paraphrase the following articles

Coatings

The surface of a component is usually the most important engineering factor. While it is in use it is often the surface of a workpiece that is subjected to wear and corrosion. The complexity of the tribological properties of materials and the economic aspects of friction and wear justify an increasing research effort. In industrialized countries some 30% of all energy generated is ultimately lost through friction, In the highly industrialized countries losses due to friction and wear are put at between 1 and 2% of gross national product. To an increasing degree therefore, the search is on for surface modification techniques, which can increase the wear resistance of materials. Unfortunately, there exists an alomost dewildering choice of surface treatments that cover a wide range of thickness. The choice has to be such that the surface treatment does not impair too much the properties of the substrate for which it was originally chosen; that is to say, it should not reduce the load-bearing overlooked frequently in surface engineering, with emphasis put rather more on the protective coating itself. Equally, the surface treatment chosen should be suitably related to the problem to be solved. If a thin protective layer may do the job, it does not make much sense in concentrating on processing of a thick layer on top of a substrate. It worth noting here that wear resistance is a property not of materials but of systems, since the material of the workpiece always wears against some other medium. It is its relation to its environment ( lubrication and speed of sliding/ rotation) that determines the wear resistance of the material in a given construction. As a general rule, wear is determined by the interplay of two opposing properties: ductility and hardness. Wear can be reduced by modifying the surface layer in such a way that it acquires higher ductility. So, that greater plastic deformation can occur without particles breaking off. Soft surface layers can be very effective in reducing wear due to delamination. Resistance to wear by abrasion, on the other hand, is then low. However, wear can also be reduced by making the surface layer harder. Then again, increasing hardness also means an increase in the elasticity strain limit and a reduction in ductility, leading to a lowering of fatigue resistance and hence to brittle failure. The characteristics of the system ( whether the wear is caused by delamination or abrasion) determine which of surface engineering methods should be chosen. An interesting approach is decreasing the grain size, which could lead to both an increase in mechanical strength and fracture toughness.

Graphene has been used to make the thinnest coating known world over can be used for protecting metal against corrosion. The potential use of graphene as anticorrosion coating was discussed at American Chemical Society, ACS Nano by D. Prasai and his colleagues. Rusting and other corrosion of metals is an important global problem. Contact of metal with air, water, or other substances can cause corrosion. Graphene is a single layer of carbon atoms. It is evaluated for use as anticorrosion coating. An ounce of graphene arranged in a single layer and comprised of rows of benzene rings can fill the size of 28 football fields. Graphene whether made directly on copper ornickel or transferred onto another metal can be used to prevent corrosion. Copper coated with graphene by CVD, chemical vapor deposition, was found to corrode seven times faster than uncoated copper. Nickel coated with corrode seven times faster than uncoated copper. Nickel coated with multiple layers of organic coating. Graphene coating may be ideal for applications in industrial microelectronics. They can be used in aircrafts, implants, and as interconnects. It is not clear whether the cost of graphene will come down to make the use of it as corrosion resistant coating profitable.

Challenges and opportunities

Making an appropriate microstructure of a nanostructured coadting is an epitome in material design. This is so because the concentration of lattice defects and the details of the numerous interfaces, including the topology of the triple junctions between the interfaces, determine the overall mechanical response. The overarching challenge is therefore the design of nanostructured coating that is free of defects that degrade the structural and functional behavior. As will be discussed in various chapters in this book, from experimental and theoretical analyses, one can conclude, with a certain confidence, that deformation in nanocrystalline materials, in particular metals, is at least partially carried by dislocation activity for grain size above a critical value around 10-15 nm. Below that critical value, plastic deformation is mostly carried by grain boundary processes. Nevertheless, in many investigations it has been overlooked quite often that several deformation processes might act simultaneously. This means that even though dislocations are observed above the critical grain size and less below the critical grain size, various grain boundary processes are likely to occur at the same time. In evaluating the performance of a nanostructured coating, it is essential to examine the defect content as well as the microstructural features, in particular, grain-size dispersion, distribution of interface misorientation angles, and internal strains. It can be anticipayed that control of the grain-size dispersion is extremely important in the experimental design of these nanostructured coatings. A nanostructured material with a broad grain-size dispersion will exhibit a lower overall flow stress that a material with the same average grain size but with a much smaller grain-size distribution. Consequently, experimental control over the grain-size distribution is important to investigate concepts in materials design of nanostructured coatings.

Brief History of Graphene

Graphene is a new addition to the family of carbon nanostructures, and was recently discovered by Geim and Novoselov(2004) at Manchester University. This discovery accelerated research activity in the area of its synthesis and characterization, properties, and applications. Graphene is a two-dimensional (2D) one- atom-thick planar sheet of sp2 bonded carbon atoms densely packed in a honeycomb crystal lattice. It is known as the mother element of some carbon allotropes, including graphite, carbon nanotubes(CNTs), carbon nanofiber, and fullerenes as shown in Figure 6.1 [1.2]. However until 2004, single-layer graphene (SLG) was believed to be thermodynamically unstable under ambient conditions. It is an exotic material of the twenty-first century and received worldwide attention due to its exceptional charge transport, thermal optical, and mechanical properties [4-7].( https://books.google.com/books?id=KekbDAAAQBAJ&pg=PA74&dq=history+nanostructured+graphene+coating&hl=en&sa=X&ved=0ahUKEwjSl7Dk-u3SAhXm8YMKHSB6D84Q6AEISzAJ#v=onepage&q=history%20nanostructured%20graphene%20coating&f=false)