Ni50.1Mn24.1Ga20.3Fe5.5形状记忆合金多晶纤维的双程形状记忆效应

通过熔体抽拉技术制备Ni_50.1Mn_24.1Ga_20.3Fe_5.5多晶纤维,采用步进式热处理释放因快速凝固引起的内应力和缺陷,利用场发射扫描电子显微镜、透射电子显微镜、XRD衍射仪对其微结构和相结构进行表征,采用动态机械拉伸仪测试其相变行为和双程形状记忆性能。结果表明:热处理后原子有序度显著提高,孪晶界平直,在恒应力作用下一个热循环中母相和马氏体相的形状得到完全恢复。双程形状记忆曲线显示了热弹性马氏体相变的两个基本特征:可逆性和热滞性。在热循环实验中,纤维被加载到198 MPa时,其马氏体态总应变达到1.32%。根据热机械拉伸测量,发现相变温度遵循Clausius-Clapeyron关系式。与诸如Ti-Ni和Cu-Al-Ni的其他合金相比,Fe掺杂的纤维显示出较小的应变-应力依赖性,在恒应变输出的驱动中是有益的。     

Deformation behaviour and shape memory effect of near equi-atomic NiTi alloy

The mechanical shape memory effect associated with the martensitic-type transformation which occurs in polycrystalline Ti-50.3 at. % Ni alloy has been investigated using the techniques of transmission and optical microscopy. Deformation of initially partially transformed material within the recoverable strain range was found to occur by: (1) stress-induced transformation of the most favourably oriented existing martensite variants at the expense of adjacent unfavourably oriented variants and retained high temperature phase (2) stress-induced re-orientation of favourably oriented martensite by utilizing the most favourably oriented twin system, and (3) stress-induced twin-boundary migration within the martensite. The reverse transformation during heating restores the original grain structure of the high-temperature phase in a highly coherent manner. It was concluded that deformation modes limited to those involved in the transformation process and the reversibility of the transformation give rise to the memory effect.     

Investigation on ferromagnetic shape memory alloys

Ferromagnetic shape memory alloys, exhibiting large recoverable strain and rapid frequency response, appear to be promising shape memory actuator material. These materials exhibit large shape memory effect associating with martensitic transformation, and magnetic-field-induced strain in the martensite state. The recent development in researches on NiMnGa, NiFeGa, and CoNiGa in our group is briefly reviewed. The perspectives of the ferromagnetic shape memory alloy are also described.     

NiTiHf-based shape memory alloys

Abstract

NiTiHf-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.     

Effect of thermomechanical training temperature on the two-way shape memory effect of TiNi and TiNiCu shape memory alloys springs

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.     

Surface form memory in NiTi shape memory alloys by laser shock indentation

An indentation-planarization method for NiTi shape memory alloys has been developed that produces a robust surface topographical memory effect that we call "surface form memory", or SFM. Surface form memory entails reversible transitions between one surface form (flat) and another (say, wavy) that occur on changing temperature. These transitions are cyclically stable and exhibit very high mechanical energy density. Our previous study has demonstrated SFM transitions in NiTi alloys derived from quasistatic (i.e., low strain rate) spherical indents, as well as other geometries. Here, we report on experiments using confined laser ablation to indent a similar martensitic NiTi substrate, but in the dynamical regime (very high strain rate). As in the quasistatic case, subsurface plastic strain gradients are created via martensite twinning reactions, and later by dislocation-mediated slip. The resulting defects and stress fields support the two-way shape memory effect underlying SFM. In the dynamical case however, relative cyclic two-way displacements are found to be significantly larger, when normalized to the initial indent depth, than is the case with quasistatic indentation. This confers certain processing and boundary condition advantages. Analysis of the shock dynamics is found to be consistent with the observed surface displacements.     

Effect of precipitation on two-way shape memory effect of melt-spun Ti50Ni25Cu25 ribbon

In the present work, effect of precipitation on two-way shape memory effect and deformation induced martensite stabilization of Ti₅₀Ni₂₅Cu₂₅ ribbon was investigated. The two-way shape memory effect developed as a result of martensite deformation is affected by formation of precipitates. After straining martensite to 5.5%, a two-way shape memory strain of 1.25% was obtained in a sample annealed at 800 °C for 300 s that does not introduce B11 precipitates. Results also show that the deformed Ti₅₀Ni₂₅Cu₂₅ ribbon containing precipitates has multiple-stage transformation characteristics during the first heating.     

Finite element simulation of low velocity impact on shape memory alloy composite plates

Delamination of composite materials due to low velocity impacts is one of the major failure types of aerospace composite structures. The low velocity impact may not immediately induce any visible damage on the surface of structures whilst the stiffness and compressive strength of the structures can decrease dramatically.

Shape memory alloy (SMA) materials possess unique mechanical and thermal properties compared with conventional materials. Many studies have shown that shape memory alloy wires can absorb a lot of the energy during the impact due to their superelastic and hysteretic behaviour. The superelastic effect is due to reversible stress induced transformation from austenite to martensite. If a stress is applied to the alloy in the austenitic state, large deformation strains can be obtained and stress induced martensite is formed. Upon removal of the stress, the martensite reverts to its austenitic parent phase and the SMA undergoes a large hysteresis loop and a large recoverable strain is obtained. This large strain energy absorption capability can be used to improve the impact tolerance of composites. By embedding superelastic shape memory alloys into a composite structure, impact damage can be reduced quite significantly.

This article investigates the impact damage behaviour of carbon fiber/epoxy composite plates embedded with superelastic shape memory alloys wires. The results show that for low velocity impact, embedding SMA wires into composites increase the damage resistance of the composites when compared to conventional composites structures.     

Detecting NiTi two-way shape memory effect based on microstructural and macromechanical parameters

ABSTRACT

The 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.     

Martensitic transformation,crystal structure and shape memory effect in Ni55−xMn25Ga20Cox alloys

ABSTRACT

The effect of cobalt addition instead of nickel on the crystal structure, martensitic transformation behaviour and shape memory effect were investigated. Within the analysed range of chemical composition, a single non-modulated martensite was detected at ambient temperature. Cobalt addition modified the lattice parameters and, thus, affected the tetragonality of the martensite unit cell. The hysteresis of martensitic transformation was differently affected by the type of heat treatment applied. For furnace cooled samples, the hysteresis decreased from 50°C to 30°C; in the case of water quenched samples, the hysteresis sharply increased up to 60°C. The shape memory effect, measured as the recoverable strain upon annealing after compression tests, reached a fully recoverable deformation at 10?at.-% of cobalt.

This paper is part of a Thematic Issue on The Crystallographic Aspects of Metallic Alloys.     

Temperature memory effect in two-way shape memory TiNi and TiNiCu springs

An incomplete thermal cycle upon heating in a shape memory alloy (arrested at a temperature between A_s and A_f) induced a kinetic stop in the next complete thermal cycle. The kinetic stop temperature is closely related to the previous arrested temperature. This phenomenon is named temperature memory effect (TME). In this article, the TME in two-way shape memory TiNiCu and TiNi springs was investigated by performing either a single incomplete cycle, or a sequence of incomplete cycles. N points of temperatures could be memorized if N times of incomplete cycles on heating were performed with different arrested temperatures in a decreasing order. The capability is enhanced by performing repetitive incomplete cycles with the same temperature, and the TME can be eliminated by appropriate complete transformation cycle. The TME is originated from the relaxation of both the strain energy between martensite and coherent strain between parent phase and martensite.     

Improved shape memory composites combined with TiNi wire and shape memory epoxy

In order to develop high functionality of shape memory materials, the shape memory composites combined with TiNi wire and shape memory epoxy were fabricated, and the mechanical and thermomechanical properties were studied. The results showed that TiNi wire can compensate for the stiffness decrease of SMPs at elevated temperature, and the strength of interface and strength of interface matrix were important to further increase elevated temperature mechanical properties. The recovery stress of composites could be adjusted by changing the pre-strain, and the maximum recovery stress was obtained at 8% which was TiNi wire maximum recoverable strain. The addition of 1 vol% TiNi wire could increase the maximum recovery stress from 1.36 MPa to 4.04 MPa, which was almost 3 times of the matrix and at the same time maintained the rates of shape fixity and shape recovery close to 100%.     

Degeneration and rejuvenation of shape memory effect associated with the precipitation of coherent nano-particles in a Co-Ni-Si shape memory alloy

In a solution treated Co-20Ni-6Si shape memory alloy,coherent nano-particles were precipitated after annealing at 873 K for 1 min,but the shape memory effect almost vanished.It is attributed to that the coherent nano-particles not only suppressed the stress-induced face-centered cubic to close-packed hexagonal martensite transformation but also damaged the crystallographic reversibility of reverse martensite transformation.After further annealing at 1073 K for 1 min,the shape memory effect was reju-venated owing to the dissolution of nano-particles.Besides,the recovery strain significantly increased to 5.1％ from the solution treatment of 3.1％ after annealing at 1073 K for 1 min.     

Tailoring the microstructure,martensitic transformation and strain recovery characteristics of Ti-Ta shape memory alloys by changing Hf content

In the present work,the microstructure features,martensitic transformation,mechanical properties and strain recovery characteristics of Ti-Ta based shape memory alloys were tailored by changing Hf contents.The single α"martensite phase was dominated in Ti-Ta alloy with 2 at.％H f.Upon Hf content exceeded 2 at.％,β phase started to appear.Moreover,the amount of β phase gradually increased with Hf content increasing.The martensitic transformation temperatures continuously decreased with the increased Hf content,which was attributed to the rising of valence electron concentration.Meanwhile,Hf addition improved the thermal cycling stability of Ti-Ta alloys due to the suppression of ω precipitation.The yield stress of Ti-Ta based alloys firstly decreased and then increased with Hf content increasing.In addition,the completely recoverable strain of 4％can be obtained in Ti-Ta alloy with 6 at.％Hf as a consequence of the higher critical stress for dislocation slip.Besieds,the Ti-Ta based alloy containing 8 at.％Hf had the superior superelasticity behavior with the fully recoverable strain of 2％at room temperature.     

Fe-Mn-Si-Cr-Ni系形状记忆合金管接头形状记忆效应和耐腐蚀性能的研究

研究了Fe-Mn-Si-Cr-Ni系形状记忆合金管接头形状记忆效应和耐腐蚀性能。结果表明,随着预变形量的增加,管接头的形状记忆效应下降,而恢复应变呈上升趋势,当预变形超过5.3%左右时,上升幅度不大;连接状态的管接头在模拟油田介质中的耐腐蚀性能比3.5%的NaCl溶液中的抗蚀性差;在模拟油田介质中,连接状态和未连接的管接头相比,由于回复应力使表面产生拉应力以及应力诱发ε马氏体的存在,使连接状态的管接头耐腐蚀性能下降;随着预变形的增大,由于回复应力、管接头裂纹以及晶体缺陷密度增加的共同作用,使连接状态的管接头耐腐蚀性能降低。     

Effect of Zr content on mechanical properties of Ti-Ni-Zr shape memory alloy films prepared by dc magnetron sputtering

To further understanding of the effect of Zr content on the shape memory behavior of ternary Ti-Ni-Zr alloy films, ternary alloy films were deposited with various Zr contents using triple source dc magnetron sputtering. Deposited films annealed at 700 °C showed martensite transformation accompanied with shape memory behavior. Martensitic transformation start (Ms) temperature of the ternary alloy film was found to increase with increasing Zr content for a Zr content higher than 10 at%. The highest Ms temperature attained was ∼170 °C for a Zr content of 19.5 at%. Critical stress against plastic deformation was found to increase with increasing Zr content up to 10 at%. Although further increase of Zr content caused embrittlement, the Ti_32.3Ni_48.2Zr_19.5 film showed a shape memory effect with a recoverable strain of ∼1.3% under a constant stress of 250 MPa. This indicates that the Ti-Ni-Zr alloy film is a promising candidate for cantilever type micro-actuators.     

Two-way shape memory effect in polymer laminates

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.     

Ni–Mn–Ga shape memory alloys development in China

Study on Ni–Mn–Ga ferromagnetic shape memory alloys recently keeps active. Intermartensitic transformation was found. Magnetic field enhanced phase transformation strain was discovered, and achieved up to 4%. Fifteen percent super high strain induced by variant reorientation under stress was obtained in non-modulated martensite. Six percent large magnetic field induced strain was achieved, and the temperature dependence was investigated in 5-layered martensite single-variant Ni–Mn–Ga alloys. Several other systems of magnetic shape memory alloys and high temperature shape memory alloy Ni–Mn–Ga are also reviewed.     

Two way shape memory loss in Cu---Zn---Al alloy

Investigation is carried out to understand the reasons behind the degradation of two way shape memory effect in Cu---Zn---Al alloy which exhibits a complete loss in its two way memory effect after a finite number of transformation cycles. It is observed that the two-way memory loss is attributable to a chemical effect viz. the precipitation of intermetallics at the martensite plate boundaries. Since repetitive thermal cycling is related to some kind of ageing effects, the present investigation also includes the study on the ageing behaviour of the alloys. The ageing effects are finally co-related with the observed two-way shape memory loss to describe the transformation fatigue found in the Cu---Zn---Al alloy.     

Microstructures of 18R martensite induced by deformation and thermomechanical cycles in CuZnAl shape memory alloy

Microstructures of martensite in a Cu-26.4Zn-4.8Al shape memory alloy after deformation and thermomechanical cycles are reported. By detailed transmission electron microscopy investigation, it is clearly established that the microstructure induced by deformation is different from that induced by thermomechanical cycles, and the effects on the thermoelastic martensite transformation are also not the same at all. The microstructure of martensite induced by deformation is mainly deformation twins when the deformation exceeds the range of recoverable strain of the shape memory alloy. The main microstructure characteristic of martensite which has undergone thermomechanical cycles is regularly distributed dislocations, which are mainly aligned but sometimes tangled. Micro-twins similar to those found in deformed martensite and crossed bands also exist inside the martensite of samples after thermomechanical cycles, but the amounts are too small to be regarded as important microstructure features.