Due to the strong in-plane but weak out-of-plane bonding, it is relatively easy to separate nanosheets of two-dimensional (2D) materials from their respective bulk crystals. This exfoliation of 2D materials can yield large 2D nanosheets, hundreds of micrometers wide, that can be as thin as one or a few atomic layers thick. However, the underlying physical mechanisms unique to each exfoliation technique can produce a wide distribution of defects, yields, functionalization, lateral sizes, and thicknesses, which can be appropriate for specific end applications. The five most commonly used exfoliation techniques include micromechanical cleavage, ultrasonication, shear exfoliation, ball milling, and electrochemical exfoliation. In this review, we present an overview of the field of 2D material exfoliation and the underlying physical mechanisms with emphasis on progress over the last decade. The beneficial characteristics and shortcomings of each exfoliation process are discussed in the context of their functional properties to guide the selection of the best technique for a given application. Furthermore, an analysis of standard applications of exfoliated 2D nanosheets is presented including their use in energy storage, electronics, lubrication, composite, and structural applications. By providing detailed insight into the underlying exfoliation mechanisms along with the advantages and disadvantages of each technique, this review intends to guide the reader toward the appropriate batch-scale exfoliation techniques for a wide variety of industrial applications.
This paper aims to investigate the effectiveness of super-hard ceramic coatings by evaluating tool wear when drilling carbon fiber-reinforced plastics (CFRP) composite. The drilling experiments of CFRP are conducted with diamond-like carbon (DLC) coated, AlMgB14 (BAM) coated, AlCrN and Si3N4 and TiN (simply denoted as (AlCrSi/Ti)N) coated, and uncoated tungsten carbide drills. Each coating, dictated by its unique processing technique, provides unique thickness and morphology, and its physical properties, which makes the comparison among the coatings much difficult but enables to deduce the desirable attributes in the prospective coating ideally suited in drilling CFRP. To do so, after the drilling experiments, the tool wear was captured using the scanning electron and confocal laser scanning microscopes to construct the wear evolution that enables us to evaluate each coating qualitatively as well as quantitatively. Among the drills tested, the (AlCrSi/Ti)N-coated drills provided the best performance despite of the fact that (AlCrSi/Ti)N coating particularly are not harder than any other coating. The superior performance of the (AlCrSi/Ti)N coating can be explained by the comparable stiffness to the carbide substrate, 7.3 μm-thick coating consisting of the numerous nanoscale alternating layers between nanocomposite of AlCrN and Si3N4 and TiN coatings and the enhanced adhesion, which provide the effective cutting of carbon fibers. However, the thin DLC coating despite of its superior hardness and the BAM coating despite of its low friction did not perform at the level that the (AlCrSi/Ti)N coating was able to achieve.
This paper aims to investigate the effectiveness of several superhard ceramic coatings on carbide drills when drilling carbon fiber reinforced plastics (CFRP) composite/Ti-6Al-4V alloy (titanium or Ti) stacks. The drilling experiments of CFRP/Ti stack are conducted with diamond-like coating (DLC) coated, alternating layers of the nanocomposite of AlCrN & Si3N4 and TiN or (AlCrSi/Ti)N coated, and uncoated tungsten carbide drills. Tool wear evolution of each drill is measured qualitatively as well as quantitatively using the scanning electron and confocal laser scanning microscopes (CLSM) by interrupting after making certain numbers of hole. Based on our drilling experiments, the performance of each coating when drilling CFRP/Ti stack are discussed. Among these coated and uncoated drills, uncoated and DLC coated drills failed before making 5 holes while (AlCrSi/Ti)N coated drills performed the best making more than 80 holes. The DLC coating, despite of high hardness of DLC coating, does not provide any significant protection especially when drilling Ti layer.
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