613 research outputs found
High damping NiTi/Ti3Sn in situ composite with transformation-mediated plasticity
No full textThe concept of transformation-induced plasticity effect is introduced in this work to improve the plasticity of brittle intermetallic compound Ti3Sn, which is a potent high damping material. This concept is achieved in an in situ NiTi/Ti3Sn composite. The composite is composed of primary Ti3Sn phase and (NiTi + Ti3Sn) eutectic structure formed via hypereutectic solidification. The composite exhibits a high damping capacity of 0.075 (indexed by tan delta), a high ultimate compressive strength of 1350 MPa, and a large plasticity of 27.5%. In situ synchrotron high-energy X-ray diffraction measurements revealed clear evidence of the stress-induced martensitic transformation (B2 -> B19') of the NiTi component during deformation. The strength of the composite mainly stems from the Ti3Sn, whereas the NiTi component is responsible for the excellent plasticity of the composite. (C) 2014 Elsevier Ltd. All rights reserved
Instrumental and sensory characteristics of a baked product containing barley flour with varying amounts of beta-glucan and sugar substitute
No full textThe objective of this study was to determine the influence of varying levels of beta-glucan in barley flour on selected properties of a model baked product. Another aim was to reduce sugar levels in the product by incorporating a natural sweetener stevia and to monitor its influence using instrumental and sensory analysis. Batter rheology was studied using a lubricated squeezing flow technique, pasting profiles of the barley flours were determined with a rheometer, viscoelastic properties were evaluated using dynamic oscillatory rheology to measure G’ and G”, and firmness of the baked products was monitored using a texture analyzer, for changes occurring due to varying β-glucan levels in barley flour and removal of sugar. L a* b* color values of barley flour and muffins were obtained using a colorimeter. A descriptive sensory panel was trained to observe changes in product attributes when stevia was used to replace sugar in the high betaglucan product. Water absorption index was found to be significantly higher for high β-glucan barley flour. The color of both barley flours also had a significant difference in L* (lightness) and b* (yellowness) values. Similarly, muffin samples prepared without sugar, using stevia, were significantly lighter in surface color (higher L*), while the interior colors were darker (higher b*). Low beta-glucan dough showed a lower biaxial extensional viscosity compared to the high beta-glucan dough, which indicates that the level of beta-glucan present in the barley flour has an impact on the dough viscosity. The pasting profiles of the flours were also found to be significantly different, where the high beta-glucan barley flour resulted in a significantly higher peak viscosity but lower peak time compared to low β-glucan barley flour. Muffin firmness was found to be significantly higher when sugar was omitted from the formulation, but there was no significant difference in firmness among the two beta-glucan levels in the muffins. The sensory descriptive panel found significantly higher firmness, surface roughness, and bitterness attributes for the high β-glucan muffins prepared with stevia. Additional efforts will be needed to mask the undesirable attributes in the model baked product occurring due to the removal of sugar.M.S.Includes bibliographical referencesby Niti Lathi
Highly biocompatible porous NiTi alloys
No full textNickel Titanium alloys have proved to be a perfect choice for materials used for medical devices like catheters, pacemakers and stone removal mesh. However, there are some challenges related to the shape and size modifications required to suffice the applications. The alloy needs improvements particularly in the areas of porosity for bone replacement, radiopacity, super elasticity and fatigue strength. There is a wide range of applications of biocompatible Porous NiTi alloys in the areas of inter body fusion devices, synthetic bone grafting, etc. Although it cannot be denied of the possibility of high corrosion factor of Porous NiTi alloys as compared to solid NiTinol due to greater surface area in contact with the body fluids. Such cases include definite surface preparation to cater to the need for increased biocompatibility. This paper includes the synthesis of porous NiTi alloys through the sintering process along with a check of the surface treatments and its effects on the properties related to corrosion of Porous NiTinol. The Alloys were subjected to different treatments like dry heating, boiling in water and passivation. The corrosion resistance, after and before the treatments were evaluated
Healing cracks in additively manufactured NiTi shape memory alloys
No full textThe pursuit of enhancing NiTi superelasticity through laser powder bed fusion (L-PBF) and [001] texture creation poses a challenge due to increased susceptibility to hot cracking in the resulting microstructure with columnar grains. This limitation restricts NiTi's application and contributes to material waste. To overcome this, we introduce a pioneering approach: utilising spark plasma sintering (SPS) to heal directional cracks in [001] textured L-PBF NiTi shape memory alloy. Diffusion bonding and oxygen utilisation for Ti2NiOx formation was found to successfully heal the cracks. SPS enhances mechanical properties, superelasticity at higher temperatures, and two-way shape memory strain during thermomechanical cycling. This work provides an alternative solution for healing cracks in L-PBF parts, enabling the sustainable reuse of cracked materials. By implementing SPS, this approach effectively addresses hot cracking limitations, expanding the application potential of L-PBF NiTi parts while improving their functional and mechanical properties.Team Vera PopovichTeam Marcel Herman
NiTi thin films on a flexible substrate: Fabrication & Characterization
No full textNiTi (Nickel Titanium) is a shape memory alloy (SMA) known for shape memory effect and superelasticity. The shape memory effect and superelasticity allows NiTi to be strained reversibly unto 6-8%. NiTi thin films are of technological interest as actuator materials in microelectromechanical systems (MEMS) because they possess a large deformation and recovery force compared to other performance materials proposed for fabricating microactuators . Several early attempts were made to fabricate NiTi thin films and build NiTi thin film based microactuator prototypes, such as micropumps and microvalves, microgrippers and microsensors. The aim of this PhD thesis is to study the optimization of the deposition conditions for the formation of NiTi films on polyimide flexible substrates and to exploit the shape memory and superelastic property of NiTi for flexible deformable devices. In order to achieve this goal, a three-magnetron sputter deposition chamber has been used allowing to heat and to apply a bias voltage to the substrate. Prior to the deposition of NiTi, a thin layer of Cr (~10nm) was sputter deposited onto flexible polyimide substrates. Cr acts as an adhesion layer between NiTi and the flexible substrate. This equipment is mounted with a wafer curvature setup enabling an in-situ characterization of film stress during their growth. In addition to the in-situ studies, complementary ex-situ characterization techniques such as X-ray diffraction (XRD), cross-sectional transmission electron microscopy (X-TEM), Atomic force microscopy (AFM) and electrical resistivity (ER) measurements during temperature cycling have been used for a fine structural characterization. To test the maximum strain the NiTi/polyimide composite structure can withstand in-situ measurements of film resistance as a function of strain were performed. Measurements of the resistance of the samples yields insight in the strain at which the film fails.Precision and Microsystems EngineeringMechanical, Maritime and Materials Engineerin
In situ synchrotron X-ray diffraction study of deformation behavior and load transfer in a Ti2Ni-NiTi composite
No full textThe deformation behavior and load transfer of a dual-phase composite composed of martensite NiTi embedded in brittle Ti2Ni matrices were investigated by using in situ synchrotron x-ray diffraction during compression. The composite exhibits a stage-wise deformation feature and a double-yielding phenomenon, which were caused by the interaction between Ti2Ni and NiTi with alternative microscopic deformation mechanism. No load transfer occurs from the soft NiTi dendrites to the hard Ti2Ni matrices during the pseudoplastic deformation (detwinning) of NiTi, which is significantly different from that previously reported in bulk metallic glasses matrices composites. (c) 2014 AIP Publishing LLC
Study on highly biocompatible porous NiTi alloys
No full textNickel Titanium alloys have shown to be an excellent choice for medical equipment such as catheters, pacemakers, and stone removal mesh. However, there are some challenges related to the shape and size modifications required to suffice the applications. The alloy needs improvements particularly in the areas of porosity for bone replacement, radiopacity, super elasticity and fatigue strength. There is a wide range of applications of biocompatible Porous NiTi alloys in the areas of inter body fusion devices, synthetic bone grafting, etc. Although it cannot be denied of the possibility of high corrosion factor of Porous NiTi alloys as compared to solid NiTinol due to greater surface area in contact with the body fluids. Such cases include definite surface preparation to cater to the need for increased biocompatibility. This paper includes the synthesis of porous NiTi alloys through the sintering process along with a check of the surface treatments and its effects on the properties related to corrosion of Porous NiTinol. The Alloys were subjected to different treatments like dry heating, boiling in water and passivation. The corrosion resistance, after and before the treatments were evaluated. It is concluded that NiTi alloys can be distinctively used for interbody fusions and can be designed into various very useful components for replacements in biomedical implants
Mechanical and shape memory properties of NiTi triply periodic minimal surface structures fabricated by laser powder bed fusion
No full textPorous NiTi lattice structures are widely used in the manufacture of crucial components owing to their excellent shape memory effect, superelasticity, and high damping capacities. However, the specific strength and lightweight characteristics of porous NiTi lattice structures fabricated by conventional technologies are limited by unpredictability. In this work, three types of porous NiTi structures based on triply periodic minimal surface (TPMS) – Diamond, Gyroid, and Primitive – were designed and manufactured by the laser powder bed fusion (LPBF) additive manufacturing process. This work demonstrates LPBF is a feasible and efficient approach to fabricate highly accurate porous NiTi TPMS structures. Moreover, the influence of each of these structures on the mechanical and shape memory properties was investigated. Among the three structures, Gyroid had the smallest volume fraction deviation. Furthermore, the Diamond structure had the largest compressive modulus (782.82 MPa) and ultimate yield strength (163.14 MPa). The Gyroid and Primitive structures exhibit excellent elastic recovery deriving from high values of compressive modulus (662.44 MPa, and 703.29 MPa), and can maintain reliable structural robustness. The Primitive structure exhibited the lowest mechanical properties (37.80 MPa). During the cyclic compression test, Gyroid and Primitive show a smaller unrecovered strain than Diamond. Primitive shows the largest recovered strain during the heating process (6.98%). The higher mechanical flexibility of Primitive structure endows this structure with higher recovery ratio. During the direct compression test, the residual strain exhibits a positive correlation with the loading strain. All three structures exhibit good deformation recovery capability with a strain of 4%. At a strain of 12%, recovered strain during heating became the dominant factor in the recovery of the TPMS structure. Overall, porous NiTi TPMS structures are capable of reversible compressibility composed of rapid elastic recovery and controllable shape memory recovery. The unique performance of porous NiTi TPMS structure fabricated by LPBF renders it a highly efficiency energy-absorbing structure.Green Open Access added to TU Delft Institutional Repository 'You share, we take care!' - Taverne project https://www.openaccess.nl/en/you-share-we-take-care Otherwise as indicated in the copyright section: the publisher is the copyright holder of this work and the author uses the Dutch legislation to make this work public.Biomechanical Engineerin
In-situ investigation of dynamic deformation in NiTi shape memory alloys under laser induced shock
No full textThe free surface particle velocity of NiTi target shocked with a pulsed laser beam was measured with a photonic Doppler velocimetry (PDV) system to study the dynamic deformation behavior of NiTi alloys at ultra-high strain rate of 10(6)similar to 10(7)/s. Through the analysis of the particle velocity profiles, the shock wave intensity was found to have the influence on the process of austenite-martensite transformation. Theoretical analysis of shock wave propagation showed that the first plateau in the velocity profile was caused by martensitic transformation and the second plateau if existing is caused by the subsequent plastic yielding of shock induced martensite. Residual martensite of the NiTi, which exhibited as needlelike structures, was observed in the laser shocked region. Based on the present results, and the studies by Nemat-Nasser et al. (2005), Liao et al. (2012), and Wang et al. (2013), we concluded that laser induced shock can cause the martensitic transformation as long as the laser induced shock pressure reaches a critical value. The dynamic transition stress and the dynamic tensile strength of NiTi alloys were also determined from the experimentally measured surface velocity profile. (C) 2017 Elsevier Ltd. All rights reserved
Effect of heat treatment on microstructure and functional properties of additively manufactured NiTi shape memory alloys
No full textAdditive manufacturing of NiTi shape memory alloys has attracted attention in recent years, due to design flexibility and feasibility to achieve four-dimensional (4D) function response. To obtain customized 4D functional responses in NiTi structures, tailorable phase transformation temperatures and stress windows as well as one-way or two-way shape memory properties are required. To achieve this goal, various heat treatments, including direct aging, annealing and annealing followed by aging, were optimized for the Ti-rich NiTi (Ni49.6Ti (at. %)) fabricated by laser powder bed fusion (L-PBF). Microstructural evolution, phase transformation, precipitation and shape memory behaviour were systematically investigated by multiscale correlative microstructural, differential scanning calorimetry analysis and thermomechanical analysis. Based on optimized heat treatments, ∼25 K phase transformation temperature windows and ∼90 MPa stress windows were achieved for the one-way shape memory effect. Solutionized annealing was found to be the most effective way to improve one-way shape memory degradation resistance, due to the reduction of defects and solid solution strengthening. One of the main findings of this study is that the heterogonous microstructures between hard intergranular Ti2NiOx and soft NiTi matrix, induced by solutionized annealing with subsequent aging, result in strain partitioning and enclosing the internal stress state, which was found to promote a pronounced two-way shape memory effect response. The results of this work provide in-depth knowledge on tailoring and designing functional shape memory characteristics via heat treatments, which contributes to expanding L-PBF NiTi application fields, such as biomedical implants, aerospace components, and other advanced engineering applications.Team Vera PopovichQN/AfdelingsbureauTeam Maria Santofimia NavarroTeam Marcel Herman
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