Browsing by Author "Liaw, Peter K."

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Amino-functionalization on graphene oxide sheets using an atomic layer amidation technique
(2020-01-14)
Gu, Siyong
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Hsieh, Chien-Te
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Mallick, Bikash Chandra
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Gandomi, Yasser Ashraf
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Chang, Jeng-Kuei
Nitrogen functionalization on graphene sheets has solely been demonstrated with a stepwise amidation implementation within the literature. The present work proposes an atomic layer amidation (ALN) technique to linearly adjust the surface amidation level on the carbon nanostructures. The ALN cycling protocol proposed in this work consists of an ammonia pulse, nitrogen pulse, and pumping at 100 and 150 degrees C. Both surface amidation and oxidation levels were linearly controlled by the ALN cycle number. The ALN technique was demonstrated as a self-limiting process capable of step-by-step N-functionalizing graphene oxide (GO) sheets on the atomic scale. The amidation reaction rates were ca. 0.023 (100 degrees C) and 0.028 atomic percent (at%) cycle(-1) (150 degrees C), and the apparent activation energy was determined to be 14.3 kJ mol(-1) (= 0.148 eV atom(-1)) from the Arrhenius equation. The amidation mechanism for forming the "chemical N" and "lattice N" at an atomic level was also proposed. Linearly controlling the optical band-gap with the ALN cycle number was suggested as a robust method for tuning the oxidation as well as the amidation level on the GO sheets. In this sense, nitrogen functionalization can be utilized for engineering any desirable properties within the graphene sheets.
Fatigue-Crack-Growth Behavior of Two Pipeline Steels
(2016-12)
Chen, Bilin
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Wang, Gongyao
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Chen, Shuying
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Muralidharan, Govindarajan
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Stalheim, Doug
The fatigue-crack-growth behavior of two types of pipeline steels, Alloy B [Fe-0.05C-1.52Mn-0.12Si-0.092Nb, weight percent (wt%)] and Alloy C (Fe-0.04C-1.61Mn-0.14Si-0.096Nb, wt%), have been investigated. Compact-tension (CT) specimens have been tested at various frequencies (10, 1, and 0.1 Hz) and different R ratios (0.1 and 0.5, R = P-min/P-max where P-min is the minimum applied load, and P-max is the maximum applied load) in air. It is concluded that higher R ratios lead to faster crack-growth rates (FCGRs), while frequency does not have much influence on FCGRs. Moreover, Alloy B tends to have better fatigue resistance than Alloy C under various test conditions in air.
High-temperature materials for structural applications: New perspectives on high-entropy alloys, bulk metallic glasses, and nanomaterials
(2019-11-01)
Huang, E-Wen
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Liaw, Peter K.
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材料科學與工程學系
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Department of Materials Science and Engineering
Tougher, lighter, and more formable and machinable metals for broader ranges of applications at higher temperatures are needed now more than ever. High-performance computing, high-resolution microscopy, and advanced spectroscopy methods, including neutrons and synchrotron x-rays, together with advances in metallurgy and metal mixology, reveal the potential of multicomponent advanced metals, such as multicomponent bulk metallic glasses and advanced high-entropy alloys. The development of new experimental approaches relates bulk properties and voxel-associated optimized properties throughout structures with high resolution. The correlations from in situ measurements greatly improve crystal plasticity-based models. This issue of MRS Bulletin overviews recent progress in the field, and this article highlights the importance of these new perspectives. The latest progress and directions in the science and technology for prospective high-temperature metals for structural applications are reported.
Mechanical and Magnetic Properties of the High-Entropy Alloys for Combinatorial Approaches
(2020-03-01)
Huang, E-Wen
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Hung, Guo-Yu
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Lee, Soo Yeol
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Jain, Jayant
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Chang, Kuan-Pang
This review summarizes the state of high-entropy alloys and their combinatorial approaches, mainly considering their magnetic applications. Several earlier studies on high-entropy alloy properties, such as magnetic, wear, and corrosion behavior; different forms, such as thin films, nanowires, thermal spray coatings; specific treatments, such as plasma spraying and inclusion effects; and unique applications, such as welding, are summarized. High-entropy alloy systems that were reported for both their mechanical and magnetic properties are compared through the combination of their Young's modulus, yield strength, remanent induction, and coercive force. Several potential applications requiring both mechanical and magnetic properties are reported.
Origin of serrated flow in bulk metallic glasses
(2019-03-01)
Xie, Xie
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Lo, Yu-Chieh
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Tong, Yang
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Qiao, Junwei
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Wang, Gongyao
Bulk metallic glasses (BMGs) possess amorphous structure and show unique mechanical properties, such as extremely high strength and excellent damage tolerance, entitling them as potential structural materials. So far a great amount of work has been conducted to study BMGs' macroscopic mechanical properties and examine corresponding microscopic deformation defects. However, the connection between macroscopic inhomogeneous deformation at room temperature and microscopic deformation carriers is still poorly understood, due to the lack of an appropriate experimental technique to directly probe the inhomogeneous deformation process on the proper spatial and temporal scales. Here we present the deformation details via in situ thermal imaging about the evolution of heat bands associated with successive serration behavior. For the first time, our experimental work clarifies the coupling of serrated flows with shear band activities, especially the often omitted fine serrations induced by shear band nucleation or the early stage of propagation. Meanwhile, serration behavior of BMGs is simulated through the kinetic Monte Carlo (kMC) method by integrating local heating (thermal softening and beta-relaxation) effects, which exhibits good agreement with experimental results. These findings will advance our fundamental understanding of the shear band operation down to microscopic level, which may shed light on the control of shear banding for the application of BMGs. (C) 2018 Elsevier Ltd. All rights reserved.
Phase transformation assisted twinning in a face-centered-cubic FeCrNiCoAl0.36 high entropy alloy
(2019-12-01)
Yu, Peijun
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Feng, Rui
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Du, Junping
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Shinzato, Shuhei
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Chou, Jyh-Pin
The FeNiCoCr-based high entropy alloys (HEAs) exhibit excellent mechanical properties, such as twin-induced plasticity (TWIP) and phase transformation plasticity (TRIP) that can reach a remarkable combination of strength and ductility. In the present work, the face-centered-cubic (FCC) single-crystal FeNiCoCrAl0.36 HEAs were studied, using the density functional theory (DFT) combined with the phonon calculation to estimate the stacking fault energies, temperature-dependent phase stabilities of different structures. And the kinetic Monte Carlo (kMC) was used to predict the substructures evolution based on the transition state energies obtained from DFT calculations. We proposed two different formation paths of nano-twins in this Al-composited HEA and found that short-range hexagonal-close-packed (HCP)-stacking could occur in this HEA. The DFT calculations suggest that this HEA has negative stacking fault energy (SFE), HCP formation energy, and twin-formation energy at OK. Phonon calculations indicate that at the finite temperature, the competing FCC/HCP phase stability and propensity for twinning make it possible to form HCP-like twin boundaries. The kMC simulations suggest that under deformation, TWINs could form within the HCP laths which differs from the study of others. With the great agreement of results from kMC simulations and experiments, this twin-hcp laminated substructure formation path offers a new concept of designing TWIP HEAs containing tunable twin structures with HCP and TWIN lamellae structures, which could result in better mechanical properties of HEAs. (C) 2019 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.