Fe-Mn-Si-Cr-Ni形状记忆合金约束下相变的电阻原位分析

通过同步测量约束加热和冷却过程中合金的电阻率和回复应力与温度的关系,对Fe-Mn-Si-Cr-Ni形状记忆合金约束下的转变过程进行了详细研究,结果表明,变形约束加热后的冷却过程中,回复应力随温度降低而增加,当回复应力增加到大于合金的屈服强度时,将首先发生塑性变形;然后随温度的进一步降低,回复应力到达应力诱发ε马氏体相变的临界应力时,回复应力将诱发ε马氏体相变,导致回复应力随温度的降低而下降,塑性变形和应力诱发ε马氏体相变都将显著松弛回复应力,降低合金冷却到室温时的回复应力,建立了合金加热和冷却过程中回复应力的方程,提出了该记忆合金管接头成分设计原则。

约束态相变中TiNi形状记忆合金的马氏体自拉伸过程

研究了约束态加热过程中产生的回复力对TiNi形状记忆合金剩余马氏体的影响．结果表明,产生的回复力使剩余马氏体发生了塑性变形,使逆相变温度升高,剩余马氏体分数和其逆相变温度之间存在特定的函数关系．但是,外部约束条件的变化对马氏体的自拉伸过程所造成的剩余马氏体分数与其逆相变温度之间的关系影响很小．

Ti-Ni-Cu形状记忆合金快速凝固条带的研究进展

回顾了Ti-Ni-Cu形状记忆合金快速凝固条带的研究进展。主要介绍了Ti-Ni-Cu合金条带的组织结构、晶化行为、织构和析出物、马氏体相变温度及其形状记忆特性。合金条带的铸态组织随工艺参数不同可在非晶-晶态之间变化;独特的析出物和织构影响其相变行为和形状记忆性能;条带具有良好的形状记忆效应和超弹性性能,与体材相比,其相变应变大而相变应力滞后小。总结了研究中存在的问题并展望了未来的研究方向。

基于选择性相溶解的内生增强镁基非晶复合材料实验工艺设计

针对材料成形实验教学中内生增强复合材料的制备工艺设计困难问题,该文以具备较好非晶形成能力的Mg_(65)Cu_(7.5)Ni_(7.5)Zn_(5)Ag_(5)Y_(10)(at.%)为基体,基于选择性相溶解法在非晶基体中成功引入原位自生B2-NiTi相。利用电弧熔炼制备Ni-Ti-Cu-Y预合金,通过成分设计使其析出B2-NiTi相,再将上述预合金浸入剩余元素(Mg,Zn,Ag)组成的熔体中。预合金中除B2-NiTi相以外的其他组成相会选择性溶解进入熔体中,组成Mg-Cu-Ni-Zn-Ag-Y熔体,B2-NiTi相分布其中。通过预先成分配比设计,使熔体成分与目标成分接近,具备较好的非晶形成能力。通过快速冷却制备得到原位自生B2-NiTi相增强镁基非晶复合材料。B2-NiTi形状记忆相在应力加载时会发生马氏体相变吸收能量,并阻碍主剪切带快速扩展,提高复合材料室温强韧性。复合材料断裂强度超过1 GPa,断裂应变为5.6%,屈服强度为730 MPa,塑性应变为4.6%,综合力学性能优于所选用的非晶基体合金。该工艺可适用于多种内生增强复合材料制备,为材料设计及组织性能表征实验教学提供了很好的范例。

形状记忆晶相/铜基非晶复合材料的组织和微观力学行为（英文）

采用悬浮熔炼-水冷铜模吸铸法制备Cu_(50)Zr_(42)Al_8锥形试样,研究了合金不同直径处的组织和微观力学行为,分析了尺寸效应和裂纹自愈合行为。结果表明,复合材料组织中包括非晶基体相、金属间化合物Al Cu_2Zr相、奥氏体B_2-Zr Cu相和热致马氏体B19’-Zr Cu相。纳米压痕结果表明,单一非晶结构的试样心部硬而表面较软,呈现越小越软趋势,而较大尺寸的非晶复合材料由于析出相的存在,心部软而表面较硬。形状记忆晶相由TRIP效应对非晶基体增强增韧,而Al Cu_2Zr相析出使基体脆化。经150℃/10 min退火后,微观压痕产生的裂纹表现出自愈合行为。加载时,形变诱导B2奥氏体向B19’马氏体相转变并伴随着体积的膨胀,而高于逆转变温度退火,B19’转变为B2相,体积收缩并在组织应力作用下驱动裂纹愈合。

Ti基金属玻璃复合材料的腐蚀行为

采用水冷铜坩埚悬浮熔炼-铜模吸铸法制备了直径为3mm的(Ti0.5Ni0.5)80Cu20金属玻璃复合材料试样,对合金的组织结构进行表征,用电化学工作站三电极体系测试了不同腐蚀介质中的动电位极化曲线,并分析表征电化学腐蚀后的形貌和腐蚀产物。结果表明:合金组织由非晶基体+形状记忆晶体相组成,在铸造过程的温度梯度下呈现梯度组织,边缘为快冷形成的无序密堆非晶结构,心部主要析出相为过冷奥氏体相。在人工海水和模拟人体的PBS溶液中,合金均表现出良好的耐蚀性。与晶态TC4合金相比,自腐蚀电位高,腐蚀的热力学倾向小;自腐蚀电流密度低,极化电阻高,腐蚀的动力学速率低。合金在PBS溶液中由于介质中活性阴离子浓度低,比在人工海水中表现出更优异的抗蚀性。在腐蚀形貌中未发现点蚀坑,边缘区的氧化膜较心部区域更为致密均匀。

Influence of cooling rate on phase transformation and microstructure of Ti-50.9%Ni shape memory alloy

Heat treatment of Ti-50.9%Ni （mole fraction） alloy was studied by differential scanning calorimetry, X-ray diffraction, scanning electron microscopey and energy dispersive X-ray analysis to investigate the influence of cooling rate on transformation behavior and microstructures of NiTi shape memory alloy. The experimental results show that three-stage phase transformation can be induced at a very low cooling rate such as cooling in furnace. The cooling rate also has a great influence on the phase transformation temperatures. Both martensitic start transformation temperature （Ms） and martensitic finish transformation temperature （Mf） decrease with the decrease of the cooling rate, and decreasing the cooling rate contributes to enhancing the M→A austenite transformation temperature. The phase transformation hysteresis （Af-Mf） increases with the decrease of the cooling rate. Heat treatment is unable to eliminate the textures formed in hot working of NiTi sample, but can weaken the intensity of them. The cooling rate has little influence on the grain size.

Influence of Ni_4Ti_3 precipitates on phase transformation of NiTi shape memory alloy

Ni Ti shape memory alloy samples were aged for 2 h at 573, 723 and 873 K, respectively. Two R-phase variants are observed in the Ni Ti samples aged at 573 and 723 K, where the orientation relationship between the two R-phase variants and the B2 matrix is determined. In the Ni Ti samples aged at 573 and 723 K, fine and homogeneous Ni4Ti3 precipitates are coherent with the B2 austenite matrix. The Ni4Ti3 particles precipitate in the grain interior and at the grain boundaries, where the heterogeneous Ni4Ti3 precipitates are coherent, semi-coherent and incoherent with the B2 matrix in the Ni Ti sample aged at 873 K. As for the Ni Ti sample aged at 873 K, one-stage phase transformation from B19＇ martensite to B2 austenite occurs on heating, but two-stage phase transformation of B2-R-B19＇ arises on cooling. The Ni Ti sample aged at 723 K shows two-stage phase transformation of B2-R-B19＇ on cooling as well, but exhibits two-stage phase transformation of B19＇-R-B2 on heating. The Ni Ti sample aged at 573 K exhibits three-stage transformation on cooling due to local stress inhomogeneity and local composition inhomogeneity around the Ni4Ti3 precipitates.

Effects of second phases on mechanical properties and martensitic transformations of ECAPed TiNi and Ti-Mo based shape memory alloys

TiNi and Ti-based shape memory alloys were processed by equal channel angular pressing （ECAP） at 673-773 K along Bc route to obtain ultrafine grains for increasing the strength of parent phase and improving the functional properties. The effects of both thermodynamically stable and metastable second phases on the mechanical properties and martensitic transformations of these alloys were investigated. It is found that thermodynamically stable Ti2Ni phase has no effect on martensitic transformation and superelasticity of Ti-rich TiNi alloy, thermodynamically stable α phase is harmful for ductility of Ti-Mo-Nb-V-Al alloy, but metastable Ti3Ni4 phase is effective for R phase transformation, martensitic transformation and superelasticity of Ni-rich TiNi alloy. The mechanisms of the second phases on the martensitic transformations and mechanical properties were discussed.

Microstructure and transformation behavior of Ni_(54)Mn_(25)Ga_(15)Al_6 high-temperature shape memory alloy

The microstructure, martensitic transformation behavior, mechanical properties and shape memory effect of Ni54Mn25Ga15Al6 high-temperature shape memory alloy were investigated. By comparing with the Ni54Mn25Ga21 alloy, the effect of Al addition on the properties of Ni-Mn-Ga alloys was analyzed. The results show that the Ni54Mn25Ga15Al6 alloy has a single-phase tetragonal non-modulated martensite structure with lamellar twins. The martensitic transformation start temperature of this alloy is up to 190 ℃, displaying the promising application as a high-temperature shape memory alloy. Al addition in Ni-Mn-Ga alloy can decrease the martensitic transformation temperatures due to the effect of size factor and improve the strength and plasticity. However, the shape memory effect is reduced remarkably with the Al addition.

Magnetocaloric effect in Ni-Mn-In-Co microwires prepared by Taylor-Ulitovsky method

Ni-Mn-In-Co microwires with diameter of 30-100 μm are prepared by glass-coated metal filaments（Taylor–Ulitovsky） method. The effects of magnetic field on martensite transformation temperature in the as-prepared and annealed microwires are investigated using a physical property measurement system（PPMS）. Magnetocaloric effect（MCE） attributed to field-induced austenite transformation in the as-prepared and annealed microwires is analyzed indirectly from the isothermal magnetization（M-B） curves. The as-prepared microwire has a 7-layer modulated martensite structure（7M） at room temperature. The changes of austenite starting temperature induced by an external magnetic field（ΔAs/ΔB） in the as-prepared and annealed microwires are-1.6 and-4 K/T, respectively. Inverse martensite to austenite transformation exists in annealed microwires when an external magnetic field is applied at temperatures near As. The entropy change（ΔS） obtained in the annealed microwires is 3.0 J/（kg·K）, which is much larger than that in the as-prepared microwires 0.5 J/（kg·K）. The large entropy change and low price make Ni-Mn-In-Co microwires a potential working material in magnetic refrigeration.

Modeling of Ni_4Ti_3 precipitation during stress-free and stress-assisted aging of bi-crystalline NiTi shape memory alloys

The phase field method was applied to study the microstructure evolution of Ni4Ti3 precipitates during stress-free and stress-assisted aging of bi-crystalline NiTi shape memory alloys （SAMs） with two different initial Ni-contents of 51.5% and 52.5% （mole fraction）, respectively. The simulation results show that, during stress-free aging of the NiTi alloy with a low supersaturation of Ni （i.e., Ti-51.5%Ni）, the Ni4Ti3 precipitates exhibit a heterogeneous distribution with a high number density of particles at the grain boundary, leaving most of the grain interiors free of precipitates; while for the NiTi alloy with a high supersaturation of Ni （i.e., Ti-52.5%Ni）, the Ni4Ti3 precipitates show a homogeneous distribution across the entire simulation system. The stress-assisted aging can give rise to homogeneous distribution of the precipitates, regardless of the initial Ni-content; however, the distribution of variant type within the two grains is heterogeneous.

Effects of Co and Al addition on martensitic transformation and microstructure in ZrCu-based shape memory alloys

The effect of ternary alloying element Al and quaternary alloying element Co on the martensitic transformation of ZrCu-based shape memory alloy was investigated. The results show that the addition of Al and Co in ZrCu alloy decreases both the martensitic transformation temperature and the martensitic transformation temperature hysteresis. Transmission electron microscope (TEM) observations reveal that theCm martensite structure is the preferential formation phase. The intervariant structures in ZrCuAlCo alloy are (021) type I twins, while the dominant substructures inside the martensite variant are the (001) compound twins. With the increase of Co content, tensile fracture strength and strain are improved obviously.

Microstructural,mechanical and shape memory characterizations of Ti-Mo-Sn alloys

As a β stabilizing element in Ti-based alloys,the effect of Mo on phase constitution,microstructure,mechanical and shape memory properties was investigated.Different compositions of Ti-xMo-3Sn alloys(where x=2,4,6,at.%) were prepared by arc melting.A binary composition of Ti-6 Mo alloy was also prepared for comparison.Ti-xMo-3Sn alloys show low hardness and high ductility with 90% reduction in thickness while Ti-6 Mo alloy shows high hardness,brittle behavior,and poor ductility.Field emission scanning electron microscopy(FESEM) reveals round morphology of athermal ω(ωath) precipitates.The presence of ωath phase is also confirmed by X-ray diffraction(XRD)in both as-cast and solution-treated and quenched conditions.The optical microscopy(OM) and FESEM show that the amount of martensite forming during quenching decreases with an increase in Mo content,which is also due to β→ω transformation.The hardness trends reinforce the presence of ωath too.The shape memory effect(SME) of 9% is the highest for Ti-6 Mo-3Sn alloy.The SME is trivial due to ωath phase formation;however,the increase in SME is observed with an increase in Mo content,which is due to the reverse transformation from ωath and the stress-induced martensitic transformation.In addition,a new and very simple method was designed and used for shape memory effect measurement.

Stress-induced martensite phase transformation of FeMnSiCrNi shape memory alloy subjected to mechanical vibrating polishing

Fe66Mn15Si5Cr9Ni5(wt.%)shape memory alloy(SMA)withγaustenite andεmartensite was subjected to mechanical vibrating polishing and consequently its surface suffered from plastic deformation in the case of compressive stress.Almost completeεmartensite transformation is found to occur in FeMnSiCrNi sample subjected to mechanical vibrating polishing,where stress-induced martensite transformation plays a predominant role.Stressinduced martensite transformation of FeMnSiCrNi SMA is closely related to the orientation of external stress.The complicated compressive stress which results from the mechanical vibrating polishing contributes toεmartensite transformation fromγaustenite of FeMnSiCrNi SMA.Mechanical vibrating polishing has a certain influence on the surface texture ofεmartensite of FeMnSiCrNi SMA,where■<0001>texture appears in the polished FeMnSiCrNi SMA.

Thermo-electric behaviour of NiTi shape memory alloy

The thermo-electric behavior of shape memory alloy （SMA） wire was presented. When the wire was electrically heated above its transformation temperature by current, a large mechanical force is exerted due to transformation in its phases. In order to make use of SMA wire as an actuator, different parameters and their relationships were investigated. These parameters are recoverable strain （displacement）, temperature hysteresis and electrical resistance variation under different stress levels. Optimum safe heating current was assessed and phase transformation temperatures were estimated by heat transfer model. The wire was heated and cooled by 680 mA of current for 796 s under natural air convection. The strain recovered is 4.33% and corresponding change in resistance is 11.2% at 43 MPa of stress. The resistance variation shows linearly with displacement and current during heating and cooling cycle respectively. This study will be useful in precisely controlling of SMA wire actuator with and without external sensor feedback.

Analytical Solutions of the Equations One Mechanical Thermal Model of a Helical Spring NiTi for Use in Heat Engine

Shape memory effect is capability of certain materials to recover its original shape after an apparently permanent deformation. The NiTi alloy of the composition is approximately equiatomic and it is the materials that exhibit the best characteristics for application of these properties, especially in the biomedical area, because of their excellent biocompatibility as： in the manufacture of medical and dental instruments, orthodontic wires, orthopedic materials, guide wires, stents, filters and components to realize the less invasive surgeries. In other areas, they are used for confections of electronic keys, spectacle frames, application in controllers, junction of pipes and electronic connectors among others. New research topics involving the application of these alloys super-elasticity are also known as pseudo elasticity. This event has an isothermal nature and involves the storage of potential energy in the shape memory effect and super-elasticity. In this context, this work falls within the scope of use of the technologies being an example of the work undertaken, in the course Graduate of Federal University of Pernambuco in skills in these technologies. It will present the results of a heat engine which engine element is a helical spring made of a NiTi alloy equiatomic with memory effect reversibly. The spring is triggered by a hot source （- 373.15 K） and a cold source （273.15 K）. The machine is capable of producing a reciprocating oscillating between the two sources. Heat equations and the equations that describe the dynamic behavior of the spring were developed. Through the development of dynamic equations, it can determine the minimum mass for the motion of the machine, as well as the instantaneous and average power and overall efficiency. You can check the functionality of the machine by way of the inclination angle of the propeller and the coefficient of static friction. Among the main results, it was observed that the overall performance of the machine compared to the machines of this category showed the feasibility of the project.

Microstructure and martensitic transformation in quaternary NiTiHfV alloy

The effect of age hardening on the microstructure,martensitic transformation behavior,and shape memory properties of the(Ni_(50)Ti_(30)Hf_(20))_(95)V_(5)alloy was investigated by scanning electron microscopy,transmission electron microscopy,X-ray diffraction,differential scanning calorimetry,microhardness,and bending tests.The results demonstrate a significant influence of V addition on the microstructure of the alloy.V addition leads to the formation of a(Ni,V)_(2)(Ti,Hf)-type Laves phase,which coexists with B19'martensite at room temperature.Aging at 550℃results in precipitation hardening due to the formation of nano-scale orthorhombic H-phase,with the peak hardness observed after 3 h of aging.The alloy at peak hardness state exhibits higher transformation strain and lower unrecovered strain compared to the solution-treated sample.The aged sample achieves a maximum transformation strain of 1.56%under 500 MPa.

高强韧Ti-Ni基块体金属玻璃复合材料高温变形行为

采用水冷Cu坩埚悬浮熔炼-Cu模吸铸法制备了Ti-Ni基块体金属玻璃复合材料(BMGCs)试棒,研究了合金的微观组织、热力学行为以及室温和高温力学性能。结果表明,该铸态合金组织由非晶基体和过冷奥氏体及热致马氏体组成,且晶体相尺寸由表及里增大。在室温压应力加载时,合金表现出优异的综合力学性能,其屈服强度为1286 MPa,断裂强度为2256 MPa,且塑性应变为12.2%。在过冷液相区压应力加载时,合金在高的变形温度和低应变速率下,表现出近Newtonian流变特征,其最佳变形温度为T>480℃且与过冷液相区(SLR)的交集部分。温度为560℃、应变速率为5×10-4s-1时,合金应力敏感指数m和能量耗散率y分别为0.81和0.895。

Process structuring of polymers by solid phase orientation processing

Solid phase orientation of polymers is one of the most successful routes to enhancement of polymer properties.It unlocks the potential of molecular orientation for the achievement of a range of enhanced physical properties.We provide here an overview of techniques developed in our laboratories for structuring polymers by solid phase orientation processing routes,with a particular focus on die drawing,which have allowed control of significant enhancements of a single property or combinations of properties,including Young's modulus,strength,and density.These have led to notable commercial exploitations,and examples of load bearing low density materials and shape memory materials are discussed.