Measurements of electrical resistivity, X-ray diffraction, and tensile test at room temperature and ？196°C were performed to investigate the effects of Al addition substituting Ni on the phase transformation beh...Measurements of electrical resistivity, X-ray diffraction, and tensile test at room temperature and ？196°C were performed to investigate the effects of Al addition substituting Ni on the phase transformation behaviors, the mechanical properties, and the shape memory effects of Ti50Ni47Fe2Al1 and Ti50Ni46.5Fe2.5Al1 alloys. It is found that 1at% Al addition dramatically decreases the martensitic start transformation temperature and expands the transformation temperature range of R-phase for TiNiFeAl alloys. The results of tensile test indicate that 1at% Al improves the yield strength of Ti50Ni47Fe2Al1 and Ti50Ni46.5Fe2.5Al1 alloys by 40% and 64%, but de- creases the plasticity to 11% and 12% from 26% and 27% respectively. Moreover, excellent shape memory effect of 6.6% and 7.5% were found in Ti50Ni47Fe2Al1 and Ti50Ni46.5Fe2.5Al1 alloys, which results from the stress-induced martensite transformation from the R-phase.展开更多
Mechanical and shape memory properties of a Ti50Ni47Fe3 alloy annealed at 450-750 °C for 1 h after a cold-rolled reduction of 25% were investigated by phase transformation analysis and microstructure characteriza...Mechanical and shape memory properties of a Ti50Ni47Fe3 alloy annealed at 450-750 °C for 1 h after a cold-rolled reduction of 25% were investigated by phase transformation analysis and microstructure characterization using tensile tests, Vickers hardness tests, electrical resistivity-temperature tests, SEM and TEM. From the results of the tensile, it can be inferred that the fracture stress and yield stress decreased and the fracture elongation increased as the annealing temperature increased for the rolled Ti50Ni47Fe3 alloy. They reached stead values when the temperature was above 650 °C. The change in Vickers hardness corresponded to the change in the fracture stress and yield stress. The electrical resistivity-temperature curves suggest that a two- stage martensitic transformation（B2-R-B19′） occurred during cooling and heating. The transformation temperatures decreased to lower temperatures when the annealing temperature was increased and maintained the same after the annealing temperature reached 650 °C. TEM revealed the distinct processes occurring at elevated temperatures： recovery, polygonization, and recrystallization.展开更多
In this work, transformation behaviors and mechanical properties of cold-rolled shape memory alloy TisoNia9Fel by severe plastic deformation （SPD） were intensively investigated. The phase transformation behaviors, p...In this work, transformation behaviors and mechanical properties of cold-rolled shape memory alloy TisoNia9Fel by severe plastic deformation （SPD） were intensively investigated. The phase transformation behaviors, phase analysis, and microstructures were characterized by differential scanning calorimetry （DSC）, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）, respectively. Tensile testing was performed to analyze the effect of SPD on the mechanical properties and shape memory of TisoNi49Fel alloy. When the thickness reduction is beyond 30 %, the martensitic transformation is suppressed. After cold-rolling, the alloy is mainly com- posed of B2 parent phases with some stress-induced martensitic B 19t phases, and high density of dislocations are generated and the grains are obviously refined. The yield stress ab significantly raises from 618 MPa of 0 % cold rolling to 1,338 MPa of 50 % SPD. Shape-memory effect increases from 6.5 % without cold rolling to 8.5 % after 30 % SPD, ascribed to the induced defects in cold rolling. Those results indicate that TisoNi49Fel alloy has improved mechanical properties and potential commercial applications after SPD.展开更多
This study investigated a peculiar phenomenon of self-reorientation of thermally formed R phase in nanocrystalline Ti_(50)Ni_(45.5)Fe_(4.5)by means of in-situ syn-chrotron high energy X-ray diffraction(HE-XRD).Two sam...This study investigated a peculiar phenomenon of self-reorientation of thermally formed R phase in nanocrystalline Ti_(50)Ni_(45.5)Fe_(4.5)by means of in-situ syn-chrotron high energy X-ray diffraction(HE-XRD).Two samples with different average grain sizes of 40 and 90 nm were investigated.R phase in the 40-nm grain size sample was found to self-reorient gradually upon cooling,whereas the same phenomenon did not occur in the 90-nm grain size sample.This self-reorientation process is attributed to the development and evolution of an internal stress anisotropy caused by the second order continuous lattice distortion of R phase upon further cooling in the small nanograined matrix,which lacks the self-accommodation mechanism for internal stress cancellation.展开更多
文摘Measurements of electrical resistivity, X-ray diffraction, and tensile test at room temperature and ？196°C were performed to investigate the effects of Al addition substituting Ni on the phase transformation behaviors, the mechanical properties, and the shape memory effects of Ti50Ni47Fe2Al1 and Ti50Ni46.5Fe2.5Al1 alloys. It is found that 1at% Al addition dramatically decreases the martensitic start transformation temperature and expands the transformation temperature range of R-phase for TiNiFeAl alloys. The results of tensile test indicate that 1at% Al improves the yield strength of Ti50Ni47Fe2Al1 and Ti50Ni46.5Fe2.5Al1 alloys by 40% and 64%, but de- creases the plasticity to 11% and 12% from 26% and 27% respectively. Moreover, excellent shape memory effect of 6.6% and 7.5% were found in Ti50Ni47Fe2Al1 and Ti50Ni46.5Fe2.5Al1 alloys, which results from the stress-induced martensite transformation from the R-phase.
基金Project(51201014)supported by the National Natural Science Foundation of China
文摘Mechanical and shape memory properties of a Ti50Ni47Fe3 alloy annealed at 450-750 °C for 1 h after a cold-rolled reduction of 25% were investigated by phase transformation analysis and microstructure characterization using tensile tests, Vickers hardness tests, electrical resistivity-temperature tests, SEM and TEM. From the results of the tensile, it can be inferred that the fracture stress and yield stress decreased and the fracture elongation increased as the annealing temperature increased for the rolled Ti50Ni47Fe3 alloy. They reached stead values when the temperature was above 650 °C. The change in Vickers hardness corresponded to the change in the fracture stress and yield stress. The electrical resistivity-temperature curves suggest that a two- stage martensitic transformation（B2-R-B19′） occurred during cooling and heating. The transformation temperatures decreased to lower temperatures when the annealing temperature was increased and maintained the same after the annealing temperature reached 650 °C. TEM revealed the distinct processes occurring at elevated temperatures： recovery, polygonization, and recrystallization.
基金supported by the National Natural Science Foundation of China (No. 50921003)the Industry, Education and Research Projects of the China Aviation Industrial (No. cxy2012BH04)
文摘In this work, transformation behaviors and mechanical properties of cold-rolled shape memory alloy TisoNia9Fel by severe plastic deformation （SPD） were intensively investigated. The phase transformation behaviors, phase analysis, and microstructures were characterized by differential scanning calorimetry （DSC）, X-ray diffraction （XRD）, and transmission electron microscopy （TEM）, respectively. Tensile testing was performed to analyze the effect of SPD on the mechanical properties and shape memory of TisoNi49Fel alloy. When the thickness reduction is beyond 30 %, the martensitic transformation is suppressed. After cold-rolling, the alloy is mainly com- posed of B2 parent phases with some stress-induced martensitic B 19t phases, and high density of dislocations are generated and the grains are obviously refined. The yield stress ab significantly raises from 618 MPa of 0 % cold rolling to 1,338 MPa of 50 % SPD. Shape-memory effect increases from 6.5 % without cold rolling to 8.5 % after 30 % SPD, ascribed to the induced defects in cold rolling. Those results indicate that TisoNi49Fel alloy has improved mechanical properties and potential commercial applications after SPD.
基金financially supported by the National Natural Science Foundation of China (Nos.51731010, 51831006,51871241,51971243 and 91963112)Australian Research Council (No.DP190102990)
文摘This study investigated a peculiar phenomenon of self-reorientation of thermally formed R phase in nanocrystalline Ti_(50)Ni_(45.5)Fe_(4.5)by means of in-situ syn-chrotron high energy X-ray diffraction(HE-XRD).Two samples with different average grain sizes of 40 and 90 nm were investigated.R phase in the 40-nm grain size sample was found to self-reorient gradually upon cooling,whereas the same phenomenon did not occur in the 90-nm grain size sample.This self-reorientation process is attributed to the development and evolution of an internal stress anisotropy caused by the second order continuous lattice distortion of R phase upon further cooling in the small nanograined matrix,which lacks the self-accommodation mechanism for internal stress cancellation.
