The reverse martensitic transformation of TiNi alloy wires prestrained in the parent phase was studied. Experimental results shou, that the reverse transformation of the TiNi allogys prestrained in the parent phase is...The reverse martensitic transformation of TiNi alloy wires prestrained in the parent phase was studied. Experimental results shou, that the reverse transformation of the TiNi allogys prestrained in the parent phase is significantly different from that of the TiNi alloys prestrained in the martensite phase. Three continual peaks appear on the DSC curves of wires with a small prestrain and one high temperature peak appears on the DSC curves of wires with a large prestrain.展开更多
Butt welding of 0.2 mm-thick TiNi shape memory alloy sheet （SMA） was carried out using impulse laser, and tensile strength, fracture morphology, microstructure and phase change behaviour of welded joint were studied...Butt welding of 0.2 mm-thick TiNi shape memory alloy sheet （SMA） was carried out using impulse laser, and tensile strength, fracture morphology, microstructure and phase change behaviour of welded joint were studied. The results show that using impulse laser can realize good butt welding of TiNi SMA sheet, tensile strength of welded joint is 683 MPa, which achieves 97% of that of cold rolled base metal, and the fracture mode of welded joint is ductile type as well as base metal. The welded joint can be divided into four zones according to grain size and microstructure. The microstructures of welded seam center zone are fine equiaxed crystals and the microstructures of both lower surface and upper surface edge zones are columnar crystals. When welded joint is vacuum annealed after welding, the phase transformation process is basically similar to the annealed base metal.展开更多
The effect of pre-strain on phase transformation of TiNi shape memory alloy film was studied by differential scanning calorimeter measurement (DSC). Compared with un-defarmed TiNi film, the reverse transformation of p...The effect of pre-strain on phase transformation of TiNi shape memory alloy film was studied by differential scanning calorimeter measurement (DSC). Compared with un-defarmed TiNi film, the reverse transformation of pre-strained specimens was elevated to a higher temperature on the first heating, but martensite and reverse transformation on subsequent thermal cycles occurred at a lower temperature. The evolution of transformation behavior in pre-strained TiNi film was related to the change of elastic strain energy, irreversible energy and internal stress field.展开更多
Both sputtering conditions and crystallizing temperatures have great influence on the microstructures and phase transformation characteristics for Ti 51 Ni 44Cu 5. By means of the resistance temperature measurement, X...Both sputtering conditions and crystallizing temperatures have great influence on the microstructures and phase transformation characteristics for Ti 51 Ni 44Cu 5. By means of the resistance temperature measurement, X ray diffraction and atomic fore microscopic study, the results indicate that the transformation temperatures of the thin films increase and the "rock candy" martensitic relief is more easily obtained with promoting the sputtering Ar pressure, sputtering power, or crystallizing temperature. However, when sputtering Ar pressure, sputtering power, or crystallizing temperature are lower, a kind of "chrysanthemum" relief, which is related with Ti rich GP zones, is much easier to be observed. The reason is that during crystallization process, both of the inherent compressive stresses introduced under the condition of higher sputtering pressure or higher crystallizing temperature are helpful to the transition from GP zones to Ti 2(NiCu) precipitates and the increase of the transformation temperatures. The addition of copper to substitute for 5% nickel in mole fraction can reduce the transformation hysteresis width to about 10 ～ 15?℃.展开更多
The Pd content dependence of the crystallization process of Ti–Ni–(19.1–35.3)Pd(at.%)thin films fabricated by a sputter-deposition method was investigated.Ti–Ni–(19.1–26.1)Pd(at.%)as-deposited thin films were fo...The Pd content dependence of the crystallization process of Ti–Ni–(19.1–35.3)Pd(at.%)thin films fabricated by a sputter-deposition method was investigated.Ti–Ni–(19.1–26.1)Pd(at.%)as-deposited thin films were found to be amorphous,whereas Ti–Ni–(29.1–35.3)Pd(at.%)thin films were crystalline in the as-deposited condition.Both the crystallization temperature and activation energy for the crystallization of the amorphous thin films decrease with increasing Pd content.The shape memory effect was confirmed in the in situ crystallized thin film.The finer grain size in the in situ crystallized thin film results in a higher critical stress for slip and a smaller recovery strain when compared with the thin film crystallized by post annealing.展开更多
基金Funded by the National Natural Science Foundation of China(No.50071037)
文摘The reverse martensitic transformation of TiNi alloy wires prestrained in the parent phase was studied. Experimental results shou, that the reverse transformation of the TiNi allogys prestrained in the parent phase is significantly different from that of the TiNi alloys prestrained in the martensite phase. Three continual peaks appear on the DSC curves of wires with a small prestrain and one high temperature peak appears on the DSC curves of wires with a large prestrain.
基金Project(200804)supported by State Key Laboratory of Advanced Welding and Joining,Harbin Institute of Technology,China
文摘Butt welding of 0.2 mm-thick TiNi shape memory alloy sheet （SMA） was carried out using impulse laser, and tensile strength, fracture morphology, microstructure and phase change behaviour of welded joint were studied. The results show that using impulse laser can realize good butt welding of TiNi SMA sheet, tensile strength of welded joint is 683 MPa, which achieves 97% of that of cold rolled base metal, and the fracture mode of welded joint is ductile type as well as base metal. The welded joint can be divided into four zones according to grain size and microstructure. The microstructures of welded seam center zone are fine equiaxed crystals and the microstructures of both lower surface and upper surface edge zones are columnar crystals. When welded joint is vacuum annealed after welding, the phase transformation process is basically similar to the annealed base metal.
文摘The effect of pre-strain on phase transformation of TiNi shape memory alloy film was studied by differential scanning calorimeter measurement (DSC). Compared with un-defarmed TiNi film, the reverse transformation of pre-strained specimens was elevated to a higher temperature on the first heating, but martensite and reverse transformation on subsequent thermal cycles occurred at a lower temperature. The evolution of transformation behavior in pre-strained TiNi film was related to the change of elastic strain energy, irreversible energy and internal stress field.
文摘Both sputtering conditions and crystallizing temperatures have great influence on the microstructures and phase transformation characteristics for Ti 51 Ni 44Cu 5. By means of the resistance temperature measurement, X ray diffraction and atomic fore microscopic study, the results indicate that the transformation temperatures of the thin films increase and the "rock candy" martensitic relief is more easily obtained with promoting the sputtering Ar pressure, sputtering power, or crystallizing temperature. However, when sputtering Ar pressure, sputtering power, or crystallizing temperature are lower, a kind of "chrysanthemum" relief, which is related with Ti rich GP zones, is much easier to be observed. The reason is that during crystallization process, both of the inherent compressive stresses introduced under the condition of higher sputtering pressure or higher crystallizing temperature are helpful to the transition from GP zones to Ti 2(NiCu) precipitates and the increase of the transformation temperatures. The addition of copper to substitute for 5% nickel in mole fraction can reduce the transformation hysteresis width to about 10 ～ 15?℃.
基金supported by the Grants-in-Aid for Fundamental Science Research(Wakate B(2006-2007)Kiban C(2008-2010))from the Ministry of Education,Culture,Sports,Science and Technology,Japansupported by WCU(World Class University)program through the National Research Foundation of Korea funded by the Ministry of Education,Science and Technology(grant number:R32-2008-000-20093-0).
文摘The Pd content dependence of the crystallization process of Ti–Ni–(19.1–35.3)Pd(at.%)thin films fabricated by a sputter-deposition method was investigated.Ti–Ni–(19.1–26.1)Pd(at.%)as-deposited thin films were found to be amorphous,whereas Ti–Ni–(29.1–35.3)Pd(at.%)thin films were crystalline in the as-deposited condition.Both the crystallization temperature and activation energy for the crystallization of the amorphous thin films decrease with increasing Pd content.The shape memory effect was confirmed in the in situ crystallized thin film.The finer grain size in the in situ crystallized thin film results in a higher critical stress for slip and a smaller recovery strain when compared with the thin film crystallized by post annealing.
