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Martensitic Transformation (martensitic + transformation)

Distribution by Scientific Domains

Polymers and Materials Science	56%
Physics and Astronomy	25%
Chemistry	12%

Selected Abstracts

In Situ SEM Observation and Analysis of Martensitic Transformation During Short Fatigue Crack Propagation in Metastable Austenitic Steel,

ADVANCED ENGINEERING MATERIALS, Issue 4 2010
Ulrich Krupp
Abstract High cycle fatigue (HCF) life of metastable austenitic steels is governed by the ability of the parent austenite phase to transform into ,, martensite via metastable , martensite. The mechanism of this strain-induced transformation is closely related to the grain size, the crystallographic orientation distribution, as well as to amplitude, and cyclic accumulation of plastic strain. Aim of the present study is to identify and to quantitatively describe the basic principles of strain-induced martensite formation by means of in situ cyclic deformation experiments in a scanning electron microscope (SEM) in combination with electron back-scattered diffraction (EBSD) and numerical modeling using a boundary element approach. It was shown that during HCF loading martensite formation is inhomogeneous and not directly linked with crack initiation. Only when the fatigue crack propagates by operating multiple slip systems, the cyclic plastic zone exhibits martensitic transformation. [source]

Crystal Symmetry and the Reversibility of Martensitic Transformations.

CHEMINFORM, Issue 19 2004
Kaushik Bhattacharya
No abstract is available for this article. [source]

Localization Events and Microstructural Evolution in Ultra-Fine Grained NiTi Shape Memory Alloys during Thermo-Mechanical Loading,

ADVANCED ENGINEERING MATERIALS, Issue 6 2010
Andreas Schaefer
Subjecting a thin NiTi specimen to uniaxial tension often leads to a localized martensitic transformation: macroscopic transformation bands form and propagate through the specimen, separating it into regions of fully transformed martensite and original austenite. In the present study, the alternating current potential drop (ACPD) technique is used to analyze the change in electrical resistance of ultra-fine grained NiTi wires subjected to a broad range of thermo-mechanical load cases: (i) uniaxial tensile straining at constant temperatures (pseudoelastic deformation); (ii) cooling and heating through the transformation range at constant load (actuator load case); (iii) a combination of mechanical and thermal loading. We monitor the ACPD signals in several zones along the gauge length of specimens, and we demonstrate that a localized type of transformation is a generic feature of pseudoelastic as well as of shape memory deformation. Moreover, the ACPD signals allow to differentiate between temperature-induced martensite (formed during cooling at no or relatively small loads), stress-induced martensite, and reoriented martensite (formed under load at low temperatures). [source]

In Situ SEM Observation and Analysis of Martensitic Transformation During Short Fatigue Crack Propagation in Metastable Austenitic Steel,

Nanoindentation of a Pseudoelastic NiTiFe Shape Memory Alloy,

ADVANCED ENGINEERING MATERIALS, Issue 1-2 2010
Janine Pfetzing-Micklich
Nanoindentation is a suitable tool for characterizing the local mechanical properties of shape memory alloys (SMA) and to study their pseudoelastic behavior. There is a special interest in indenting with different indenter tips (as not all tips are associated with strain states that predominantly induce the martensitic transformation) and in indenting at different temperatures, where different phases are present. In this study, we perform nanoindentation on a ternary NiTiFe SMA with different indenter tips and at various testing temperatures. For nanoindentation with spherical tips, load,displacement hystereses clearly indicate pseudoelastic behavior, whereas indentation with Berkovich tips results in more pronounced plastic deformation. Testing at different temperatures is associated with different volume fractions of austenite, martensite, and R-phase. The corresponding nanoindentation responses differ considerably in terms of pseudoelastic behavior. Best pseudoelastic recovery is found at testing temperatures close to the R-phase start temperature, even though this temperature is below the austenite finish temperature, which is a well-known lower temperature bound for full recovery in macroscopic tests. Our results are discussed considering micromechanical aspects and the interaction between stress-induced phase transformation and dislocation plasticity. [source]

In situ Investigation of Structural Changes during Deformation and Fracture of Polymers by Synchrotron SAXS and WAXS,

ADVANCED ENGINEERING MATERIALS, Issue 6 2009
Konrad Schneider
By simultaneous mechanical characterisation and synchrotron wide-angle x-ray scattering (WAXS) and small-angle x-ray scattering (SAXS), it is possible to characterise on-line local changes in a polymer's structure with a rather-high time and space resolution, together with the mechanical properties. In this contribution, we discuss the experimental requirements for such investigations as well as three examples. The evolution of structural features during tensile deformation of a polyethylene copolymer, as depicted by WAXS (top) and SAXS (bottom) are shown in the figure. The deformation leads to a martensitic transformation from the orthorhombic to monoclinic system and the formation of nanocavities. [source]

Cruciform fillet welded joint fatigue strength improvements by weld metal phase transformations

FATIGUE & FRACTURE OF ENGINEERING MATERIALS AND STRUCTURES, Issue 2 2008
PH. P. DARCIS
ABSTRACT Arc welding typically generates residual tensile stresses in welded joints, leading to deteriorated fatigue performance of these joints. Volume expansion of the weld metal at high temperatures followed by contraction during cooling induces a local tensile residual stress state. A new type of welding wire capable of inducing a local compressive residual stress state by means of controlled martensitic transformation at relatively low temperatures has been studied, and the effects of the transformation temperature and residual stresses on fatigue strength are discussed. In this study, several LTTW (Low Transformation-Temperature Welding) wires have been developed and investigated to better characterize the effect of phase transformation on residual stress management in welded joints. Non-load-carrying cruciform fillet welded joints were prepared for measurement of residual stresses and fatigue testing. The measurement of the residual stresses of the three designed wires reveals a compressive residual stress near the weld toe. The fatigue properties of the new wires are enhanced compared to a commercially available wire. [source]

Shape Memory Materials: Identification of Quaternary Shape Memory Alloys with Near-Zero Thermal Hysteresis and Unprecedented Functional Stability (Adv. Funct.

ADVANCED FUNCTIONAL MATERIALS, Issue 12 2010
Mater.
On page 1917, R. Zarnetta et al. report that for the reversible martensitic transformation in shape memory alloys the compatibility at the austenite/martensite interface is directly related to the width of the thermal hysteresis and to the functional stability. A "perfect" compatibility results in the growth of twinless martensite (blue) within the austenite (red), as shown in the TEM image for a Ti50Ni39Pd11 shape memory alloy (image provided courtesy of R. Delville). [source]

Identification of Quaternary Shape Memory Alloys with Near-Zero Thermal Hysteresis and Unprecedented Functional Stability

ADVANCED FUNCTIONAL MATERIALS, Issue 12 2010
Robert Zarnetta
Abstract Improving the functional stability of shape memory alloys (SMAs), which undergo a reversible martensitic transformation, is critical for their applications and remains a central research theme driving advances in shape memory technology. By using a thin-film composition-spread technique and high-throughput characterization methods, the lattice parameters of quaternary Ti,Ni,Cu,Pd SMAs and the thermal hysteresis are tailored. Novel alloys with near-zero thermal hysteresis, as predicted by the geometric non-linear theory of martensite, are identified. The thin-film results are successfully transferred to bulk materials and near-zero thermal hysteresis is observed for the phase transformation in bulk alloys using the temperature-dependent alternating current potential drop method. A universal behavior of hysteresis versus the middle eigenvalue of the transformation stretch matrix is observed for different alloy systems. Furthermore, significantly improved functional stability, investigated by thermal cycling using differential scanning calorimetry, is found for the quaternary bulk alloy Ti50.2Ni34.4Cu12.3Pd3.1. [source]

Martensitic Phase Transformation of Isolated HfO2, ZrO2, and HfxZr1,,,xO2 (0,<,x,<,1) Nanocrystals,

ADVANCED FUNCTIONAL MATERIALS, Issue 10 2005
J. Tang
Abstract We previously reported that, during the reactions to make nanocrystals of HfO2 and Hf-rich HfxZr1,,,xO2, a tetragonal-to-monoclinic phase transformation occurs that is accompanied by a shape change of the particles (faceted spherical to nanorods) when the temperature at which the reaction is conducted is changed from 340,to 400,°C. We now conclude that this concomitant phase and shape change is a result of the martensitic transformation of isolated nanocrystals in a hot liquid, where twinning plays a crucial role in accommodating the shape-change-induced strain. That such change was not observed during the reactions forming ZrO2 and Zr-rich HfxZr1,,,xO2 nanocrystals is attributed to the higher driving force needed in those instances compared to that needed for producing HfO2 and Hf-rich HfxZr1,,,xO2 nanocrystals. We also report here the post-synthesis, heat-induced phase transformation of HfxZr1,,,xO2 (0,<,x,<,1) nanocrystals. As temperature increases, all the tetragonal nanocrystals transform to the monoclinic phase accompanied by an increase in particle size (as evidenced by X-ray diffraction and transmission electron microscopy), which confirms that there is a critical size for the phase transformation to occur. When the monoclinic nanorods are heated above a certain temperature the grains grow considerably; under certain conditions a small amount of tetragonal phase appears. [source]

Microstructure of ball milled and compacted Co,Ni,Al alloys from the , range

JOURNAL OF MICROSCOPY, Issue 2 2009
W. MAZIARZ
Summary Two powder alloys from the , phase region of compositions Co28.5Ni36.5Al35 and Co35Ni30Al35 were ball milled for 80 h in a high energy ball mill. The formation of amorphous structure was observed after 40 h of milling and further milling did not change their structure. The analytical and high-resolution transmission electron microscopy (TEM, HREM) examination of powder structure showed that nanoparticles of L10 phase of size of about 5 nm were present within the amorphous matrix. The vacuum hot pressing of the milled powders under pressure of 400 MPa at 700°C for 12 min resulted in the formation of compacts with density of about 70% of the theoretical one. The additional heat treatment at 1300°C for 6 h followed by water quenching, led to significant improvement of density and induced the martensitic transformation manifested by a broad heat effect. The characteristic temperatures of the transformation were determined using DSC measurements, which revealed only small differences within the examined alloys compositions. TEM structure studies of heat-treated alloys allowed to identify the structure of an ordered , (B2) phase and L10 martrensite. [source]

Microstructures of metal grains in ordinary chondrites: Implications for their thermal histories

METEORITICS & PLANETARY SCIENCE, Issue 3 2000
Hugues LEROUX
Three ordinary chondrites, Saint Séverin (LL6), Agen (H5), and Tsarev (L6) were selected because they display contrasting microstructures, which reflects different thermal histories. In Saint Séverin, the microstructure of the Ni-rich metal grains is due to slow cooling. It consists of a two-phase assemblage with a honeycomb structure resulting from spinodal decomposition similar to the cloudy zone of iron meteorites. Microanalyses show that the Ni-rich phase is tetrataenite (Ni = 47 wt%) and the Ni-poor phase, with a composition of ,25% Ni, is either martensite or taenite, these two occurring adjacent to each other. The observation that the Ni-poor phase is partly fcc resolves the disagreement between previous transmission electron microscopy (TEM) and Mössbauer studies on iron meteorites and ordinary chondrite metal. The Ni content of the honeycomb phase is much higher than in mesosiderites, confirming that mesosiderites cooled much more slowly. The high-Ni tetrataenite rim in contact with the cloudy zone displays high-Ni compositional variability on a very fine scale, which suggests that the corresponding area was destabilized and partially decomposed at low temperature. Both Agen and Tsarev display evidence of reheating and subsequent fast cooling obviously related to shock events. Their metallic particles mostly consist of martensite, the microstructure of which depends on local Ni content. Microstructures are controlled by both the temperature at which martensite forms and that at which it possibly decomposes. In high-Ni zones (>15 wt%), martensitic transformation started at low temperature (<300 °C). Because no further recovery occurred, these zones contain a high density of lattice defects. In low-Ni zones (<15 wt%), martensite grains formed at higher temperature and their lattice defects recovered. These martensite grains present a lath texture with numerous tiny precipitates of Ni-rich taenite (Ni = 50 wt%) at lath boundaries. Nickel composition profiles across precipitate-matrix interfaces show that the growth of these precipitates was controlled by preferential diffusion of Ni along lattice defects. The cooling rates deduced from Ni concentration profiles and precipitate sizes are within the range 1,10 °C/year for Tsarev and 10,100 °C/year for Agen. [source]

Internal friction investigation of reverse martensitic transformation in oil-quenched Ni64Al36 alloy

PHYSICA STATUS SOLIDI (A) APPLICATIONS AND MATERIALS SCIENCE, Issue 12 2008
Z. C. Zhou
Abstract Low-frequency internal friction investigation of reverse martensitic transformation in oil-quenched Ni64Al36 alloy has been carried out using a multifunctional internal friction apparatus from room temperature to 400 °C and additionally differential scanning calorimetry and X-ray diffraction experiments were also completed. It has been shown that an internal friction peak presents at about 220 °C in the internal friction,temperature curve during heating for the oil-quenched Ni64Al36 alloy but not for the furnace-cooled Ni64Al36 alloy. The peak still appears during cooling and the peak temperature shifts to lower temperature. The changes of the peak temperature positions cannot be visibly observed when the vibration frequency is changed. The peak heights increase with decreasing vibration frequency and increasing heating rate, being linearly directly proportional to It has been suggested that the internal friction peak results from reverse martensitic transformation of L10 , , during heating and originates from martensitic transformation of , , L10 during the subsequent cooling process. The influence of the thermal cycles on the transformation is not observed for the limited thermal cycles. (© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

ARPGE: a computer program to automatically reconstruct the parent grains from electron backscatter diffraction data

JOURNAL OF APPLIED CRYSTALLOGRAPHY, Issue 6 2007
Cyril Cayron
A computer program called ARPGE written in Python uses the theoretical results generated by the computer program GenOVa to automatically reconstruct the parent grains from electron backscatter diffraction data obtained on phase transition materials with or without residual parent phase. The misorientations between daughter grains are identified with operators, the daughter grains are identified with indexed variants, the orientations of the parent grains are determined, and some statistics on the variants and operators are established. Some examples with martensitic transformations in iron and titanium alloys were treated. Variant selection phenomena were revealed. [source]