Formation mechanism of ordered stress-relief patterns in a free sustained Cu film system

A nearly free sustained copper （Cu） film system has been successfully fabricated by thermal evaporation deposition of Cu atoms on silicone oil surfaces, and a characteristic ordered pattern has been systematically studied. The ordered pattern, namely, band, is composed of a large number of parallel key-formed domains with different width w but nearly uniform length L; its characteristic values of w and L are very susceptible to the growth period, deposition rate and nominal film thickness. The formation mechanism of the ordered patterns is well explained in terms of the relaxation of the internal stress in the films, which is related to the nearly zero adhesion of the solid-liquid interface. By using a two-time deposition method, it is confirmed that the ordered patterns really form in the vacuum chamber.

An internal cooling grinding wheel:From design to application

The cooling and lubrication conditions during the grinding process significantly impact the nickel-based superalloy’s final service performance.The existing jet cooling and heat pipe technology can solve the heat conduction problem in the grinding process of superalloy.Still,managing cooling,lubrication,and chip removal are difficult.This paper describes the design and fabrication of a novel central fluid-through internal cooling slotted grinding wheel with an ordered grain pattern to improve the grinding machinability of a nickel-based superalloy.The pressurized grinding fluid was ejected into the grinding zone via the pipe and tool holder from the lower-end face of the inner cooling wheel.The structure of the grinding wheel was optimized using computational fluid dynamics(CFD).The flow field in the grinding area achieved the highest overall flow rate,distribution homogeneity,and effective exit flow when the internal flow channel had four throughholes.The exit for the inner runner is located at the abrasive edge and diamond staggered pattern.Single-layer brazing was used to create cubic boron nitride(CBN)abrasive rings with various abrasive patterns.The internal cooling wheel matrix and various components were prepared according to the optimized grinding wheel geometry model.A grinding test bench was built to conduct an experimental study of grinding the nickel-based alloy GH4169.The results show that,under the same conditions,a diamond-shaped staggered pattern obtains lower grinding temperature,lower surface roughness,better surface morphology,and more significant residual compressive stress distribution than an abrasive cluster diagonal circular staggered pattern or disordered pattern.The average effective flow rate calculated by CFD is increased by 42.3%when compared to the disordered pattern.In the experiment,compared to the disordered arrangement,with the increase of grinding wheel’s rotating speed and coolant pressure,the average grinding temperature of abrasive grain with diamond-interleaved arrangement decreases by 58.2%and 51.7%respectively,and its surface hardening degree decreases by 11.1%and 11.7%respectively.

Fabrication of virus-like particles with strip-pattern surface：A two-step self-assembly approach

Spherical nanostructures with striped patterns on the surfaces resembling the essential structures of natural virus particles were constructed through a two-step self-assembly approach of polystyrene-boligo（acrylic acid）（PS-b-oligo-AA） and poly（γ-benzyI L-glutamate）-b-poly（ethylene glycol）（PBLG-bPEG） copolymer mixtures in solution.On the basis of difference in hydrophilicity and self-assembly properties of the two copolymers,the two-step self-assembly process is realized.It was found that PS-boligo-AA copolymers formed spherical aggregates by adding a certain amount of water into polymer solutions in the first step.In the second step,two polymer solutions were mixed and water was further added,inducing the self-assembly of PBLG-b-PEG on the surfaces of PS-b-oligo-AA spheres to form striped patterns.In-depth study was conducted for the indispensable defects of striped patterns which are dislocations and ＋1/2 disclinations.The influencing factors such as the mixing ratio of two copolymers and the added water content in the first step on the morphology and defects of the striped patterns were investigated.This work not only presents an idea to interpret mechanism of the cooperative self-assembly behavior,but also provides an effective approach to construct virus-like particles and other complex structures with controllable morphology.