clarify its effect on mechanical properties. Two types of TRIP steels containing almost the same amount but the different morphology of retained austenite were used. A steel containing large amount of lath-shaped retained austenite exhibits superior ductility, and sustains high work-hardenability in a high strain region. On the contrast, a steel containing large amount of blocky retained austenite exhibits low ductility.  The work-hardenability increased steeply to the maximum at a low strain region, and then reduced in a high strain region. The stability of the blocky austenite has been found to be poor with respected to martensite transformation. The lath-shaped retained austenite remains until a high strain region whereas the blocky retained austenite transformed into martensite in a low strain region. Carbon content was higher in the lath-shaped retained austenite than in the blocky retained austenite. Stability of retained austenite is, however, inexplicable only by the carbon content, and would be affected by the different morphology and the resulting restraint conditions.
Authors: R.H. Zhou, Qing Ping Sun
Abstract: Superelastic NiTi polycrystalline tubes, when subjected to quasi-static stretching, transform from an initial austenite phase to a high-strain martensite phase by the formation and growth of a macroscopic self-organized helical domain as deformation progresses. This paper performed an experimental study on the effects of the externally applied stretching and tube geometry (length L, wall-thickness h and tube radius R) on the martensitic helical domains in the tubes under very slow (isothermal) stretching. The evolution of the helical domains with the applied strain in different tube geometries are quantified by in-situ optical measurement. We demonstrate that the shape of the self-organized helical domain and its evolution are governed by the competition between bending strain energy and domain front energy in minimizing the total energy of the tube system. The former favors a long slim helical domain, while the latter favors a short fat helical domain. The experimental results provide a strong support to the recently developed theoretical relationship.
Authors: Zhi Shan Yuan, Zhao Wei Feng, Wei Dong Miao, Jiang Bo Wang, Jin Zhou, Ming Zhu
Abstract: TiNi shape memory alloys exhibiting high damping capacity are currently expected to be used as structural materials for energy dissipation or vibration control applications. In this paper, the characterization of damping behaviour of a binary TiNi SMA was performed by dynamic mechanical analyzer (DMA) instrument and differential scanning calorimetry (DSC) equipment. Damping tests measuring Tanδ, storage modulus E' and loss modulus E" of Ti49.2Ni50.8 binary shape memory alloy were investigated at different temperature, using different frequency and strain amplitude. It shows that quenching rate has a significant effect on the damping capacity of TiNi SMA by exhibiting different phase transformation behavior. Internal friction values (Q-1) corresponding to cubic B2 parent phase to rhombohedral R phase transformation, B2-R, and R-B19' monoclinic martensite transformation are as high as 0.177 and 0.078, respectively. The occurrence of R-phase significantly softens the storage modulus and thus promotes the damping capacity of TiNi SMAs.
Authors: Yuri N. Koval, Georgiy Firstov, Valeri V. Odnosum
Abstract: The present paper is dedicated to the first observation of the martensitic transformation (MT) and associated shape memory effect (SME) in HfIr equiatomic intermetallic compound. Differential scanning calorimetry allowed determining MT temperatures, which are above 700 K. It was also shown that MT taking place at such high temperatures is associated with SME measured in 3 point bending. MT temperatures and crystal structure changes in the homogeneity range of HfIr compound were also studied. SME behavior changes in the homogeneity range of HfIr compound are discussed
Authors: Matthias Droste, Horst Biermann
Abstract: Metal Matrix Composites (MMC) based on a TRIP (TRansformation Induced Plasticity)- or TWIP (TWinning Induced Plasticity)-steel matrix reinforced with MgO-partially stabilized zirconia (Mg-PSZ) are an interesting research field as both components exhibit a deformation-induced or stress-assisted martensitic phase transformation and twinning, respectively. The present work deals with the fatigue characteristics of a reinforced CrMnNi-steel as a function of the ceramic particle size. Therefore, the particles were classified into three grades (grade 1: <10 μm; grade 2: 10-30 μm; grade 3: 30-50 μm) whereas the volume fraction concerning the composite material was kept constant at 10 vol.%. The composites were produced using the hot pressing technique. The tests were performed under total strain control in a range of 0.2% ≤ Δεt ≤ 1.2%. The microstructure of fatigued specimens was examined using scanning electron microscopy.
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