共查询到20条相似文献,搜索用时 31 毫秒
1.
Xueling Fei Corey J. O’Connell D. S. Grummon Yang-Tse Cheng 《Journal of Materials Science》2011,46(23):7401-7409
Indentation-induced two-way shape memory leads to pronounced temperature dependence of the depth of spherical indents made
in martensitic NiTi shape-memory alloys. They are shallower when austenitic, and depth varies during both M → A and A → M
transformations. If the impression is planarized, by metallographic grinding at T < M
f
, a protrusion rises at the site when warmed past A
f
. If cooled again this “exdent” retreats, restoring optical flatness. The cycle is repeatable, and exdent heights can exceed
15% of prior indent depth. Since it maps between macroscopically distinguishable topographies, or forms, at orders greater
length scale than the surface roughness, we call the effect “surface form memory”—SFM. Notable regarding potential applications
is that, when loaded in compression by planar contact with a strong base metal, exdents exert sufficient pressure to indent
the latter, suggesting that subsurface transformational mechanisms operate at volumetric work-energy densities >107 J/m3, fully ~10% of the M → A enthalpy. 相似文献
2.
ABSTRACTThe two-way shape memory effect in NiTi shape memory alloys is identified according to the evolution of the apparent modulus of the martensite during mechanical cycling. The microstrain and texture index of the NiTi samples are evaluated with synchrotron data to relate the evolution to the changes in the NiTi microstructure caused by mechanical cycling. The results show that a progressive decrease in the apparent modulus of the martensite during load, together with an increase in the apparent modulus of the reoriented martensite, are a sign that the NiTi sample is developing the two-way memory effect by mechanical cycling. When the two moduli show the same value, the two-way shape memory effect is fully developed in the NiTi alloy.This paper is part of a thematic issue on Titanium. 相似文献
3.
Metal injection molding (MIM) was applied for the production of shape memory parts using prealloyed NiTi powders with different Ni contents as starting materials. The MIM process allows the production of near-net-shape components without the occurrence of rapid tool wear as found in the case of conventional machining operations. With optimized manufacturing conditions, including feedstock preparation, injection parameters and sintering conditions, densities of more than 98% of the theoretical value could be achieved. Determination of the phase transformation behavior, as a basic requirement for the shape memory effect, was done by differential scanning calorimetry (DSC). In a first approach, tensile tests in the austenitic state showed pseudoelastic behavior. An elongation at failure of 3.8% was found. For martensite, up to 5% was obtained. Reasons for the lower strain compared to melted NiTi alloys are discussed. For martensitic samples the one-way shape memory effect (1WE) was demonstrated. 相似文献
4.
J. L. Xu Z. C. Zhong D. Z. Yu F. Liu J. M. Luo 《Journal of materials science. Materials in medicine》2012,23(12):2839-2846
In this paper, the effects of micro-arc oxidation (MAO) surface modification (alumina coatings) on the phase transformation behavior, shape memory characteristics, in vitro haemocopatibility and cytocompatibility of the biomedical NiTi alloy were investigated respectively by differential scanning calorimetry, bending test, hemolysis ratio test, dynamic blood clotting test, platelet adhesion test and cytotoxicity testing by human osteoblasts (Hobs). The results showed that there were no obvious changes of the phase transformation temperatures and shape memory characteristics of the NiTi alloy after the MAO surface modification and the coating could withstand the thermal shock and volume change caused by martensite-austenite phase transformation. Compared to the uncoated NiTi alloys, the MAO surface modification could effectively improve the haemocopatibility of the coated NiTi alloys by the reduced hemolysis ratio, the prolonged dynamic clotting time and the decreased number of platelet adhesion; and the rough and porous alumina coatings could obviously promote the adherence, spread and proliferation of the Hobs with the significant increase of proliferation number of Hobs adhered on the surface of the coated NiTi alloys (P?<?0.05). 相似文献
5.
Jafar Khalil-Allafi Behnam Amin-Ahmadi Mehrnoush Zare 《Materials science & engineering. C, Materials for biological applications》2010,30(8):1112-1117
Due to unique properties of NiTi shape memory alloys such as high corrosion resistance, biocompatibility, super elasticity and shape memory behavior, NiTi shape memory alloys are suitable materials for medical applications. Although TiO2 passive layer in these alloys can prevent releasing of nickel to the environment, high nickel content and stability of passive layer in these alloys are very debatable subjects. In this study a NiTi shape memory alloy with nominal composition of 50.7 atom% Ni was investigated by corrosion tests. Electrochemical tests were performed in two physiological environments of Ringer solution and NaCl 0.9% solution. Results indicate that the breakdown potential of the NiTi alloy in NaCl 0.9% solution is higher than that in Ringer solution. The results of Scanning Electron Microscope (SEM) reveal that low pitting corrosion occurred in Ringer solution compared with NaCl solution at potentiostatic tests. The pH value of the solutions increases after the electrochemical tests. The existence of hydride products in the X-ray diffraction analysis confirms the decrease of the concentration of hydrogen ion in solutions. Topographical evaluations show that corrosion products are nearly same in all samples. The biocompatibility tests were performed by reaction of mouse fibroblast cells (L929). The growth and development of cells for different times were measured by numbering the cells or statistics investigations. The figures of cells for different times showed natural growth of cells. The different of the cell numbers between the test specimen and control specimen was negligible; therefore it may be concluded that the NiTi shape memory alloy is not toxic in the physiological environments simulated with body fluids. 相似文献
6.
N. Levintant 《Vacuum》2007,81(10):1283-1287
Experimental results of an accumulation and return strain behaviour of the modified surface of NiTi alloy, as well as mechanical and shape memory behaviour, are shown in this paper.Surface of equiatomic NiTi shape memory alloy (in martensitic form) has been modified by high-dose ion-implantation technique using nitrogen ion beam. The low-energy (65 keV) and following high doses have been used: 1×1017, 5×1017 and 1×1018 J/cm2. Correlation between subsurface layers elemental composition of NiTi alloy, microstructure and shape memory properties is shown. 相似文献
7.
Adam T. Clare Paul R. Chalker Sean Davies Christopher J. Sutcliffe Sozos Tsopanos 《International Journal of Mechanics and Materials in Design》2008,4(2):181-187
Selective laser melting has been used to build high aspect ratio, three-dimensional NiTi micro-electro-mechanical components.
Cantilever beams manufactured in this way have been two-way trained and actuated by ohmic heating demonstrating the suitability
of the process for applications in micro-electromechanical technologies. The influence of laser dwell time and raster pitch
on the density of NiTi shape memory alloy parts and the resolvable feature sizes achievable are discussed. The shape memory
effect properties of solid parts produced by selective laser melting are also reported in contrast to those properties exhibited
by NiTi alloys resulting from other processes. 相似文献
8.
AbstractNiTiHf-based shape memory alloys have been receiving considerable attention for high temperature, high strength and two-way shape memory applications since they could have transformation temperatures above 100°C, shape memory effect under high stress (above 500 MPa) and superelasticity above 100°C. Moreover, their shape memory properties can be tailored by microstructural engineering. However, NiTiHf-based alloys have some drawbacks such as low ductility and high slope in stress induced martensite transformation region. In order to overcome these limitations, studies have been focused on microstructural engineering by aging, alloying and processing. It has been revealed that microstructural control is crucial to govern the shape memory properties (e.g. transformation temperatures, matrix strength, shape recovery strain, twinning type, etc.) of NiTiHf-based alloys. A summary of the most recent improvements on selected NiTiHf-based systems is presented to point out their significant shape memory properties, effects of alloying, aging and microstructure of transforming phases and precipitates. 相似文献
9.
Shape-memory alloys (SMAs) are a unique class of metal alloys that after a large deformation can, on heating, recover their original shape. In the many practical applications of SMAs, the most commonly used material is NiTi (nitinol). A full atomic-level understanding of the shape-memory effect in NiTi is still lacking, a problem particularly relevant to ongoing work on scaling down shape-memory devices for use in micro-electromechanical systems. Here we present a first-principles density functional study of the structural energetics of NiTi. Surprisingly, we find that the reported B19' structure of NiTi is unstable relative to a base-centred orthorhombic structure that cannot store shape memory at the atomic level. However, the reported structure is stabilized by a wide range of applied or residual internal stresses. We propose that the memory is stored primarily at the micro-structural level: this eliminates the need for two separate mechanisms in describing the two-way shape-memory effect. 相似文献
10.
《Materials Letters》2003,57(9-10):1501-1507
In this article, the effect of thermomechanical training temperature on the two-way shape memory effect (TWSME) of TiNiCu and TiNi alloys springs were investigated. The results showed that when the springs were thermomechanical-trained at pure martensite, there is an increase of the recovery rate to a saturated value, the maximum recovery rate was about 55% and 45% for TiNiCu and TiNi alloys, respectively. As the springs were thermomechanical-trained at pure austensite and martensite+austensite, there is an increase of the recovery rate to a maximum value and decreased with ongoing training after having passed the maximum value and the maximum TWSME recovery rate is less than that of the shape memory alloys spring-trained at pure martensite. Dislocations generated by martensite reorientation were effective in developing two-way memory effect. Since the amount of the stress-induced martensite variants is less than that of thermal-induced martensite variants, thus, the recovery rate showed a different rule with increasing thermomechanical training cycles at different training temperature. 相似文献
11.
12.
A three-dimensional micromechanical model for pseudoelasticity is implemented into ABAQUS to study the mechanical behavior
of a polycrystalline NiTi shape memory alloy under biaxial loading. The model is firstly validated by numerical method and
then used to simulate a thin-wall tube under non-proportional extension-torsion loading. When the tensile strain remains constant,
the tensile stress decreases with increasing of the shear strain. While unloading the shear strain, the tensile stress increases.
This is consistent with experimental results. The model can be used to get an idea of the pseudoelastic behavior of NiTi alloys
under complex stress states. 相似文献
13.
The martensitic phase transition which produces shape memory is connected with a hysteresis. Some of the applications of shape memory alloys require small hysteresis loops, other require large ones. It is therefore important to be able to control the size of the hysteresis. For that purpose three different methods were introduced in the present paper. Mechanical vibration narrowed the hysteresis loops in both NiTi and CuZnAl alloys by up to 17%, while the width of the hysteresis loops in an NiTi alloy was decreased 3 to 4 times by addition of a third element, copper. With the help of a special heat treatment a nearly hysteresis-free phase transition occurred in a Ti-51 at % Ni alloy. The size of the hysteresis is determined by the interfacial energies of the phase boundaries and these will be big, if the E-modulus and the lattic distortion are big. 相似文献
14.
《材料科学技术学报》2020,(10)
An intrinsic two-way shape memory effect with a fully recoverable strain of 1.0% was achieved in an as-prepared Ni_(50)Mn_(37.5)Sn_(12.5) metamagnetic shape memory microwire fabricated by Taylor-Ulitovsky method. This two-way shape memory effect is mainly owing to the internal stress caused by the retained martensite in austenite matrix, as revealed by transmission electron microscopy observations and highenergy X-ray diffraction experiments. After superelastic training for 30 loading/unloading cycles at room temperature, the amount of retained martensite increased and the recoverable strain of two-way shape memory effect increased significantly to 2.2%. Furthermore, a giant recoverable strain of 11.2% was attained under a bias stress of 300 MPa in the trained microwire. These properties confer this microwire great potential for micro-actuation applications. 相似文献
15.
A. P. Jardine 《Journal of Materials Science》1989,24(7):2587-2593
The latent heat and entropy changes of NiTi shape memory effect (SME) alloys have been evaluated by three different calorimetric techniques; adiabatic calorimetry, differential scanning calorimetry and a Clapeyron analysis of isothermal stress-strain data. It is found that these techniques provide consistent estimates for the enthalpy and entropy to within 20% for NiTi and noble metal SME alloys. From published thermodynamic data for SME alloys, thermal efficiencies were calculated based on an ideal SME heat engine cycle. It was found that NiTi provides the maximum thermal efficiency with the highest temperature transformation range. 相似文献
16.
17.
The effect of boundary condition on the mechanical behavior of superelastic NiTi shape memory alloys is investigated in this paper. Experimental tests were carried out on NiTi tubes subjected to tension and torsion with different boundary conditions including fixed and free end cases. Results revealed that anisotropy strain/stress appears in the material depending on the end boundary condition of the sample when martensite transformation occurs. This phenomenon is believed to be a result of anisotropy developed in NiTi during material processing and/or training procedures. Based on experimental findings, a new extension is considered to a 3-D phenomenological constitutive model to capture the anisotropic transformation strain/stress generation observed during different loading conditions. Numerical correlations between predicted and experimental data demonstrate the success of the modified model. 相似文献
18.
19.
F. X. Gil J. M. Manero J. A. Planell 《Journal of materials science. Materials in medicine》1996,7(7):403-406
NiTi shape memory alloys showing pseudoelastic behaviour have great potential in dental and orthopaedic applications where constant correcting loads may be required. In most of the clinical applications the device may have been heat treated and during its life in service it will be cyclically deformed. It is therefore important to investigate the effect of cyclic straining and heat treatments upon the transformation stresses and temperatures of the material. The aim of this work is to study the thermal and mechanical ageing of a pseudoelastic NiTi shape memory alloy, as well as the environmental in vitro degradation of the alloy due to the effect of artificial saliva.This paper was accepted for publication after the 1995 Conference of the European Society of Biomaterials, Oporto, Portugal, 10–13 September. 相似文献
20.
Two-way shape memory effect in polymer laminates 总被引:1,自引:0,他引:1
Novel polymer laminate exhibiting two-way shape memory effect has been prepared by layer technique with the shape memory polymer and elastic polymer. In this paper, we demonstrate the two-way shape memory behavior, i.e., bending on heating and reverse bending on cooling; describe the preparation procedure; and investigate its two-way shape memory mechanism. Finally, it suggests that the mechanism can be ascribed to the release of elastic strain of shape memory polymer layer upon heating, and the elastic strain recovery induced by the bending force of substrate layer upon cooling. 相似文献