Browsing by Author "Yang, Jenn-Ming"

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Conformal Electrodeposition of Co-Ni to Improve the Mechanical Properties of Three-Dimensional Ordered Macroporous Ni Films
(2020-01-22)
Wang, Guang-Ren
;
Hung, Pei-Sung
;
Chang, Shou-Yi
;
Yang, Jenn-Ming
;
Tseng, Yuan-Chieh
Three-dimensional ordered macroporous Ni films, known as Ni inverse opals, are fabricated via a template approach in which polystyrene (PS) microspheres (820 nm in diameter) are assembled in closely-packed colloidal crystals via a vertical electrophoresis process, followed by electroplating of Ni into the interstitial voids within the colloidal crystals and the selective removal of PS microspheres. To improve its mechanical strength, a conformal Ni-Co layer (45 similar to 64 nm) is electrodeposited on the skeletons of the Ni inverse opals by cyclic voltammetry. After coating, from nano-indentation tests, the hardness and reduced elastic modulus are enhanced considerably (172 similar to 220% for hardness; 72 similar to 79% for reduced elastic modulus), as compared to those of pristine inverse opals. After an annealing treatment for the interdiffusion of Ni and Co, the sample reveals an even stronger hardness. X-ray diffraction patterns indicate that the finite thickness of the inverse opals skeletons induces preferential growth of the (111) plane. In short, a combined effect of solid solution alloying, thickening of inverse opals skeletons for greater load bearing, and a predominant (111) plane is responsible for the improved mechanical strength of the Ni inverse opals. (C) 2020 The Author(s). Published on behalf of The Electrochemical Society by IOP Publishing Limited.
Deformation mechanisms in ultrahigh-strength and high-ductility nanostructured FeMnAlC alloy
(2014-02-15)
Lin, Chih-Lung
;
Chao, Chuen-Guang
;
Juang, Jenh-Yih
;
Yang, Jenn-Ming
;
Liu, Tzeng-Feng
The deformation mechanisms of a bulk nanostructured Fe-30Mn-9.5Al-2.0C (in wt.%) alloy were investigated. After aging at 450 degrees C for 9-12 h, the alloy exhibits an exceptional strength-ductility combination (e. g. yield strength similar to 1406 MPa with elongation similar to 32%). The aged alloy exhibits a novel microstructure with isolated austenite nano-channels bounded by an extremely high volume fraction of directional nano-sized (Fe,Mn)(3)AlC carbides (kappa'-carbides). The plastic deformation was found to be dominated by bursting dislocation nucleation within the isolated austenite nano-channels. (C) 2013 Elsevier B. V. All rights reserved.