scholarly journals Структурные аспекты деформационной аморфизации кристаллического сплава Ti-=SUB=-50-=/SUB=-Ni-=SUB=-25-=/SUB=-Cu-=SUB=-25-=/SUB=- при кручении под высоким давлением

2018 ◽  
Vol 60 (6) ◽  
pp. 1157
Author(s):  
Р.В. Сундеев ◽  
А.В. Шалимова ◽  
А.М. Глезер ◽  
Е.А. Печина ◽  
М.В. Горшенков
Keyword(s):  
Grain Boundary ◽  
Crystalline Phase ◽  
Crystalline State ◽  
Room Temperature ◽  
High Pressure Torsion ◽  
Amorphous State ◽  
Nanocrystalline Phase ◽  
Torsional Moment ◽  
Variation Curve

AbstractThe evolution of the structure of the Ti50Ni25Cu25 crystalline alloy during high-pressure torsion at room temperature has been studied. The torsional moment variation curve as a function of the strain value was fixed in situ, which allowed directly observing the transition of the material from the crystalline state to the amorphous state during the HPT. It was found that the amorphization of the material in the course of the HPT begins on the grain boundaries and fragments of the crystalline phase. Amorphized boundaries form a “grain-boundary carcass” in the cells of which the high-defect nanocrystalline phase is formed. Growth of deformation leads to broadening of the “grain-boundary carcass,” loss of stability of the crystalline phase, and, as a consequence, to the phase transition “crystal → amorphous” state.

An investigation into the temperature phase transitions of synthesized lithium titanate materials doped with Al, Co, Ni and Mg by in situ powder X-ray diffraction

2020 ◽  
Vol 35 (4) ◽  
pp. 233-246
Author(s):  
X. van Niekerk ◽  
E. E. Ferg ◽  
C. Gelant ◽  
D. G. Billing
Keyword(s):  
Phase Transitions ◽  
Crystalline Phase ◽  
Room Temperature ◽  
Spinel Phase ◽  
Sol Gel ◽  
Amorphous State ◽  
Amorphous Structure ◽  
Temperature Phase ◽  
Prolonged Heating

Li4Ti5O12 (LTO) and its doped analogues Li4Ti4.95M0.05O12 (M = Al3+, Co3+, Ni2+, and Mg2+) were synthesized and characterized using in situ PXRD to monitor the phase transitions during the sol–gel synthesis of the spinel material. These results are complimented by thermogravimetric analysis, which illustrates the decomposition of the materials synthesized, where the final LTO products are seen to form at approximately 550 °C. The material has an amorphous structure from room temperature, coupled with a crystalline phase which is speculated to be H2Ti2O5·H2O. This crystalline phase disappears at 250 °C, with the material still in the amorphous state. The crystalline LTO phase starts at approximately 550 °C, with anatase co-crystallizing with the spinel phase. Rutile appears at 600 °C and co-crystallizes with the final product at 850 °C, where anatase is no longer seen. The rutile impurity remains present after cooling the material to room temperature, and results indicate that prolonged heating at 850 °C is required to reduce the rutile content. Rietveld refinement of diffraction patterns show that the unit-cell parameter increases with increasing temperature, coupled with a decrease when cooling the sample. The crystallite sizes follow the same trend, with a significant increase above temperatures of 750 °C.

scholarly journals In Situ Atomic-Scale Observation of Dislocation Climb and Grain Boundary Transformation in Nanostructured Metal

2021 ◽  
Author(s):  
Shufen Chu ◽  
Pan Liu ◽  
Yin Zhang ◽  
Xiaodong Wang ◽  
Shuangxi Song ◽  
...  
Keyword(s):  
Monte Carlo ◽  
Grain Boundary ◽  
Room Temperature ◽  
Atomic Plane ◽  
Dislocation Core ◽  
Dislocation Climb ◽  
Atomic Scale ◽  
Atomic Column ◽  
Nanostructured Metal

Abstract We report atomic-scale observations of grain boundary (GB) dislocation climb in nanostructured Au during in situ straining at room temperature. Climb of a dislocation occurs by stress-induced reconstruction of two atomic columns at the edge of an extra half atomic plane in the dislocation core. Different from the conventional belief of dislocation climb by destruction or construction of a single atomic column at the dislocation core, the new atomic route is demonstrated to be energetically favorable by Monte Carlo simulations. Our in situ observations also reveal GB transformation through dislocation climb, which suggests a means of controlling microstructures and properties of nanostructured metals.

Deformation-Induced Nanocrystallization in Al-Rich Metallic Glasses

2006 ◽  
Vol 114 ◽  
pp. 123-132 ◽  
Author(s):  
Nancy Boucharat ◽  
Rainer J. Hebert ◽  
Harald Rösner ◽  
Gerhard Wilde
Keyword(s):  
Metallic Glasses ◽  
Room Temperature ◽  
High Pressure Torsion ◽  
In Situ Tem ◽  
Number Density ◽  
High Number Density ◽  
Glass Forming ◽  
Processing Strategies ◽  
Improved Performance

Deformation-induced nanocrystallization has been investigated in a marginally Al88Y7Fe5 glass forming alloy. Conventional calorimetry and microstructural analyses of materials that have been subjected to high pressure torsion straining (HPT) at room temperature indicate the development of an extremely high number density of small Al nanocrystals. The nanocrystals appear to be distributed homogeneously throughout the sample without any evidence of strong coarsening. Moreover, the comparison between nanocrystallization caused by the application of either HPT, cold-rolling or in-situ TEM tensile straining yielded the identification of the probable mechanisms underlying the formation of nanocrystals. These results form the basis for the development of advanced processing strategies for producing new nanostructures with high nanocrystal number densities which allow increased stability and improved performance.

Texture Evolution of Magnesium Single Crystals Deformed by High-Pressure Torsion

2008 ◽  
Vol 584-586 ◽  
pp. 263-268 ◽  
Author(s):  
Bartlomiej J. Bonarski ◽  
Erhard Schafler ◽  
Borys Mikułowski ◽  
Michael Zehetbauer
Keyword(s):  
High Pressure ◽  
Single Crystals ◽  
Room Temperature ◽  
High Pressure Torsion ◽  
Texture Evolution ◽  
In Situ Stress ◽  
Higher Symmetry ◽  
Strain Measurements ◽  
X Ray

Single crystals of technical purity Magnesium (99.8 wt.%) of initial orientations [ ] 2 1 10 and [ ] 2 2 11 were subjected to HPT deformation at room temperature up to strains of 10. The microstructural evolution has been analyzed by X-ray microtexture investigations and by in-situ stress-strain measurements. The results can be described in terms of shear arising from HPT deformation and - with higher strains - in terms of recrystallization. In crystals with hard orientation[ ] 2 2 11 , these features occur at smaller strains than in crystals with soft orientation [ ] 2 1 10 , i.e. with higher symmetry. In general, the observed textures and strength variations are much stronger than those reported for fcc HPT deformed metals.

scholarly journals Атомное разупорядочение и ОЦК -> ГЦК превращение в сплаве Гейслера Ni-=SUB=-54-=/SUB=-Mn-=SUB=-20-=/SUB=-Fe-=SUB=-1-=/SUB=-Ga-=SUB=-25-=/SUB=-, подвергнутом мегапластической деформации кручением под высоким давлением

2020 ◽  
Vol 90 (4) ◽  
pp. 627
Author(s):  
В.Г. Пушин ◽  
Н.Н. Куранова ◽  
Е.Б. Марченкова ◽  
А.В. Пушин
Keyword(s):  
Martensitic Transformation ◽  
High Pressure Torsion ◽  
Structural Phase ◽  
Amorphous State ◽  
Recrystallization Annealing ◽  
X Ray Diffraction ◽  
Thermoelastic Martensitic Transformation ◽  
Degree Of Deformation ◽  
Megaplastic Deformation

Heusler L21 alloy Ni54Mn20Fe1Ga25 subjected to megaplastic deformation by high pressure torsion was first systematically investigated by in situ phase x-ray diffraction, transmission and scanning electron microscopy. It is established that shear deformation by torsion at room temperature grinds the polycrystalline structure of the alloy to a nanocrystalline and partially amorphous state. It is found that as the pressure value (from 3 to 5 GPa) and the degree of deformation (from 2 to 5 revolutions) increases, total atomic disordering and stepwise structural-phase transformation according to the scheme B2(BCC)→A2(BCC)→A1(FCC) occur. It is shown that annealing at temperatures below 570 K entails devitrification of the amorphous phase, and at 620 K and above – the restoration of the L21 structure. The dimensional effect of suppressing thermoelastic martensitic transformation in a nanostructured austenitic L21 alloy with a grain size less than 80 nm while its cooling down to 120 K. The ability to thermoelastic martensitic transformation and shape memory effect in submicrocrystalline ultrafine alloy after recrystallization annealing at temperatures exceeding 600 K is restored.

Overview of the Grain Size Effects on the Mechanical and Deformation Behaviour of Electrodeposited Nanocrystalline Nickel − From Nanoindentation to High Pressure Torsion

2009 ◽  
Vol 633-634 ◽  
pp. 85-98 ◽  
Author(s):  
B. Yang ◽  
Horst Vehoff ◽  
Reinhard Pippan
Keyword(s):  
Grain Size ◽  
High Pressure ◽  
Grain Boundary ◽  
Strain Rate ◽  
High Pressure Torsion ◽  
Deformation Mechanisms ◽  
Nanocrystalline Nickel ◽  
Deformation Processes ◽  
Rate Controlled

A summary of experimental results from nanoindentation, strain rate-controlled tension, in-situ bending and high pressure torsion on bulk electrodeposited nanocrystalline nickel, focusing on the effects of grain size on the mechanical behaviour and deformation mechanisms is presented. The interaction between dislocations and grain boundaries was locally examined by studying the dependence of nanohardness on grain size and indentation size; this is done by always performing nanoindents in the center of individual grains and by varying the grain size and indentation depth systematically. The grain size effects on the different deformation mechanisms of nanocrystalline nickel were revealed by strain rate-controlled tension and nanoindentation experiments, which show that with decreasing grain size the strain rate sensitivity increases and the activation volume decreases, indicating increased grain boundary mediated deformation processes in nanocrystalline nickel. Creep experiments at room temperature revealed that in nanocrystalline nickel grain boundary sliding or diffusion along the interface may dominate at lower stress levels, but with increasing stresses the deformation process is mainly controlled by dislocation creep. In-situ bending experiments in an atomic force microscope revealed directly that grain boundary mediated deformation processes play a significant role in nanocrystalline nickel, which is also supported by the observation of grain coarsening and softening of nanocrystalline nickel caused by high pressure torsion.

In situ observation of the “crystalline⇒amorphous state” phase transformation in Ti 2 NiCu upon high-pressure torsion

2017 ◽  
Vol 679 ◽  
pp. 1-6 ◽  
Author(s):  
R.V. Sundeev ◽  
A.V. Shalimova ◽  
A.M. Glezer ◽  
E.A. Pechina ◽  
M.V. Gorshenkov ◽  
...  
Keyword(s):  
High Pressure ◽  
Phase Transformation ◽  
High Pressure Torsion ◽  
Amorphous State ◽  
In Situ Observation

Systematic Study of Polycrystalline Flow during In Situ Tension Test by SEM of Pb-50%Sn at Room Temperature

2014 ◽  
Vol 793 ◽  
pp. 113-118 ◽  
Author(s):  
A.J. López-Ramírez ◽  
Juan Daniel Muñoz-Andrade ◽  
E. Garfias-García ◽  
M. Aguilar-Sánchez
Keyword(s):  
Activation Energy ◽  
Grain Boundary ◽  
Deformation Process ◽  
Room Temperature ◽  
Grain Boundary Sliding ◽  
Tension Test ◽  
Irreversible Deformation ◽  
Chatelier Effect ◽  
Boundary Sliding

Microstructural evolution during in situ tension test at constant crosshead velocity of 0.38 mm/min, at room temperature of polycrystalline Pb-50%Sn alloy are reported. Direct observation during four steps of deformation, with a total deformation (εT) of 0.684, allows establish that the trajectories of grains during irreversible deformation process obey a sigmoidal motion. Such behaviour is related with dynamic recrystallization phenomenology and associated with grain boundary sliding between neighbouring grains and subsequent cavitation in order to allow emerging grains from the inner volume to free surface of Pb-50%Sn, as the main mechanisms of superplastic flow. The curve of true stress versus true deformation presented several fluctuations during irreversible deformation process in a similar way of the Portevin Le Chatelier effect. Also is observed in the early steps of plastic flow, hardening deformation, up to 27 MPa associated with the maximum stress. The activation energy values for polycrystalline flow, calculated in this work are between 67.5 to 68.07 kJ/mol and there are in a closed agreement with the activation energy of 65.7 kJ/mol, for grain boundary diffusion.

In situ studies on grain boundary migration in ceria-stabilized TZP

1990 ◽  
Vol 48 (4) ◽  
pp. 192-193
Author(s):  
Herbert K Schmid
Keyword(s):  
Grain Boundary ◽  
Grain Boundaries ◽  
Room Temperature ◽  
Boundary Migration ◽  
Tetragonal Zirconia ◽  
In Situ Tem ◽  
Grain Boundary Migration ◽  
Thin Foils ◽  
Prepared State

Tetragonal zirconia polycrystals (TZP) have become of interest due to their exceptionally good combination of mechanical properties. In a previous study the microstructure/microchemistry of grain boundaries (GBs) in CeO2 stabilized ZrO2 (Ce-TZP) was investigated and evidence was found on the existence of vitreous ana crystalline intergranular phases in these ceramics. Recently, the observation of wavy GBs in ceria-zirconia was reported. This phenomenon was attributed to diffusion-induced grain boundary migration (DIGM). In the present work, the in-situ TEM observation of GB migration in Ce-TZP, nominally at room temperature, is reported.Thin foils for TEM observations were prepared from a Ce-TZP ceramic nominally composed of 90 mol% ZrO2 plus 10 mol% CeO2 and were examined in a Philips EM 420 analytical STEM, operated at 120 kV. Grain boundaries were observed to migrate in specimen areas exposed to extensive electron irradiation during TEM experiments. The micrograph in Fig. 1 shows a BF image of a triple grain junction (TJ) area in the as-prepared state.

scholarly journals Microstructural Changes Influencing the Magnetoresistive Behavior of Bulk Nanocrystalline Materials

2020 ◽  
Vol 10 (15) ◽  
pp. 5094
Author(s):  
Stefan Wurster ◽  
Martin Stückler ◽  
Lukas Weissitsch ◽  
Timo Müller ◽  
Andrea Bachmaier
Keyword(s):  
Nanocrystalline Materials ◽  
Giant Magnetoresistance ◽  
Room Temperature ◽  
Annealing Temperature ◽  
High Pressure Torsion ◽  
Ex Situ ◽  
Thermal Treatments ◽  
Synchrotron Diffraction ◽  
Bulk Nanocrystalline

Bulk nanocrystalline materials of small and medium ferromagnetic content were produced using severe plastic deformation by high-pressure torsion at room temperature. Giant magnetoresistive behavior was found for as-deformed materials, which was further improved by adjusting the microstructure with thermal treatments. The adequate range of annealing temperatures was assessed with in-situ synchrotron diffraction measurements. Thermally treated Cu–Co materials show larger giant magnetoresistance after annealing for 1 h at 300 °C, while for Cu-Fe this annealing temperature is too high and decreases the magnetoresistive properties. The improvement of magnetoresistivity by thermal treatments is discussed with respect to the microstructural evolution as observed by electron microscopy and ex-situ synchrotron diffraction measurements.

Sign in / Sign up

Export Citation Format

Share Document