Abstract:TiNi-TiCu quasibinary system alloys with a high Cu content produced by rapid quenching from liquid state in the form of thin amorphous ribbons exhibit pronounced shape memory effect after crystallization and are promising materials for miniaturized and fast operating devices. There is currently no complete clarity of the mechanisms of structure formation during crystallization from the amorphous state that determine the structure-sensitive properties of these alloys. This work deals with the effect of the init… Show more
“…Treatment in the amorphous state does not change the structure of the specimens to a visible extent within the resolution of SEM. As shown earlier [15,28], the electropulse treatment of amorphous ribbons dramatically changes the crystallization pattern in comparison with isothermal annealing (Figure 9). Cross-sectional SEM images of electropulse-crystallized 25 at.% Cu alloy ribbons show a bimorphic structure: columnar crystals form near the ribbon surface, whereas discrete or clustered large grains with a typical size of 3 to 12 µm and a subgrain structure form in the ribbon bulk (Figure 9a-c).…”
Section: Cross-sectional Microstructure Of Rapidly Quenched Ribbonssupporting
confidence: 71%
“…Investigations of the fine structure of the alloy were carried out on a JEOL JEM 2100 (JEOL Ltd., Tokyo, Japan) transmission electron microscope (TEM). The specimens for the TEM study were prepared with the focused ion beam (FIB) technique by means of an FEI Strata 201 FIB setup (Thermo Fisher Scientific Inc., Hillsboro, OR, USA) equipped with an Omniprobe ® (Oxford Instruments plc, High Wycombe, UK) nanomanipulator [15]. The XRD analysis was performed using a PANalytical Empyrean diffractometer (Malvern Panalytical plc, Malvern, UK) in Cu-K α radiation at an angle range of 20-90 • at a step of 0.1 • with exposure time 5 s both at room temperature and at 90 • C.…”
Section: Methodsmentioning
confidence: 99%
“…Their properties largely depend on the structure of the initial amorphous material. We have recently shown [15] that the thermal and deformation treatment of rapidly quenched high-copper TiNi-TiCu system alloys in the amorphous state has a major effect on the structure formation and phase transformations in the alloys, e.g., on the shape and size of grains, the number of defects in the subgrain structure, and the critical temperatures of the martensitic transformation. In this study, the amorphous alloys were subjected to additional heat treatment using the so-called rejuvenation procedure, which involves the structural excitation of amorphous materials and leads to an increase in the enthalpy and free volume, i.e., triggering a reverse aging process [16][17][18].…”
Alloys of the quasibinary TiNi-TiCu system manufactured by melt quenching in the form of thin 20–50 μm ribbons have proven to show good potential as materials for the fabrication of micromechanical devices. At high cooling rates (about 106 K/s), this method allows producing high-copper (more than 20 at.%) amorphous alloys which exhibit an excellent shape-memory effect after crystallization. Their properties are known to largely depend on the crystallization conditions and the structure of the initial amorphous material acting as a precursor for the formation of crystal phases. It has been shown recently that the rejuvenation procedure (cryogenic thermocycling) of metallic glasses is one of the most promising methods of improving their properties. In this study, we investigated for the first time the effect of cryogenic thermocycling of rapidly quenched amorphous TiNiCu on the initial state, as well as on structure formation and the phase transformation patternsof subsequent crystallization conducted using various methods. The effect was analyzed utilizing the methods of scanning and transmission electron microscopy, X-ray diffraction analysis, and differential scanning calorimetry. The results show that rejuvenation treatment slightly reduces the glass transition and crystallization onset temperatures and moderately changes the sizes of structural features (grains, martensite plates), the quantity of the martensite phase, and the characteristic temperatures and enthalpy of the martensitic transformation.
“…Treatment in the amorphous state does not change the structure of the specimens to a visible extent within the resolution of SEM. As shown earlier [15,28], the electropulse treatment of amorphous ribbons dramatically changes the crystallization pattern in comparison with isothermal annealing (Figure 9). Cross-sectional SEM images of electropulse-crystallized 25 at.% Cu alloy ribbons show a bimorphic structure: columnar crystals form near the ribbon surface, whereas discrete or clustered large grains with a typical size of 3 to 12 µm and a subgrain structure form in the ribbon bulk (Figure 9a-c).…”
Section: Cross-sectional Microstructure Of Rapidly Quenched Ribbonssupporting
confidence: 71%
“…Investigations of the fine structure of the alloy were carried out on a JEOL JEM 2100 (JEOL Ltd., Tokyo, Japan) transmission electron microscope (TEM). The specimens for the TEM study were prepared with the focused ion beam (FIB) technique by means of an FEI Strata 201 FIB setup (Thermo Fisher Scientific Inc., Hillsboro, OR, USA) equipped with an Omniprobe ® (Oxford Instruments plc, High Wycombe, UK) nanomanipulator [15]. The XRD analysis was performed using a PANalytical Empyrean diffractometer (Malvern Panalytical plc, Malvern, UK) in Cu-K α radiation at an angle range of 20-90 • at a step of 0.1 • with exposure time 5 s both at room temperature and at 90 • C.…”
Section: Methodsmentioning
confidence: 99%
“…Their properties largely depend on the structure of the initial amorphous material. We have recently shown [15] that the thermal and deformation treatment of rapidly quenched high-copper TiNi-TiCu system alloys in the amorphous state has a major effect on the structure formation and phase transformations in the alloys, e.g., on the shape and size of grains, the number of defects in the subgrain structure, and the critical temperatures of the martensitic transformation. In this study, the amorphous alloys were subjected to additional heat treatment using the so-called rejuvenation procedure, which involves the structural excitation of amorphous materials and leads to an increase in the enthalpy and free volume, i.e., triggering a reverse aging process [16][17][18].…”
Alloys of the quasibinary TiNi-TiCu system manufactured by melt quenching in the form of thin 20–50 μm ribbons have proven to show good potential as materials for the fabrication of micromechanical devices. At high cooling rates (about 106 K/s), this method allows producing high-copper (more than 20 at.%) amorphous alloys which exhibit an excellent shape-memory effect after crystallization. Their properties are known to largely depend on the crystallization conditions and the structure of the initial amorphous material acting as a precursor for the formation of crystal phases. It has been shown recently that the rejuvenation procedure (cryogenic thermocycling) of metallic glasses is one of the most promising methods of improving their properties. In this study, we investigated for the first time the effect of cryogenic thermocycling of rapidly quenched amorphous TiNiCu on the initial state, as well as on structure formation and the phase transformation patternsof subsequent crystallization conducted using various methods. The effect was analyzed utilizing the methods of scanning and transmission electron microscopy, X-ray diffraction analysis, and differential scanning calorimetry. The results show that rejuvenation treatment slightly reduces the glass transition and crystallization onset temperatures and moderately changes the sizes of structural features (grains, martensite plates), the quantity of the martensite phase, and the characteristic temperatures and enthalpy of the martensitic transformation.
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