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Effect of Laser Positioning on the Microstructure and Properties of NiTi-Copper Dissimilar Laser Welds
摘要： Dissimilar pulsed laser welding of 400-lm NiTi and Cu wires was used to investigate the effect of laser positioning on NiTi-Cu joint performance. Laser positioning was found to have a significant role in the microstructure due to the difference in mixing patterns and composition distributions. Homogenous element distribution was observed in both the NiTi offset and the centerline joints, while complex mixing patterns were observed in the Cu offset joints. Changing the laser position resulted in a change in alloy content in the weld pool that affected the mixing patterns, and the phases that were formed in the weld zone of each sample. By moving the laser beam from NiTi toward Cu, NiTi and NiTiCu in the weld zone were replaced by pure Cu which resulted in a decreased average hardness from 512 to 158 HV. However, high hardness values were found inside the weld zone of Cu offset welds due to the presence of hard and brittle ternary intermetallic compounds. The 100-lm Cu offset joint displayed the worst mechanical response due to its inhomogeneous microstructure and the presence of cracks and pores. It was shown that positioning the laser beam on the NiTi or on the centerline resulted in a better transition in microstructure that led to acceptable mechanical properties without optimizing laser parameters or inserting any interlayers.
关键词： dissimilar welding,copper,laser welding,laser positioning,shape-memory alloys,NiTi alloy
更新于2025-09-23 15:19:57
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Microstructural Variation at Interface during Fiber Laser Joining of NiTi/Ti6Al4V and effect of Mechanical Strength
摘要： The mechanical analysis of the weldments reveals that minimum tensile strength of the welded joint is more than the ultimate tensile strength of the weakest intermediate material (copper). The study had presents the possibility of using high melting point intermediate layer material during welding of nitinol with other materials to avoid the formation of unwanted phases.
关键词： Fracture analysis,Radiographic,Dissimilar welding,Interlayer,Ti6Al4V,NiTi,Cu
更新于2025-09-23 15:19:57
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Effect of Ultrasonic Nanocrystal Surface Modification on the Microstructure and Martensitic Transformation of Selective Laser Melted Nitinol
摘要： Nitinol has significant potential for biomedical and actuating-sensing devices, thanks to its functional properties. The use of selective laser melting (SLM) with Nitinol powder can promote novel applications aimed to produce 3D complex parts with integrated functional performances. As the final step of the production route, finishing processing needs to be investigated both for the optimization of the surface morphology and the limit alteration of the Nitinol functional properties. In this work, the effect of an advanced method of surface modification, ultrasonic nanocrystal surface modification (UNSM), on the martensitic transformation and microstructure of SLM built Ni50.8Ti49.2 (at.%) was investigated. Scanning electron microscopy, X-ray diffraction, and differential scanning calorimetry indicated that the UNSM process can generate stress-induced martensite, at least partially suppressing the martensitic transformation. The microhardness profile indicates that the UNSM process can affect the mechanical properties of the SLMed Nitinol sample in a range of up to approximately 750 μm in depth from the upper surface, while electron backscatter diffraction analysis highlighted that the initial austenitic phase was modified within a depth below 200 μm from the UNSMed surface.
关键词： NiTi,ultrasonic nano-crystal surface modification,EBSD,XRD,selective laser melting,microstructure
更新于2025-09-16 10:30:52
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Micro-channel fabrication on NiTi shape memory alloy substrate using Nd <sup>3+</sup> : YAG laser
摘要： Microchannel has been fabricated on NiTi shape memory alloy (SMA) sheet employing nanosecond Nd3+: YAG laser in open-air and underwater processing conditions. Microchannels were fabricated using three different laser wavelengths (1064, 532 and 355 nm) and scanning speeds (4, 10, 14 μm/s). A comparison of the effect of processing condition (open-air and underwater) and scanning speed on the kerf dimension has been examined. The scanning electron micrographs revealed no debris formation and no recast layer formation in underwater conditions whereas the surface irregularities were predominant in the open-air environment. Further, the influence of machining on NiTi in open-air and underwater was studied using UV-Vis spectroscopy. The austenitic phase attributed to shape memory characteristics was evident in processed material in comparison to unmachined material using the X-ray diffraction technique. In addition, differential scanning calorimetry demonstrated the phase transformation temperatures. The samples processed in open-air and underwater environment showed a significant shift in phase transformation temperatures. These laser-based processing techniques are highly useful in preserving smart material characteristics and fabrication of microchannels used in controlled volume drug delivery, microfluidic and waste or body heat-based actuated devices.
关键词： underwater,Nd3+: YAG,UV,NiTi,SMA,micro channeling,transformations,Laser
更新于2025-09-16 10:30:52
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A prediction model for finding the optimal laser parameters in additive manufacturing of NiTi shape memory alloy
摘要： Shape memory alloys (SMAs) have been applied for various applications in the fields of aerospace, automotive, and medical. Nickel-titanium (NiTi) is the most well-known alloy among the others due to its outstanding functional characteristics including superelasticity (SE) and shape memory effect (SME). These particular properties are the result of the reversible martensite-to-austenite and austenite-to-martensite transformations. In recent years, additive manufacturing (AM) has provided a great opportunity for fabricating NiTi products with complex shapes. Many researchers have been investigating the AM process to set the optimal operational parameters, which can significantly affect the properties of the end-products. Indeed, the functional and mechanical behavior of printed NiTi parts can be tailored by controlling laser power, laser scan speed, and hatch spacing having them a crucial role in properties of 3D-printed parts. In particular, the effect of the input parameters can significantly alter the mechanical properties such as strain recovery rates and the transformation temperatures; therefore, using suitable parameter combination is of paramount importance. In this framework, the present study develops a prediction model based on artificial neural network (ANN) to generate a nonlinear map between inputs and outputs of the AM process. Accordingly, a prototyping tool for the AM process, also useful for dealing with the settings of the optimal operational parameters, will be built, tested, and validated.
关键词： Shape memory alloys,Modeling,NiTi,Artificial neural network,Additive manufacturing
更新于2025-09-12 10:27:22
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[ASME ASME 2018 International Design Engineering Technical Conferences and Computers and Information in Engineering Conference - Quebec City, Quebec, Canada (Sunday 26 August 2018)] Volume 4: 23rd Design for Manufacturing and the Life Cycle Conference; 12th International Conference on Micro- and Nanosystems - New Insights Into Shape Memory Alloy Bimorph Actuators Formed by Electron Beam Evaporation
摘要： In order to create shape memory alloy (SMA) bimorph microactuators with high-precision features, a novel fabrication process combined with electron beam (E-beam) evaporation, lift-off resist and isotropic XeF2 dry etching method was developed. To examine the effect of E-beam deposition and annealing process on nitinol (NiTi) characteristics, the NiTi thin film samples with different deposition rate and overflow conditions during annealing process were investigated. With the characterizations using scanning electron microscope and x-ray diffraction, the results indicated that low E-beam deposition rate and argon employed annealing process could benefit the formation of NiTi crystalline structure. Besides, SMA bimorph microactuators with high-precision features as small as 5 microns were successfully the thermomechanical performance was experimentally verified and compared with finite element analysis simulation results.
关键词： microfabrication,annealing,microactuators,bimorph,lift-off resist,electron beam evaporation,XeF2 dry etching,NiTi,x-ray diffraction,shape memory alloy
更新于2025-09-09 09:28:46