Hierarchical heterogeneous microstructure for enhanced wear resistance of CoCrFeMnNi high-entropy alloy coatings via in-situ rolling assisted laser cladding

Heterogeneous high-entropy alloys (HEAs) are promising materials due to their excellent mechanical properties. In this study, hierarchical heterostructures were introduced into CoCrFeMnNi HEA via an in-situ rolling (ISR) assisted laser cladding (LC) process. The microstructural evolution and tribological behavior of the ISR-assisted LC coating were investigated. Results indicate that porosity and surface roughness are significantly reduced, as the plastic flow during ISR-assisted LC closes pore and fills the surface valley. ISR induces a gradient distribution of dislocation density and grain size along the depth direction, and the thermal effect of subsequent laser track deposition leads to a tilted-strip distribution of grain size and geometrically necessary dislocations (GNDs) along the overlapping direction. During ISR-assisted LC process, the combined effects of deformation and recrystallization reduce the average grain size from 93.84 mu m to 32.47 mu m, decrease the texture intensity from 9.83 to 4.23, and extend the strain depth to 950 mu m. The reduction in porosity, increase in microhardness, and hierarchical heterostructure strengthening collectively enhance the wear resistance of the ISR-assisted LC coating. The volume wear rate reduces significantly from 1.740 x 10-4 mm3 center dot N- 1 center dot m- 1 to 0.133 x 10-4 mm3 center dot N- 1 center dot m- 1. This study provides a novel approach for the design of wear-resistant HEA coatings

Hierarchical heterogeneous microstructure for enhanced wear resistance of CoCrFeMnNi high-entropy alloy coatings via in-situ rolling assisted laser cladding

Heterogeneous high-entropy alloys (HEAs) are promising materials due to their excellent mechanical properties. In this study, hierarchical heterostructures were introduced into CoCrFeMnNi HEA via an in-situ rolling (ISR) assisted laser cladding (LC) process. The microstructural evolution and tribological behavior of the ISR-assisted LC coating were investigated. Results indicate that porosity and surface roughness are significantly reduced, as the plastic flow during ISR-assisted LC closes pore and fills the surface valley. ISR induces a gradient distribution of dislocation density and grain size along the depth direction, and the thermal effect of subsequent laser track deposition leads to a tilted-strip distribution of grain size and geometrically necessary dislocations (GNDs) along the overlapping direction. During ISR-assisted LC process, the combined effects of deformation and recrystallization reduce the average grain size from 93.84 mu m to 32.47 mu m, decrease the texture intensity from 9.83 to 4.23, and extend the strain depth to 950 mu m. The reduction in porosity, increase in microhardness, and hierarchical heterostructure strengthening collectively enhance the wear resistance of the ISR-assisted LC coating. The volume wear rate reduces significantly from 1.740 x 10-4 mm3 center dot N- 1 center dot m- 1 to 0.133 x 10-4 mm3 center dot N- 1 center dot m- 1. This study provides a novel approach for the design of wear-resistant HEA coatings

Impact response of pearlitic steel dominated by ferrite/cementite interface

It is experimentally difficult to ascertain the role of ferrite/cementite interface in the impact properties and structural evolution of pearlitic steel. In this paper, we propose a solution based on molecular dynamics simulations of planar shocks of pearlitic steel. It is found that the ferrite/cementite interface reflects the part of a shock wave and facilitates the nucleation of voids and dislocations. Consequently, the disturbance and plastic wave details are added to free surface velocity-time profiles. The evolution of voids contributes to the subsequent occurrence of spallation at interface, generating a power law relationship between the tensile strain rate and spall strength with an exponent of 2.7, which differs from that of 4.0 as spallation happens in polycrystalline ferrite regions

Instability in centrifugally stable shear flows

We investigate the linear instability of flows that are stable according to Rayleigh's criterion for rotating fluids. Using Taylor-Couette flow as a primary test case, we develop large-Reynolds-number-matched asymptotic expansion theories. Our theoretical results not only aid in detecting instabilities previously reported by Deguchi (Phys. Rev. E, vol 95, 2017, p. 021102(R)) across a wide parameter range, but also clarify the physical mechanisms behind this counterintuitive phenomenon. Instability arises from the interaction between large-scale inviscid vortices and the viscous flow structure near the wall, which is analogous to Tollmien-Schlichting waves. Furthermore, our asymptotic theories and numerical computations reveal that similar instability mechanisms occur in boundary layer flows over convex walls

一种嵌入式表皮心电采集电极

本实用新型涉及医疗器械用具心电电极技术领域，具体公开了一种嵌入式表皮心电采集电极，包括电极安装组件、由上电极扣与下电极扣组成的电极扣、粘接胶层。电极安装组件设有蛇形电极网络、装配贴合部和装配孔，装配孔沿装配贴合部中心设置，蛇形电极网络沿装配贴合部外周区域设置；上电极扣与下电极扣均设有隆起部与平整部，下电极扣隆起部穿过电极安装组件的装配孔，并使其平整部与装配贴合部靠近人体端的一侧贴合；上电极扣隆起部套设在下电极扣隆起部上过盈配合，其平整部与装配贴合部另一侧贴合；蛇形电极网络沿其与装配贴合部连接处整体向人体端变形偏移，使所述蛇形电极网络靠近人体端一侧与下电极扣平整部底端位于同一平面

Optimized dynamic similarity models to predict SGS backscatter in 2D decaying turbulence

Large eddy simulation (LES) of two-dimensional (2D) turbulence is often used in the geostrophic flows. However, some basic dynamics underlying traditional SGS models are absent in 2D turbulence, e.g. the vortex stretching. Hence, this research proposes an optimized dynamic similarity model (DSM) for the SGS stress, which is constructed through the dynamic procedure based on the Germano identity. In addition, a modification is made to the dynamic mixed model (DMM) for the sake of realizability condition. The optimized DSM is justified in comparison with the DMM, through the a priori and a posteriori verifications, in the context of the 2D decaying turbulence with turbulent Reynolds number of Re = 3.7 x 104 and turbulent Mach number of Mt = 0.1. Special attention is paid to the consistency of the verification procedure, so that the filtering operations used in the direct numerical simulation (DNS) and LES are optimally equivalent. The SGS transport phenomena, especially the SGS backscatter, predicted by these two models are studied in detail. In addition, the optimized DSM and the DMM are extended for the modified SGS transport vectors of passive scalars to show their capability in calculating 2D turbulent mixing. The numerical results show the optimized DSM provides larger correlation coefficient, better locality, and stronger SGS backscsatter than the DMM does, and therefore it is more suitable for the LES of 2D turbulence

一种基于电磁驱动的两动体高速碰撞实验装置及方法

本发明公开了动体碰撞实验技术领域的一种基于电磁驱动的两动体高速碰撞实验装置，包括两个相对设置的电磁驱动系统，两个电磁驱动系统的出射端之间形成有碰撞区域；两个电磁驱动系统用于分别驱动一个动体以相同或者不同的预设速度向碰撞区域运动；在两动体预设速度不相同时，电磁驱动系统控制动体发射的时间，以使两个动体能够在碰撞区域发生碰撞；碰撞区域的侧面设置有数据采集模块，且数据采集模块的采集端面向碰撞区域，以获取两个动体碰撞时的数据

Effects of molecular interaction and liver sinusoidal mechanical properties on leukocyte adhesions

It is interesting to find pathologically that leukocytes, especially neutrophils, tend to adhere in the liver sinusoids dominantly but not in the postsinusoidal venules. While both views of receptor-ligand interactions and physical trapping are proposed for mediating leukocyte adhesion in liver sinusoids, integrated investigations for classifying their respective contributions are poorly presented. With a combination of Monte Carlo simulation and immersed boundary method, this study explored numerically the effects of molecular interaction kinetics and sinusoidal mechanical properties on leukocyte adhesion in liver sinusoid jointly. Results showed that, within the range of biological limitations, the lumen stenosis ratio, leukocyte stiffness, Disse space stiffness and endothelium permeability regulate the comprehensive adhesion process in a descending order of significance in the presence of receptor-ligand interactions. While leukocyte adhesions could be mutually promoted with proper combinations of leukocyte stiffness, lumen stenosis, and molecular interaction, the binding affinity is insensitive under the conditions with low leukocyte stiffness in normal lumen stenosis and high leukocyte stiffness in high lumen stenosis. This work deepens the understanding of recruitment mechanism of leukocyte in liver sinusoids

High-strength nanostructured copper alloys via mechanical consolidation of pure copper and Fe-Si-B glassy powers

High-strength nanostructured copper alloys were fabricated through the mechanical consolidation of pure copper and Fe-Si-B glassy powders using a two-step high-pressure torsion (HPT) process. Structural characterization by transmission electron microscopy and electron backscatter diffraction revealed that, after overall 20 HPT revolutions, 1 wt% Fe78Si9B13 glassy powders can be fully decomposed and homogeneously supersaturated into the copper matrix. The resulting Cu-1 wt.% FeSiB alloy exhibited a compositionally uniform nanostructure with an average grain size of 63.3 nm and a high proportion of low-angle grain boundaries (54.2 %), achieving an ultimate tensile strength of 1246 MPa. In contrast, the addition of 5 wt% Fe78Si9B13 glassy powder under the identical HPT conditions resulted in a crystal-glass composite structure with an ultimate tensile strength of 895.8 MPa. This work advances a hybrid method that integrates bottom-up particle bonding with top-down grain refinement to fabricate high-performance alloys

Holographic images of a charged black hole in Lorentz symmetry breaking massive gravity

Using the AdS/CFT correspondence, this paper investigates the holographic images of a charged black hole within the context of Lorentz symmetry breaking massive gravity. The photon rings, luminosity-deformed rings, or light points from various observational perspectives are obtained. We also study the influences of both the chemical potential and temperature on the Einstein ring. Unlike the previous work, which primarily examines the effect of chemical potential on ring radius at high temperatures and find no change in the radius with varying chemical potential, we also investigate the effect of chemical potential on the ring radius at low temperature besides at high temperature. Our findings indicate that at low temperatures, the photon ring radius decreases with increasing of chemical potential, while at high temperatures, the results are consistent with previous studies. Additionally, we explore the impact of the model parameter lambda on the Einstein ring radius and find the the ring radius increases as the model parameter lambda increases. More interestingly, for the large chemical potential, u = 1, the temperature dependence of the photon ring radius is reversed for lambda = 2 and lambda = 4. Conversely, for a small chemical potential u = 0.1, the temperature dependence of the Einstein ring stays the same as lambda = 2 and lambda = 4