Effect of Sn substitution and heat treatment on microstructure and microhardness of Co_(38)Ni_(34)Al_(28-x)Sn_x magnetic shape memory alloys

Sn was used to replace Al in Co38Ni34Al28 alloy. The microstructure and microhardness of Co38Ni34Al28-xSnx （x=0, 1, 2, 3） magnetic shape memory alloys were investigated at different heat treatment temperatures （1373 K, 1473 K, and 1573 K） for 2 h. The results show that more Sn substitution reduces the content of γ-phase and a partial phase of martensite can be obtained in Co38Ni34Al28-xSnx （x=1, 2, 3） alloys after treatment at 1573 K for 2 h. The maximum martensite phase appears when 2% Al is substituted by Sn. The reverse martensitic transformation temperature of Co38Ni34Al28-xSnx alloys increases at x=1 and 2, then decreases as x=3. As the content of Sn and the temperature increase, the microhardness will increase.

Effect of Co substitution on magnetic properties of Ni-Mn-Sn magnetic shape memory alloys

The effect of Co substitution on magnetic properties of Ni-Mn-Sn shape memory alloy was revealed by first-principles calculations. Large magnetization difference in Ni-Mn-Sn alloy obtained by addition of Co arises from enhancement of magnetization of austenite due to change of Mn-Mn interaction from anti-ferromagnetism to ferromagnetism. Total energy difference between paramagnetic and ferromagnetic austenite plays an important role in magnetic transition of Ni-Co-Mn-Sn. The altered Mn 3d states due to Co substitution give rise to difference in magnetic properties.

Experimental Study on Characteristics of NiMnGa Magnetically Controlled Shape Memory Alloy

The static and dynamic magnetic controlling characteristics of NiMnGa magnetically controlled shape memory alloy （MSMA） were experimentally studied. The results show that the characteristics of induced strain with respect to the magnetic field are nonlinear with saturation nature, and dependent on the temperature as well as the load applied to the MSMA. The magnetic shape memory effect can be observed only in complete martensite phase at room temperature. The magnetic permeability of MSMA is not constant and reduces with the increment of magnetic field. The relative saturation magnetic permeability of MSMA is about 1.5.

INFLUENCE OF MAGNETIZATION ROTATION ON MARTENSITE REORIENTATION IN MAGNETIC SHAPE MEMORY ALLOY

A large field-induced strain of magnetic shape memory alloy is developed by the martensite variant reorientation. It is widely recognized that the martensite reorientation in a magnetic shape memory alloy （MSMA） can develop if the magnetic field is large enough. However, it has been shown in the literature that the magnetization rotation may block variant reorientation via energy minimization approach. In this paper, based on a micromechanicat model associated with the thermodynamic theory, authors show that there are some limits for the martensite reorientation, which is hindered by the magnetization rotation. Some useful conclusions are obtained.

COMPOSITION TRIANGLE DIAGRAMS OF Ni-Mn-Ga MAGNETIC SHAPE MEMORY ALLOYS

A statistical work has been done to collect the composition ranges of Ni-Mn-Ga alloys exhibiting different structures and martensite start temperature （M,）, large magnetostrain or the co-existence of magnetic and structural transitions. The alloys with five-layered （5M）, seven-layered （7M） modulated and non-modulated （T） martensitic structures were mapped in the graph. An empirical formula has been presented to reflect the effect of elements nickel （Ni ）, manganese （ Mn ） and gallium （Ga）, on the martensite start temperature （M3）. The martensitic structure is sensitive to the composition and the martensitic transformation temperature is most drastically affected by the Ni content. The alloys with large magnetostrain or co-existence effect of the magnetic and structural transitions were also listed in a limited area.

Hybrid control based on inverse Prandtl-Ishlinskii model for magnetic shape memory alloy actuator

The hysteresis characteristic is the major deficiency in the positioning control of magnetic shape memory alloy actuator. A Prandtl-Ishlinskii model was developed to characterize the hysteresis of magnetic shape memory alloy actuator. Based on the proposed Prandtl-Ishlinskii model, the inverse Prandtl-Ishlinskii model was established as a feedforward controller to compensate the hysteresis of the magnetic shape memory alloy actuator. For further improving of the positioning precision of the magnetic shape memory alloy actuator, a hybrid control method with hysteresis nonlinear model in feedforward loop was proposed. The control method is separated into two parts: a feedforward loop with inverse Prandtl-Ishlinskii model and a feedback loop with neural network controller. To validate the validity of the proposed control method, a series of simulations and experiments were researched. The simulation and experimental results demonstrate that the maximum error rate of open loop controller based on inverse PI model is 1.72%, the maximum error rate of the hybrid controller based on inverse PI model is 1.37%.

Martensitic Transformation and Magnetic-Field-Induced Strain in Magnetic Shape Memory Alloy NiMnGa Melt-Spun Ribbon

A magnetic shape memory alloy with nonstoichiometric Ni50Mn27Ga23 was prepared by using melt-spinning technology. The martensitic transformation and the magnetic-field-induced strain (MFIS) of the polycrystalline melt-spun ribbon were investigated. The experimental results showed that the melt-spun ribbons underwent thermal-elastic martensitic transformation and reverse transformation in cooling and heating process and exhibited typical thermo-elastic shape memory effect. However the start temperature for martensitic transformation decreased from 286 K for as-cast alloy to 254 K for as-quenched ribbon and Curie temperature remains approximately constant. A particular internal stress induced by melt-spinning resulted in the formation of a texture structure in the ribbons, which made the ribbons obtain larger martensitic transformation strain and MFIS. The internal stress was released substantially after annealing, which resulted in a decrease of MFIS of the ribbons.

Pressure effects on magnetic properties and martensitic transformation of Ni–Mn–Sn magnetic shape memory alloys

The mechanism for the effects of pressure on the magnetic properties and the martensitic transformation of Ni-Mn- Sn shape memory alloys is revealed by first-principles calculations. It is found that the total energy difference between paramagnetic and ferromagnetic austenite states plays an important role in the magnetic transition of Ni-Mn-Sn under pressure. The pressure increases the relative stability of the martensite with respect to the anstenite, leading to an increase of the martensitic transformation temperature. Moreover, the effects of pressure on the magnetic properties and the martensitic transformation are discussed based on the electronic structure.

Effect of Co on magnetic property and phase stability of Ni-Mn-Ga ferromagnetic shape memory alloys:A first-principles study

The effect of Co content on magnetic property and phase stability of Ni50-xMn25Ga25Cox ferromagnetic shape memory alloys has been investigated using first-principles calculations. The total energy difference between paramagnetic and ferromagnetic state of austenite plays an important role in the magnetic transition. The high Curie temperature can be attributed to the stronger Co-Mn exchange interaction as compared to the Ni-Mn one. The phase stability of Niso-xMn25Ga25Cox austenite increases with increasing Co content, which is discussed based on the electronic structure.

Martensitic Transformation in Magnetically Controlled Shape Memory Alloys Co_(50)Ni_(20)Ga_(30)

The martensitic transformation for Co50Ni20Ga30 ribbon synthesized by the melt-spinning technique was studied by means of X-ray diffraction and ac magnetic susceptibility. The Co50Ni20Ga30 ribbon, having bcc phase with calculated lattice parameters of a=0.57431 nm at 313 K. It exhibits a structure transition from parent phase to martensite during cooling. The martensitic phase in Co50Ni20Ga30 ribbon is tetragonal structure with lattice parameters of a=b=0.5422 nm and c=0.6401 nm. (c/a>1). According to the changing of diffraction intensity for martensite and the change of ac magnetic susceptibility, the process of the martensitic transformation can be divided into three parts during cooling from 283 K to 213 K. When the temperature decreasing sequentially from 193 K to 110 K, the structure of the martensite has a change in which the a-axis decreases and c-axis increases. The morphologies of selfaccommodation were observeds. The parallelogram morphology, the diamond morphology and the fork morphology were found.

STUDY ON THE MAGNETISM AND PHASE TRANSFORMATIONIN Fe-Mn-Si-C SHAPE MEMORY ALLOYS

The hyperfine interactions of two shape memory alloys have been studied by Mossbauer effect measurement at various temperatures. The Mossbauer spectra exhibit a mag-netic change from antiferro magnetic state to paramagnetic state when the temperuture rises. The Fe-Mn-Si alloys have a small hyperfine field and silicon element increases the hyperfine field and magnetic susceptibility. Thermo-induced γ→ ε trunsforma-tions are suppressed by Neel transition and by increasing carbon content, whereas stress induced γ→ ε transformation occurs in both alloys. Antiferromagnetic spin order can suppress thermo-induced γ→εtransformations efficiently, but cannot sup-press stress induced γ → ε transformation.

Magnetic and mechanical properties of Ni–Mn–Ga/Fe–Ga ferromagnetic shape memory composite

A ferromagnetic shape memory composite of Ni-Mn-Ga and Fe-Ga was fabricated by using spark plasma sintering method. The magnetic and mechanical properties of the composite were investigated. Compared to the Ni-Mn-Ga alloy, the threshold field for magnetic-field-induced strain in the composite is clearly reduced owing to the assistance of internal stress generated from Fe-Ga. Meanwhile, the ductility has been significantly improved in the composite. A fracture strain of 26% and a compressive strength of 1600 MPa were achieved.

Martensitic Transformation and Magnetic-Field-Induced Strain in Ni-Mn-Ga-RE (RE=Tb, Sm) Alloys

The effects of microamount additions of RE (Tb, Sm) on martensitic transition, the magnetic-field-induced strain and the bending strength of highly textured polycrystalline Ni_(48)Mn_(33)Ga_(19) alloy were investigated. The experimental results show that the addition of RE elements decreases the martensitic transformation temperature and the Curie temperature. But the bending strength of Ni-Mn-Ga-RE (RE=Tb, Sm) alloys increases remarkably because of the grain refinement. As a result, Ni-Mn-Ga-RE alloys will be applied practically with higher reliability and stability due to favorable plasticity and toughness. In addition, the replacement of small amounts Ga by Tb or Sm decreases the magnetic-field-induced strain of the alloys at room temperature.

Microstructural,phase transformation and magnetic properties of Ni-Mn-Ga alloy fabricated by spark plasma sintering

The microstructural, phase transformation and magnetic properties of Ni Mn-Ga alloy fabricated using the spark plasma sintering method have been investigated. The results show that both the as-sintered and annealed sintered specimens exhibit typical martensitic transformation behaviours. The martensite of the sintered specimen after annealing exhibits a ferromagnetic nature. Moreover, study of the fracture surface indicates that the transgranular fracture con- tributes to the higher ductility of sintered Ni-Mn-Ga alloy. In addition, the transformation strain in sintered Ni-Mn-Ga alloy is studied for the first time.

Alloying and magnetic disordering effects on phase stability of Co_(2)YGa(Y=Cr,V,and Ni)alloys:A first-principles study

The alloying and magnetic disordering effects on site occupation,elastic property,and phase stability of Co_(2)Y Ga(Y=Cr,V,and Ni)shape memory alloys are systematically investigated using the first-principles exact muffin-tin orbitals method.It is shown that with the increasing magnetic disordering degree y,their tetragonal shear elastic constant C′(i.e.,(C_(11)-C_(12))/2)of the L2_(1) phase decreases whereas the elastic anisotropy A increases,and upon tetragonal distortions the cubic phase gets more and more unstable.Co_(2)Cr Ga and Co_(2)VGa alloys with y≥0.2 thus can show the martensitic transformation(MT)from L2_(1)to D0_(22)as well as Co_(2)Ni Ga.In off-stoichiometric alloys,the site preference is controlled by both the alloying and magnetic effects.At the ferromagnetism state,the excessive Ga atoms always tend to take the Y sublattices,whereas the excessive Co atom favor the Y sites when Y=Cr,and the excessive Y atoms prefer the Co sites when Y=Ni.The Ga-deficient Y=V alloys can also occur the MT at the ferromagnetism state by means of Co or V doping,and the MT temperature TMshould increase with their addition.In the corresponding ferromagnetism Y=Cr alloys,nevertheless,with Co or Cr substituting for Ga,the reentrant MT(RMT)from D0_(22)to L2_(1)is promoted and then TMfor the RMT should decrease.The alloying effect on the MT of these alloys is finally well explained by means of the Jahn-Teller effect at the paramagnetic state.At the ferromagnetism state,it may originate from the competition between the austenite and martensite about their strength of the covalent banding between Co and Ga as well as Y and Ga.

Influence of Magnetic Field Intensity on the Temperature Dependence of Magnetization of Ni2.08Mn0.96Ga0.96 Alloy

Results of investigation of the temperature dependence of magnetization of Ni2.08Mn0.96Ga0.96 alloy in the magnetic fields of various intensities are reported. An abrupt change in magnetization at transformation of low temperature phase to the high temperature one is observed. Magnetization increases during the phase transition in the magnetic field having intensity below 500 kA/m and decreases at higher intensities. The explanation is based on zigzag configuration of domains in twinned structure. In the Curie temperature region the ferromagnetic ? paramagnetic phase transition occurs sharply at low field strength, while at higher field strength the transition is smooth. It is concluded that the increase in flatness of the curve σ = f (T) and the increase of ferromagnetic state destruction temperature with increase of the intensity of the magnetic field is indicative of the main role of Mn in magnetization of the alloy.

MSMA自感知执行器的优化设计及试验验证

以磁控形状记忆合金为核心元件的自感知执行器是一种能够自我感知并自主响应的执行器,其具有很高的灵活性和智能性。针对现有自感知执行器的结构进行了优化设计。基于电磁理论分析和数学分析软件,以减小自感知执行器的磁路磁阻和励磁功率、增大气隙磁感应强度为优化目标,对自感知执行器的铁心和永磁体尺寸进行了优化设计;优化后的自感知执行器磁路磁阻减小,气隙磁感应强度增大,磁场分布均匀;通过搭建试验平台对自感知执行器的性能进行试验测试和分析,结果表明:在外加磁场大小相同和励磁线圈匝数相同时,优化后的自感知执行器与优化前的自感知执行器相比可显著提高感应电压峰-峰值并降低励磁功率,验证了自感知执行器结构优化设计的正确性与合理性。

一种新型MSMA差动式驱动器的研究

设计了一种实验装置,对磁控形状记忆合金MSMA(M agnetically controlled Shape M emory A lloy)材料的外特性进行了系统的研究,得出了磁场、温度、压力与形变之间的关系.在此基础之上,设计了一种新型差动式磁控形状记忆合金执行器,阐述了其工作原理,给出了样机和实验结果.

MSMA直线驱动器的数学模型及控制系统

针对新型功能材料磁控形状记忆合金(Magnetically Controlled Shape Memory Alloy简称MSMA)在磁场作用下变形量大、动态响应频率高、功率密度大和机电能量转换效率高的特点,提出了一种基于MSMA材料的新型直线驱动器及其控制系统的设计方案,在分析了其工作原理的基础上,建立了系统的动力学模型,并进行了分析计算;给出了MSMA驱动器的样机和实验结果,实验结果表明:模型的正确性和实用性,为MSMA材料在智能系统中的应用提供了理论和实验基础。

MSMA振动能量采集器的设计与实现

采用智能材料磁控形状记忆合金(MSMA)将机械振动能量转换成电能为无线电子设备供电已备受关注。该文利用MSMA的维拉利效应(逆磁致伸缩效应)分析了MSMA振动能量采集器工作原理,计算并确定了振动能量采集系统的磁轭、线圈、保护系统、固定装置的尺寸和性能参数。利用ANSYS软件对系统进行了仿真,验证了各部分结构参数和材料选型的正确性。在此基础上,设计制作了MSMA振动能量采集器样机,搭建了MSMA振动能量采集器实验平台,进行了振动力激振实验,得到了在不同输入频率和应力大小条件下感应电压的输出曲线,实验和仿真结果表明,利用MSMA材料可将机械振动能量转化为电能,为振动能量收集利用提供了参考依据。