Papers by Keyword: Nitinol

Abstract: Additively manufactured Nitinol components often exhibit rough surfaces and defects that affect functional performance. This study investigates the feasibility of electropolishing Nitinol in a deep eutectic solvent (ethaline). Linear sweep voltammetry was used to identify anodic potentials suitable for controlled dissolution, and electropolishing was performed at selected potentials. Surface evolution was analysed by SEM, EDX, optical microscopy, and confocal microscopy. Electropolishing in ethaline effectively reduced surface scratches and produced more homogeneous surfaces without altering alloy composition. Higher applied potentials (12.5 V) resulted in complete removal of surface scratches and visually homogeneous surfaces, whereas lower potentials (6 V) mainly reduced the visibility of surface scratches. Compared to conventional inorganic electrolytes, the process exhibits a lower dissolution rate, offering a safer and more controllable approach.

Abstract: In this research work, Ni rich superelastic Nickel-Titanium(NiTinol) alloy rods were joined using a fully automated direct-driven rotary friction welding machine at 1900 rpm. Samples were subjected to heat treatment after the removal of flash bead. Corrosion behavior of the NiTinol samples were carried out using weight loss method and Potentiodynamic Polarization (PDP) technique using 3.5% NaCl and 1N HCl solution in interval of 12h, 24h, 36h, and 48h at different temperature conditions such as 25°C, 35°C, 45°C, and 55°C respectively. Research has been carried out to find the corrosion characteristics for both annealed and cryogenically treated samples. Research findings revealed that, in weight loss method the impact of corrosion has no effect in the welded zone. In PDP method, the corrosion rate is found to be less and insignificant compared to any other alloys. Hence, the material proved as anti-corrosive in nature. This fact is due to the formation of Titanium oxides (TiO₂) and Titanium nitrides passive layers which hinders the rate of corrosion. However, more corrosion resistance was seen in cryogenically treated welded samples compared to the other samples.

Abstract: Nano silica was synthesized using the Stober process with ammonia, ethanol, and tetraethyl orthosilicate (TEOS) solution. Equiatomic titanium-nickel pre-alloyed particles were reinforced with silica nanoparticles of constant volume percent with sizes varying as proceeding 50, 100, 250, and 500 nm. The weighed compositions were mixed in a planetary ball mill, followed by compaction via uniaxial compression of 50 MPa. The resultant green pellets were sintered in an argon atmosphere at 1223K for a period of 4 hrs. Following that, by using EDM, the composite pellets were sectioned, soldered, and cold-mounted. Microstructure was analyzed by optical microscopy, mechanical properties by micro-Vickers hardness testing, and electrochemical analysis by Tafel curves, whereas the effect of particle size at constant volume on the densification was determined via Archimedes' Principle. The reinforcement showed increasing hardness up to 120HV and an increase in phase distribution, in addition to the effect complemented by the transformation of silica, whereas the electrochemical evaluation was affected by both reinforcement and phase distribution. Electrochemical corrosion resistance was measured at 6.88mpy in pure TiNi and 10.93mpy in TiNi nano-silica composite.

Abstract: This work analyzes a shape memory alloy Stirling heat engine through an integrated thermal, mechanical, and materials approach. It builds on our previously published framework by generalizing behavior of shape memory alloys (SMA) beyond the nanoscale and extends it to elastocaloric applications, where mechanical work can be used to induce the stress-induced phase transformation. Parallels between stress-strain and enthalpy-temperature behavior underline this extension. Heat engine performance is evaluated in terms of torque and speed, and consideration is given to fatigue service life. Heat transfer and transformation energetics are examined with implications for heat engine performance. The resulting work supports shape memory alloy based heat engines and refrigerators for thermal management in space applications.

Abstract: Shape setting is a particular thermo-mechanical process used to imprint the desired shape in Nitinol (NiTi) shape memory alloy semi-finished products. It is a critical step as it must simultaneously ensure precise shape definition and specific transformation temperatures (TTs), on which the achievement of functional properties is based. Once a shape setting treatment has been optimized, it becomes highly relevant in industrial production to assess whether the same parameters can be applied to components with different geometries, therefore involving different mold designs. This study investigates the influence of mold geometry on the TTs of NiTi tubes, shape set to obtain different kinds of annuloplasty rings. Starting from the same tube batch and applying identical heat treatment parameters, two mold designs were used to impart different shapes and the phase transformation behavior was investigated. The results show that mold geometry does not significantly affect the TTs, indicating that the same shape setting parameters can be applied across different component geometries.

Abstract: This study investigates the careful investigation of cutting parameters to improve machining effectiveness and increase tool life while milling Nickel-Titanium Shape Memory alloy (NiTiNOL). The NiTiNOL material is employed to manufacture components such as, dental braces, seismic dampers and medical implants. Using Finite Element (FE) simulation, the research closely examines the intricate interactions among parameters, such as feed rate (f_r), depth of cut (D), and cutting speed (V_c). The use of Response Surface Methodology (RSM) and Taguchi has been used to determine the most optimal settings for tool longevity and machining efficiency. The FE simulation model provides a strong framework to investigate how cutting parameters affect necessary reactions. The present study examines interactions among parameters like cutting speed, depth of cut, and feed rate. Moderate cutting speed, lower depth of cut, and the highest feed rate has induced lower stress in the workpiece. This study adds to understanding NiTiNOL alloy machining fundamentals and offers useful information for industry applications. To attain better machining results while milling NiTiNOL alloy, the results are intended to guide an optimization technique

Abstract: Laser Powder Bed Fusion (L-PBF) is turning out to be very promising for biomedical components production and stents are among the devices that would be suitable for tailor-made production. One of the most common stent types are the self-expandable, manufactured with Nitinol (NiTi). The use of NiTi alloy with L-PBF needs to be well controlled, as Ni evaporation during the process leads to significant variations in the final component properties. In the present work, prototype NiTi stents were produced via L-PBF and heat treated to examine the possibility of employing this technology for their application, also considering the Ni evaporation resulting from the layer-by-layer deposition. Samples were characterized through differential scanning calorimetry (DSC), microstructural observations, and compression tests in plate-to-plate configuration according to the standard. In parallel, a commercially available stent manufactured with traditional technology was tested for comparison.

Abstract: Shape memory alloys (SMAs) are a type of smart material and have excellent engineering and medical applications. TiNi binary alloys possess remarkable shape recovery, mechanical properties, corrosion resistance, and excellent biocompatibility. By ternary elements addition just like Au, Pt, Pd, Hf, and Zr, increases transformation temperatures, leading to high-temperature shape memory alloys (more than 100°C) but other elements (Fe, Cu, Co, and Mo) form low-temperature shape memory alloys, (lower than 100°C). In the present work, it is reported that the effect of ternary element addition on microstructural properties, shape memory properties, mechanical properties, corrosion resistance, and biocompatibility of ternary shape memory alloys. Ag, Au, and Cu-based TiNi ternary alloys have excellent biocompatibility. The addition of ternary elements such as Ag and Nb increases corrosion resistance, Fe rises the hysteresis loop, Hf enhances thermal stability, and Mo raises workability.

Abstract: The research of deposition of a nitinol sample in an equiatomic ratio from a powder mixture of nickel and titanium 55Ni-45Ti (in wt.%) is aimed at studying the heterogenicity of the chemical composition in the cross-section of a thin-walled and multilayer (bulk) cylindrical sample. The main task of the study was to determine the presence or absence of the chemical composition deviation from layer to layer, and mechanical properties. Analysis on an optical microscope, EDS analysis, and microhardness measurement, a thin-walled sample was studied. A chemical gradient was detected in the sample from the base along with its entire height. An increase in the content of the Ti element and a decrease of the Ni element was detected with an increase in the number of layers and the height of the sample, and a change in the microstructure and hardness were found. The increase in hardness from the base to the top point of the sample reaches 50%. X-ray phase analysis (XRD) showed the presence of NiTi phases in the martensitic and austenitic state, the side phases of NiTi2 in a thin-walled sample, and the presence of the Ni4Ti3 phase and the TiO2 oxide phase in a cylindrical bulk sample. The chemical composition of the cylindrical bulk sample agrees with the chemical composition of the mixture loaded into the powder feeder 55:45 Ni and Ti in wt. %. To indirectly determine the shape memory effect of the final alloy, mechanical tests were carried out for compression of cylindrical samples with subsequent heating, which confirmed the presence of the shape memory effect with a degree of reversible deformation of about 40%.

Abstract: Over the recent years, Nitinol (Ni-Ti) shape memory alloys have gained popularity in the medical, aerospace and energy sectors, due to their superelasticity, shape memory effect, low stiffness, good biocompatibility and corrosion resistance. Compared to steels and other common metallic materials, it is difficult to model the mechanical behavior of Ni-Ti due to the inherent functional properties caused by the diffusion-less solid-state phase transformations. With the help of Laser Powder Bed Fusion (L-PBF) process, these transformational characteristics can be controlled. This will ultimately lead to controlling the mechanical and thermal properties for specific applications. In this work, Finite Element Analysis (FEA) was conducted to replicate the actual mechanical phenomenon occurring in Nitinol. Models were generated for simulating the superelastic and plastic behaviors, and were validated against actual experimental data. The ability to model the complex mechanical response of Nitinol will enable exploration into the sensitivity of material response to phase volumes, material composition, and strain rate. Robust models of these phenomenal also provide the potential for tailoring in-silico the microstructure required for specified desired macroscopic material properties.