Characteristics Of Shape Memory Effect Research Articles

Smart alloy metalized novel photonic NEMS photodiode with CuAlV/n-Si/Al junction structure

In this work, a novel smart (shape memory) alloy metalized photonic silicon wafer photodiode with Schottky type CuAlV/n-Si/Al contact structure as a nano-electro-mechanical-system (NEMS) photodevice was fabricated by thermal evaporation technique. The CuAlV memory alloy used as the top Schottky metal contact electrode was produced by arc melting technique and a subsequent quenching in an iced-brine water medium, and its shape memory effect characteristics were revealed by thermal and structural tests. The fabricated photonic NEMS photodiode was characterized by different photo-electrical (I-V, I-t) and frequency/time dependent and illuminated capacitance (C–V/f, C-t, C–V/ill.) and conductance-voltage (G-V) measurements under different frequencies and artificial light intensity power conditions. The I-V tests showed an excellent current rectifying ability and very well net photocurrent generation features of the photodiode. The specific detectivity of the photodiode was found as high as almost approaching 1011 Jones. The SCLC (space charge limited current conduction) analyses made on the double-log I-V plots of the photodiode revealed that the trap-filling TFL-SCLC and trap-free SCLC current conduction mechanisms are the two prevailing conduction mechanisms in the forward bias voltage region. The density of interface states (Dit) of the fabricated photodiode was determined. Moreover, an excellent reproducibility of light-induced photocapacitance formation of the novel photodiode was demonstrated by C–V/t measurements under different artificial light power intensities.

Role of Zr and thermomechanical treatment on phase transformation and functional properties of NiTi-based shape memory alloys

A systematic investigation was conducted to evaluate the role of Zr addition on the martensitic phase transformation behavior and properties of NiTi-based shape memory alloys. Equiatomic binary NiTi alloy and ternary Ni50Ti45Zr5 and Ni50Ti40Zr10 alloys (at.%) were processed by a simple thermomechanical treatment including cold rolling followed by post-deformation annealing at 450 °C for 30 and 60 min. The microstructural investigation and thermal analyses reveal that martensitic phase transformation is suppressed by adding Zr. Solid solution strengthening due to Zr addition, strain hardening due to cold rolling and formation of (Ti,Zr)2Ni precipitates in a dual-phase microstructure during annealing leads to a significant increase in hardness in the thermomechanically treated alloys (e.g., up to 550 Hv for Ni50Ti45Zr5 alloy). The stress-strain curve of martensitic Ni50Ti50 alloy reveals the essential characteristics of shape memory effect, however, Ni50Ti45Zr5 alloy shows typical features of pseudoelasticity with significantly high stress plateau (∼600 MPa) and remarkable recovered strain of 3.5% during unloading.

Novel Quaternary CuAlZnMg High Temperature Shape Memory Alloy (HTSMA) Fabricated by Minor Batch of Zn and Mg Additions

Shape memory alloys (SMAs) constitute the second largest commercial smart material class after piezoelectric materials. Different SMA alloy systems or SMAs with miscellaneous functionalities and characteristic properties have been designed for using in different applications until today. High temperature shape memory alloys (HTSMAs) are also widely desired to be used in various smart materials applications. HTSMAs with different functional and characteristic properties are muchly demanded for different tasks to be done by these alloys or devices designed by these alloys. A common and practical way to fabricate SMAs or HTSMAs with different shape memory effect (SME) and other properties is to fabricate them with different alloying compositions and add different additive elements. In this work, a quaternary CuAlZnMg HTSMA with an unprecedented composition consisting minor amount of zinc and magnesium additives was produced by arc melting method. As a result of applying post-homogenization in high β–phase temperature region and immediate quenching, the microstructural mechanism of a SME property was formed in the produced alloy. After then, to examine SME characteristics of the CuAlZnMg alloy some differential thermal analysis (DTA), microstructural (XRD) and magnetization (VSM) characterization tests were carried out. The DTA results showed that the alloy is a HTSMA exhibiting reverse martensitic transformations at temperature range between 167 °C and 489 °C. The XRD pattern obtained at room temperature revealed the martensite phases formed in the alloy, which phases are the base mechanism of the reversible martensitic transformation (the SME property) of the alloy. The VSM test showed that the alloy exhibit a diamagnetic property with a weak ferromagnetic coercivity contribution.

Application of memory alloy materials in power system

The shape memory alloy (SMA) is a new kind of metal intelligent material, which has the characteristics of shape memory effect (SME), pseudo-elasticity (PE) and high damping (HD). Therefore, it is widely used in many industries, such as construction engineering, mechanical engineering, space shuttle, energy engineering, medical engineering and so on. In order to solve the heating defects of fittings, the typical six split fittings joints in the main flow circuit of converter station was selected in this paper. And the memory alloy intelligent gaskets and ordinary steel spring gaskets on both sides of the fitting joints were installed. The experimental research on the influence of current on the temperature rise of fittings with different types of gaskets were carried out. The test results showed that the shape memory alloy gasket could automatically generate the deformation force which increased with the increase of temperature, so as to reduce the contact resistance of the joint and the temperature of the contact during operation.

The photo response properties of shape memory alloy thin film based photodiode

In this work, the CuAlMn shape memory alloy (SMA) composed as Cu-12.28Al-2.84Mn in wt.% (=72.49Cu-24.70Al-2.81Mn in at.%) was used as a thin Schottky contact layer on an n-Si wafer to produce a Schottky type Al/CuAlMn/n-Si/Al photodiode. To do this, in the first stage of the experimental route, the CuAlMn alloy was prepared in succession by casting in arc melter, homogenizing in β-phase region and lastly by quenching in iced-brine water. Then, the shape memory effect characteristics were revealed by the widely-used thermal (DSC and DTA) and structural (EDS and XRD) characterization tests that been carried out on the alloy. Then, the alloy was thermally evaporated and deposited on the n-Si wafer as a thin film nano layer to make the Al/CuAlMn/n-Si/Al photodiode. The current-voltage (I-V) analysis of the diode taken under dark and different light intensities revealed the rectifying behavior of the diode. The work function value of CuAlMn alloy film was determined as 4.747±0.17 eV. The reverse bias current values of the diode under light were found to be greater than the value observed under dark. The results showed that the diode has a considerable photoconducting feature. The characteristic electrical diode parameters of the junction were computed by using the traditional I-V method. By taking into consideration the literature works related to SMA layered photodiodes, some of the photodiode parameters such as responsivity, photosensitivity, and detectivity, not been reported so far, were determined for the first time. The SMA/n-Si device showed an excellent photosensitivity (~105) performance, and also good merits of responsivity, and detectivity. Which implied that the produced device can be used in various optoelectronic applications. The transient photocurrent (TPC) measurement was performed under the various light intensity conditions and the related characteristic photodiode parameters were determined. Additionally, the capacitance-voltage (C-V) measurement of the SMA-layered photodiode was also carried out at room temperature and different frequencies. The capacitance of the device was observed to be quite sensitive to frequency. Furthermore, a solution suggestion for SMA film cracks and related fractures was also discussed.

Analysis of Thermo-Mechanical Behavior of Shape Memory Alloys

Shape Memory Alloy (SMA) is widely used and plays an important role in various engineering fields due to its special characteristics of shape memory effect and super-elasticity. In this paper the phase transformation behavior and thermo-mechanics behavior of 50.0at%Ni-Ti SMA are investigated though differential scanning colorimeter (DSC) and tensional tests respectively. Optical micrographs show the transformation of austenite and twinned martensite. The comparing numerical calculation result with tensional test result shows the new macro-mechanical constitutive equation can express the thermo-mechanical behavior of SMA effectively.

Shape memory effect characteristics of a VT22I alloy

The effect of the temperature of heating for quenching on the thermomechanical characteristics of the shape memory effect of a titanium VT22I structural alloy is studied. It is shown that, after deformation to 10–15%, the shape of a sample is partly recovered upon subsequent heating to 200–300°C, and the recovered torsional strain is maximal (5%) after quenching from a β-field temperature. If the recovery of the shape of a deformed sample is constrained, reactive stresses appear in it and the sample does a shape recovery work up to 0.6 MJ/m3. As compared to TN1 nitinol, the thermomechanical characteristics of the VT22I alloy are approximately two times lower; nevertheless, they can be effectively used in some types of functional constructions (e.g., in couplings for assembling pipelines).

Multiple shape-memory behavior and thermal-mechanical properties of peroxide cross-linked blends of linear and short-chain branched polyethylenes

Thermally induced shape-memory effect (SME) in tensile mode was investigated in binary and ternary blends of two ethylene-1-octene copolymers with a degree of branching of 30 and 60 CH3/1000C and/or nearly linear polyethylene cross-linked after melt mixing with 2 wt% of liquid peroxide 2,5-dimethyl-2,5-di-(tert.butylperoxy)-hexane at 190°C. The average cross-link density estimated by means of the Mooney-Rivlin equation on the basis of tensile test data was character- ized between 130 and 170 mol·m-3 depending on the blend composition. Thermal analysis points out multiple crystalliza- tion and melting behavior of blends caused by the existence of several polyethylene crystal populations with different perfection, size and correspondingly different melting temperature of crystallites. That agrees well with the diversity of blends phase morphology characterized by atomic force microscopy. However, triple- and quadruple-SME could be observed only after two- and accordingly three-step programming of binary and tertiary blends, respectively, at suitable temperatures and strains. Compared to performances obtained for the same blend after single-step programming above the maximal melting temperature the significantly poorer characteristics of SME like strain fixity and strain recovery ratio as well as recovery strain rate occurred after multi-step programming.

The shape memory effect in high-strength precipitation–hardening austenitic steels

The structure, values of the shape memory effect (SME) and mechanical properties of austenitic manganese steels, which are strengthened by precipitation of nanosized vanadium carbides under different aging conditions at 600–720 °C, have been analyzed. The formation of VC carbides having different degrees of dispersion can stabilize or destabilize the austenite relative to the formation of the strain-induced ɛ-martensite. Therefore, it is possible to control both SME and the degree of hardening. Large SME (2–2.5%) and high-strength characteristics ( σ 0.2 ∼ 1000 MPa) were obtained for the steels studied.

A study on mechanical properties of Ti-Ni shape memory alloy. Experiments on cyclic characteristics of shape memory effect.

A study on mechanical properties of Ti-Ni shape memory alloy. Experiments on cyclic characteristics of shape memory effect.