Effect of inclusion on 4H-SiC during nano-scratching from an atomistic perspective.

Inclusion, a common three-dimension defect, can be introduced during SiC epitaxy. In this study, we constructed nano-scratching molecular dynamics models embedded in two common types of inclusion-C-inclusion and Si-inclusion-to explore the effect of inclusion during scratching. Furthermore, the microstructure and atomistic behavior, surface morphology, scratching force, stress, and temperature were analyzed to bridge the simulation and processing parameters. The results showed that inclusion could affect the microstructure and atomistic behavior, and machinability. To eliminate inclusion completely, high penetration depth was required, but it would promote the process parameter sensitivity of inclusion. In summary, the behavior of C-inclusion embedded in SiC more likes a hard particle, while the behavior of Si-inclusion embedded in SiC more likes a soft particle.

Investigation of the Turbulent Drag Reduction Mechanism of a Kind of Microstructure on Riblet Surface.

With the k-ε renormalization group turbulence model, the drag reduction mechanism of three- dimensional spherical crown microstructure of different protruding heights distributing on the groove surface was studied in this paper. These spherical crown microstructures were divided into two categories according to the positive and negative of protruding height. The positive spherical crown micro-structures can destroy a large number of vortexes on the groove surface, which increases relative friction between water flow and the groove surface. With decreasing the vertical height of the spherical crown microstructure, the number of rupture vortexes gradually decreases. Due to the still water area causes by the blocking effect of the spherical crown microstructure, it was found that the shear stress on the groove surface can be reduced, which can form the entire drag reduction state. In another case, the spherical crown microstructures protrude in the negative direction, vortexes can be generated inside the spherical crown, it was found that these vortexes can effectively reduce the resistance in terms of pressure and friction. In a small volume, it was shown that the surface drag reduction rate of spherical crown microstructures protrudes in negative directions can be the same as high as 24.8%.

A powder-metallurgy-based strategy toward three-dimensional graphene-like network for reinforcing copper matrix composites.

Three-dimensional graphene network is a promising structure for improving both the mechanical properties and functional capabilities of reinforced polymer and ceramic matrix composites. However, direct application in a metal matrix remains difficult due to the reason that wetting is usually unfavorable in the carbon/metal system. Here we report a powder-metallurgy based strategy to construct a three-dimensional continuous graphene network architecture in a copper matrix through thermal-stress-induced welding between graphene-like nanosheets grown on the surface of copper powders. The interpenetrating structural feature of the as-obtained composites not only promotes the interfacial shear stress to a high level and thus results in significantly enhanced load transfer strengthening and crack-bridging toughening simultaneously, but also constructs additional three-dimensional hyperchannels for electrical and thermal conductivity. Our approach offers a general way for manufacturing metal matrix composites with high overall performance.