Magnetic shape memory alloys (MSMAs) are expected to be implemented into micro actuators and sensors because they have a large magnetic field induced strain combined and high response frequency. On the other hand, when dimensions of metallic materials are reduced from a bulk size to the micrometer scale, the mechanical response would vary along with the dimension change. Therefore, it is important to evaluate the mechanical properties of microscale specimens of shape memory alloys to be implemented in miniaturized devices. In the present work, the superelastic properties of the single crystal of Ni 50 Fe 19 Co 4 Ga 27 (at.%) MSMA have been studied by a micro-compression testing. The specimens were micropillars, fabricated by a focus ion beam technique. The compression stress-strain hysteretic dependences show typical superelastic behavior in a wide temperature range alongside a tendency to disappearance of hysteresis near the critical point at about 373K. The temperature shifts the martensitic transformation start stress with a rate of ~1.1 MPa/K, which is similar in value to the bulk alloy. Thus, the studied alloy could retain the superelastic properties, including in a postcritical region, down to microscale.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
An entry from the Cambridge Structural Database, the world’s repository for small molecule crystal structures. The entry contains experimental data from a crystal diffraction study. The deposited dataset for this entry is freely available from the CCDC and typically includes 3D coordinates, cell parameters, space group, experimental conditions and quality measures.
Pd-decorated carbon nanotube (CNT) nanocomposites were added to a UV photopolymer resin to be used as the ink in the printing of three-dimensional (3D) structures. The nanocomposites were prepared with a UV-induced reduction method, in which Pd nanoparticles with a size ranging from 10 to 150 nm were produced and decorated on CNTs. The printed 3D structures from the resin containing 1.0 wt % Pd-decorated CNTs exhibited much improved mechanical properties, achieving a 40% enhancement in fracture strength and a 40% increase in microhardness over the 3D structures printed from the bare resin. In the presence of Pd-decorated CNTs as catalyst seeds, further deposition of defect-free, nearly conformal Ni–P layer on the 3D-printed structures at a high deposition rate can be realized. The cross-cut adhesion testing revealed a significantly enhanced adhesion between the deposited Ni–P layer and the 3D-printed structures. The metallized 3D-printed structures displayed superior electrical conductivity, showing an electrical resistance down to 0.11 Ω as 1.0 wt % Pd-decorated CNTs were incorporated. The findings from this work highlight the merits of employing Pd-decorated CNTs as both mechanical property enhancer and catalyst seeds in the advanced manufacturing of 3D-printed structures.
Au materials fabricated by electroplating are commonly used as contact materials for high reliability circuit boards, electrical connectors, relays, and micro- and nano-scale electronic components for many decades because of their high electrical conductivity, chemical stability, corrosion resistance, and ductility. In recent years, Au has become a promising material to be used as the movable structures and proof mass in micro-electrical-mechanical system (MEMS) accelerometer devices, mostly because of the high density (19.3×10 3 kg/m 3 at 298 K), which is about 10 times higher than that of silicon (2.33×10 3 kg/m 3 at 298 K) [1]. However, Au is known to be a soft material. The mechanical strength becomes a concern in miniaturization of the MEMS device. Yield stress of bulk Au is reported to be 55~200 MPa [2]. Decreasing grain size of the Au materials is expected to further enhance the mechanical properties according to the Hall-Petch relationship [3]. Pulse electroplating (PE) has been reported to be effective in fabricating Au materials with fine grains, high uniformity, and low porosity [4]. Also, it is possible to control the composition and the film thickness by regulating the pulse amplitude and width. Most importantly, an increase in the nuclei density could be achieved to obtain electroplated films with finer grains. On the other hand, for evaluating mechanical properties of the electroplated films, Vickers micro-hardness test is the most popular method. However, the hardness results are often affected by the substrate. It cannot show the real strength of the electroplated materials, especially for films in mico-/nano-scale. Therefore, it is necessary to evaluate micro-mechanical strength of the Au electroplated films for the practical applications in the miniaturized devices. Au electrolyte used in this study was a commercially available sulfite-based electrolyte provided by Matex Japan (Matex Gold NCA). The electrolyte contains 50 g/L of Na 2 SO 3 , 50 g/L of (NH 4 ) 2 SO 3 , and 21.63 g/L of Na 3 [Au(SO 3 ) 2 ] with pH of 8.0 and 5% sodium gluconate. Cu plates and Pt plates were used as the cathode and anode, respectively. For the PE, the pulse current (I on ) was 10 mA/cm 2 , and the off-time current (I off ) was 0 mA/cm 2 . The on-time (T on ) of the PE varied from 1 to 100 ms, and the off-time (T off ) was 10 ms. The reaction temperature was 40 ºC for the gold electroplating. The Au films prepared by the PE showed less defect, lower surface roughness, finer grain size, and denser texture when compared with the Au films prepared by the conventional constant-current electroplating (CE). Micro-mechanical properties of Au micro-pillars fabricated from the Au films were evaluated by micro-compression test. Dimensions of the fabricated pillars were 10 μm×10 μm×20 μm. The compression tests were carried out using a test machine specially designed for micro-sized specimens equipped with a flat-ended diamond indenter at a constant displacement of 0.1μm/s. The Au micro-pillars prepared by the PE showed controllable high strength ranged from 500 to 800 MPa, where the grain size was adjusted by the PE parameters. Finest grain size was estimated to be 10.4 nm, and the highest compressive strength was 800 MPa [5]. The compressive strength obtained is much higher than the values reported in other studies [6,7]. The high strength is suggested to be due to the grain-boundary strengthening mechanism. The results demonstrated that the PE method and the sulfite-based electrolyte are promising for applications in miniaturization of the MEMS devices. To the best of our knowledge, this is the also first report on micro-mechanical strength of pure Au materials fabricated by the PE. References: [1] D. Yamane, T. Konishi, T. Matsushima, K.Machida, H. Toshiyoshi, K. Masu, Appl. Phys. Lett. 104 (2014) 074102. [2] H.D. Espinosa, B.C. Prorok, B. Peng, J. Mech. Phys. Solid 52 (2004) 667–689. [3] N. J. Petch, J. Iron Steel Inst. 174 (1953) 25–28. [4] J. Horkens, L. T. Romankiw, J. Electrochem. Soc. 124 (1977) 1499–1505. [5] C.Y. Chen, M. Yoshiba, T. Nagoshi, T.F.M. Chang, D. Yamane, K. Machida, K. Masu, M. Sone, Electrochem. Commun., 67 (2016) 51–54. [6] D. Jia, K.T. Ramesh, E. Ma, Acta Mater. 51 (2003) 3495–3509. [7] Z. Gan, Y. He, D. Liu, B. Zhang, L. Shen, Scripta Materialia 87 (2014) 41–44.
This study reports on the use of supercritical CO2 (scCO2) for the metallization of ultrahigh-molecular-weight polyethylene (UHMW-PE) filaments, which are used as functional components in weavable devices. UHMW-PE is well known for its chemical and impact resistance, making it suitable for use in bulletproof clothing and shields. However, its chemical resistance poses a challenge for metallization. By utilizing scCO2 as the solvent in the catalyzation process, a uniform and defect-free layer of Ni-P is successfully deposited on the UHMW-PE filaments. The deposition rate of Ni-P is enhanced at higher temperatures during the scCO2 catalyzation. Importantly, the durability of the Ni-P-metalized UHMW-PE filaments is improved when the scCO2 catalyzation is carried out at 120 °C, as evidenced by minimal changes in electrical resistivity after a rolling test.
Pulse-current electrodeposition and a sulfite-based electrolyte were used in fabrication of pure gold films. Surface of the pulse-electrodeposited gold film possessed less defect, lower roughness, smaller grain size, and denser texture when compared with the gold film prepared by constant-current electrodeposition. Microstructures and compressive yield strength of the electrodeposited gold could be controlled by regulating the pulse on-time and off-time intervals in pulse-current electrodeposition. The gold film prepared under the optimum conditions showed an average grain size at 10.4 nm, and the compressive yield strength reached 800 MPa for a pillar-type micro-specimen having dimensions of 10 μm × 10 μm × 20 μm fabricated from the pulse-electrodeposited gold film. Average grain size of the pulse-electrodeposited gold film was much smaller, and the compressive yield strength was much higher than the values reported in other studies. The high strength is due to the grain boundary strengthening mechanism known as the Hall-Petch relationship. In general, the pulse-electrodeposited gold films showed yield strength ranging from 400 to 673 MPa when the average grain size varied by adjusting the pulse-electrodeposition parameters.
Micro-mechanical properties of electrodeposited cobalt films were investigated by micro-compression tests for application in miniaturized magnetic electronic devices. FCC and HCP crystal structures were both present in the electrodeposited cobalt. Nanotwins were also confirmed in the HCP lamellas. The average grain size was ranged from 13.8 to 15.4 nm obtained from the Scherrer equation. Yield strengths of the micro-pillars were ranged from 948 to 1075 MPa, which were about twice that of the bulk cobalt. The high yield strength obtained from the micro-compression test was a result of the fine grain size and the small sample size used in the compression test, which correspond well to the Hall-Petch relationship and the sample size effect, respectively.
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